Characterization of Pakistani purified bentonite suitable for possible pharmaceutical application

Applied Clay Science 83–84 (2013) 50–55

Contents lists available at ScienceDirect

Applied Clay Science journal homepage: www.elsevier.com/locate/clay

Research paper

Characterization of Pakistani purified bentonite suitable for possible pharmaceutical application Liaqat Ali Shah a,⁎, Maria das Graças da Silva Valenzuela b,c, Abdul Mannan Ehsan d, Francisco Rolando Valenzuela Díaz b, Nazir Shah Khattak e a

Institute of Physics & Electronics, University of Peshawar, Peshawar, Pakistan Polytechnic School, University of Sao Paulo, 05508-900 São Paulo, SP, Brazil Centro Universitário Estácio Radial de São Paulo, São Paulo, SP, Brazil d Pakistan Council Scientific & Industrial Research Complex, Lahore, Pakistan e Dean Faculty of Science & IT, Sarhad University of Science & IT, Peshawar, Pakistan b c

a r t i c l e

i n f o

Article history: Received 26 October 2012 Received in revised form 3 February 2013 Accepted 6 August 2013 Available online 3 September 2013 Keywords: Montmorillonite Bentonite Pharmaceutical sector Purification Pakistan

a b s t r a c t The aim of this study is to assess the suitability of Pakistani bentonite for its possible pharmaceutical use in raw and purified forms. The purified samples were obtained by two different methods i.e. simple sedimentation and classical NaCl treatment. Prior to bentonite application in pharmacy, it is imperative that they must comply with some general features as high mineral, chemical and microbial purity. The physicochemical properties especially gel formation and swelling capacity are also important to be tested to investigate its specific use. The mineralogical study reveals that the raw sample is bentonite containing mainly montmorillonite with minor contents of kaolinite, illite and quartz. The quartz impurities were removed by the purification methods as confirmed by the Xray diffraction patterns and the other properties were also improved. In view of the fundamentals of major pharmacopeias for use of bentonite in pharmacy and considering the chemical composition, microbiological results we could designate a pharmaceutical acceptable denomination for Pakistani purified bentonite samples. The two purified samples vary in interlayer cations, chemical composition and other properties that would present different behavior in pharmacy. The studied bentonite in purified form could be used as suspending and disintegrating agent because of its excellent swelling capacity and sedimentation volume. The high cation exchange capacity, high surface area and pore size distribution suggest their use as a good adsorbent of drugs and a drug carrier in controlled drug release system. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Clay is the most important, plentiful, and low cost naturally occurring material, found everywhere, in all types of rocks, in different types of water resources and in atmospheric aerosols (Gomes and Silva, 2007; Murray, 2000; Pedro, 1994; Sanfeliu et al., 2002). From prehistoric era mankind has used it for therapeutic purposes for its abundance in nature and special properties. In the 20th century, the scientific development has allowed to understand its effect on human health and to study the reasons of its utility and amazing properties. The properties for which clay is used in pharmaceutical formulations are fundamentally a high specific surface area, adsorptive capacity, rheological properties, chemical inertness and low or null toxicity for the patient (Carretero et al., 2006; Lin et al., 2002).

⁎ Corresponding author at: Institute of Physics & Electronics, University of Peshawar, Jamrude Road, Khyber Pakhtunkhwa, Postal code: 25120, Pakistan . E-mail addresses: [email protected] (L.A. Shah), [email protected] (M.G. da Silva Valenzuela), [email protected] (A.M. Ehsan), [email protected] (F.R. Valenzuela Díaz), [email protected] (N.S. Khattak). 0169-1317/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.clay.2013.08.007

Natural clay samples may vary in composition, and texture. Therefore, before considering their use, certain pharmaceutical tests should be made to estimate their possible uses in pharmacy (Viseras and Lopez-Galindo, 1999). However, a limited number of clays are used for the purpose due to its certain utility and fulfillment of fundamentals. Among them, bentonite is the one which is mostly used as both pharmaceutical excipient and active principle in the forms of liquid (suspensions, emulsions), semisolid (creams, ointments) and solid (capsules, tablets and powders) either for topical or oral administration (Carretero, 2002; Ferrand and Yvon, 1991; Kibbe, 2000; Lopez-Galindo and Viseras, 2004; Poensin et al., 2003; Viseras et al., 2007). In spite of its uses in the pharmaceutical sector, the meaning of bentonite is still ambiguous. According to mineralogists and chemists, the term bentonite corresponds to a rock mainly consisting of minerals of the smectite group. The specific pharmacopoeia monograph defines, bentonite as a native, colloidal, hydrated aluminum silicate (European Pharmacopoeia, 2005; US Pharmacopoeia, 2007), whereas purified bentonite corresponds to a colloidal montmorillonite that has been processed to remove grit and nonswellable components (US Pharmacopoeia, 2007). Bentonite must confirm the guidelines set forth by major pharmacopoeias

L.A. Shah et al. / Applied Clay Science 83–84 (2013) 50–55

(European Pharmacopoeia, 2005; US Pharmacopoeia, 2007) before considering its use in the pharmaceutical sector. Likewise crystalline silica (both quartz and cristobalite) above 2% should be avoided in bentonite proposed for pharmaceutical use (Viseras et al., 2006), as it offers sufficient evidence of carcinogenicity in laboratory animals and to some extent in humans (IARC, 1997). The use of clay in health must also be legally bound due to side effects of the toxic trace elements on humans (Mascolo et al., 1999, 2004). Attention must be paid to the amount of Pb and As which should not exceed the pharmacopoeial limits for bentonite and purified bentonite being 40 and 15 ppm for Pb and 5 and 3 ppm for As respectively (US Pharmacopoeia, 2007). In Pakistan, there are many deposits of bentonite but none of them have been investigated for pharmaceutical purposes. Now it is an emerging interest to study the development of Pakistani bentonite and thus to utilize the domestic resources with lower cost. With this aim, the Pakistani bentonite was purified by two different methods and evaluated for its suitability for possible pharmaceutical applications. 2. Materials and methods 2.1. Raw bentonite The raw bentonite used in this study was collected from a Pakistani mining site of Khyber Pakhtunkhwa province located in Shagia, locally called Karak bentonite, for the mine situated in district Karak. This bentonite deposit occurs at 33 ° 04.572/N latitude and 071 ° 09.140/E longitude, spread over an area of about 18 km2. The existence of 36 million tons of bentonite has been estimated in this deposit (Ahmad and Siddiqi, 1995). The bentonite found in Karak is mainly containing smectite, illite, and kaolinite (Saleemi and Ahmed, 2000). The color of this clay is gray and the thickness of the beds over which the deposits occur varies from 3 to 5 m. Mirza et al. (2009) evaluated its feasibility of utilizing as partial replacement for Ordinary Portland cement (OPC) in mortar and concrete mixtures. Recently its phase and micro structural analysis was also studied by Khan (2012). This study is aimed to evaluate its suitability for pharmaceutical purposes. This research will enable us to utilize domestic bentonite with lower cost and excellent properties. In order to investigate Karak bentonite, the raw bentonite was first sieved by wet sieving method using mesh number 325 and dried at 60 °C. To obtain fine powder for experimental use the dried samples were ground, sieved through mesh number 120 (ASTM) and stored in tightly closed bottles in dry controlled environment. 2.2. Purification of raw bentonite 2.2.1. Method-I: simple sedimentation The first method is a simple sedimentation using sodium hexametaphosphate Na (PO3)6 as a dispersing agent. In this method 5 g of raw bentonite was suspended in 1 L of deionized water with about 0.25 g of dispersant (Na (PO3)6) and stirred magnetically for 1 h. The suspension was allowed to stand at constant temperature. The supernatant of clay suspension above certain depth was separated after a specific time estimated by the following relation based on Stokes law assuming the spherical shape of the solid particle.   2 t ¼ 18 ηh= ðρ−σ Þ gd where ρ = density of the spherical material = 2.65(106) g/m3 σ = density of liquid = 0.99 (10)g/m3 η = viscosity of the fluid = 0.992 g/ms h: depth = 0.10 m

51

g: gravitational acceleration = 9.8 m/s2 d: diameter of the particle = 2(10 −6)m The sedimentation process was applied at least three times successively on each clay fraction until the mass ratio of the dispersed particle collected in the solution was found negligible with respect to the total amount of pristine material (i.e. 5 g). The separated supernatant was washed at least two times with distilled water to remove the traces of dispersant. 2.2.2. Method-II: classical NaCl treatment The second method is the classical NaCl treatment. This classical treatment is well described in the Handbook of Clay Science (Bergaya et al., 2006). 30 g of raw bentonite was added in 500 mL of 1 M NaCl solution, stirred magnetically overnight and centrifuged. The centrifuged slurry was dispersed three times successively in the same volume of 1 M NaCl. Finally chloride free slurry was obtained by washing with deionized water (tested by AgNO3). The purified clay was obtained through sedimentation technique by dispersing 5 g of dried treated bentonite in 1 L deionized water and collected the supernatant dispersion of particles b2 μm above (10.5 cm) depth after 8 h at 25 °C and dried at 60 °C. The dried sample was ground and fine powder was obtained for experimental use. 2.3. Mineralogy and geochemistry X-ray diffraction (XRD) was used to confirm the presence of the smectite (montmorillonite) through conventional procedures: air dried, ethylene glycol solvated, heated at 500 °C for 4 h and Li-250 °Cglycerol solvated (after Lithium saturation the sample was heated overnight at 250 °C and solvated with glycerol for 16 h at 90 °C). For qualitative analysis, the oriented samples of raw, treated and purified bentonite were obtained by deposition of their dispersion on glass slides. XRD patterns of all oriented samples were recorded by Siemens D500 diffractometer equipped with a graphite monochromatic, and Cu Kα radiation at 40 kV and 40 mA. The samples were scanned in the 2θ range of 2–70° with a step scan of 1 s per step of 0.02°. For mineral phase quantification, the sample was prepared by random powder method and XRD pattern was recorded in the same condition except for angular range 2–90° 2θ and counting time 10 s per step of 0.02°. The Rietveld method was used to quantify the clay sample by using Topas academic software. The chemical compositions were determined through X-ray fluorescence (XRF) for the most abundant elements, with their relative oxides. The sample preparation included grinding and sieving, followed by the fusion with Lithium Borate. The analysis was performed through Philips X-ray fluorescence spectrometer, model PW2400. The spectrometer was calibrated using international standard reference materials suitable for sediments and rock material. Trace elements (Pb, As, and Cd) were also measured in triplicate by using inductively coupled plasma-atomic emission spectrometry (ICP-AES), Spectro Brand Model Arcos, SOP. 2.4. Thermogravimetry/derivative thermogravimetry (TGA/DTG) Thermogravimetric analysis (TGA/DTG) of raw and purified bentonite samples was performed by Shimadzu model TGA-51, in temperature range from ambient to 900 °C. All experiments were carried out by placing about 20 mg of each sample under the dynamic atmosphere of air (50 mL min−1) with a constant heating rate of 10 °C min−1. The program TA 60 was used to determine the temperatures involved in the thermal events. 2.5. Surface area, porosity and particle size analysis The surface and pore properties were determined from N2 adsorption–desorption isotherms gained at T = 77 K, with a

52

L.A. Shah et al. / Applied Clay Science 83–84 (2013) 50–55

Micromeritics ASAP 2010 apparatus. The N2 molecular cross sectional area 0.1620 nm2 was always taken. The specific surface area and pore size distribution were estimated by Brunauer, Emmett and Teller (BET) method and Barrett Joyner–Halenda (BJH) model (Barrett et al., 1951) respectively. The t-plot method was used to calculate the micropore volume and external surface area. The particle size distribution (PSD) of the natural and purified samples was measured by means of a Laser granulometer (Master-sizer 2000, hydro 2000 MU; Malvern Instruments Ltd., Malvern, UK) based on a laser light scattering technique. Before measurements, particles were dispersed in water and sonicated.

incubated at 37 °C. The media was examined for growth, and than 1 mL of this Pre-enriched culture was transferred into two vessels having, respectively, 10 ml of Fluid Selenite–Cystine and Fluid Tetrathionate media, mixed, and incubated for 12 to 24 h at 37 °C. 2.7.2.1. Test for Salmonella species. Streaked portions from both the Selenite–Cystine and Tetrathionate media were placed on the surface of a bismuth sulfite agar medium and a Xylose–Lysine–Desoxycholate agar medium. The Petri dishes were incubated at 37 °C for 24 h. After incubation the plates were examined for the presence of the characteristic colonies of Salmonella species.

2.6. Cation exchange capacity (CEC) The technique based on ammonium acetate method was used for determining the cation exchangeable capacity (CEC) values of the samples (Chapman, 1965). 5.0 g of each sample was added in 200 mL of 3 M ammonium acetate solution of pH 7.2, stirred magnetically for 12 h and placed undisturbed for overnight. The next day the sedimented clay samples were washed three times with ethanol and dried at 60 °C. The determination of the CEC values was made by Kjeldahl Nitrogen Analyzer, model MA 036/Plus from Marconi Company. 1.5 g of treated clay along with 50 mL of distilled water and 1 mL of phenolphthalein were transferred to a Kjeldahl tube. After attaching the tube to an analyzer, 50% NaOH solution was added dropwise to the clay dispersion until the appearance of pink color. The distillation step was started and the distillate was collected in a recipient with 50 mL of boric acid mixed buffer, which was titrated with 0.1 N hydrochloric acid solution. The volume of HCl used in titration was used to determine the CEC values, listed in Table 2, by using the following relation. CEC ¼ ð100  N  V HCl Þ=m where N VHCl m

Normality of standard acid (HCl) volume of acid (HCl) used for titration mass of the sample in gram

The CEC of each sample was calculated in duplicate and the average of two values was taken as a CEC (meq/100 g) of the sample.

2.7.2.2. Test for E. coli. A portion from the remaining Fluid Lactose media was streaked on the surface of MacConkey agar medium containing in the Petri dishes. The Petri dishes were incubated at 37 °C. After incubation the presence of the characteristic colonies of E. coli were checked. 2.8. Pharmaceuticals tests 2.8.1. Swelling capacity The technique based on US Pharmacopoeia (2007) specifications, the swelling capacity of entire samples were measured in suspensions of 2 g bentonite in 100 mL by quantifying the apparent sediment volumes after 2 h. 2.8.2. Gel formation or sedimentation volume The sedimentation volumes of entire samples were measured according to the European pharmacopoeia (2005). The suspension of 6 g of each bentonite sample in 200 mL of water was prepared with a high-speed mixer operating at 10,000 RPM. Transferred 100 mL of each suspension to 100 mL graduated cylinder and allowed to remains undisturbed. The sedimentation volume was then measured by quantifying the clear supernatant volume of water after 24 h. 2.8.3. pH measurement According to US Pharmacopoeia (2007), the pH values of clay water suspensions (4 g/200 mL) were measured after 2 min of continuous stirring.

2.7. Microbiological analysis

3. Results and discussion

The microbial limit tests of all samples were carried out, according to the US Pharmacopoeia (US Pharmacopoeia, 2007).

3.1. Mineral composition and the effects of purification

2.7.1. Total aerobic microbial count Ten gram of each bentonite sample was taken in 100 mL of phosphate buffer adjusted to pH 7.2. This represents 1:10 dilution. Further dilutions were made in similar way as 102, 103, 104 etc. The soybeancasein digest agar medium (oxide) was used as culture media. Media was sterilized and cooled back to 45 °C. 1 mL of each dilution of bentonite samples (in duplicate) was poured in sterilized Petri dishes. After this, 15 mL of soybean-casein digest agar medium was added to each plate. The plates were shaken and kept for some time to solidify, inverted and incubated for 48 to 72 h at 37 °C. The colonies were counted by means of colony counter and the plates comprising 30 to 300 colonies were taken into consideration while the other plates were rejected. The average of the counted colonies for the two plates were calculated and multiplied by dilution factor and expressed as number of microorganism per gram of sample 2.7.2. Test for E. coli and Salmonella species For the assessment of E. coli and Salmonella species a Fluid Lactose medium was added to each bentonite sample to make 100 mL, and

The diffraction patterns of the air dried, ethylene glycolated, heated and Li-250 °C-glycerol solvated raw samples are shown in Fig. 1. The expansion of the basal spacing d001 for the glycolated Karak clay from d = 1.5 nm to d = 1.71 nm reveals that this major peak corresponds to smectite (Fig. 1). The d001 peak of lithium saturated clay sample collapsed after treatment with glycerol for 16 h at 90 °C (Fig. 1), reflecting the presence of montmorillonite (Lim and Jackson, 1986). The XRD results confirmed that the raw sample is bentonite, mainly composed of montmorillonite with small amounts of kaolinite, illite and quartz. The mineral percentage quantified by Rietveld method shows that the studied sample at raw form has 75% montmorillonite, 9% kaolinite, 12% illite and 4% quartz. The quartz impurities from local bentonite were successfully removed by both purification methods as shown in Fig. 2. Montmorillonites with sodium interlayer cations have the basal spacing (d001) of about 1.25 nm in its air dried state (Grim, 1968; Grim and Guven, 1978). The basal spacing d001 of the X-ray diffraction pattern of the sample purified by method-II decreased from 1.5 nm to 1.25 nm (Fig. 2). This result indicates that Pakistani raw bentonite has been converted to Na+-bentonite.

001 M = 1.71 nm

L.A. Shah et al. / Applied Clay Science 83–84 (2013) 50–55

001 K = 0.72 nm

Intensity (a.u.)

001 M = 0.96 nm

001 M = 1.5 nm

but also decreases the content of calcium oxide. It is interesting to note that sodium oxide increased significantly reflects the conversion of Ca2+-bentonite into Na+-bentonite. The contents of Fe2O3, TiO2 and MnO were comparatively low in both the purified samples attributing to its whiteness. The loss of ignition (LOI) also significantly decreased in purified sample (method-II) (Table 1). The mass percent of K2O also decreased in purified samples showing the reduction in illite or other negligible contents of impurities The Pakistani bentonite was found chemically innocent for its Pb and As, as in both raw and purified samples it was 0.05 ppm and 0.01 ppm respectively which is too less than pharmacopoeia limit i.e. not more than 40 and 5 ppm for raw bentonite, 15 and 3 ppm for purified bentonite respectively (US Pharmacopoeia, 2007).

(d)

3.3. Surface area, porosity and particle size analysis

(c) (b)

001 I = 1.05 nm

5

(a)

10

15

53

20

25

30

35

40

2 Theta (degree) Fig. 1. XRD patterns of b2 μm fraction of Karak bentonite (a) oriented (b) glycolated (c) heated at 500 °C (d) Li-250 °C-glycerol solvated. The basal spacing d (00l) of montmorillonite, kaolinite and illite are labeled 001M, 001K, and 001I.

3.2. Chemical composition

001 M =1.48 nm

001 M =1. 25nm

Chemical analyses of raw and purified samples are shown in Table 1. The slight decrease and increase in silica and aluminum oxide respectively confirmed the removal of minor amount of impurities such as quartz and a proportional increase in the clay mineral content consistent with the XRD results. The purification by method-II greatly affects not only aluminum and silica oxide like the sample purified by method-I

The value of specific BET surface area, micropore volumes/area and pore size distribution obtained from N2 adsorption-desorption isotherms applying BET, t-plot and BJH methods respectively of all the samples are summarized in Table 2. The isotherm profiles of raw and purified samples (not shown) were of type IV (IUPAC classification) curve presenting an H4 hysteresis loop indicating a slit shaped porosity between plates like particles (Gregg and Sing, 1982). The characteristic features of the hysteresis loop were due to the capillary condensation of liquid nitrogen taking place in slit like pores (mesopores). The two parts of the isotherm profile below the point p/p0 = 0.4 and above p/p0 = 0.9 corresponded respectively to adsorption in microspores and macropores. As estimated by the isotherm profile, the surface area was not mainly external but the micro porous surface contributed nearly equal for all samples (Table 2). The increase in the surface and pore properties of the studied bentonite was observed by purification process. The sample in raw form showed bimodal particle size distribution. The one with higher volume percentage centered at 4 μm attributed to the clay particle and the other centered at 12 μm showed the traces of non clay mineral particles such as quartz (Fig. 3). After purification by method-I the volume percentage of the fine particle size increased dramatically while it became negligible for the particle larger than 4 μm. The sample obtained after classical NaCl treatment followed by sedimentation showed particle size distribution with two maxima (one centered at 0.5 μm and other centered at 1.5 μm), hence attributed to the pure clay particles (Fig. 3). The purification methods especially method-II gave a significant increase in the amount of submicron-size particles (b2 μm) which revealed the presence of negligible amount of impurities.

quartz

004 M = 0.312 nm

quartz

002 M = 0. 6 2 nm

001 K = 0.7 2 nm

001 I = 1.05 nm

Intensity(a.u.)

3.4. Thermogravimetric analysis

(c) (b) (a)

5

10

15

20

25

30

35

40

2 Theta (degree) Fig. 2. XRD diffractograms of Karak bentonite (a) before purification (b)purified by method-I (c)purified by method-II. The basal spacing (d00l) of montmorillonite kaolinite and illite is labeled 001M, 001K, and 001I.

Fig. 4 shows the TGA/DTG curves of bentonite samples. The samples analyzed in this experiment displayed stepwise weight loss summarized by endothermic DTG peaks. The low temperature DTG endothermic peak that occurred in the temperature range 65–90 °C mainly corresponds to the removal of remaining adsorbed liquid and interlayer water. The higher temperature endothermic peak which occurred in the range 674–694 °C is attributed to the dehydroxylation of clay minerals. According to TGA/DTG significant differences in the thermal behavior of purified and raw samples were observed. The low temperature endothermic peak shifted to the higher temperatures in the sample purified by method-II, while it remained constant in method-I. The appearance of shouldered (double) peak between ambient and 230 °C in raw and the sample purified by method-I shows the divalent (Ca2+) cation in exchange layer as already studied (Charles, 1988). After sodium chloride treatment with purification (method-II) the double peak was found to have disappeared and the broadness of the peak decreased reflecting the replacement of Ca2+ cation by Na+ in the interlayer (Charles, 1988). It was also observed that the area of dehydroxylation

54

L.A. Shah et al. / Applied Clay Science 83–84 (2013) 50–55

Table 1 Chemical composition (in %) of raw and the samples purified by method-I and method-II.

Raw Method-I Method-II

SiO2

Al2O3

Fe2O3

MgO

Na2O

CaO

K2O

MnO

TiO2

P2O5

LOI

59.59 58.63 60.42

17.99 18.89 19.37

2.90 2.74 2.37

6.71 6.85 5.92

0.24 0.47 3.77

1.59 1.25 0.13

1.02 0.89 0.56

0.082 0.084 0.082

0.32 0.27 0.22

0.064 0.140 0.041

9.65 9.78 6.47

3.6. Microbiological analysis

Table 2 Surface area, porosity and CEC of raw and purified samples. Raw

Specific surface area m2/g Micropore volume cm3/g Micropore area m2/g External surface area m2/g Total pore volume(cm3/g) CEC(meq/100 g)

75.2 0.014 32.49 42.71 0.078 80

Purified Method-I

Method-II

95.29 0.018 41.28 54.00 0.094 89

96.24 0.019 42.76 53.48 0.096 98

The results obtained by microbiological test revealed that the entire sample has no pathogenic bacteria and it was also observed that the total amount of bacteria was in the range of different pharmacopoeias established for total aerobic acceptance limit for bentonite used in the preparation of pharmaceutical products (US Pharmacopoeia, 2007). None of the sample was contaminated by E. coli, which is again the requirement of the pharmacopoeia (US Pharmacopoeia, 2007). 3.7. Pharmacopoeial requirements

endothermic peak slightly increased and shifted to lower temperature in both the purified samples indicating the removal of impurities. The total weight loss was about 19% for the raw sample. But in the samples purified by methods-I and -II it was 20% and 16% respectively. This variation in weight loss is associated to hydration water of exchangeable cations. The difference in temperature required to eliminate the hydrated water from the two purified samples was observed. It was 235 °C and 143 °C for samples purified by method-I and method-II respectively. This effect is related to the lower link energy of the monovalent (Na+) with respect to divalent (Ca2+) ion–water link (Viseras and Lopez-Galindo, 1999), which shows the confirmation of Na+–montmorillonite obtained by method-II.

The supernatant volume prepared for sedimentation volume measurement or gel formation and pH value of all the samples meets the pharmacopoeia requirements, with pH values between 8.5 and 10.5, and sedimentation volume measurements b 2 mL (Table 3). The swelling property of raw bentonite was 7 mL which was slightly improved by purification method-I i.e. 14 mL, and the maximum value of 34 mL was obtained by method-II which was greater than the pharmacopoeia minimum required swelling power of 20–24 mL (Table 3). The significant increase in swelling power of the sample purified by method-II indicates that predominantly cation i.e. Ca2+ has been replaced by Na+ ion. This cation exchange increased the distance between the layers structure allowing the entrance of more water, hence increased the swelling volume of bentonite.

3.5. Cation exchange capacity

4. Conclusion

The exchange capacities of raw and purified samples are shown in Table 2. It was observed that the CEC value was increased by both purification methods but relatively high value was obtained for sample purified by method-II. On the basis of high CEC value not only the purified but also the raw bentonite was considered suitable for pharmaceutical purposes.

Identification of clay fraction smaller than 2 μm by XRD confirms that the studied sample is mainly composed of montmorillonite. The results also show that the sample is bentonite containing Ca2+–montmorillonite and also small amounts of illite, kaolinite and quartz. The chemical composition, particularly toxic trace elements i.e. Pb and As, microbial content limit and other pharmacopoeia suspension tests except the swelling power of the studied raw sample confirm major pharmacopoeial requirements. The purified samples were found free from quartz with considerably improved properties. Also these samples were found chemically and microbiologically innocent fulfilling all the fundamental

4

Volume in %

3

Raw Bentonite Method-I

TGA %

DrTGA mg/min

100.0

0.0

Method-II

Raw Bentonite Raw Bentonite Method-I Method-I Method-II Method-II

95.0

2

5.0%

90.0

TGA DTG TGA DTG TGA DTG

-0.1

-0.2

1

85.0 -0.3 80.0

0

-0.4

0.1

1

10

100

Particle Size (µm) Fig. 3. Distribution of particle size of Karak bentonite before and after purification.

0

100

200

300

400

500

600

700

800

900

Temp [C] Fig. 4. TGA/DTG curves of Karak bentonite before and after purifications.

L.A. Shah et al. / Applied Clay Science 83–84 (2013) 50–55 Table 3 The values of pH, swelling volume, gel formation and pharmacopeia specification. Raw

PH value (4 g/200 mL) Swelling volume (2 g/100 mL) Gel formation (6 g/200 mL)

8.33 9 mL b2 mL

Purified Method-I

Method-II

8.5 11 mL 1 mL

9.7 34 mL b1 mL

Pharmacopeia specification 9–10.5 ≥22 mL ≤2 mL

pharmacopoeial requirements. Hence these purified samples could be considered suitable for pharmaceutical and cosmetic applications. The possibility as disintegrating agent in tablet formulation depends on the swelling capacity (Fielden, 1996; Viseras et al., 2001; Wai et al., 1966). Thus for excellent use the sample purified by method-II could be preferred because of its high swelling capacity. The high CEC and pore size distribution of purified samples ensure its use as adsorbent to delay drug release. Difference in pore size distribution and CEC of the two purified samples may give different performance for supporting drugs as already proved for similar material (Cerezo et al., 2001). The difference in surface area and pore size distribution in the two purified samples could testify changes in adsorption capacity, as this effect for bentonite was previously studied (Bojemueller et al., 2001) As the two purified bentonites vary in their interlayer cation and CEC, this variation could result in changes in drug loading ability or adsorption capacity as studied already (Aguzzi et al., 2005). The purified bentonite particularly the sample purified by method-II could preferably be used as suspending agent because of its greater sedimentation volume and high swelling capacity, as recently reported (Lopez-Galindo et al., 2007).

Acknowledgments The authors would like to gratefully acknowledge the Higher Education Commission (HEC) of Pakistan for the financial support to this work under the projects “IRSIP and 5000 Indigenous Fellowship Program”.

References Aguzzi, C., Viseras, C., Cerezo, P., Rossi, S., Ferrari, F., López-Galindo, A., Caramella, C., 2005. Influence of dispersion conditions of two pharmaceutical grade clays on their interaction with some tetracyclines. Applied Clay Science 30 (2), 79–86. Ahmad, Z., Siddiqi, R.A., 1995. Minerals and rocks for industry. 202–245. Barrett, E.P., Joyner, L.G., Halenda, P.P., 1951. The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. Journal of the American Chemical Society 73 (1), 373–380. Bergaya, F., Theng, B.K.G., Lagaly, G., 2006. Handbook of Clay Science, 1st ed. Elsevier Publication, Amsterdam. Bojemueller, E., Nennemann, A., Lagaly, G., 2001. Enhanced pesticide adsorption by thermally modified bentonites. Applied Clay Science 18, 277–284. Carretero, M.I., 2002. Clay minerals and their beneficial effects upon human health. A review. Applied Clay Science 21, 155–163. Carretero, M.I., Gomes, C.S.F., Tateo, F., 2006. Clays and human health. In: Bergaya, F., Theng, B.K.G., Lagaly, G. (Eds.), Handbook of Clay Science. Elsevier, Amsterdam, pp. 717–741.

55

Cerezo, P., Viseras Iborra, C., López Galindo, A., Ferrari, F., Caramella, C., 2001. Use of water uptake and capillary suction time measures for the evaluation of the anti-diarrhoeic properties of fibrous clays. Applied Clay Science 20, 81–86. Chapman, H.D., 1965. Cation exchange capacity. In: Black, C.A., et al. (Ed.), Methods of Soil Analysis. Part 2. American Society of Agronomy, Madison, pp. 891–901. Charles, M.E., 1988. Compositional Analysis by Thermogravimetry. ASTM Special technical publication 997, Philadelphia, PA. European Pharmacopoeia, 2005. Bentonite, 5th Ed. European Pharmacopoeia Convention, Strasbourg, France 1068. Ferrand, T., Yvon, J., 1991. Thermal properties of clay pastes for pelotherapy. Applied Clay Science 6, 21–38. Fielden, K.E., 1996. Water-dispersible tablets. US patent 5556639. Gomes, C.S.F., Silva, J.B.P., 2007. Mineral and clay minerals in medical geology. Applied Clay Science 36, 4–21. Gregg, S.J., Sing, K.S.W., 1982. Adsorption, Surface Area and Porosity. Academic press, New York. Grim, R.E., 1968. Clay Mineralogy. McGraw-Hill, New York. Grim, R.E., Guven, N., 1978. Bentonites- Geology, Mineralogy, Properties and Uses. Developments in sedimentologyElsevier, New York. Khan, M.A., 2012. Phase and Microstructure of Bentonite from Khyber Pakhtunkhwa (Pakistan). (M. Phil Thesis) University of Peshawar, Pakistan. Kibbe, A.H., 2000. Handbook of Pharmaceutical Excipients. American pharmaceutical Association, Washington, DC. Lim, C.H., Jackson, M.L., 1986. Expandable phyllosilicate reaction with lithium on heating. Clays and Clay Minerals 34 (3), 346–352. Lin, F.H., Lee, Y.H., Jian, C.H., Wong, J.M., Shieh, M.J., Wang, C.Y., 2002. A study of purified montmorillonite intercalated with 5-fluorouracil as drug carrier. Biomaterials 23, 1981–1987. Lopez- Galindo, A., Viseras, C., 2004. Pharmaceutical and cosmetic application of clays. In: Wypych, F., Satyanarayana, K.G. (Eds.), Clay Surfaces: Fundamentals and Applications. Elsevier, Amsterdam, pp. 267–289. Lopez-Galindo, A., Viseras, C., Cerezo, P., 2007. Compositional, technical and safety specifications of clays to be used as pharmaceutical and cosmetic products. Applied Clay Science 36, 51–63. Mascolo, N., Summa, V., Tateo, F., 1999. Characterization of toxic elements in clays for human healing use. Applied Clay Science 15, 491–500. Mascolo, N., Summa, V., Tateo, F., 2004. In vivo experimental data on the mobility of hazardous chemicals elements from clays. Applied Clay Science 25, 23–28. Mirza, J., Riaz, M., Naseer, A., Rehman, F., Khan, A.N., Ali, Q., 2009. Pakistani bentonite in mortar and concrete as low cost construction material. Applied Clay Science 45, 220–226. IARC, 1997. Monographs on the evaluation of carcinogenic risks to humans. Silica, 68. International Agency for Research on Cancer, Lyon, France, p. 41. Murray, H.H., 2000. Traditional and new applications for kaolin, smectite, and palygorskite: a general overview. Applied Clay Science 17, 207–221. Pedro, G., 1994. Clay mineral in weathered rock materials and soils. In: Paquat, H., Clauer, N. (Eds.), Soil and Sediments: Mineralogy and Geochemistry. Elsevier-Verlag, Berlin, pp. 1–20. Poensin, D., Carpentier, P.H., Fechoz, C., Gasparini, S., 2003. Effects of mud pack treatment on skin microcirculation. Joint, Bone, Spine 70, 367–370. Saleemi, A.A., Ahmed, Z., 2000. Mineral and chemical composition of Karak mud stone, Kohat plateau, Pakistan: implications for smectite–illitization and provenance. Sedimentary Geology 130, 229–247. Sanfeliu, T., Gomez, E.T., Alvarez, C., Hernandez, D., Martin, J.D., Ovejero, M., Jordan, M.M., 2002. A valuation of the particulate atmospheric aerosol in the urban area of castellon, Spain. In: Galan, E., Zezza, F. (Eds.), Protection and Conservation of the Cultural Heritage of the Mediterranean Cities. Balkem, Publishers, pp. 61–65. US Pharmacopoeia 30-NF 25, 2007. US Pharmacopoeial Convention, Rockville, MD. (a) Bentonite, 1066; (b) purified bentonite, 1067; (c) microbial limit test. 83. Viseras, C., Lopez-Galindo, A., 1999. Pharmaceutical applications of some Spanish clays (sepiolite, palygorskite, bentonite): some preformulation studies. Applied Clay Science 14 (1–3), 69–82. Viseras, C., Ferrari, F., Yebra, A., Rossi, S., Caramella, C., López-Galindo, A., 2001. Disintegrant efficiency of special phyllosilicates: smectite, palygorskite, sepiolite. STP Pharma Science 11 (2), 137–143. Viseras, C., Cultrone, G., Cerozo, P., Aguzzi, C., Baschini, M.T., Valles, J., Lopez-Galindo, A., 2006. Characterization of northern Patagonian bentonites for pharmaceutical uses. Applied Clay Science 31, 272–281. Viseras, C., Aguzzi, C., Cerezo, P., Lopez-Galindo, A., 2007. Uses of clay minerals in semisolid health care and therapeutic products. Applied Clay Science 36, 37–50. Wai, K.N., Dekay, H.G., Banker, G.S., 1966. Applications of the montmorillonites in tablet making. Journal of Pharmaceutical Sciences 55 (11), 1244–1248.