ISSN 0030-9885 Coden: PSIRAA 48 (1) 1-74 (2005) Vol. 48, No. 1, January-February, 2005 Pakistan Journal of Scientific and Industrial Research Published Bimonthly by Scientific Information Centre Pakistan Council of Scientific and Industrial Research Karachi, Pakistan This Journal is indexed/abstracted in Biological Abstracts and Biological Abstracts Reports, Chemical Abstracts, Geo Abstracts, CAB International, BioSciences Information Service, Zoo- logical Record, BIOSIS, NISC, NSDP, Current Contents, CCAB, Rapra Polymer Database, Re- views and Meetings and their CD-ROM counterparts, etc. Subscription rates (including handling and Air Mail postage): Local: Rs. 2000 per volume, single issue Rs. 350; Foreign: US$ 400 per volume, single issue US$ 70. Electronic format of this journal is available with: Bell & Howell Information and Learning, 300 North Zeeb Road, P.O. 1346, Ann Arbor, Michigan 48106, U.S.A; Fax. 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Editorial Address: Executive Editor, Pakistan Journal of Scientific and Industrial Research, PCSIR Scien- tific Information Centre, PCSIR Laboratories Campus, Shahrah-e- Dr. Salimuzzaman Siddiqui, Karachi-75280, Pakistan. Tel: 92-21-4651739-40, 4651741-43 Fax: 92-21-4651738 E-mail: pcsirsys@super.net.pk; pcsir-sic@cyber.net.pk PROF. W. LINERT Vienna University of Technology, Vienna, Austria PROF. B. HIRALAL MEHTA University of Mumbai, Mumbai, India PROF. E. MIRALDI University of Siena, Siena, Italy DR. J. OZGA University of Alberta, Edmonton, Canada DR. J. R. OGREN Editor, Journal of Materials Engineering and Performance, Los Angeles, USA PROF. H. M. ORTNER Technical University of Darmstadt, Darmstadt, Germany DR. H. AKHTAR Agriculture and Agri-Food Canada, Ontario, Canada PROF. M. AKHTAR, FRS University of Southampton, Southampton, United Kingdom DR. A. G. ATTKINS University of Reading, Reading, United Kingdom PROF. G. BOUET University of Angers, Angers, France DR. M. A. KHAN King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia DR. M. J. QURESHI Nuclear Institute for Food and Agriculture, Peshawar, Pakistan DR. ZAFAR SAIED SAIFY University of Karachi, Karachi, Pakistan DR. F. M. SLATER Cardiff University, Powys, United Kingdom PROF. M. A. WAQAR International Centre for Chemical Sciences, University of Karachi, Karachi-75270, Pakistan Editors Ghulam Qadir Shaikh Gulzar Hussain Jhatial Shagufta Y. Iqbal Shahida Begum Sardar Ahmad Nazish Sajid Ali Production Riazuddin Qureshi Irshad Hussain Chairman Editorial Board Dr. Anwar ul Haq S.I., Pride of Performance, Tamgha-e-Baqa, FPAS, FTWAS Chairman, PCSIR Dr. Saeed Iqbal Zafar Dr. Kaniz Fizza Azhar Editor-in-Chief Executive Editor Editorial Board Pakistan Journal of Scientific and Industrial Research Pakistan Journal of Scientific and Industrial Research Vol. 48, No. 1 Contents Jan. - Feb. 2005 Physical Sciences Mass Transfer Rates and Column Heights in Reactive Extraction Processes M. T. Saeed, R. Khanam and M. Y. Shaheen 1 Humidity Effect on the Disintegrant Property of ααααα-Cellulose and the Implication for Dissolution Rates in Paracetamol Tablets M. U. Uhumwangho and R. S. Okor 8 Proximate, Mineral and Phytate Profiles of Some Selected Spices Found in Nigeria E. I. Adeyeye and E. D. Fagbohun 14 Effects of Exposures to Cement Dust and Powder on Workers in Cement Distribution/Retail Outlets in Benin City, Nigeria I. F. Obuekwe and L. I. Okoh 23 Determination and Seasonal Variation of Heavy Metals in Algae and Sediments in Sewers from Industrial Areas in Lagos State, Nigeria O. R. Awofolu 28 Short Communication Screening of Fused Pyrimidines as Antimicrobial Agents: Inhibitory Activities of Some Tetrahydrobenzothieno-Pyrimidines M. M. H. Bhuiyan and M. Fakruddin 37 Biological Sciences Determination of Trace Metals in Silver Cat Fish (Chryssichthys nigrodigitatus) Associated with Water and Soil Sediments from Beach-Line Fish Ponds O. O. Ayejuyo, O. G. Raimi and O. R. Moisili 39 Development of a High Yielding Wheat Variety “Bahawalpur-97” for Southern Punjab, Pakistan M. Ahmad, L. H. Akhtar, S. Z. Siddiqi, M. Hussain, A. Rashid, G. Hussain, M. Aslam, M. Safdar, M. M. Akhtar, M. Arshad and A. H. Tariq 42 Studies on the Lipolytic Enzymes of Carica papaya Seed Powder M. A. Javed, M. Naeem and R. Amjad 47 Characterisation of Amidohydrolytic Activity of Bacillus megaterium in Submerged Fermentation Q. Syed, N. Bashir and M. A. Kashmiri 51 Short Communications Mechanism of Monocarpic Senescence of Momordica dioica: Source - Sink Regulation by Reproductive Organs A. Ghosh 55 Status of Grain Smut Sphacelotheca sorghi and Long Smut Tolyposporium ehrenbergii of Sorghum in Sindh and Balochistan, Pakistan A. A. Hakro and A. Khan 57 Technology The Dyeability Potential of Cellulosic Fibres Using African Yellow Wood (Enantia chlorantha) A. O. Adetuyi, A. V. Popoola, L. Lajide and M. O. Oladimeji 59 The Effect of Local Materials (Fillers) on the Crosslink Density, Hardness, Resilience and Hysteresis of Natural Rubber B. F. Adeosun and O. Olaofe 63 Preparation and Characterisation of Alkyd Resins Using Crude and Refined Rubber Seed Oil E. U. Ikhuoria and F. E. Okieimen 68 Erratum 74 Introduction Continuous counter current contactors are usually designed assuming interfacial equilibrium. In the case of mass transfer with interfacial chemical reaction, this assumption is only valid if the chemical reaction is very fast with respect to the mass transfer rate (Chapman et al., 1975). In hydrometallurgical pro- cessing, the use of liquid-liquid extraction systems are already very popular. The successful application of such related ex- traction processes has encouraged fundamental research on the extraction equilibria and kinetics leading to development of mathematical models for the solvent extraction of metals. The kinetics of these systems is generally controlled by a combination of diffusion and chemical rate factors and a prop- erly developed model could become a design equation hav- ing practical significance. If all the parameters relating to the system, namely physicochemical, hydrodynamics, mass trans- fer, and the reaction kinetics are known, it would be possible to design extraction column from first principles. In this paper a mathematical model is developed for interfa- cial flux, which is based on simultaneous interfacial chemical reactions and diffusion processes. An attempt has also been made to predict the column height from first principles. The system comprises the extraction of zinc ions from acidic aque- ous phase by di(2-ethylhexyl) phosphoric acid (DEHPA) in n-heptane diluent. In order to check the validity of the model for design purposes, the predicted values are compared with actual heights. Model formulation. In a column for continuous extraction in aqueous phase, with interfacial chemical reactions, the mass balance of zinc ions over a differential height δ h for unsteady state operation may be given as follows (Saeed and Jamil, 1998a): (1) The first term on the right hand side of equation (1) accounts for convection, the second term for axial mixing and the third one represents the overall rate of interfacial transfer. The term on the left hand side represents the variation of zinc concen- tration with time. A similar differential mass balance equation can be derived for metals in the dispersed organic phase (Saeed and Jamil, 1998a): (2) Under steady state conditions, assuming constant flow rates and neglecting backmixing, equations (1) and (2) re- duce to: (3) and (4) which on integration give the contactor height: (5) and (6) Mass Transfer Rates and Column Heights in Reactive Extraction Processes Muhammad Tariq Saeed*, Razia Khanam and Muhammad Yar Shaheen PCSIR Laboratories Complex, Shahrah-e-Jalaluddin Roomi, Lahore-54600, Pakistan (received August 24, 2002; revised July 15, 2004; accepted July 28, 2004) Abstract. A mathematical model, which is based on the simultaneous interfacial chemical reactions and diffusion processes, is developed for the extraction of zinc ions from sulphate solution by di(2-ethylhexyl) phosphoric acid in n- heptane diluent. Actual column heights were compared with the predicted ones, using the design algorithm based on chemical kinetics. The experimental values of mass transfer coefficients could be varied and were in the range of industrial interest. Using the physicochemical data, hydrodynamics, mass transfer coefficient parameters and reaction kinetics pertaining to the system, it was possible to predict the interfacial flux and column height from first principles with a reasonable degree of accuracy. Keywords: interfacial flux, reactive extraction, chemical kinetics, zinc/DEHPA, spray column (1- φD) = + E ax,c (1- φD) ∂ 2Cza ∂h 2 ∂Cza ∂t Lc S ∂Cza ∂h - Rz ac (1- φD) ∂Czo ∂t φD = - Ld S ∂Czo ∂h + E ax,d φD ∂ 2Czo ∂h2 + Rz ad φD dCza dh Lc = Rz ac S (1- φD ) Pak. J. Sci. Ind. Res. 2005 48(1) 1-7 *Author for correspondence = Rz ad S φD Ld ∂Czo ∂h Hc = Lc S dCza Rz ac (1- φD) ∫∫ 2 1 Hc = Ld S dCzo Rz ad φD ∫ 2 1 1 In the extraction column the local volumetric extraction rate, rz , is given by: rz = Rz ac (7) Since chemical reactions are also involved, the interfacial flux, Rz, would be a function of chemical as well as mass transfer parameters, while the specific interfacial area depends on the operating conditions of the column, i.e., dispersed phase hold- up and mean drop diameter. In order to integrate equations (5) and (6) for calculating contactor height in a given extraction system, knowledge of R z , a c , a d and φ D is essential. Interfacial area. Interfacial area between droplets and con- tinuous phase is a function of drop size and dispersed phase holdup. The interfacial area per unit volume of the continu- ous phase is expressed as (Pilhofer and Schroter, 1986): a c = (8) (9) A correlation has been proposed that predicts the drop size in spray columns which claimed to be valid both for the absence or presence of mass transfer (Kumar and Hartland, 1984): (10) for, We n < 8.64 With a view to obtaining the holdup for the static continuous phase, φ, the following equation should be employed for cal- culating the countercurrent holdup, φ D : (11) Mass transfer coefficients. In liquid-liquid extraction pro- cesses, the mass transfer coefficient would be dependent on whether the drops are rising, falling, internally circulating, or in oscillating state through continuous but immiscible liquid phase. However, it was observed both visually and from the analysis of photographic films taken with a cine camera for the dispersion in the column that the rising drops were oscil- lating (Saeed and Jamil, 1998a). Accordingly, the correlations for continuous phase and dispersed phase, mass transfer co- efficients are dewelled upon only for oscillating drops. The following correlation has been proposed for continuous phase mass transfer coefficient (Yamaguchi et al., 1975): (12) The correlation of Rose and Kintner (1966) for dispersed phase mass transfer coefficient is: (13) Diffusion coefficients. The diffusivity of strong electrolytes at infinite dilution on the assumption of complete dissocia- tion can be calculated from the Nernst-Haskell equation (Reid et al., 1977) as given below: (14) Harned and Hudson (1951) introduced a correction factor by taking into account the influence of ion-pair formation on the diffusion coefficient given as: D 12 = D° 12 [1 + 38.16 x 10-2 (1- α)] (15) The most general and widely used correlation for the prediction of diffusion coefficients of non-electrolytes in or- ganic solvents at infinite dilution is that of Wilke and Chang (1955): (16) A modified expression was proposed by Leffler and Cullinan (1970) for higher concentrations, taking viscosity into due account: (17) Extraction equilibria. The extraction chemistry of zinc with di(2-ethylhexyl) phosphoric acid (DEHPA) has been studied by numerous workers. Ajawin et al. (1983) reported the over- all equilibrium as: (18) From the extraction equilibrium studies, Murthy (1987) reported that two complexes of zinc-DEHPA are formed in n-heptane according to the stoichiometry of the reactions: (19) (20) where bars indicate the species in the organic phase and (HL) 2 in DEHPA in dimer form. Extraction kinetics. From the kinetic studies (Murthy, 1987; Ajawin et al., 1983; 1980) conducted in a cell with constant ∂ φD d32 (1- φD) Σnd 3 Σnd 2d32 = d32 = dn EÖ -0.38 1.28 + exp (- 0.16 Fr) ∆ρ 0.3 ρd [ ] ][ K d = 0.95 Dd 0.5 8 σ (100 d32) 0.225 0.25 d 3 32 (3ρ d + 2ρ c ) [ ] D° AB = 1.173 x 10 -16 (Φ MB )0.5 T µBVA 0.6 Zn2+ + 1.5 (HL) 2 ZnL2.HL + 2H + Ud Ud Uc φ φ D (1- φD) us = = + DAB µAB f th = (D°AB µB) XB (D°BA µA) XA Zn2+ + 1.5 (HL) 2 ZnL2.HL + 2H + Zn2+ + 2 (HL) 2 ZnL 2 (HL) 2 + 2H + 2 M. T. Saeed et al. D°12 = RT F 2 1 + 1 n+ n- 1 + 1 λ° + λ°- ρ c ω d 2 32 0.5 µc [ ] µc 0.5 ρ c Dc [ ]Kc = 1.4 Dc d32 interfacial area in the chemical control regime, it has been reported that reactions (19) and (20) take place at the interface. The extraction rate of zinc ions is proportional to their concen- tration in the aqueous phase, dimeric DEHPA activity and inversely proportional to hydrogen ion concentration: (21a) (21b) where: k I = 2 k/γ o While stripping rate is first order with respect to zinc-DEHPA complex concentration, it is first order with respect to hydro- gen ion concentration and is inversely proportional to the dimeric DEHPA activity factor (ao+ 0.75 √ ao): (22) From equations (21b) and (22), the overall extraction rate can be expressed as: (23) or (24) The above equations indicate that reaction is independent of mass transfer control and, therefore, expected to yield the maximum interfacial flux for a given set of concentrations. Baes and Baker (1960) have proposed the following relation- ship for the activity coefficients of the DEHPA dimer in ali- phatic diluents: log γ o = - 0.586 C 1/3 oD + 0.565 CoD (25) Activity coefficient correlation for zinc-DEHPA complex proposed by Koncar et al. (1988) is: = 1 + 0.616 (26) The mechanism of transfer of the solute from one phase to the other may be very complexed. The trend of mass transfer is assumed to proceed according to the following three steps: (i) zinc ions and DEHPA diffuse to the interface from the aqueous and the organic phases, respectively, (ii) zinc ions and DEHPA react according to reactions (19) and (20), and (iii) the liberated hydrogen ions and zinc-DEHPA complex diffuse from the interface into the aqueous and organic phases, respectively. The three steps take place simultaneously and thus inter- fere mutually. A schematic diagram of the concentration profiles for all the species at the interface during zinc extrac- tion is shown in Fig. 1. In the mixed control regime, the interfacial flux depends on the kinetics of both mass trans- fer and interfacial reaction. In the present case, the interfa- cial rate of extraction is still given by equation (24), but for the interfacial instead of bulk concentrations. Since the in- terfacial concentrations are normally not directly measureable quantities, these, it involve some mathematical manipulation as given below: R z = K za (C za - C zai ) R z = 1/1.7 Ko (ao - aoi) R z = - 1/2 K H (C H - C Hi ) R z = - K zo (C zo - C zoi ) (27) Cza CoD CH rze = 2 k ac (Ajawin et al., 1983; 1980) rzs = k′I ac Czo CH ao + 0.75 √ao rzs = kI ac - k′I ac Czo CH ao + 0.75 √ao Cza ao CH 1 γ Zo 1.7 Czo 1.387 ao [ ] Cza CoD γo CH rze = kI ac = kI ac Czo ao CH Rz = = kI - k′I Cza ao CH rz ac Czo CH ao + 0.75 √ao 3Mass Transfer Rates in Reactive Processes Fig. 1. Concentration profiles at the interface during metal extraction. Aqueous phase i Organic phase CH Cza Czai CH i CoDi Czoi CoD Czo Eliminating the interfacial values from equations (24) and (27), the final kinetic expression for the interfacial flux comes out to be: (28) This gives Rz in terms of bulk concentrations of the species involved, individual mass transfer coefficients, and specific reaction rate constants for the extraction and stripping reactions. azo + Rz Kzo [ ] ao – 1.7 Rz Ko + 0.75√ ao – 1.7 CH + 2 Rz KH Rz Ko Rz = kI Cza – Rz Kza [ ] ao – 1.7 Rz Ko CH + 2 Rz KH [ ] – k′I [ ] [ ] Aqueous phase ionic equilibria. The aqueous phase under consideration is a solution of zinc sulphate, sulphuric acid and sodium sulphate. It may be assumed that sodium sul- phate completely dissociates, whereas dissociation of zinc sulphate and bisulphate ions is incomplete, being according to the following equations: ZnSO 4 Zn2+ + SO 4 2- (29) HSO 4 H + + SO 4 2- (30) In the aqueous phase, the species namely zinc, sulphate, hydrogen, sodium, bisulphate and zinc sulphate ion-pair are being considered to be present in ionic form while higher order associations are ignored. The ionic strength, I, of any solution is defined by the follow- ing equation: (31) where: Ci and Zi are the molar concentration and ionic charge of the species i, respectively. In the light of equations (29) and (30), equilibria constants and mass balances for various ionic species may be repre- sented by the following relationships: zinc sulphate ion-pair dissociation constant: K m = (32) bisulphate ion dissociation constant: K b = (33) hydrogen ion balance: [H + ] = 2M H 2 SO 4 _ [HSO 4 _ ] (34) sulphate ion balance: [SO 4 2-] = MSO 4 2- - [HSO 4 _ ] - [ZnSO 4 ] (35) zinc ion balance: [Zn2+] = Czt - [ZnSO 4 ] (36) sodium ion balance: [Na+] = 2 (MSO 4 2- - MH 2 SO 4 - Czt) (37) where: MH 2 SO 4 , MSO2- 4 and Czt are the formal concentration of sulphuric acid, the formal total sulphate concentration and formal total concentration of zinc sulphate, respectively. Nomenclature used in the paper. a c = interfacial area per unit volume of continuous phase, m-1; a d = interfacial area per unit volume of dispersed phase, m-1; a o = activity of DEHPA dimer, kmol/m3; a zo = activity of organic zinc, kmol/m3; C = molar concentration, kmol/m3; D = diffusion coefficient, m2/s; d 32 = Sauter mean drop diameter, m; d n = inside nozzle diameter, m; Eö = nozzle Eotvos number, ∆ρd n 2 g/σ; E ax = axial dispersion coefficient, m2/s; F = Faraday constant, 9.65 x 10 7 C/kg equiv; Fr = Froude number, u n 2 /g d n ; f th = thermodynamic factor; H c = column height, m; K = mass transfer coefficient, m/s; k = con- centration-based extraction rate constant, m/s; k I = extraction rate constant, m/s; k/ I = stripping rate constant, m/s; L = volu- metric flow rate, m3/s; L / = volumetric flow rate m3/s; M = molecular weight; n + , n- = valences of cation and anion re- spectively; R = gas constant, 8.314x 10 3 J/kmol K; R z = zinc interfacial flux, kmol/m2 s; r z = volumetric extraction rate, kmol/ m3 s; S = cross-sectional area of column, m2; T = absolute temperature, K; t = time, s; U = superficial velocity through the column, m/s; u s = slip velocity of drops relative to continu- ous phase, m/s; VA = molar volume of extractant at its normal boiling point, m3/kmol; We n = nozzle Weber number, ρ d d n u n 2/ σ; x = mole fraction. Greek letters used in the paper. α = degree of dissociation of zinc sulphate; γ = activity coefficient; σ = interfacial tension, N/m; ρ = density, kg/m3; ∆ρ = desnity difference, kg/m3; µ = viscosity, kg/m s; ω = frequency of oscillation, √48 σ/π2 d3 32 (3ρ d + 2ρ c ), s-1; λ0 + , λ − 0 = limiting (zero concentra- tion) ionic conductances, S m2/kg equiv; Φ = an association parameter for solvent; φ = dispersed phase holdup for U c = 0; φ D = dispersed phase holdup for countercurrent flow. Subscripts used in the paper. 1 = outlet; 2 = inlet; A = extrac- tant; B = organic solvent; AB = organic solution; c = continu- ous phase; d = dispersed phase; H = hydrogen ion; i = inter- face, interfacial values; o,oD = DEHPA dimer; za = aqueous phase zinc ions; zo = organic phase zinc; zt = total aqueous phase zinc. Materials and Methods The continuous aqueous phase contains zinc sulphate, so- dium sulphate and sulphuric acid, whereas the dispersed phase consists of di(2-ethylhexyl) phosphoric acid (DEHPA) dissolved in n-heptane. The n-heptane used was of knock- testing grade without purifying anymore. The DEHPA was of technical grade obtained from BDH and was further purified by Partridge and Jensen (1969) method. The use of DEHPA to extract zinc was considered as a recommended system for liquid-liquid extraction studies (Hancil et al.,1990). These authors claimed that the use of glycol alone to remove monoester impurities from DEHPA adversely affected the I = ½ Ci Zi 2 n Σ i = 1 [Zn2+] [SO 4 2-] [Zn SO 4 ] [H + ] [SO 4 2- ] [H SO 4 ] 4 M. T. Saeed et al. subsequent zinc extraction kinetics. For impure DEHPA with monoester content ≤ 3 mol%, the kinetics of extrac- tion were the same as for highly purified DEHPA produced using the copper precipitation method. The zinc sulphate, sodium sulphate and sulphuric acid were Analar grade. All the experiments were carried out at 25 °C and an ionic strength of 1 mol/dm3. Experiments were performed in a glass spray column of 0.05 m diameter with provision to adjust height. Effective heights of 1.25-2.4 m were used. The column was operated in a semi-batch mode, that is, the continuous aqueous phase was kept stagnant and the dispersed organic phase was not recirculated. The coalesced dispersed organic phase was drawn off from the top of the reservoir by a glass capillary siphon that resulted in a continuous flow of the coalesced phase. Full detail of the apparatus description, procedure and photo- graphic set-up is given elsewhere (Saeed and Jamil, 1994a). The concentrations and operating conditions in the column are given below: C zt , initial aqueous phase zinc conc = 1.5x 10 -3 -0.02 kmol/m3; initial pH = 2.7-3.07; C oD , DEHPA conc (dimer) = 0.025-0.075 kmol/m3; diluent = n-heptane; L d , dispersed phase flow rate = 3.67 x 10 -7 -2 x 10 -6 m3/s; d n , nozzle diameter = 0.8 x 10 -3 -3.0 x 10 -3 m; H c , effective column height = 1.25-2.4 m. Results and Discussion Equations (32-36) are solved simultaneously for constant values of K m and K b to yield a cubic equation in zinc ion concentration. For the calculation of the values of MH 2 SO 4 and MSO2- 4 , which would give the required composition of the aqueous phase, that is, [Zn2+], [H + ] and ionic strength, 5Mass Transfer Rates in Reactive Processes dC za dt the iteration method was employed by using guessed values of MH 2 SO 4 and MSO2- 4 for a given value of zinc sulphate. Baes (1957) reported the values of dissociation constant of bisulphate ion, K b , for the system sodium sulphate-sulphuric acid, as a function of total sulphate concentration. His results showed that at constant total sulphate concentration, K b is nearly constant as the composition is changed, even though the accompanying change in ionic strength is considerable. Baes values were employed for calculating K b , while K m value was taken from elsewhere (Smith and Martell, 1976). Comparison of actual and predicted column heights. Analysis of photographic films gave drop size distribution, dispersed phase holdup and specific interfacial area. The values of hydrodynamic and mass transfer parameters for the system are given in Table 1. Considering Rz and ac constant along the height and the column was operated while there was no net flow of continuous phase across the section, equation (1) becomes: = _ R z a c (38) The physicochemical data for zinc/DEHPA system understudy is given below: λ o + (½ Zn2+) = 5.3 S m2/kg equiv; λo – (½ SO 4 2-) = 8.0 S m2/kg equiv; µB = 4 x 10 -4 kg/m s; Φ = 1.0 (for n-heptane solvent); MB = 100.2; VA = 0.853 m3/kmol (for DEHPA dimer); D za = 1.08 x 10 -9 m2/s; Do = 7.34 x 10 -10 m2/s; Dzo = 5.78 x 10 -10 m2/ s; ρc = 1040 kg/m3; ρd = 695 kg/m3; µc = 1.023 x 10 -3 kg/m s; µd = 4.733 x 10-4 kg/m s; σ = 20.5 x 10 -3 N/m; k = 4.25 x 10 -7 m/ s (Ajawan et al., 1983) and kI = 2k/γ 0 ; k/ I* = 2.96 x 10 -5 m/s (*modified value based on DEHPA and zinc-DEHPA com- plex activities). Table 1. Measured and calculated hydrodynamic and mass transfer parameters in a spray column for Zn/DEHPA system; CoD = 0.075 mol/dm3 dn x 10 3 L/ d x 10 8 d e x 10 3 d 32 x 10 3 φ x 10 3 a c Kza x 10 4 Ko x 10 4 m m3/s m m m-1 m/s m/s 0.8 9.2 3.99 3.99 1.55 2.32 2.43 1.1 11.2 3.68 3.68 1.88 3.07 2.23 1.12 1.1 10.8 5.22 5.25 1.77 2.08 2.05 0.91 12.5 5.0 5.04 2.09 2.58 2.12 0.92 17.5 4.94 5.0 3.0 3.7 2.22 0.92 23.3 2.81 2.86 4.0 8.5 2.65 1.24 23.3 2.99* 3.03 4.12 8.27 2.55 1.39 3.0 24.2 6.28 6.31 4.15 4.1 1.98 0.69 33.3 6.23 6.25 5.73 5.7 2.11 0.8 50 6.07 6.09 8.54 8.73 1.95 0.79 *C oD : 0.025 mol/dm3 The values of various physical properties for the system needed in the calculation of Sauter mean drop diameter, diffu- sion and mass transfer coefficients were determined experi- mentally. The solution of DEHPA in n-heptane behaves like a non-ideal solution. The thermodynamic factor for the system was obtained from the slope of lnao versus lnx A graph. The mass transfer coefficient of organic zinc complex was esti- mated using the penetration theory model which provides that the mass transfer coefficient is directly proportional to the square root of the molecular diffusivity. Although the intrinsic diffusivities of zinc and hydrogen ions are different, in order to maintain electric neutrality, Kza is taken equal to K H . The calculated values of hydrodynamic and mass transfer parameters using different correlations agree well with the experimental values (Saeed and Jamil, 1998b; Saeed et al., 1994; Saeed and Jamil, 1994a). The experimental interfacial flux data fits well in the design equation based on interfacial chemical kinetics (Table 1) (Saeed and Jamil, 1994b). The values of chemical reaction rate constants at 25 °C and an ionic strength of 1 mol/dm3 have been reported by Murthy (1987) and Ajawin et al. (1983; 1980). The authors have as- sumed complete dissociation of zinc sulphate in the aque- ous phase for the purpose of calculations of reaction rate and equilibrium constants. The modified values of these con- stants, taking into account the incomplete dissociation of aqueous phase zinc sulphate, were used in the interfacial flux model. Equations (2) and (38) were solved numerically by the method of finite difference using the equation (28) for the interfacial flux. A numerical calculation routine (CO 2 AEF), written by Numerical Algorithm Group (NAG), was used to solve the polynomial equation (28). In all cases, which were considered, there was only one real root for positive interfa- cial concentration. Samples of the outlet dispersed organic phase were taken directly from the outflow of the siphon to estimate the zinc concentration. A known volume of the organic phase sample was stripped with 2 mol/dm3 H 2 SO 4 and the aque- ous phase was analyzed using the atomic absorption spec- trophotometer at λ 213.9 nm. In order to predict column heights for the corresponding outlet organic phase zinc concentrations, the required constants and other param- eters such as Sauter mean drop diameter, mass transfer coefficients for continuous and dispersed phases, etc., were calculated using respective relationships as detailed in the preceeding paragraphs. In the calculations, the following assumptions were made: • DEHPA diffuses in the diluent as a dimer; • mass transfer rate during drop formation and coalescence was the same as the one rate of rising drops; • the rising velocity of the drops is the same throughout the column; and • analysis of the samples of the continuous aqueous phase taken at different points along the column showed no variation of zinc concentration with height, therefore, the dispersive term in equation (2) was assumed to be negli- gible. Comparison of actual and predicted heights using the de- sign equation based on the interfacial chemical kinetics is shown in Fig. 2. The predicted values agree well with the actual ones showing that it is possible to design spray col- umns from first principles provided that the reliable physico- chemical data, hydrodynamic and mass transfer parameters are available. 6 M. T. Saeed et al. 2.6 2.2 1.8 1.4 1.0 1.0 1.4 1.8 2.2 2.6 Fig. 2. Comparison of actual and predicted heights using design algorithm based on interfacial chemical kinetics. Hc, actual H c , p re d ic te d Conclusion The extraction of zinc from an acidic aqueous sulphate solu- tion by di(2- ethylhexyl) phosphoric acid in n-heptane diluent has been carried out in a spray column of variable heights operated under semi-batch mode. A comparison between actual heights and those predicted using the design algorithm based on the interfacial chemical kinetics indicates its applicability, being in good agreement. If all the parameters relating to the system, namely, physico- chemical, hydrodynamics, mass transfer and the reaction ki- netics are known, it is possible to design extraction column from first principles. References Ajawin, L. A., de Ortiz, E. S. P., Sawistowski, H. 1983. Extrac- tion of zinc by di(2-ethylhexyl) phosphoric acid. Chem. Engg. Res. Des. 61: 62-66. Ajawin, L. A., de Ortiz, E. S. P., Sawistowski, H. 1980. Kinetics of extraction of zinc by di(2-ethylhexyl) phosphoric acid in n-heptane. In: Proceedings of International Solvent Extraction Conference, pp. 80-112, Liege, Belgium. Baes Jr., C. F. 1957. The estimation of bisulphate ion dissocia- tion in sulphuric acid sodium sulphate solutions. J. Am. Chem. Soc. 79: 5611-5616. Baes Jr., C. F., Baker, H. T. 1960. The extraction of iron (III) from acid perchlorate solutions by di(2-ethylhexyl) phospho- ric acid in n-octane. J. Phys. Chem. 64: 89-94. Chapman, T. W., Caban, R., Tunison, M. E. 1975. Rates of liquid-liquid ion exchange in metal extraction pro- cesses. Am. Inst. Chem. Engrs. Symp. Series. No. 152, 71: 128-135. Hancil, V., Slater, M. J., Yu, W. 1990. On the possible use of di(2-ethylhexyl) phosphoric acid/Zn as recommended system for liquid-liquid extraction: the effect of impurities on kinetics. Hydrometallurgy 25: 375-386. Harned, H. S., Hudson, R. M. 1951. The diffusion coefficient of zinc sulphate in dilute aqueous solution at 25 °C. J. Am. Chem. Soc. 73: 3781-3783. Koncar, M., Bart, H. J., Marr, R. 1988. Extraction of zinc by bis (2-ethylhexyl) phosphoric acid: influence of activity and high loading. In: Proceedings of International Solvent Extraction Conference, pp. 3-44, 175-178, Moscow, USSR. Kumar, A., Hartland, S. 1984. Correlations for drop size in liquid-liquid spray columns. Chem. Engg. Commun. 31: 193-207. Leffler, J., Cullinan, H. T. 1970. Variation of liquid diffusion coefficients with composition: binary systems. Ind. Engg. Chem. Fundam. 9: 84-88. Murthy, C. V. R. 1987. Modelling of the Rate of Stripping of Zinc from Di(2-Ethylhexyl) Phosphoric Acid in n-Hep- tane. Ph.D. Thesis, University of London, UK. Partridge, J. A., Jensen, R. C. 1969. Purification of di(2- ethylhexyl) phosphoric acid by precipitation of cop- per (II) di(2-ethylhexyl) phosphate. J. Inorg. Nucl. Chem. 31: 2587-2589. Pilhofer. T., Schroter, J. 1986. Design and performance of countercurrent extraction columns. Ger. Chem. Engg. 1: 1-7. Reid, R., Prausnitz, J. W., Sherwood, T. K. 1977. The Proper- ties of Gases and Liquids, p. 591, 4th edition, McGraw Hill Company, New York, USA. Rose, P. M., Kintner, R. C. 1966. Mass transfer from large oscil- lating drops. Am. Inst. Chem. Engrs. J. 12: 530-534. Saeed, M. T., Jamil, M. 1998a. Mass transfer parameters for a reactive system in an extraction column. Part-I. Model- ling and experimental results. Bangladesh J. Sci. Ind. Res. 33: 162-169. Saeed, M. T., Jamil, M. 1998b. Mass transfer parameters for a reactive system in an extraction column. Part-II. Compari- son with model predictions. Bangladesh J. Sci. Ind. Res. 33: 397-403. Saeed, M. T., Jamil, M. 1994a. Drop size and dispersed phase holdup in a spray column. Pak. J. Sci. Ind. Res. 37: 303-308. Saeed, M. T., Jamil, M., de Ortiz, E. S. P. 1994. Drop size and drop size distribution in a liquid-liquid extraction spray column. Pak. J. Sci. Ind. Res. 37: 297-302. Saeed, M. T., Taj, F., Jamil, M. 1994b. Modelling of mass trans- fer in the solvent extraction of zinc by di(2-ethylhexyl) phosphate. Sci. Int. 6: 303-306. Smith, R. M., Martell, A. E. 1976. Critical Stability Constants: Inorganic Complexes, vol.4: p.196, Plenum Press, NY, USA. Wilke, C. R., Chang, P. 1955. Correlation of diffusion coeffi- cients in dilute solutions. Am. Inst. Chem. Engrs. J. 1: 264-270. Yamaguchi, M., Watanabe, S., Katayama, T. 1975. Experimen- tal studies of mass transfer rate around single oscillating drops in liquid-liquid systems. J. Chem. Engg. Japan 8: 415-417. 7Mass Transfer Rates in Reactive Processes Introduction The polymer α-cellulose is that part of cellulosic materials which is insoluble in 17.5% w/w solution of sodium hydroxide at 20 °C (Seymour, 1971). This property distinguishes it from β- and γ-celluloses. It is obtained from wood pulp (Nitz, 1994) or more recently from agricultural wastes such as maize cob, rice husk or groundnut shell (Okhamafe et al., 1991). It has potential in tablet formulations as a disintegrant and a direct compression base (Okhamafe et al., 1992). The polymer is readily hydrated being capable of absorbing approximately 4 and a 1/2 times its own weight of water (Okhamafe et al., 1991). This swelling ability is its greatest asset as a disintegrant in tablet formulations. Swelling of the α-cellulose inside the tablet causes localized stress, which leads to tablet rupture. The hydrophilic swelling property of α-cellulose has also been exploited in controlled drug release from matrices which are non-disintegrating tablets (Okor et al., 1992). The previous studies (Nitz, 1994; Okor et al., 1992; Okhamafe et al., 1992; 1991) on the applicability of α-cellulose in tableting relate to freshly made tablets only, with no consideration for ageing effects. Therefore, information on its long-term performance under different conditions of storage is rare in the literature. In the tropics, high humidities prevail through- out the year. Hence, in the present study, humidity effect on the particle structure and disintegrant property of α-cellu- lose was investigated. Materials and Methods ααααα-Cellulose powder. The polymer α-cellulose was used as the test disintegrant. It was obtained locally as a fine white pow- der of irregular shaped particles from an agricultural waste, maize cob, by sodium hydroxide and sodium sulphite diges- tion process already described in detail elsewhere (Okhamafe et al., 1991). It is readily hydrated and swells in water and other aqueous fluids. Maize starch (BP grade) was also used as disintegrant in a comparative study. Magnesium stearate (BDH) was used as lubricant. Paracetamol powder (pharma- ceutical grade) was used as the test drug. It was selected for the study because it forms poorly disintegrating tablets on its own (i.e., without a disintegrant). Granulation and tableting. Paracetamol granules were formed by wet granulation technique using starch mucilage (20% w/w) as the binder fluid and dried on a tray in a hot air oven (Kottermann, Germany) to moisture content, 1.3 ± 0.2% w/w. The lubricant (1% w/w) and the disintegrant (5% w/w) were added to the granules and compressed with a single punch machine (Manesty, Type F3) to form flat faced tablets of diameter 12.5 mm, thickness 3.38 mm, and weight 550 mg. The compression load was 27.5 (arbitrary unit on the load scale) and held on the tablet for 30 sec for consolidation before releasing the load. Evaluation of the tablets. Storage tests. Twenty tablets, freshly made, were stored in each of the three chambers of different relative humidities (RH) of 1%, 78% and 100% for various time Humidity Effect on the Disintegrant Property of α-Cellulose and the Implication for Dissolution Rates in Paracetamol Tablets Michael U. Uhumwangho* and Roland S. Okor Department of Pharmaceutics and Pharmaceutical Technology, University of Benin, Benin City, Nigeria (received December 16, 2003; revised September 22, 2004; accepted September 28, 2004) Abstract. A study has been carried out to determine the effect of humidity on the disintegrant property of α-cellulose in tablet formulations. Paracetamol tablets containing α-cellulose (5% w/w) as disintegrant were employed in the study. The tablets were tested for hardness, disintegration time and dissolution rates before and after their exposure to different relative humidities (RH) of 1%, 78% and 100% at 30 °C (room temperature) for various time intervals upto a maximum of 2 weeks. Humidity effect on the particle structure of α-cellulose was determined by photomicroscopy. Tablets exposed to RH of 1% and 78% disintegrated very fast, within a minute, similar to the fresh samples. In contrast, tablets exposed to RH 100% for ≥ 24 h failed to disintegrate within 60 min even though the tablets became softer. Tablet dissolution rate was also markedly impaired in this set of tablets. Exposure of the α-cellulose powder to RH 100% for 24 h caused the particles to gel, which accounted for the impairment of its disintegrant property. Keywords: α-cellulose, disintegrant property, gel formation, humidity effect *Author for correspondence Pak. J. Sci. Ind. Res. 2005 48(1) 8-13 8 intervals up to a maximum of two weeks to avoid possible microbial degradation. To obtain RH 1%, a desiccator was charged with dried silica gel and to obtain RH 78% or 100% a beaker containing a supersaturated solution of sodium chlo- ride or distilled water was placed, respectively, in a glass cham- ber. Ambient temperature in the chambers was 30+2 °C. Moisture uptake experiments. The weight of 10 freshly made tablets was individually determined and the mean weight (M0) obtained. The tablets (10 each) were stored under the different RH values described above at room temperature for two weeks. At selected time intervals, the samples were removed from the chambers to determine their mean weight, Mt. The percent of moisture uptake (degree of hydration of the tablet) was calculated from the expres- sion as follows: Mt – M0 M0 The experiment was carried out in triplicate by using different batches of the tablets. Disintegration test. The method described in the British Phar- macopoeia (BP, 1988) was employed. Six tablets were used in each determination, which was carried out in triplicate. Dissolution test. The stirred beaker method was employed, details of which have been described previously (Okor et al., 1991). The leaching fluid was 0.1 N hydrochloric acid main- tained at 37±2 °C. Samples (5 ml) were withdrawn from the leaching fluid at selected time intervals and analysed for con- tent of paracetamol, spectrophotometrically at λ max, 245 nm. The dissolution rates were obtained by dividing the maximum amount of drug released by the time (M/T). The determination was carried out in triplicate and the mean results reported. Hardness test. This was carried out using the monsanto hardness tester (Brook and Marshall, 1968). Ten tablets were used in each determination, which was applied to three batches of tablets to obtain mean results. Test for reversibility of humidity effect on the tablets. Tablets of an initial moisture content 1.3+0.2% (w/w) were placed in a humidity chamber (RH 100%) for 24 h, after which they were dried at 60 °C for 3 h in a hot air oven to a moisture content of about 1.2% (w/w). The dried tablets were re-evaluated for hard- ness, disintegration times and dissolution rates. The test was carried out in triplicate to obtain mean results. Control tablets were stored in a desiccator (RH 1%) for 24 h and similarly tested. Test for humidity effect on the particle structure of the disintegrant powders. The disintegrant powder (α-cellulose or maize starch) was dried at 60 °C for 3 h in a hot air oven. A sample of the dried powder was spread thinly on a microscope slide, which was stored in a desiccator (RH 1%) or in a humidity chamber (RH 100 %) for 24 h at 30±2 °C. The slides were exam- ined under a microscope at the magnification of x40. Photomi- crographs of representative fields of view were taken. Results and Discussion Moisture uptake profiles of the tablets. No measurable mois- ture uptake was recorded for tablets stored in the desiccator (RH 1%) while those stored under RH (78%) showed no appreciable moisture uptake over the 2-week period. The results for tablets exposed to RH 78% and 100% are given in Table 1 where it can be seen that moisture uptake was about twice greater in tablets containing α-cellulose compared with maize starch. The maximum uptakes were about 4% (tablets with α-cellulose) and 2% (tablets with maize starch). Humidity effect on tablet disintegration time. The results on the effect of humidity on tablet disintegration time are presented in Table 2. Tablets stored in the desiccator or in the humidity chamber (RH 78%) disintegrated rapidly within Table 1. Effect of humidity on the moisture uptake (degree of hydration) of tablets containing α-cellulose or maize starch as disintegrant (5% w/w) Storage Moisture uptake (% w/w) in the time tablets containing the disintegrant (h) α-Cellulose Maize starch RH 78% 3 0.2 6 0.2 9 0.2 0.1 12 0.3 0.1 24 0.7 0.3 48 0.9 0.4 72 1.0 0.4 96 1.2 0.7 RH 100% 3 0.8 0.3 6 0.9 0.5 9 1.0 0.6 12 1.2 0.8 24 2.1 1.7 48 2.3 1.8 72 3.1 2.0 96 4.3 2.0 Note: there was no measurable moisture uptake at RH 1% (i.e., when tablets were stored in a desiccator) x 100% 9Humidity Effect on the Disintegrant Property of α-Cellulose Table 2. Effect of humidity on the disintegration time of tab- lets containing α-cellulose or maize starch (5% w/w) as disintegrant Storage Disintegration time (min) of time tablets with disintegrant (h) α-Cellulose Maize starch RH 1% 0 0.7 0.5 3 0.7 0.5 6 0.7 0.5 9 0.7 0.5 12 0.7 0.5 24 0.7 0.5 48 0.7 0.5 72 0.8 0.5 96 0.7 0.5 RH 78% 0 0.7 0.5 3 0.7 0.6 6 0.6 0.6 9 0.7 0.7 12 1.2 0.7 24 1.4 0.7 48 2.3 0.7 72 2.3 0.7 96 2.2 0.8 RH 100% 0 0.70 0.51 3 0.68 0.50 6 0.65 0.88 9 2.05 0.85 12 21.00 1.01 24 > 60.00 1.62 48 > 60.00 2.10 72 > 60.00 2.82 96 > 60.00 3.02 Table 3. Hardness profile of tablets stored under different relative humidities for various time intervals containing α-cellulose or maize starch as the disintegrants Storage Hardness (kg) of tablets time with disintegrant (h) α-Cellulose Maize starch RH 1% 0 11.5 10.5 3 11.2 10.5 6 11.0 10.2 9 11.1 10.1 12 11.4 10.1 24 11.5 10.5 48 11.2 10.8 72 11.5 10.2 96 11.1 10.4 RH 78% 0 11.5 10.5 3 11.0 10.3 6 10.8 10.0 9 10.1 9.3 12 10.0 9.0 24 9.0 8.6 48 8.2 8.0 72 7.6 7.9 96 7.0 7.2 RH 100% 0 11.5 10.5 3 10.0 10.0 6 9.0 9.6 9 8.8 9.1 12 8.2 8.8 24 5.1 7.4 48 4.0 6.1 72 2.0 4.2 96 2.0 3.5 a minute, similar to the freshly made tablets. Also, tablets with maize starch as the disintegrant, which were exposed to the higher humidity (RH 100%), disintegrated rapidly. This means that humidity had no effect on the disintegra- tion profile of these tablets. However, in the case of tablets with α-cellulose the higher humidity increased the disinte- gration time remarkably with an increase in the duration of exposure. These tablets failed to disintegrate within 60 min after their exposure to the high humidity for ≥ 24 h. This humidity seriously affected the disintegration time of these tablets. Humidity effect on tablet hardness. There was no marked change in the hardness of tablets stored at RH 1% and RH 78%, but at the higher relative humidity (100%) tablet hard- ness decreased appreciably with an increase in the duration of exposure (Table 3). For instance, after 24 h exposure, tablet hardness decreased from an initial value of about 11.5 kg to 5.1 kg (α-cellulose) and from about 10.5 kg to 7.4 kg (maize starch). The decrease was, therefore, more pronounced in tablets containing α-cellulose as the disintegrant. Humidity effect on tablet dissolution rates. The amounts of drug dissolved were plotted against time (Fig. 1). The disso- 10 M. U. Uhumwangho, R. S. Okor Fig. 1. Dissolution profile of tablets stored under different relative humidities RH 1% ( ), 78% ( ) and 100% ( ) for 24 h: disintegrant (i) α-cellulose or (ii) maize starch, (5% w/w); (×) α-cellulose released from redried tablets after previous exposure to RH 100% for 24 h. lution rates were obtained as described above and are pre- sented in Table 4. The results showed that storage of the tablets at RH 78% had no appreciable effect on their dissolu- tion rates. At the higher RH of 100%, tablets with α-cellu- lose exhibited a retarded dissolution rate. In contrast, the dissolution rates of the tablets with maize starch were not affected by exposure to the higher humidity to any appre- ciable extent. Reversibility of humidity effect on the tablets. Three sets of tablets were involved in this study: (i) tablets stored in a desiccator (RH 1%) for 24 h, (ii) tablets exposed to RH 100%, and (iii) dried tablets previously exposed to RH 100%. Results of their hardness, disintegration time and dissolution rate are presented in Table 5. The results showed that expo- sure of the tablets to the higher humidity decreased tablet hardness, prolonged the disintegration time (> 60 min), and retarded the dissolution rates of tablets with α-cellulose. Of these three parameters, drying reversed only tablet hardness. Humidity effect on the particle structure of the disinte- grant powders. Photomicrographs of the powder samples stored in a desiccator (RH 1%) and under high humidity (RH 100 %) are presented in Fig. 2. In the control samples, Table 5. Comparison of hardness (kg), disintegration time (min) and disolution rate (mg/min) of tablets containing α- cellulose (i) stored for 24 h in a dessicator, (ii) exposed to RH 100% for 24 h, and (iii) dried after previous exposure to RH 100% for 24 h Parameters evaluated Set of tablets (i) (ii) (iii) Hardness (kg) 11.5 2.0 9.2 Disintegration time (min) 0.7 60.0 60.0 Dissolution rate (mg/min) 10.6 3.3 4.4 Table 4. Amount dissolved in 45 min from tablets stored for 24 h in a desicator (RH 1%) and in humidity chambers, RH 78% and 100% Dissolution rate (mg/min) of the tablets with the disintegrant RH % α-Cellulose Maize starch 1 (control) 11.33 11.24 78 10.56 10.78 100 3.29 10.00 Leaching time (min) 11Humidity Effect on the Disintegrant Property of α-Cellulose A m ou nt r el ea se d (m g) 0 10 20 30 40 50 600 500 400 300 200 100 0 0 10 20 30 40 50 600 500 400 300 200 100 0 A m ou nt r el ea se d (m g) (i) (ii) the particles were discrete and appeared in the micrographs as elongated fibres. Exposure of the maize starch powder to high humidity appeared not to have any effect on the structure of the particles, as they remained discrete. In the case of α-cellulose, however, high humidity caused the par- ticles to swell and fuse to a coherent mass, indicating that the particles had gelled. Exposure of the tablets to the higher RH of 100% impaired the disintegrant property of α-cellulose, whereas maize starch was not susceptible to this humidity effect. This finding relates to the observation that α-cellulose pow- der gelled at room temperature upon moisture sorption, while maize starch did not display a similar gelling. The results of the moisture uptake experiments under these conditions showed that the tablets containing α-cellu- lose as the disintegrant were more easily hydrated than similar tablets containing maize starch as the disintegrant. Besides, maize starch would only gel at high tempera- tures (> 60 °C), which explains why the disintegration time of tablets containing this disintegrant was not suscep- Fig. 2. Photomicrographs showing the gelling effect of humidity on the particle structure of α-cellulose and maize starch powder. α - Cellulose Maize starch Samples exposed to RH 100% for 24 h 12 M. U. Uhumwangho, R. S. Okor tible to the humidity effect at room temperature. The disintegrant property of α-cellulose depends on its abil- ity to swell in the tablet to cause its rupture whenever the tablet is placed in an aqueous fluid (Okhamafe et al., 1992, 1991). Having swelled and gelled due to moisture sorp- tion, the capacity of α-cellulose to further swell when the tablet was placed in the disintegration fluid will be com- promised. The lower RH (1% and 78%) did not impair its disintegrant property because of the negligible moisture uptake under these conditions. Drying of the tablets after their initial exposure to higher hu- midity did not reverse the observed humidity effect on the tablets with α-cellulose. Instead, the tablets became harder. This finding suggests that the α-cellulose gel in the tablets may have formed a xerogel (dried gel) during drying of the tablets. Xerogels are known to function as binders rather than as disintegrants because of their tensile strength and rigidity (Richards, 1972). The tablets became softer due to hydration when stored under higher humidity. The decrease in hardness was more pronounced in the tablets with α-cellulose compared with maize starch because of the higher potential of the former for moisture uptake (Table 1). This decrease in hardness was expected to lead to a faster disintegration rate since it reflects a weaker interparticulate bonding within the tab- lets. On the contrary, the disintegration time (in case of the tablets with α-cellulose) actually became prolonged. This apparent abnormality is attributable to the impairment of the disintegrant property of α-cellulose, as already dis- cussed above . Although the tablets became softer, some degree of internal swelling was required before the tablets can disintegrate. The dissolution rates of the tablets with α-cellulose, that were exposed to higher humidity, were markedly retarded (Table 4) as the tablets failed to disintegrate throughout the time course of the leaching experiment. Tablets with maize starch, which were similarly exposed to the higher humidity, gave fast dissolution rates because they disintegrated readily. The explanation is that disintegration increases the particle surface area for dissolution. Conclusion The study has shown that humid conditions can cause gel- ling of α-cellulose powder at room temperature and by this mechanism impairs its disintegrant property in tablet formula- tions, with serious implications for dissolution rates. This find- ing underlines the need to protect such tablets from moisture. References BP. 1988. British Pharmacopoeia, vol. II: p. A101, Her Majesty’s Stationery Office, London, UK. Brook, D. B., Marshall, K. 1968. Crushing strength of com- pressed tablets. 1. Comparison of testers. J. Pharm. Sci. 57: 481-484. Nitz, O. T. 1994. Cellulose. In: The Encyclopaedia Americana, vol. 6: p. 139, International Edition, Grolier Incorporated, New York, USA. Okhamafe, A. O., Igboechi, A. C., Obasaeki, T. O. 1991. Cellu- lose extracted from groundnut shell and rice husk. 1. Preliminary physicochemical characterisation. Pharm. World J. 8: 120-123. Okhamafe, A. O., Igboechi, A. C., Ubrufih, C. E., Akinyemi, B. O., Ighalo, M. O. 1992. Celluloses extracted from ground- nut shell and rice husk. 2. Disintegrant properties. Pharm. World J. 9: 11-16. Okor, R. S., Iwu-Anyanwu, U., Okhamafe, A. O. 1992. Swellability of acrylate methacrylate-cellulose matrix systems and the effect on solute diffusion rates. J. Appl. Polym. Sci. 44: 749-750. Okor, R. S., Otimenyin, S., Ijeh, I. 1991. Coating of certain ma- trix core with aqueous-based systems of acrylates meth- acrylates, a watersoluble copolymer and drug release profile. J. Controll. Release 16: 349-354. Richards, J. H. 1972. Disperse Systems in Tutorial Pharmacy, S. T. Carter (ed.), p. 70, 6th edition, Pitman, London, UK. Seymour, R. B. 1971. Carbohydrates. In: General Organic Chem- istry, pp. 432-433, Barnes and Noble Inc., New York, USA. 13Humidity Effect on the Disintegrant Property of α-Cellulose Proximate, Mineral and Phytate Profiles of Some Selected Spices Found in Nigeria E. I. Adeyeye* a and E. D. Fagbohunb aChemistry Department, University of Ado-Ekiti, PMB 5363, Ado-Ekiti, Nigeria bMicrobiology Department, University of Ado-Ekiti, PMB 5363, Ado-Ekiti, Nigeria (recieved December 12, 2002; revised September 20, 2004; accepted September 30, 2004) Pak. J. Sci. Ind. Res. 2005 48(1) 14-22 Abstract. The proximate, mineral and phytate (phy) compositions, as well as the calculations for fatty acid, metabolisable energy, phy:Zn, Ca:phy and [Ca] [phy]/[Zn] were determined in 13 spices (S11 - S23) used as seasoning agents in Nigeria. The mean values of various parameters for proximate composition (g/100 g) were: moisture (3.61±3.56), dry matter (96.39±3.56), crude fat (5.46±10.02), crude fibre (27.0±17.34), crude protein (13.78±9.84), ash (4.57±2.22) and carbo- hydrates (45.58±22.25). Fatty acids were noted to be 4.37±8.02 (g/100 g) and energy was 1211.23±317.64 (kJ/100 g). Significant differences (P < 0.05) existed in moisture, dry matter, fat, fibre, crude protein and fatty acid levels. Minerals (mg/100 g) included: Na (183.08±144.19), K (1621.54±1703.99), Ca (505.38±463.24), Mg (243.08±235.74), Zn (434.92±945.86), Fe (72.54±92.38) and P (740±624.64), while Pb, Cu and Co, were not detected. The relationships between Na and K as well as between Ca and P were mostly within the desirable range with the respective ratios of Na/K (0.59±0.87) and Ca/P (2.20±3.32). Significant differences existed among the levels of Na, K, Ca, Mg, Zn, Fe, Na/K and Ca/P. The [Ca] [phy]/[Zn] had an overall mean value of 1.45±1.74 showing that the bioavailability of zinc in the spices may be low (except in S21, S22 and S23) due to the high phytate content of the spices. Keywords: spices, chemical composition, metabolisable energy, phytate levels *Author for correspondence Introduction Broadly speaking, spices are aromatic vegetable products of tropical origin that are used, in a pulverised state, primarily for seasoning or garnishing foods and beverages. They are characterised by pungency, strong odour, and sweet or bitter taste. Included in this category are hard or hardened parts of plants such as pepper, cinnamon, cloves, ginger, cardamom, turmeric, nutmeg and mace, all spices, and vanilla. In ancient times, they were valued as basic components of incense, embal- ming preservatives, ointments, perfumes, antidotes against poison, cosmetics and medicines, and were little used in food. It was only in the first century AD that spices found their way into the kitchen (Kochhar, 1986). Spices cannot be classed as foods since they are used in foods at levels that yield no sig- nificant nutritive value, but impart certain aroma and flavour to the food. The importance of spices in our daily diet is as follows (Kochhar, 1986): (1) to give an agreeable flavour and aroma (piquancy or tang) to otherwise monotonous or insipid food, particularly in the tropics where it consists mainly of starchy grains or roots, thereby adding greatly to the pleasure of eating; (2) to stimulate appetite and increase the flow of gastric juices, for which reason they are often termed as food ‘accessories’ or ‘adjuncts’; (3) to camouflage or disguise the slightly unpleasant taste of many dried meats; and (4) to increase the rate of perspiration, thus having a cooling effect on the body. The spices analysed in this work have been variously descri- bed (Akinadewo, 2001; Gill, 1992; McGraw-Hill Encyclope- dia of Science and Technology, 1987; Kochhar, 1986; Shaw, 1973). Despite the wide utilization of spices, little work has been reported on their nutritional composition. Most works have been concentrated on tropical chillies (Adeyeye and Otokiti, 1999; Fagbemi and Oshodi, 1993; Bamgbose et al., 1991; Keshinro and Ketiku, 1981). Other works on spices include: isolation of vitamin C in paprika in 1937 (Kochhar, 1986), proximate and mineral composition of black pepper (Piper guineense) (Udosen, 1995) and the determination of calcium, zinc, phytate, phy/Zn, Ca/phy and [Ca] [phy]/[Zn] molar ratios in bell and cherry peppers, okro, tomato, onion and sugarnut (Adeyeye et al., 2000). The importance of a foodstuff as a source of dietary zinc depends upon both the total zinc content and the level of other constituents in the diet that affect zinc bioavailability. Phytic acid (myoinositol 1, 2, 3, 4, 5, 6-hexakis dihydrogen phos- phate), a compound found only in plant foods, may reduce the bioavailability of dietary zinc by forming insoluble mineral chelates at the physiological pH (Oberleas, 1983). The formation of the chelates depends on relative levels of both zinc and phytic acid (Davies and Olpin, 1979). Conse- 14 quently, the phytate:Zn molar ratio is considered a better predictor of zinc bioavailability than total phytate level alone. The critical phytate:Zn molar ratio may also depend on dietary calcium level. A kinetic synergism exists between the calcium and zinc ions resulting in a Ca:Zn:phytate com- plex which is less soluble than phytate complexes formed by either ion alone (Oberleas, 1973). Unfortunately, only lim- ited data are available on the critical phytate:Zn and [Ca] [phy]/[Zn] ratios associated with decreased zinc bioavailabi- lity in human diets. Consequently, we have determined proxi- mate and mineral composition, metabolisable energy, fatty acids, phytate, phy:Zn, Ca:phy and [Ca] [phy]/[Zn] in 13 spices available for study. Materials and Methods Samples of spices. Samples of the spices were obtained from the Oba Market, Ado-Ekiti, Nigeria. All the samples were obtained in dry form. The names of the samples (in English language, botanical nomenclature and vernacular) are given in Table 1. The identification numbers ranged from S11 to S23 corresponding to 13 samples. Various parts of the vegetables used as spices are also indicated under the column, ‘part used’. Table 2 shows the group arrangement of the samples accor- ding to the phylogenetic sequence of orders and families (Hutchinson and Dalziel, 1968; 1963; 1958; 1954). The samples were screened by removing stones and other foreign bodies. Each sample was separately ground in an all glass mortar into fine powder and packed in plastic bottles and kept in the laboratory freezer until used for analysis. Analysis of the samples. The proximate analyses of the sam- ples for moisture, ash, fibre and ether extract were done by the method of AOAC (1990). Nitrogen was determined by the micro-Kjeldahl method as described by Pearson (1976) and the percentage nitrogen was converted to crude protein by multiplying with 6.25. Carbohydrates were determined by difference. All determinations were performed in duplicate. The minerals were analysed by dry-ashing the samples at 550 °C to constant weight and dissolving the ash in volumet- ric flasks using distilled, deionised water with a few drops of concentrated hydrochloric acid. Sodium and potassium were determined by using a flame photometer (Model 405, Corning, UK), using NaCl and KCl to prepare the standards. Phosphorus was determined colourimetrically using Spec- tronic 20 (Gallenkamp, UK) as described by Pearson (1976) with KH2PO4 as the standard. All other metals were deter- mined by atomic absorption spectrophotometer (Perkin-Elmer Model 403, Norwalk CT, USA). All determinations were done in duplicate. All chemicals used were of analytical grade (BDH, London). Earlier, the detection limits of the metals had been determined according to Techtron (1975). The opti- mum analytical range was 0.1 to 0.5 absorbance units with a coefficient of variation of 0.87-2.20%. All the proximate values were reported as g/100 g, while the minerals were reported as mg/100 g. Phytate was quantified using the method described by Har- land and Oberleas (1986). The blank was also prepared as described by Harland and Oberleas. The colourimeter used was a Spectronic 20 (Gallenkamp, UK). The amount of phytate 15Mineral and Phytate Profiles of Some Selected Spices Table 1. The part used, scientific and vernacular names of the Nigerian spices analysed Identification Common Vernacular Botanical name Part b number English name name (Y) a used S11 Ethiopian pepper eeru Xylopia aethiopica fruit S12 black pepper iyere Piper guineense fruit S13 African nutmeg ariwo Monodora myristica seed S14 ginger aje Zingiber officinale rhizome S15 alligator pepper atare Aframomum melegueta c seed S16 alligator pepper atare Aframomum melegueta d seed S17 garlic ayuu Allium sativum bulb S18 clove konofuru Eugenia caryophyllus fruit S19 aridan Tetrapleura tetraptera seed S20 aridan Tetrapleura tetraptera seedcoat S21 cinnamon Cinnamomum tamala leaf S22 nutmeg Monodora fragrans seed S23 rose seed Rosa sp seed a yoruba; ball parts used were dry; c bigger variety; d smaller variety in the sample was calculated as hexaphosphate equivalent by using the formula: phytate, mg/g sample = “mean K” x A x 20/(0.282 x 1000) where: A: absorbance “mean K”: std P(µg)A/n (std) phytate: 28.2% P; the phytate values were reported in mg/ 100 g Statistical analysis of the samples. Calcium/phosphorus (Ca/ P) and sodium/potassium (Na/K) ratios were calculated for all the samples (Nieman et al., 1992). The fatty acid values were obtained by multiplying crude fat value of each sample with a factor of 0.8 (i.e., crude fat x 0.8 = corresponding fatty acid value) (Paul and Southgate, 1978). The energy values were calculated by adding up the carbohydrates (x17 kJ), crude protein (x17 kJ) and crude fat (x37 kJ) for each of the samples (Kilgour, 1987). The phy:Zn, Ca:phy and Ca x phy:Zn values were calculated according to the method of Wyatt and Triana-Tejas (1994). Mean, standard deviations and coeffi- cients of variation were also calculated. Also, F test calcula- tions were done to find out if significant differences occur- red in the various parameters determined among themselves, setting the level of significance at P < 0.05 (Christian, 1980). Results and Discussion The data on the proximate composition, energy and fatty acid values of the spices are shown in Table 3. The moisture con- tent ranged between 1.10-12.23 g/100 g with a grand mean value of 3.61±3.56 g/100 g. The low values of moisture in most of the samples ensured a long shelf life of the samples without microbial spoilage but the large variation resulted in high value of coefficient of variation (CV) among them, which was 98.61. The dry matter values were generally close with 16 E. I. Adeyeye, E. D. Fagbohun Table 2. Arrangement of samples in phylogenetic sequence of Orders and Families Botanical grouping Identification Species A. Angiospermae, Dicotyledons Division Archichlamydeae Order Annonales Family Annonaceae S22 Monodora fragrans S13 M. myristica S11 Xylopia aethiopica Order Laurales Family Lauraceae S21 Cinnamomum tamala Order Piperales Family Piperaceae S12 Piper guineense Order Myrtales Family Myrtaceae S18 Eugenia caryophyllus Order Rosales Family Rosaceae S23 Rosa sp Order Fabales Family Fabaceae S19 Tetrapleura tetraptera (seed) S20 Tetrapleura tetraptera (seedcoat) B. Angiospermae, Monocotyledons Division Calyciferae Order Zingiberales Family Zingiberaceae S15 Aframomum meleguetac S16 Aframomum meleguetad S14 Zingiber officinale Division Corolliferae Order Liliales Family Allaceae S17 Allium sativum a mean value of 96.39±3.56 g/100 g and low value of CV (3.69). The crude fat values varied highly with values ran- ging between 1.03-38.46 g/100 g with a high CV of 183.50, hence this sample fits into the group of oil seeds (Adeyeye et al., 2000) as reported for sugarnut (Irvingia gabonensis) (Oshodi and Ipinmoroti, 1990). Fat is important in diets because it promotes fat soluble vitamin absorption (Bogert et al., 1994). It is a high energy nutrient and does not add to the bulk of the diet. The crude fibre values were high (except in sample S20, Tetrapleura tetraptera) having a mean of 27.0±17.34 g/100 g. Dietary fibre has beneficial effects on the muscles of the large and small intestines (Fisher and Bender, 1995) and prevents diseases such as colon diverticula (Eastwood, 1974). The crude protein was low to high in value (5.73-38.92 g/100 g). Hot spots for the protein values were observed in S22 (Monodora fragrans, 38.92 g/100 g) and S23 (Rosa sp., 30.12 g/100 g). These values were better than the results in dry bell pepper (18.28 g/100 g) and cherry pepper (18.67 g/100 g) (Adeyeye and Otokiti, 1999). An adult man of 70 kg body weight requires 0.57 g/kg of protein (FAO/ WHO, 1973), i.e., 39.9 g of protein daily. This meant that samples S22 and S23 would almost supply the required protein, assuming complete protein absorption. The available carbo- hydrates were high for most of the samples with the excep- tion of S13 (Monodora myristica, 5.49 g/100 g) and S22 (Monodora fragrans, 17.94 g/100 g). The ash levels ranged between 1.72-8.48 g/100 g. The ash content is a reflection of the mineral content obtained in this study. The calculated fatty acid values showed that many of the samples have very low values, < 0.1 g/100 g. However, S13 (Monodora myristica) had a value of 30.77 g/100 g fatty acids. This sample needs a further study to evaluate the nutritional quality of the fatty acid composition. The calculated metabo- lisable energy values showed that most of the samples were concentrated sources of energy. The energy from cereals ranged from 1.3-1.6 MJ/100 g (Paul and Southgate, 1978) indicating that most of the samples have energy concentra- tions favourably comparable to cereals. All the parameters were subjected to F test analysis and the following parameters were significantly different (P < 0.05) among themselves, moisture, dry matter, crude fat, crude fibre, crude protein and fatty acids. The statistical compari- son was based on between the groups’ variations. This is so, as comparison within the group variation would not make any sense because of the small number of samples within the groups (Table 3). 17Mineral and Phytate Profiles of Some Selected Spices Table 3. Fatty acid, energy and proximate composition (g/100 g) of spices analysed (dry weight basis) with respect to the groups Sample Moisture Dry matter Crude fat Crude Crude Fatty Carbo- Total ash Energyb identification/ fibre protein acids a hydrates statistical test S11 7.36 92.64 5.21 36.65 10.85 4.17 34.63 5.30 965.93 S12 1.34 98.66 2.54 18.45 12.33 2.03 57.98 7.36 1289.25 S13 8.69 91.31 38.46 32.25 13.20 30.77 5.49 1.91 1740.75 S14 1.62 98.38 2.60 19.73 5.53 2.08 62.88 7.64 1259.17 S15 1.32 98.68 1.20 62.02 8.45 0.96 23.94 3.07 595.03 S16 1.21 98.79 1.34 57.71 7.00 1.07 29.29 3.45 666.51 S17 2.32 97.68 2.10 18.50 14.66 1.68 57.75 4.67 1308.67 S18 1.12 98.88 3.45 19.53 5.73 2.76 65.12 5.05 1332.10 S19 1.10 98.90 1.03 13.23 9.67 0.82 70.09 4.88 1394.03 S20 12.23 87.70 1.34 1.34 8.56 1.07 74.45 2.01 1460.75 S21 2.14 97.86 5.53 15.68 14.08 4.42 58.72 3.85 1442.21 S22 3.12 96.88 3.68 34.62 38.92 2.94 17.94 1.72 1102.78 S23 3.25 96.75 2.55 21.34 30.12 2.04 34.26 8.48 1188.81 X c 3.61 96.39 5.46 27.00 13.78 4.37 45.58 4.57 1211.23 SD d 3.56 3.56 10.02 17.34 9.84 8.02 22.25 2.22 317.64 CV e 98.61 3.69 183.50 64.22 71.41 183.52 48.82 48.58 26.22 F test 14.1 352.9 1073.2 7.6 36.2 742.5 3.5 2.4 3.4 Difference * * * * * * ns ns ns a calculated fatty acids (0.8 x crude fat); benergy, calculated metabolisable energy (kJ/100g) (protein x17 + fat x37 + carbohydrates x17); c X, mean; d SD, standard deviation; e CV, coefficient of variation; *significant value; ns, non-significant value The results of the mineral analysis are shown in Table 4. Lead, copper and cobalt were not detected in any of the samples. The samples may generally be regarded as good sources of sodium, potassium, calcium, magnesium, zinc, iron and phos- phorus. Calcium in conjunction with phosphorus, magne- sium, manganese, vitamins A, C and D, chlorine and protein, are all involved in bone formation (Fleck, 1976). Calcium is also important in blood clotting, muscle contraction and in certain enzymes in metabolic processes. Magnesium is an activator of many enzyme systems and maintains the electri- cal potential in nerves (Shils, 1973). Phosphorus assists calcium in many body reactions although it also has inde- pendent functions (Fleck, 1976). Sodium and potassium are required to maintain osmotic balance of the body fluids, pH of the body, regulate muscle and nerve irritability and con- trol of glucose absorption (Fleck, 1976; Pike and Brown, 1967). Iron is reported to be very important for normal func- tioning of the central nervous system (Vyas and Chandra, 1984). Iron also facilitates the oxidation of carbohydrates, proteins and fats. Zinc is present in all tissues of the body and it is a component of more than fifty enzymes (Bender, 1992). Consumption of meat (or other animal products) with vegetables enhances the absorption of both iron and zinc (Bender, 1992; National Academy of Sciences, 1971). The values for most of the minerals have positive correlation with the corresponding mineral values in bell and cherry peppers (Adeyeye and Otokiti, 1999). Table 4 also depicts the Na/K and Ca/P ratios. Modern diets, which are rich in animal proteins and phosphorus may promote the loss of calcium in the urine (Shils and Young, 1988). This has led to the concept of the Ca/P ratio. If the Ca/P ratio is low (low calcium, high phosphorus intake), more than the normal amount of calcium may be lost in the urine, decreasing the calcium level in bones. In animals, a Ca/P ratio above two (twice as much calcium as phosphorus) helps to increase the absorption of calcium in the small intestine. Such samples in the present results included S11, S14, S21, S22 and S23, which may help in increasing the calcium content of bones. Food is considered “good” if the ratio is above one and “poor” if the ratio is less than 0.5 (Nieman et al., 1992). This means that 38.46% of the studied samples were poor in Ca/P ratio. Sodium to potassium ratio (Na/K) is also of significance, but the Na/K ratio of 0.6 is recommended (Nieman et al., 1992). About 23.08% of the samples had Na/K values greater than 0.6, while about 76.92% had lower than 0.6. This result showed that most of the spices would not promote high blood pressure. The F test values at P < 0.05 showed that Na, K, Ca, Mg, Zn, Fe, Na/K and Ca/P were significantly 18 E. I. Adeyeye, E. D. Fagbohun Table 4. Mineral composition (mg/100 g) of spices analysed (dry weight basis) with Na/K and Ca/P ratios with respect to between the groups’ variations Sample Na K Pb Ca Mg Cu Zn Fe Co P Na/K Ca/P identification/ ratio ratio statistical test S11 180 90 nda 270 130 nda 10 360 nda 70 2.0 3.86 S12 120 50 nda 170 270 nda 10 100 nda 1550 2.4 0.11 S13 180 1090 nda 200 110 nda 10 50 nda 2040 0.17 0.10 S14 130 980 nd a 340 150 nd a 10 2 nd a 80 0.13 4.25 S15 110 4120 nd a 170 90 nd a 10 60 nd a 1040 0.03 0.16 S16 240 5540 nd a 290 20 nd a 10 30 nd a 980 0.04 0.30 S17 190 2750 nda 1330 240 nda 40 80 nda 1120 0.07 1.19 S18 60 150 nda 400 100 nda 10 100 nda 540 0.40 0.74 S19 630 340 nda 680 240 nda 20 70 nda 1090 1.85 0.62 S20 60 2440 nd a 130 100 nd a 4.0 1.0 nd a 590 0.02 0.22 S21 180 700 nd a 1580 330 nd a 3110 40.00 nd a 130 0.26 12.15 S22 180 690 nd a 270 460 nd a 650 20.00 nd a 130 0.26 2.08 S23 120 2140 nda 740 920 nda 1760 30.00 nda 260 0.06 2.85 X 183.08 1621.54 505.38 243.08 434.92 72.54 740 0.59 2.20 SD 144.19 1703.99 463.24 235.74 945.86 92.38 624.64 0.87 3.32 CV 78.76 105.08 91.66 96.98 217.48 127.35 84.41 147.46 150.91 F test value 23.90 25.80 76.6 30.6 61873.18 69.9 2.7 13.5 262.0 Difference * * * * * * ns * * nd a , not detected; *significant value; ns, non-significant value different among themselves. The statistical comparison was done between the variation in groups. The phytate, phy/Zn, Ca/phy and [Ca] [phy]/[Zn] levels of the spices are shown in Table 5. All the phytate values in this report were higher than those reported for Capsicum annuum, Piper nigrum, Hibiscus esculentus, Lycopersicon lycopersicum, Allium cepa and Irvingia gabonensis (Adeyeye et al., 2000). The above trend was not consistent for phy/Zn and Ca/phy values in the current report and literature values enumerated above. A high incidence of suboptimal zinc status may exist among rural populations of low income countries consuming cereal-based diets, low in animal products (Prasad, 1983). Indeed, the first case of severe zinc deficiency in humans was reported among rural populations in Egypt and Iran (Halsted et al., 1972; Sandstead et al., 1967; Prasad et al., 1963), where 50-75% of the dietary energy was provided by cereals (Reinhold et al., 1973). The high phytic acid level of cereals in these diets was probably a significant etiological factor in the development of zinc deficiency (Davies, 1982). Oberleas and Harland (1981) reported that foods with a molar ratio of phy:Zn less than 10 showed adequate availability of Zn, while problems were encountered when the value was greater than 15. In Table 5, samples S11, S12, S17, S18, S19, S21, S22 and S23 , i.e., in 61.54% of the samples, had phy:Zn ratio less than 15. This means Zn in 61.54% of the samples would be bioavailable. Franz et al. (1980) demonstrated a lower availability of Zn in rats when fed with foods of high molar ratios of phy:Zn. In human studies, phy:Zn molar ratios of 15:1 have also been associated with reduced zinc bioavail- ability (Turnlund et al., 1984). The high phy:Zn molar ratio in most of the Nigerian diets may have serious implications, furthermore, because animal products, which are the alterna- tive sources of zinc, are sold at unaffordable prices, particu- larly to the rural Nigerians (Adeyeye, 1996). The solubility of the phytates and the proportion of zinc bound in a mineral complex in the intestines depends on the levels of calcium (Wise, 1983). In this model, phytate pre- cipitation is not complete until dietary Ca:phy molar ratios attain a value of approximately 6:1. At Ca:phy molar ratios lower than 6:1, phytate precipitation is incomplete, so that some of the dietary zinc remains in solution. The proportion remaining in solution increases with decreasing Ca:phy molar ratios (Wise, 1983). In the present studies, only sam- ples S17, S18, S19, S21, S22 and S23 were above the critical molar ratio of 6:1. These accounted for 46.15% of the samples stu- died. In the typical rural Nigerian diet, however, a leaf, leg- 19Mineral and Phytate Profiles of Some Selected Spices Table 5. Phytate and calculated phy:Zn, Ca:phy and [Ca] [phy]/[Zn] molar ratios of the spices analysed (dry weight basis) a with respect to between the groups’ variations Sample identification/ Phytateb phy/Znc Ca/phyd [Ca] [phy] e / statistical test (phy) (mg/100g) [Zn] S11 845 8.42 5.26 0.57 S12 1141 11.37 2.45 4.88 S13 1648 16.42 0.20 0.83 S14 6210 61.90 0.90 5.31 S15 2154 21.47 1.30 0.92 S16 2070 20.63 2.31 1.52 S17 972 2.41 22.53 0.80 S18 929 9.26 7.09 0.94 S19 887 4.39 12.62 0.73 S20 2873 71.36 0.74 2.34 S21 820 0.03 31.79 0.01 S22 390 0.06 11.42 0.004 S23 540 0.03 22.51 0.01 X 1652.08 17.52 9.32 1.45 SD 1546.42 13.10 10.32 1.74 CV 93.60 131.84 110.73 120.00 F test value 70.9 48.9 19.15 45.79 Difference * * * * a mean of duplicate determinations; b phytate content calculated by assuming that it contains 28.2% phosphorus; c mg of phy/MW (molecular weight) of phy: mg of Zn/MW of Zn; d mg of Ca/MW of Ca: mg of phy/MW of phy; e [mol/kg Ca] x [mol/kg phy] / [mol/kg Zn]; *significant value ume, or fish relish is always consumed with spices as seaso- ning agents. Such relishes, with the exception of legumes, are high in calcium (Adeyeye et al., 2000). Hence, the cal- cium content of the relishes in these diets may be sufficient to promote phytate-induced decrease in zinc bioavailability (Ferguson et al., 1988). Ferguson et al. (1989) showed that the molar ratio varies with different foods and recommended that this value be used in conjunction with other data to explain the availability of Zn using the Ca:phy ratio. The results for [Ca] [phy]/[Zn] are shown in Table 5. Ellis et al. (1987), and Davies and Warrington (1986) indicated that the ratio of Ca x phy:Zn is a better predictor of Zn avail- ability and noted that if the value was greater than 0.5 mol/ kg, then there would be interference with the availability of Zn. In the present results, Ca x phy:Zn values were greater than 0.5 mol/kg in S11, S12, S13, S14, S15, S16, S17, S18, S19 and S20 samples, in other words 76.92% of the samples would interfere with the Zn bioavailability. However, 23.08% of the samples would promote Zn bioavailability among the spices, which had the following corresponding mol/kg molar ratios: S21 (0.01), S22 (0.004) and S23 (0.01). This means only samples S21, S22 and S23 could satisfy the critical values of phy:Zn (< 10-15), Ca:phy (< 6.0) and Ca x phy:Zn (< 0.50 mol/kg). Statistical values of F test (P < 0.05) showed that phytate, phy:Zn, Ca:phy and Ca x phy:Zn were all significantly dif- ferent among themselves based on between the groups’ variations. There is a special delicacy in Nigeria called “pepper soup” prepared mainly from fish or meat, water, salt and pepper. The pungent taste of red pepper is due to capsaicin (C18H27NO3) while the pungent taste of black and white peppers is due to the alkaloid piperine (C17H19NO3). The piperine content of pepper is as high as 5%. Formation of N-nitrosopiperidine, a mutagen, by the reaction of nitrite with piperine in an acid solution (human stomach is acidic) has already been reported (Rao et al., 1981). Also, cooked meat is often laced with spices around its whole body surface (suya) before being consumed. Nigerian peasants normally consume large quantities of fruits and vegetables in their diet and these food materials usually contain ascorbic acid in appreciable amounts. This habitual ingestion of vitamin C in the diet is bound to ameliorate the toxic effect of N-nitrosopiperidine as reported by Greenblatt (1973). Conclusion Looking at the spice samples across board (Table 3-5) it is observed that samples S21 (C. tamala), S22 (M. fragrans) and S23 (Rosa sp.) have low moisture content, average crude fat, high crude fibre, high crude protein, moderate fatty acids and high metabolisable energy. These three are very good sour- ces of Na, K, Ca, Mg, Zn and non-hazardous Na/K and Ca/P ratios. 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Thousands of labourers working at cement distribution outlets are exposed to the product in vari- ous forms, ranging from dry cement powder, cement dust, wet cement, and concrete everyday, being absolutely ignorant of the underlying health hazards and consequences of their occupation. Cement dust, released and inhaled during bag han- dling and bag ‘dumping’, can irritate the skin causing xerosis, which may result in scaling, itchiness, burning and redness (Yang et al., 1996). Irritant contact dermatitis, as well as allergic dermatitis may develop. When cement is trapped, against the skin, it may take several months to heal and may involve hospi- talization and skin grafts. The most hazardous effects of cement dust are on the lungs. In the short term, such exposures irritate the mucous membrane of the nose and throat causing choking, as well as difficulty in breathing (Al-Neami et al., 2001; Yang et al.,1996). Cement has also been classified as a carcino- gen due to its silica content. Incidences of occupational health hazards amongst workers have been reported (Mwaiselage et al., 2004; Alvear-Galindo and Mendez-Ramirez, 1999; Ng et al., 1992). Workers in small- scale enterprises make up the second largest employment sec- tor in developing countries. They confront very high social and health risks with poor working conditions, employment insecurity and minimum health care. Most of the workers even do not know that they are being exposed to numerous health risks. Reports show that more than 70% of workers at small- scale enterprises hardly know and believe that they are ex- posed to certain occupational health hazards (Fell et al., 2003). The minimal occupational exposure standard for cement dust has been suggested to be 10 mg/m3 total inhalable dust and 4 mg/m3 total respirable dust. However, in developing coun- tries, these standards are hardly maintained, particularly in small-scale enterprises. Therefore, workers at these sites are exposed to greater risks of developing job-related diseases (Al Neami et al., 2001; Leffler and Milton, 1999; Yang et al., 1993). It has been reported that cement-related pneumocosis, e.g., silicosis, is attributed to the presence of silica in inhaled cement dust (Mengesha and Bekele, 1998; Ng and Lee, 1995). This is usually due to occupational exposure and inhalation of airborne crystalline silica. Silicosis is a disabling dust- related disease of the lungs. Even materials containing small amounts of crystalline silica may be hazardous if exposed to, in ways that produce high dust concentration, such as ‘bag Effects of Exposures to Cement Dust and Powder on Workers in Cement Distribution/Retail Outlets in Benin City, Nigeria Ifeyinwa Flossy Obuekwe ab* and Lovette Isioma Okoh a a Department of Pharmaceutical Microbiology, Faculty of Pharmacy, University of Benin, Benin City, Nigeria b 207-10807-47 Avenue, Edmonton, Alberta T6H 5J1, Canada (received July 15, 2003; revised October 28, 2004; accepted November 2, 2004) Pak. J. Sci. Ind. Res. 2005 48(1) 23-27 *Author for correspondence; b present address; E-mail: ifyobuekwe@yahoo.com Abstract. This study investigated the effects of exposures to cement dust and powder on workers in fifteen cement distribution/retail outlets in Benin City, Edo State, South-West Nigeria. Forty workers from these retail outlets were initially surveyed by using detailed and open-ended questionnaires as well as oral interviews. Twenty of them were finally subjected to microbiological tests and medical examinations after series of oral interviews and depending on the physical effects of the cement dusts on their skins. Skin, nose and eye swabs, as well as sputum samples of the subjects were collected and cultured using various growth media. Organisms isolated included Staphylococcus aureus, Branhamella catarrhalis, Bacillus spp., Klebsiella pneumoniae, Streptococcus and Proteus species, and some fungi, including Penicil- lium, Aspergillus, Trichophyton, Mucor and Epidermophyton species. Chest radiographs were also done to detect the occurrence of silicosis (occupational asthma). The results of this study have shown that depending on the length and level of exposure to cement dust and powder, effects may range from contact dermatitis, skin rash, immediate or delayed irritation of the eyes, as well as chest infections. Keywords: health hazard, cement dust, cement exposure, dermatitis, silicosis 23 dumping’ at cement depots during loading and unloading. Inhaling silica dust has also been seen to aggravate lung dis- eases, such as tuberculosis and lung cancer. It may be noted that pre-existing upper respiratory tract and lung diseases may be aggravated on inhalation of cement dust. Irritation of the moist mucous membranes of the nose, throat and upper respiratory systems also occur leaving unpleasant deposits in the nose. The risk of asthma attributable to occupational exposures is probably under-appreciated due to under-report- ing and inappropriate use of narrow definition of exposure (Leffler and Milton, 1999). This study investigates the health hazards associated with the exposure of workers at various cement distribution out- lets to cement dust and powder in Benin City, Nigeria and also provides information to workers and employers on how to maintain a healthy work force and suggests effective meas- ures to protect those at risk. Materials and Methods The study site. This study was carried out in Oredo and Egor Local Government Areas of Benin City, Edo State, South- West Nigeria. Fifteen major cement depots used as distribu- tion and retail outlets located in the city were used for the study. Subjects. The focus of this investigation was the effect of the length of exposure of each study-subject to cement dust. Forty subjects were initially used for the question- naire-based study and twenty subjects were finally used for the experimental procedures. They were grouped into five, based on the results of an initial questionnaire-based study (Table 1). These workers were not temporary work- ers, for some had worked with the same company for more than five years. Group A: those exposed to cement dust for less than 1 year. Group B: those exposed for 2 years. Group C: those exposed for between 3 to 4 years. Group D: those exposed for more than 5 years. Group E (the control group): those who had not worked or received exposure to cement dust previously. It was ensured that the subjects used for this study had not been exposed to any other type of dust, like wood dust, grain dust, which may have caused occupational health hazards to the subjects previously. This precaution was taken to forestall any previous exposure to other forms of dust, which may have affected the subjects in a similar manner, in the past. Sample collection. Sterile swabs were used to collect sam- ples from the skin, nostrils and eyes of the twenty subjects investigated. The swab sticks were appropriately labelled and the samples were immediately shaken in normal saline, within 3-5 min of the collection. Samples were dispensed aseptically into other tubes and serial dilutions were made until a final dilution of 10 -6 was obtained. The pour plate technique was used for the enumeration of microorganisms. Plates were incubated at 37 °C for 24-48 h for the growth of bacteria and 5-7 days at room temperature (28±2 °C) for fun- gal growth. Swab samples of twenty subjects were further studied on sterile blood agar plates, which were incubated at 37 °C for 24 h for the detection of pathogens. Radiological examinations were done to detect the presence of fibrotic nodules or silica deposits on their lungs. Appropriate bio- chemical tests were used for the identification of all isolated microorganisms. Results and Discussion The initial questionnaire-based study showed a response rate of 90%. All the workers had no previous knowledge of the hazards related with exposure to cement dust and powder. 70% of the subjects reported one or more skin problems in- cluding rashes, blisters, fissures, burning, dryness, scaling and itchiness (Table 1). None of the subjects with skin prob- lems reported lost work time, or physician visits for their prob- lems; thus, they continued to work without seeking medical treatment, setting themselves up for life-long health problems. 65% reported one eye problem or the other, including red- ness, pain, burning and itchiness. These occurred only on contact with cement dust and powder. 30% of them reported shortness of breath on exertion, and this was experienced by those who had worked in the cement depots for 4 years and above. 90 % of these subjects were chronic cigarette smokers. 24