American Journal of Materials Science and Technology (2013) 2: 10-23 doi:10.7726/jac.2013.1002

Research Article

______________________________________________________________________________________________________________________________ *Corresponding e-mail: sarang007@yahoo.co.in 1* Dr. Ira Nimdeokar P. G. & Research Centre for Chemistry, Hislop College, Civil Lines, Temple road, Nagpur- 440 001 (M.S.) India 2 Department of Chemistry, Mahatma Jyotiba Phule Educational Campus, Rashtrasant Tukdoji Maharaj Nagpur University Campus, Nagpur-440 033 (M.S.) India

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Use of Nonionic Tween-80 Surfactant Mobile Phase in Thin Layer Chromatography of Heavy Metal Cations

Sarang S. Dhote1*, Lata Deshmukh1 and L. Paliwal2

Received 28 August 2012; Published online 27 October 2012 © The author(s) 2012. Published with open access at uscip.org

Abstract The analytical potential of Tween-80, a nonionic surfactant used as a mobile phase in the thin layer chromatographic separation of heavy metal cations, is assessed. The surfactant concentrations, acidity and basicity of Tween-80solutions are investigated for the migration behavior of heavy metal cations on aminoplast+ cellulose mixture thin layer. The influence of weak or strong electrolyte and alkanol additives in the surfactant-containing mobile phase on the mobility of heavy metal cations on the aminoplast+ cellulose mixture thin layer is examined. Keywords: Tween-80; Nonionic; Acidity; Electrolyte; Aminoplast; Alkanols

1. Introduction Ion chromatography using surfactants is now the most accepted technique for analyzing inorganic cations, since it offers considerable advantages over classical methods in term of speed, precision and accuracy. This method has been used in (Mohammad et al., 1996, “a”, “b” and Sherma 1998), and the mobile phases used in inorganic solvents; or aqueous solution of acids, bases and salts. Although organic solvents like benzene, chloroform, acetone, methanol, acetonitrile, carbon tetrachloride, dioxane, acetic acid, phenols, cyclohexane and hexane are quickly removed from the sorbent layer after development, most of these are toxic to some extent. However, aqueous micellar solutions of surfactants are almost nontoxic, nonflammable and odorless. Aqueous micellar systems capable of mimicking certain properties of organic solvents (solubilizing nonpolar solutes) have been considered an attractive alternative to organic solvents as the mobile phase in the chromatographic analysis of complex mixtures. The highly selective partitioning of solutes to micelles results in unique separation possibilities for both ionic and nonionic solutes.

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Surfactants have long been used as mobile phase components in ion pair chromatography (IPC) and micellar liquid chromatography (MLC) (Bidlingmeyer et al., 1979; Knox et al., 1981; Cassidy and Elchuk, 1982; Kord and Khaledi, 1992; Hernandez-Torres et al., 1986 and Armstrong and Fendler, 1977). Since the first report by Armstrong and Henry (1980), interest in MLC has grown rapidly and it is now being used instead of traditional liquid chromatography with reversed phases(Khaledi, 1988; Amin et al., 1993; Lavine et al., 1997 and Garcia 1994). A fascinating feature of micellar systems is the presence of three phases, the micellermicropseudo, bulk mobile and stationary phases, that provide multiple interactions, resulting in unique simultaneous separation capabilities of hydrophobic and hydrophilic compounds. The applicability of a quadratic relationship between the time of mobile phase motion and the distance from the solvent entry position of the mobile phase and the front of the mobile phase was validated for micellar TLC by Boichenko (2011).The use of a micellar solution as the mobile phase in TLC was first reported by Armstrong and colleagues(1979 “a”, “b”).Despite distinct advantages, micellar systems have not been extensively used in TLC compared to their use in reversed phase high performance liquid chromatography in various areas (Landy and Dorsey, 1985;Borgerdingand Hinze, 1985;Guermouche et al., 1998; Ihara and Hobo,1993)and in micellarelectrokinetic capillary chromatography (Janini and Issaq, 1992; Fu et al., 1998; and Skocir and Prosek, 1995). Metal ions were successfully separated using anionic surfactant SDS containing amino acids by Mohammad and Sirwal(2002) and SDS with iodides and chlorides from pure soil sample by Mohammad and Jabeen (2003).Various metal ions separated on Titan-Yellow modified resin surfactant solvents (Nabi et al., 2008). Mallah et al., (2010) used SDS surfactant in micellarelectrokinetic chromatographic separation and analysis of uranium, gold and mercury in an environmental ore sample. Spectrometric estimation ofcationswas carried out using MLC by Mohammad et al. (2010). Various metal ions were separated using aminoplastsby Perisic-Janjic et al. (1991), lanthanum silicate by Ghoulipour and Husain (2000),and stannous arsenate by Husain and Mirzaie (1997) using various organic solvent systems. Rapid separation of drugs and metal ions were separated on bismuth silicate layer by Hassankhani–majd et al. (2006) and Husain and Eivazi (1975). The aim of this work was to explore the possibility of using the nonionic surfactant Tween-80 and aminoplastas a stationary phase in the separation of heavy metal cations. The roles of various factors such as surfactant concentration, pH of the medium, addition of organic modifiers (alkanols) and the addition of electrolytes (NaCl & CH3COOH) on the retention behavior of metal ions were examined.

2. Methods 2.1 Reagents Urea, formalin solution and Tween-80 were obtained from Merck, dimethylglyoxime, cellulose powder,dithizone, potassium ferrocyanide, carbon tetrachloride, methanol and ethanol were obtained from SD Fine India. All other chemicals were of analytical reagent grade.

2.2 Test Solution TLC was performed using a standard aqueous solution (1%) of the chloride, nitrate or sulphate salts of the metal ions listed.

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2.3 Detection Fe3+, Cu2+,U6+, V5+, Zr4+,and Th4+ were detected using 1% aqueous potassium ferrocyanide; Zn2+, Cd2+, Hg2+, Bi3+, Sb3+, Pb2+, Ag+, Mo6+, As3+, and W6+ using 0.5% dithizone in carbon tetrachloride; and Ni2+, and Co2+ using a 1% solution of alcoholic dimethylglyoxime. 2.4 Stationary Phase Mixture of aminoplast and cellulose powder in 1:1 (wt/wt) ratio. 2.5 Buffer Solutions Buffer solutions at pH 2.3, 4.0, 5.7, 9.0 & 11.9 were prepared by adding 0, 8.2, 10, 20 & 60ml of 0.24M NaOH, respectively, into a 100ml mixture consisting of equal volumes of boric acid (0.04M) and phosphoric acid (0.4M). 2.6 Mobile phase The various solvent systems used are found in Table 1. Table 1 List of solvent systems used as mobile phase

No. Symbol Composition A H1 Water B Aqueous surfactant solutions S1 1% Aqueous Tween-80 S2 3% Aqueous Tween-80 S3 5% Aqueous Tween-80 S4 7% Aqueous Tween-80 Buffered surfactant solutions S5 5% Aqueous Tween-80 in buffer solution of pH

2.3 C. S6 5% Aqueous Tween-80 in buffer solution of pH

4.0 S7 5% Aqueous Tween-80 in buffer solution of pH

5.7 S8 5% Aqueous Tween-80 in buffer solution of pH

9.0 S9 5% Aqueous Tween-80 in buffer solution of pH

11.9 Addition of alcohol S10 5% Aqueous Tween-80 : Methanol (9:1) (V/V) D S11 5% Aqueous Tween-80 : Methanol (8:2) (V/V) S12 5% Aqueous Tween-80 : Methanol (7:3) (V/V) S13 5% Aqueous Tween-80 : Ethanol (9:1) (V/V) S14 5% Aqueous Tween-80 : Ethanol (8:2) (V/V) S15 5% Aqueous Tween-80 : Ethanol (7:3) (V/V) S16 5% Aqueous Tween-80 : Propanol (9:1) (V/V) S17 5% Aqueous Tween-80 : Propanol (8:2) (V/V) S18 5% Aqueous Tween-80 : Butanol(9:1) (V/V) S19 5% Aqueous Tween-80 : Butanol(8:2) (V/V)

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Addition of electrolyte 1. NaCl (strong electrolyte) E S20 5% Aqueous Tween-80 containing 1g NaCl per

100ml S21 5% Aqueous Tween-80 containing 3g NaCl per

100ml 2. Acetic acid (weak electrolyte) S22 5% Aqueous Tween-80 containing 1ml acetic acid

per 100ml S23 5% Aqueous Tween-80 containing 3ml acetic acid

per 100ml

Thin-layer chromatography: 2.7 Preparation of Plates Aminoplast was prepared in the laboratory using urea and formalin solution. Mixture of aminoplast polymer and cellulose was taken in 1:1 (w/w) ratio. The TLC plates were prepared by mixing mixture of cellulose and aminoplast polymer with demineralized water in 1:2 ratios by weight with constant stirring to obtain homogenous slurry. It was then immediately applied on the glass plates by dipping method. The plates were allowed to dry overnight at room temperature and were used next day for TLC. 2.8 Procedure Test solutions were spotted onto thin-layer plates with the help of a micropipette positioned about 1.0 cm above the lower edge of the TLC plates. The spots were air-dried and the plates were then developed with the given mobile phase using the one dimensional ascending technique in glass jars. The development distance was fixed at 10 cm in all cases. Following development, the plates were again air-dried and the spots of the cations were visualized as coloring spots using the appropriate spraying reagent. RF values were then calculated. 2.9 Separation For the separation, the metal ions to be separated were mixed in equal amounts. A test solution of the resultant mixture was spotted onto the activated TLC plate, and was then air-dried. The plates were developed to a distance of 10 cm. The spots were detected and the separated metal cations were identified by their RF values. 2.10 Limits of Detection The limits of detection of the metal cations were determined by spotting different amounts of metal ion onto the TLC plates, developing the plates using the method describe above, and then detecting the spots. This method was repeated with a successive decrease in the amount of metal ion used until spots were not detected. The minimum detectable amount on the TLC plates was taken as the limit of detection.

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2.11 Semi-quantitative determination by spot-area measurement For semi-quantitative determination using the spot-area measurement method, 0.01ml volume from a series of standard solution (0.5-2%) of Cd2+ were spotted on thin layer plates. The plates were developed with (5% aqueous Tween-80: Propanol 9:1 (v/v)).

3. Results and Discussion The results of this study have been summarized in Tables 2-4 and Figs. 1-2.The mobilities of eighteen metal cationswere examined on aminoplast + cellulose layer using aqueous solution Tween-80. In order to optimize the experimental conditions, the effects of various factors such as the concentration of the surfactant, the acidity and basicity of the medium the nature of alkanols in the surfactant mobile phase, and the presence of NaCl and CH3COOH in the surfactant mobile phase on the mobility of cations was examined. 3.1 Effect of the Concentration of Surfactants In order to understand the effect of surfactant concentration, the mobility of an individual metal on aminoplast layer was determined using a wide concentration range (1%, 3%, 5% and 7%) of Tween-80. From the data in Table 2, the following trends were noticed. Table 2 RF value of the metal cations obtained on aminoplast layer developed with pure water and aqueous solution of Tween-80 as different concentration level.

RF Value

Metal Ions

water Tween-80

H1 1% 3% 5% 7%

Cu2+ 0.19T 0.30 0.37 0.45 0.47

Zn2+ 0.21T 0.22 T 0.28 0.35 T 0.35

Pb2+ 0.04 0 0 0 0

Fe3+ 0.15T 0.20 0.23 0.35 0.36

Ni2+ 0.29T 0.34 0.41 0.54 0.57

Sb3+ 0.14T 0.21 0.28 0.37 0.40

As3+ 0.15T 0.14 0.21 0.28 0.27

UO22+ 0.17T 0.19 0.25 0.30 0.28

Th4+ 0 0 0 0 0

Co2+ 0.31T 0.34 0.37 0.51 0.50

Hg2+ 0.35T 0.45 0.47 0.57 0.54

Ag+ 0.17T 0.13 0.20 0.25 0.24

Zr4+ 0.15T 0.25 0.30 0.39 0.41

VO2+ 0.14T 0.18 0.20 0.30 0.31

Cd 2+ 0.35T 0.40 0.43 0.47 0.50

Bi3+ 0.31T 0.40 0.45 0.49 0.50

W6+ 0 0 0 0 0

Mo6+ 0 0 0 0 0

T-tailed spot [RL - RT>0.3]

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1) In pure water, all metal ions except Th4+, W6+ and Mo6+ show low mobility and all these metals were found to produce tailed spots.

2) In aqueous surfactant mobile phase systems, minimum changes were observed in mobilities of metal cations.

3) The mobilities of various metal ions increase as soon as the concentration of Tween-80 increases from 1% to 5%, in later concentration mobility nearly same as in 5% concentration.

4) Pb2+, Th4+, W6+ and Mo6+ were strongly retained by aminoplast and remained at the point of application.

5) Increasing concentration of Tween-80 from 1% to 7% results in minor changes in the mobility of metal ions which indicate that the various types of concentration-dependent structures formed by surfactant molecules with concomitant change in their aggregates do not effectively influence the mobility of metal ions, as explained by Mikhal’chuk and Sardyuk (1983).

3.2 Effect of Acidity and Basicity of Medium Thin layer chromatography of metal ions was performed using aqueous 5% Tween-80 solution prepared in borate phosphate buffer of different pH values (pH-2.3, 4.0, 5.7, 9.0 and 11.9). The results obtained with the buffered surfactant solutions have been summarized in Table 3. Table 3 Mobilities of metal cations developed with buffered surfactant solutions of different pH

METAL

RF value

pH 2.3 pH 4.0 pH 5.7 pH 9.0 pH 11.9

Cu2+ 0.09sp. 0.15sp 0.44 0.13sp 0.09sp.

Zn2+ 0.13sp. 0.14sp 0.40 0.10sp 0.12sp.

Pb2+ 0 0 0 0 0

Fe3+ 0.15sp 0.13 sp 0.39 0.22sp 0.11sp

Ni2+ 0.20sp 0.25sp 0.65 0.22sp 0.12sp

Sb3+ 0.10sp 0.13 sp 0.27 0.19 sp 0.15sp

As3+ 0.14sp 0.11sp 0.25 0.15sp 0.11sp

UO22+ 0.11sp 0.11sp 0.44 0.19sp 0.09sp

Th4+ 0 0 0 0 0

Co2+ 0.17sp 0.20sp 0.66 0.16sp 0.17sp

Hg2+ 0.11 0.12 sp 0.89 0.26sp 0.17sp

Ag+ 0 0 0 0 0

Zr4+ 0.15sp 0.16 sp 0.62 0.15sp 0.15sp

VO2+ 0.13sp 0.16sp 0.63 0.13sp 0.12sp

Cd 2+ 0.11, 0.24 0.25sp 0.60 0.18sp 0.11sp

Bi3+ 0.16sp 0.13sp 0.60 0.13sp 0.06sp

W6+ 0 0 0 0 0

Mo6+ 0 0 0 0 0

sp- Spread Spot

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The following conclusions may be drawn from these results: 1) Change in pH of mobile phase systems had strong effects on the mobilities of all metal

cations except Pb2+, Th4+, Ag+, W6+ and Mo6+. All these metal ions did not show any motilities irrespective of the fact whether mobile phase medium used was acidic or basic in nature.

2) With acidic (pH = 2.3& pH=4.0) and basic (pH = 11.9& pH= 9.0) mobile phase systems, all metal ions showed little mobility with spread spots.

3) Compact spots of all metal ions except Pb2+, Th4+, Ag+, W6+ and Mo6+ were visualized in neutral range of pH (pH= 5.7).

4) Cd2+ exhibited a peculiar behavior as it gave double spots (RF = 0.11, 0.24) with mobile phase of pH=2.3.

3.3 Effect of Addition of Alcohol To investigate the retention of metal cations on aminoplast layer hybrid-mobile phase systems comprising of 5% Tween-80–water-alcohol (methanol, ethanol, propanol and butanol)were also used and better chromatographic performance in terms of promotion of differential migration of metal ions by these mobile phases over aqueous micellar mobile phase systems was observed. The RF values of metal cations were determined with micelle-water-alcohol mobile phases (S10-S19) consisting of methanol (9:1, 8:2 and 7:3 v/v), ethanol (9:1, 8:2 and 7:3 v/v), propanol (9:1 and 8:2 v/v) and butanol (9:1 and 8:2 v/v) in ratios with surfactant. In all cases, a general trend of decreasing RF values with increasing alcohol concentration was noticed. The representative’s plots are given in Fig. 1(a)& (b). The retention mechanism is connected with adsorption of surfactant of the stationary phase. As long as the surface of the amoniplast layer is saturated by the adsorbed surfactant, that is, there are no free functional groups on the layer for the interaction, metal ions move faster, showing high RF value. The addition of alcohol to the mobile phase leads to the reduction in the adsorbed amount of surfactant on the stationary phase, which causes an increase in retention of solutes and a change in selectivity. Thus, in the presence of alcohol, theaminoplast layers are not completely saturated by adsorbed surfactant and there are still free functional groups, the interaction between them and the metal cations affect the retention pattern. In these cases, the nature and polarity of alcohol plays an important role in the separation. In general, the better separation possibilities were realized with mobile phase (S16)- 5% Tween-80 + propanol (9:1 v/v ratio). We successfully used this mobile phase to estimate Cd2+ by a semi-quantitative method. Thus, moderately polar alcohol (propanol) provides superior separation of metal cations compared to more polar alcohol (methanol).

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Fig 1 (a). Mobility of metal cations on aminoplast layer developed with 5% aqueous Tween-80 containing different amounts of alcohols.

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Fig 1 (b). Mobilities of metal cations on aminoplast layers developed with 5% aqueous Tween-80 containing different amounts of alcohols.

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3.4 Effect of Addition of Electrolytes The effect of addition of weak electrolyte (CH3COOH) and strong electrolyte (NaCl) at different concentration levels in the eluent 5% aqueous Tween-80 on the mobility of metal cations was examined. The RF values of metal cations were determined with surfactant–water–electrolyte mobile phase consisting of NaCl and CH3COOH and 5% Tween-80 in various ratios (9:1 and 8:2). From the available data in Table 4, the following trends are noticeable:

1) Higher mobility and compact spots were obtained in mobile phase containing the weak electrolyte CH3COOH compared to mobile phase containing the strong electrolye NaCl.

2) Similar mobilities were obtained in all concentration ranges of CH3COOH. 3) Pb2+, Th4+, Ag+, W6+ and Mo6+ did not show any mobility in all cases of mobile phases

containing both electrolytes. Table 4 RF value of the metalcations obtained on aminoplast layer developed with 5% aqueous Tween-80 with addition of electrolytes.

RF Value

Metal Ions

S20 S21 S22 S23

Cu2+ 0.23 0.26 0.35 0.37

Zn2+ 0.12 T

0.18 0.36 T

0.35

Pb2+ 0 0 0 0

Fe3+ 0.10 0.13 0.35 0.36

Ni2+ 0.34 0.34 0.48 0.47

Sb3+ 0.21 0.20 0.37 0.40

As3+ 0.14 0.11 0.18 0.17

UO22+ 0.16 0.15 0.20 0.18

Th4+ 0 0 0 0

Co2+ 0.24 0.27 0.41 0.40

Hg2+ 0.25 0.27 0.47 0.44

Ag+ 0.13 0.20 0.25 0.24

Zr4+ 0.15 0.19 0.29 0.31

VO2+ 0.18 0.15 0.30 0.31

Cd 2+ 0.20 0.23 0.27 0.30

Bi3+ 0.14 0.15 0.29 0.30

W6+ 0 0 0 0

Mo6+ 0 0 0 0

T-tailed spot [RL - RT>0.3]

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4. Semi-quantitative Estimation of Cd2+ An attempt has been made to determine the recovery of Cd2+ spiked into water using spot area measurement method using 5% aqueous Tween-80 + propanolin a 9:1 v/v ratio mobile phase system. A linear relationship obtained when the amount of sample spotted was plotted against area of the spot follows the empirical equation ζ=km, where ζ is the area of the spot, m is the amount of solute and k is a constant. A representative plot for Cd2+is shown in Fig. 2. The linearity is maintained up to 300 µg/spot. At higher concentrations, a positive deviation from linear law was observed. The accuracy and precision was around Cd2+= ±53 %.

Fig 2. Calibration curve for semi-quantitative determination of Cd2+. Stationary Phase: Aminoplast + Cellulose

Mobile phase: 5% aqueous Tween-80 + Propanol (9:1)

5. Conclusion The monomer structure of the aminoplast Fig. 3 (a) and the polyamide Fig. 3(b) show that they possess the same functional groups, capable of hydrogen bond formation and complexation of metal ions. However, their macromolecular structures and consequently their polarities and absorptivities are different. The aminoplast is so selective that in many cases one metal ion can be separated from numerous cations. Normal phase TLC of heavy metal cations has been examined. The surfactant concentration from 1% to 7% resulted in minor changes in the mobility of individual metal ions. At neutral pH range, effective separation can be achieved. The optimum experimental conditions for separating various metal ions include the use of a 5% Tween-80 buffered surfactant solutions (pH-5.7) as the mobile phase and aminoplast as the stationary phase. Aqueous 5% Tween-80 with added alcohols, NaCl or acetic acid resulted in minor changes in mobility of most metal ions.

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Fig 3(a). Monomer structure of aminoplast Fig 3(b).Monomer structure of polyamide

6. Application The proposed method was applied for the identification of various toxic metal ions in spiked industrial waste water, river and power plant ash after separation on aminoplast layer. The resultsshown in Tables2-4 and Figures 1and 2 clearly demonstrated that this method is very useful for the separation and identification of metal cations from environmental samples as well as from multicomponent mixtures using Tween-80 with or without organic additives on aminoplastlayers.

Acknowledgements The authors would like to thank the principal and head of the Department of Chemistry, and Director of the Dr. Ira Nimdeokar P. G. & Research Centre for Chemistry Hislop College Nagpur, and M.S. India for the provision of research facilities used in our study.

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