- Email: [email protected]
Study of adsorption behavior of malachite green on polyethylene glycol micelles in cloud point extraction procedure
Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Study of adsorption behavior of malachite green on polyethylene glycol micelles in cloud point extraction procedure Jianwei Chen, Jianwei Mao, Xiaorong Mo, Juying Hang, Mingmin Yang ∗ College of Science, Nanjing Agricultural University, Nanjing 210095, China
a r t i c l e
i n f o
Article history: Received 26 December 2008 Received in revised form 14 May 2009 Accepted 14 May 2009 Available online 22 May 2009 Keywords: Adsorption Cloud point extraction Langmuir isotherm Polyethylene glycol Malachite green
a b s t r a c t Cloud point extraction (CPE) was carried out to extract malachite green (MG) from aqueous solution and shrimp samples using a series of polyethylene glycol (PEG) surfactants: PEG10000, PEG6000, PEG2000 and PEG600. The adsorption mechanism between PEG micelles and MG molecules was studied. The data of equilibrium concentrations and adsorption amounts in the four PEG–MG systems followed the Langmuir type isotherm. On some assumptions, a developed Langmuir isotherm was used to calculate the feed surfactant concentration required for the removal of MG up to an extraction efficiency of 90%. The calculated PEG concentrations were used in CPE process, and other influence factors on phase behavior were investigated. Under the optimal conditions, recoveries of MG were 82.16–92.41% in aqueous solution and 78.16–86.54% in shrimp samples. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Malachite green (MG) is an N-methylated diaminotriphenylmethane dye still used as fungicides and antiseptic in aquaculture and fisheries [1]. It is also most commonly used for the dyeing of cotton, silk, paper, leather and also in the manufacturing of paints and printing inks. Malachite green has properties that make it difficult to remove from aqueous solutions and also toxic to major microorganisms [2]. Therefore, because of its industrial importance and possible exposure to human being, malachite green poses a potential health hazard and is of environmental concern. Malachite green is highly cytotoxic to mammalian cells and also acts as a liver tumor-enhancing agent [3]. Malachite green when discharged into receiving streams will affect the aquatic life and causes detrimental effects in liver, gill, kidney, intestine, gonads and pituitary gonadotrophic cells [4]. Thus, development of novel and reliable method is necessary for the determination of malachite green in environmental samples such as shrimp samples. The pretreatment of sample, which is used to separate and concentrate analyte, is an important step in analytic process. A number of techniques aimed at preferential separation of different types of solute from matrix have been developed, the liquid–liquid extraction (LLE) [5], solid phase extraction (SPE) [6], solid phase micro-extraction (SPME) [7], supercritical extraction (SE) [8] and cloud point extraction (CPE) [9] are popular nowadays. Among all
∗ Corresponding author. Tel.: +86 25 84395204; fax: +86 25 84395255. E-mail address: [email protected] (M. Yang). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.05.015
these, CPE is one of the methods which is getting more and more attention because it is easily operated and environment-friendly, and the method is a useful and simple technique without any sophisticated instrument. The mechanism of interaction between surfactant and solute should be studied for obtaining more suitable, efficient, cheap type of surfactant. CPE is proposed to be a process of interaction between solute and micelles of surfactant, the interaction can be treated as adsorption of solute on the surface of the micelles or some other sites within micelles. The micelles of surfactant are adsorption center. The micelles have the ability to adsorb analyte inside their central core or outer palisade layers, this can be suggested by the monolayer coverage of the solute on the surface of the micelles. Therefore, this type adsorption can be expressed by Langmuir isotherm [10]. The adsorption ability of micelle is presented by the adsorption capacity (m) and the energy of adsorption (n). The values of m and n vary with temperature, characteristics of surfactant and solute. However, when a CPE system is separated into two phases at a fixed temperature, the adsorption capacity (m) and the energy of adsorption (n) are constant. Values of m and n can be calculated from the slope and intercept of the linear form of Langmuir equation [11]. As values of m and n are taken into a developed Langmuir equation, the amount of surfactant required for the removal of solute up to a desired level can be calculated. In CPE process, the adsorption area is an important factor; the sizes of micelles of surfactant have significant change with different molecular mass, because it brings about great changes of adsorption area. Therefore, the adsorption ability of surfactant of different molecular mass in CPE procedure should be investigated.
232
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
In this work, the adsorption behavior of malachite green on micelles of a series of Polyethylene glycol (PEG) was studied at fixed temperature. It was found that the experimental data of the adsorption amounts and concentration of solute fitted the Langmuir type isotherm. Values of m and n were calculated by using the linear model of Langmuir isotherm and a new Langmuir isotherm equation was derived based on some fundamental assumptions, a linear correlation between the PEG concentrations required and various feed malachite green concentrations was found. The correlation was used to design CPE process. 2. Experimental
efficiency of MG in CPE process was calculated based on the above results. 2.2.3. Sample preparation 0.5 ± 0.05 g of malachite green-free shrimp samples spiked with different concentrations of malachite green were used to test the applicability of the method to real samples. The spiked shrimp samples were ground and sonicated in the presence of 6 mL of 0.2 mol L−1 trichloroacetic acid. The mixture was filtered and 5 mL of filtered solution was introduced to centrifugal tube. The residue was re-washed with 3 mL water, and the eluant was collected with the first isolated fraction. The solution in the centrifugal tube was treated as Section 2.2.1.
2.1. Chemicals and materials 3. Results and discussions Polyethylene glycols (molecular mass 600, 2000, 6000, 10,000) were obtained from Guanghua Chemical Co. Ltd. (China). Various concentrations (w/v) of aqueous surfactant solutions were prepared by weighing appropriate amounts of the surfactant and directly dissolving the surfactant in water. Malachite green (C23 H25 ClN2 , MW364.95, 99%) was purchased from Shanghai Chemical Reagent Company (China). The stock solution containing 1.0 mg L−1 of MG was prepared by dissolving the reagent in distilled water. Working solutions were prepared daily by an appropriate dilution of the stock solution. (NH4 )2 SO4 was obtained from Nanjing Reagent Plant (China). Trichloroacetic acid was obtained from LingFeng Reagent Co. Ltd. (China), and diluted with distilled water to 0.2 mol L−1 . All the other reagents and solvents were of analytical grade. The experiments were carried out in plastic vessels to avoid adsorption of MG on glass surfaces. 2.2. Apparatus and methods A UV-1700, UV–visible spectrophotometer (Shimadzu, Japan) was used for recording absorption spectra and absorbance. A Mettler Toledo Delta 320 pH-meter equipped with a Mettler glass electrode was used for pH adjustments. A thermostat from Tongzhou Instrument Plant (China) maintained at the desired temperature within ±1.0 ◦ C was used for the cloud point experiments. A centrifuge (TDL40B) from Anke Instrument Plant (China) was used to separate dilute and coacervate phases. 2.2.1. Cloud point extraction procedure PEG–MG systems were prepared by mixing different concentrations of solutions of PEG and MG, and the mixing solutions were diluted to 10 ml with distilled water followed by adding 2.5 g of (NH4 )2 SO4 , and then the solutions were kept in thermostat bath for 10 min at (60 ± 1) ◦ C. The complete separation of dilute and coacervate phases was achieved by a centrifuge. After the dilute phase was sucked out by the aid of a syringe, the volumes of the coacervate phase and the concentrations of PEG and MG in dilute phase were measured, respectively. 2.2.2. Determination of concentrations of PEG and MG in dilute phase The concentrations of MG and PEG were determined by the Shimadzu UV-1700 spectrophotometer. Standard curve technique was used to find out the concentrations of both MG and PEG. The concentrations of PEG and MG were determined at 280 and 620 nm, respectively. In order to eliminate the interference of PEG micelles to the determination, the dilute phase was diluted to ensure that the PEGs concentrations were lower than their critical micelle concentrations (CMC). The quantities of MG and PEG in coacervate phase were calculated by material balance, respectively. The extraction
This section is divided into three parts. In first part, the effects of different factors such as concentration of (NH4 )2 SO4 , pH of the solution, temperature and equilibration time, on the extraction efficiency of MG were discussed. The values of adsorption capacity (m) and energy of adsorption (n) were defined in the second part. In last part, the expression of feed surfactant concentration (Cos) as a function of feed MG concentration (Co) was obtained and verified by application experiments. 3.1. Partition behaviors of MG in CPE procedure This part described the adsorption phenomena of MG in PEG10000, PEG6000, PEG2000 and PEG600 systems, respectively. In the four systems, the concentrations of PEGs and MG were 40 g L−1 and 6.85 × 10−5 mol L−1 , respectively. 3.1.1. Effect of pH In order to prevent the discolor of MG, MG must be kept in acid solution [12]. Fig. 1 shows the influence of pH on the extraction efficiency of MG. Changing the pH from 2.0 to 6.5, the extraction efficiencies of MG had no significant change in the four PEG systems. 3.1.2. Effect of concentration of (NH4 )2 SO4 The salting out effect made water molecular into the dilute phase, and addition of salt can accelerate phase separation and fall the cloud point of surfactant solution. (NH4 )2 SO4 is a stronger phase separation salt. The amount of salt used increased with the hydrophilicity of surfactant, the hydrophilicity of PEGs was followed an order of PEG600 > PEG2000 > PEG6000 > PEG10000. As shown in Fig. 2, in the four PEG systems, for phase separation, more amount of (NH4 )2 SO4 was required, the lower PEG molecular
Fig. 1. Effect of pH on the extraction of malachite green.
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
233
Fig. 2. Effect of salt concentration on the extraction of malachite green.
Fig. 3. Effect of temperature on the extraction of malachite green.
mass. When recovery of 95% was obtained, amounts of (NH4 )2 SO4 required were 1.1 g for PEG10000, 1.3 g for PEG6000, 1.5 g for PEG2000, and 1.9 g for PEG600.
alteration in the four PEG–MG systems. CMC of non-ionic surfactant decreases at higher temperature [13], which leads to an increase of the micelle amounts, therefore, the extraction efficiency of solute shall be increased with increasing temperature. In the following experiments, the temperature was selected at 60 ◦ C.
3.1.3. Effect of temperature The influence of temperature on the extraction efficiencies of MG was investigated in the four PEG systems. Fig. 3 shows the effect of temperature on the extraction of MG. The extraction efficiencies of MG increased with temperature in the range of 20–60 ◦ C, and beyond 60 ◦ C, the extraction efficiencies had no significant
3.1.4. Effect of equilibration time In CPE process, the equilibration time was much shorter than that of solid adsorbents in common use [14,15]. For all the
Fig. 4. Adsorption isotherms of MG over PEGs: (a) PEG10000–MG, (b) PEG6000–MG, (c) PEG2000–MG, (d) PEG600–MG.
234
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
Table 1a Mean values of slope and R.S.D. of different PEGs. PEG10000
a
PEG2000 −5
(3.592 ± 0.024) × 10 0.66
Mean R.S.D.b (%) b
PEG6000 −5
a
PEG600 −4
(6.488 ± 0.091) × 10 1.39
(3.172 ± 0.060) × 10 1.86
(3.009 ± 0.062) × 10−3 2.06
Mean value for five calculations. Standard deviation for five calculations.
Table 1b Mean values of intercept and R.S.D. of different PEGs.
Meana R.S.D.b (%) a b
PEG10000
PEG6000
PEG2000
PEG600
44.464 ± 8.422 18.94
63.216 ± 3.534 5.59
(2.240 ± 0.139) × 102 6.22
(1.299 ± 0.094) × 103 7.21
Mean value for five calculations. Standard deviation for five calculations.
four PEG systems, the extraction efficiencies increased with time and the extraction equilibrium was attained during a shorter time. The extraction efficiencies were found to be constant beyond 10 min. Therefore, the equilibrium time of 10 min was selected. 3.2. Adsorption isotherm 3.2.1. Langmuir isotherm In order to determine adsorption capacity and energy of adsorption of the different PEG–MG systems, the data of concentrations and adsorption amounts from CPE procedures of the four PEG–MG systems were applied to obtain Langmuir isotherm. The CPE procedures were carried out as described in Section 2.2.1 at pH 4.5. If an adsorption process is the formation of monolayer of adsorbate on the outer surface of adsorbent, and after that no farther adsorption takes place, this type of adsorption can be expressed as the well-known Langmuir model (Eq. (1)). q=
mnCe 1 + nCe
(1)
where q is the amount of adsorbate adsorbed per mol of adsorbent at equilibrium (mol mol−1 ), Ce is the equilibrium concentration of adsorbate in dilute phase (mol L−1 ). The constants m and n are the Langmuir constants, m signifies the adsorption capacity (mol mol−1 ) and n is related to the energy of adsorption (L mol−1 ) [16]. In this study, the adsorption behavior of MG in PEG solutions was investigated as following steps: the concentrations of MG in the feed were 6.85 × 10−5 , 1.37 × 10−4 , 2.05 × 10−4 , 2.74 × 10−4 and 5.48 × 10−4 mol L−1 , and the concentrations of PEG in the feed were varied as 40, 60, 80, 100 and 120 g L−1 for each concentration level of MG, and all experiments were carried out at (60 ± 1) ◦ C. After phase separation, the volumes of coacervate phase and the concentrations of PEG and MG in dilute phase were measured. The amounts of PEG and MG in coacervate phase were calculated by material balance. Fig. 4(a) (b), (c) and (d) shows the adsorption isotherms of PEG10000–MG, PEG6000–MG, PEG2000–MG and PEG600–MG systems, respectively, which is illustrated by plotting q vs. Ce.
Fig. 5. Plotting 1/q vs. 1/Ce for m and n calculations.
3.2.2. Evaluating the values of m and n The Langmuir equation can be linearized into the following form: 1 1 1 = + q m mnCe
(2)
According to Eq. (2), a plot of 1/q vs. 1/Ce gives a straight line with slope 1/mn and intercept 1/m. The data of m and n are determined by using slope and intercept of the linear form (Eq. (2)) of the Langmuir model. In order to accurately calculate the values of m and n, five replications were carried out for each of the PEG–MG systems. The values of slope and intercept are calculated and are tabulated in Tables 1a and 1b. The values of m and n of each PEG–MG system are calculated by the mean values of these slopes and intercepts, which are tabulated in Table 1c. The linear plots of 1/q vs. 1/Ce are shown in Fig. 5, and the solid lines were plotted with mean values of m and n. The chain length of surfactant can affect its hydrophobicity. The chain length increases with surfactant molecular mass, which leads to an increase of hydrophobicity and adsorption ability. This tendency can be observed in Table 1c. Values of adsorption capacity (m) and energy of adsorption (n) are obviously increase with PEG molecular mass and follows an order, PEG10000 > PEG6000 > PEG2000 > PEG600.
Table 1c Calculated m and n of different PEGs. PEG10000 a
−1
m (mol mol na (L mol−1 ) a
)
PEG6000 −2
(2.324 ± 0.445) × 10 (1.239 ± 0.240) × 106
Calculated by mean values of slope and intercept.
PEG2000 −2
(1.586 ± 0.079) × 10 (0.975 ± 0.055) × 106
PEG600 −2
(0.448 ± 0.026) × 10 (0.707 ± 0.048) × 106
(0.770 ± 0.047) × 10−3 (0.432 ± 0.031) × 106
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
235
Table 2 Determination results of recovery in water samples. Malachite green added (mol L−1 )
PEG
PEG addeda (mol L−1 )
Malachite green (n = 5) found (mol L−1 ), R.S.D. (%)
10000
2.74 × 10 1.37 × 10−6 2.74 × 10−6
−4
3.23 × 10 3.66 × 10−4 4.19 × 10−4
2.29 × 10 (2.50) 1.15 × 10−6 (2.44) 2.44 × 10−6 (2.25)
83.66 84.03 89.15
6000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
5.98 × 10−4 6.60 × 10−4 7.38 × 10−4
2.48 × 10−7 (2.19) 1.25 × 10−6 (2.10) 2.53 × 10−6 (1.83)
90.47 91.45 92.41
2000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.90 × 10−3 3.12 × 10−3 3.39 × 10−3
2.31 × 10−7 (3.60) 1.13 × 10−6 (3.23) 2.47 × 10−6 (2.66)
84.46 82.66 90.17
600
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.73 × 10−2 2.86 × 10−2 3.01 × 10−2
2.35 × 10−7 (3.86) 1.13 × 10−6 (3.03) 2.38 × 10−6 (3.14)
85.74 82.16 86.80
a
−7
Recovery (%)
−7
Added by the calculated concentration.
3.3. Determination of correlation between the initial surfactant concentration required and the feed solute amount
(2) The volume of dilute phase is so large that Vd can be approximate to the volume of initial solution before CPE (Vo).
3.3.1. Calculation of the surfactant concentration required for the extraction of solute up to a desire level Using Eq. (2), a calculation procedure is outlined to determine the amount of surfactant required for the extraction of solute up to a desired level. The amount of adsorption is defined as,
According to the above assumptions, combining Eqs. (2)–(5) leads to:
q=
Qd Gs
(3)
where Qd and Gs are the amount of solute and surfactant in coacervate phase, respectively. Qd E= Qo
(4)
where E is the extraction efficiency and Qo is the feed amount of solute.
1 Vo Go = + EQo m mnQo(1 − E)
(6)
Go = Cos Vo
(7)
Qo = Co Vo
(8)
where Cos and Co are the concentrations of surfactant and solute in the feed, respectively. Combining Eqs. (6)–(8) leads to: Cos =
E ECo + m mn(1 − E)
(9)
where Vd is the volume of dilute phase. For determining the correlation between the initial surfactant concentration required and the feed solute amount, some assumptions were made:
Cos is as a function of Co. The values of m and n were calculated for a forementioned four PEG–MG systems. Therefore, using the concentration of MG in feed and a desired level of extraction efficiency (E), Eq. (9) can be solved to obtain PEG concentration required (Cos). Fig. 6 shows variation of required PEG concentrations for different feed MG concentrations at (60 ± 1) ◦ C in the CPE processes when the desired extraction efficiency of 90%.
(1) The concentration of surfactant in coacervate phase is thousand times than that in dilute phase [17] and the surfactant CMC is so small in dilute phase that it can be neglected in material balance [18]. Thus Gs can represent the amount of surfactant used in the feed (Go).
3.3.2. Analysis of real samples In order to test the reliability of the proposed correlations between surfactant concentration required and the feed MG concentration, MG concentrations in the range 2.74 × 10−7 to 2.74 × 10−6 mol L−1 were spiked to aqueous samples and shrimp
Ce =
Qo(1 − E) Vd
(5)
Table 3 Determination results of recovery in shrimp samples. PEG
Malachite green added (mol kg−1 )
PEG addeda (mol L−1 )
Malachite green (n = 5) found (mol kg−1 ), R.S.D. (%)
10000
2.74 × 10 1.37 × 10−6 2.74 × 10−6
−4
3.23 × 10 3.66 × 10−4 4.19 × 10−4
2.19 × 10 (2.56) 1.12 × 10−6 (3.02) 2.35 × 10−6 (2.88)
80.19 81.64 85.75
6000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
5.98 × 10−4 6.60 × 10−4 7.38 × 10−4
2.34 × 10−7 (2.50) 1.15 × 10−6 (2.26) 2.37 × 10−6 (2.18)
85.31 84.19 86.54
2000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.90 × 10−3 3.12 × 10−3 3.39 × 10−3
2.27 × 10−7 (3.00) 1.08 × 10−6 (3.81) 2.24 × 10−6 (3.44)
82.86 78.55 81.61
600
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.73 × 10−2 2.86 × 10−2 3.01 × 10−2
2.31 × 10−7 (3.50) 1.07 × 10−6 (3.45) 2.35 × 10−6 (3.22)
84.30 78.16 85.77
a
Added by the calculated concentration.
−7
Recovery (%)
−7
236
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
(3) The relationship between the feed concentration of MG and the PEG concentration required is linearity, which may be useful to design a CPE procedure. (4) When the spiked aqueous samples are treated with the calculated PEG concentrations in CPE process, the extraction efficiencies of MG are approximately equal to the desired level. However, the extraction efficiencies of MG in the shrimp samples are less than that desired. The reason may be due to the fact that adsorption equilibrium is affected by matrix of samples. Therefore, if the solute is extracted in the complicated matrix, the surfactant concentration used shall be greater than that calculated. References
Fig. 6. Variation of required PEG concentrations for different feed concentrations of MG at 60 ◦ C with the desired extraction efficiency of 90%.
samples, respectively. Using Eq. (9), the PEG concentrations were calculated and used in the CPE processes. The determined mean recoveries were the ranges of 82.16–92.41% with the relative standard deviation (R.S.D.) of 1.83–3.86% (n = 5) in aqueous solutions and 78.16–86.54% with the R.S.D. of 2.18–3.81% (n = 5) in shrimp samples. The results are shown in Tables 2 and 3. 4. Conclusions We have applied a serial of PEGs as adsorbents for the extraction of malachite green. The result of present investigation shows that PEG have satisfactory adsorption capacity for the molecules of malachite green, and MG was successfully extracted to the desired level of recovery in CPE process by using the calculated PEG concentrations. On the bases of the experiment data obtained and results calculated, the following conclusions were made: (1) The adsorption of MG on to the micelles of PEG follows Langmuir isotherm. (2) The critical micelle concentration of PEG solutions increase with decreasing PEG molecular mass, therefore, amount of micelle in PEG solutions of same concentration increase with increasing PEG molecular mass, which leads to increase of the adsorption area in PEG systems, and adsorption capacity and energy of adsorption increase with increasing PEG molecular mass, which follows an order, PEG10000 > PEG6000 > PEG2000 > PEG600.
[1] A. Stammati, C. Nebbia, I.D. Angelis, A.G. Albo, M. Carltti, C. Rebecchi, F. Zampaglioni, M. Dacasto, Effects of malachite green (MG) and its major metabolite, leucomalachite green (LMG), in two human cell lines, Toxicol. In Vitro 19 (2005) 853. [2] L. Papinutti, N. Mouso, F. Forchiassin, Removal and degradation of the fungicide dye malachite green from aqueous solution using the system wheat bran—Fomes sclerodermeus, Enzyme Microb. Technol. 39 (2006) 848. [3] K.V.K. Rao, Inhibition of DNA synthesis in primary rat hepatocyte cultures by malachite green: a new liver tumor promoter, Toxicol. Lett. 81 (1995) 107. [4] S. Srivastava, R. Sinha, D. Roy, Toxicological effects of malachite green, Aquat. Toxicol. 66 (3) (2004) 319. [5] S.P. Bjergaard, K.E. Rasmussen, Electrical potential can drive liquid–liquid extraction for sample preparation in chromatography, Trends Anal. Chem. 27 (2008) 934. [6] M. Miró, S.K. Hartwell, J. Jakmunee, K. Grudpan, E.H. Hansen, Recent developments in automatic solid-phase extraction with renewable surfaces exploiting flow-based approaches, Trends Anal. Chem. 27 (2008) 749. [7] J.X. Wang, L. Tuduri, M. Mercury, M. Millet, O. Briand, M. Montury, Sampling atmospheric pesticides with SPME: laboratory developments and field study, Environ. Pollut. 157 (2009) 365. [8] C. Yi, J. Shi, S.J. Xue, Y. Jiang, D. Li, Effects of supercritical fluid extraction parameters on lycopene yield and antioxidant activity, Food Chem. 113 (2009) 1088. [9] E.K. Paleologos, D.L. Giokas, M.I. Karayannis, Micelle-mediated separation and cloud-point extraction, Trends Anal. Chem. 24 (2005) 426. [10] K. Kandori, R.J. Megreevy, R.S. Schecher, Solubilization of phenol in polyethoxylated nonionic micelles, J. Colloid Interf. Sci. 132 (1989) 395. [11] O. Hamdaoui, Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick, J. Hazard. Mater. B135 (2006) 264. [12] N. Pourreza, Sh. Elhami, Spectrophtometric determination of malachite green in fish farming water samples after cloud point extraction using nonionic surfactant Triton X-100, Anal. Chim. Acta 596 (2007) 62. [13] J.H. Clint, Surfactant Aggregation, Blackie, Glasgow, 1992, p. 154. [14] Y.S. Ho, G. McKay, Sorption of dye from aqueous solution by peat, Chem. Eng. J. 70 (1998) 115. [15] M.S. Chiou, H.Y. Li, Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads, J. Hazard. Mater. B93 (2002) 233. [16] M.K. Purkait, D.S. Gusain, S. DasGupta, Adsorption behavior of chrysoidine dye on activated carbon and its regeneration characteristics using different surfactants, Sep. Sci. Technol. 39 (10) (2004) 2419. [17] M.K. Purkait, S. DasGupta, S. De, Performance of TX-100 and TX-114 for the separation of chrysoidine dye using cloud point extraction, J. Hazard. Mater. B137 (2006) 827. [18] Z. Wang, F. Zhao, D. Li, Determination of solubilization of phenol at coacervate phase of cloud point extraction, Colloids Surf. A 216 (2003) 207.
Contents lists available at ScienceDirect
Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Study of adsorption behavior of malachite green on polyethylene glycol micelles in cloud point extraction procedure Jianwei Chen, Jianwei Mao, Xiaorong Mo, Juying Hang, Mingmin Yang ∗ College of Science, Nanjing Agricultural University, Nanjing 210095, China
a r t i c l e
i n f o
Article history: Received 26 December 2008 Received in revised form 14 May 2009 Accepted 14 May 2009 Available online 22 May 2009 Keywords: Adsorption Cloud point extraction Langmuir isotherm Polyethylene glycol Malachite green
a b s t r a c t Cloud point extraction (CPE) was carried out to extract malachite green (MG) from aqueous solution and shrimp samples using a series of polyethylene glycol (PEG) surfactants: PEG10000, PEG6000, PEG2000 and PEG600. The adsorption mechanism between PEG micelles and MG molecules was studied. The data of equilibrium concentrations and adsorption amounts in the four PEG–MG systems followed the Langmuir type isotherm. On some assumptions, a developed Langmuir isotherm was used to calculate the feed surfactant concentration required for the removal of MG up to an extraction efficiency of 90%. The calculated PEG concentrations were used in CPE process, and other influence factors on phase behavior were investigated. Under the optimal conditions, recoveries of MG were 82.16–92.41% in aqueous solution and 78.16–86.54% in shrimp samples. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Malachite green (MG) is an N-methylated diaminotriphenylmethane dye still used as fungicides and antiseptic in aquaculture and fisheries [1]. It is also most commonly used for the dyeing of cotton, silk, paper, leather and also in the manufacturing of paints and printing inks. Malachite green has properties that make it difficult to remove from aqueous solutions and also toxic to major microorganisms [2]. Therefore, because of its industrial importance and possible exposure to human being, malachite green poses a potential health hazard and is of environmental concern. Malachite green is highly cytotoxic to mammalian cells and also acts as a liver tumor-enhancing agent [3]. Malachite green when discharged into receiving streams will affect the aquatic life and causes detrimental effects in liver, gill, kidney, intestine, gonads and pituitary gonadotrophic cells [4]. Thus, development of novel and reliable method is necessary for the determination of malachite green in environmental samples such as shrimp samples. The pretreatment of sample, which is used to separate and concentrate analyte, is an important step in analytic process. A number of techniques aimed at preferential separation of different types of solute from matrix have been developed, the liquid–liquid extraction (LLE) [5], solid phase extraction (SPE) [6], solid phase micro-extraction (SPME) [7], supercritical extraction (SE) [8] and cloud point extraction (CPE) [9] are popular nowadays. Among all
∗ Corresponding author. Tel.: +86 25 84395204; fax: +86 25 84395255. E-mail address: [email protected] (M. Yang). 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.05.015
these, CPE is one of the methods which is getting more and more attention because it is easily operated and environment-friendly, and the method is a useful and simple technique without any sophisticated instrument. The mechanism of interaction between surfactant and solute should be studied for obtaining more suitable, efficient, cheap type of surfactant. CPE is proposed to be a process of interaction between solute and micelles of surfactant, the interaction can be treated as adsorption of solute on the surface of the micelles or some other sites within micelles. The micelles of surfactant are adsorption center. The micelles have the ability to adsorb analyte inside their central core or outer palisade layers, this can be suggested by the monolayer coverage of the solute on the surface of the micelles. Therefore, this type adsorption can be expressed by Langmuir isotherm [10]. The adsorption ability of micelle is presented by the adsorption capacity (m) and the energy of adsorption (n). The values of m and n vary with temperature, characteristics of surfactant and solute. However, when a CPE system is separated into two phases at a fixed temperature, the adsorption capacity (m) and the energy of adsorption (n) are constant. Values of m and n can be calculated from the slope and intercept of the linear form of Langmuir equation [11]. As values of m and n are taken into a developed Langmuir equation, the amount of surfactant required for the removal of solute up to a desired level can be calculated. In CPE process, the adsorption area is an important factor; the sizes of micelles of surfactant have significant change with different molecular mass, because it brings about great changes of adsorption area. Therefore, the adsorption ability of surfactant of different molecular mass in CPE procedure should be investigated.
232
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
In this work, the adsorption behavior of malachite green on micelles of a series of Polyethylene glycol (PEG) was studied at fixed temperature. It was found that the experimental data of the adsorption amounts and concentration of solute fitted the Langmuir type isotherm. Values of m and n were calculated by using the linear model of Langmuir isotherm and a new Langmuir isotherm equation was derived based on some fundamental assumptions, a linear correlation between the PEG concentrations required and various feed malachite green concentrations was found. The correlation was used to design CPE process. 2. Experimental
efficiency of MG in CPE process was calculated based on the above results. 2.2.3. Sample preparation 0.5 ± 0.05 g of malachite green-free shrimp samples spiked with different concentrations of malachite green were used to test the applicability of the method to real samples. The spiked shrimp samples were ground and sonicated in the presence of 6 mL of 0.2 mol L−1 trichloroacetic acid. The mixture was filtered and 5 mL of filtered solution was introduced to centrifugal tube. The residue was re-washed with 3 mL water, and the eluant was collected with the first isolated fraction. The solution in the centrifugal tube was treated as Section 2.2.1.
2.1. Chemicals and materials 3. Results and discussions Polyethylene glycols (molecular mass 600, 2000, 6000, 10,000) were obtained from Guanghua Chemical Co. Ltd. (China). Various concentrations (w/v) of aqueous surfactant solutions were prepared by weighing appropriate amounts of the surfactant and directly dissolving the surfactant in water. Malachite green (C23 H25 ClN2 , MW364.95, 99%) was purchased from Shanghai Chemical Reagent Company (China). The stock solution containing 1.0 mg L−1 of MG was prepared by dissolving the reagent in distilled water. Working solutions were prepared daily by an appropriate dilution of the stock solution. (NH4 )2 SO4 was obtained from Nanjing Reagent Plant (China). Trichloroacetic acid was obtained from LingFeng Reagent Co. Ltd. (China), and diluted with distilled water to 0.2 mol L−1 . All the other reagents and solvents were of analytical grade. The experiments were carried out in plastic vessels to avoid adsorption of MG on glass surfaces. 2.2. Apparatus and methods A UV-1700, UV–visible spectrophotometer (Shimadzu, Japan) was used for recording absorption spectra and absorbance. A Mettler Toledo Delta 320 pH-meter equipped with a Mettler glass electrode was used for pH adjustments. A thermostat from Tongzhou Instrument Plant (China) maintained at the desired temperature within ±1.0 ◦ C was used for the cloud point experiments. A centrifuge (TDL40B) from Anke Instrument Plant (China) was used to separate dilute and coacervate phases. 2.2.1. Cloud point extraction procedure PEG–MG systems were prepared by mixing different concentrations of solutions of PEG and MG, and the mixing solutions were diluted to 10 ml with distilled water followed by adding 2.5 g of (NH4 )2 SO4 , and then the solutions were kept in thermostat bath for 10 min at (60 ± 1) ◦ C. The complete separation of dilute and coacervate phases was achieved by a centrifuge. After the dilute phase was sucked out by the aid of a syringe, the volumes of the coacervate phase and the concentrations of PEG and MG in dilute phase were measured, respectively. 2.2.2. Determination of concentrations of PEG and MG in dilute phase The concentrations of MG and PEG were determined by the Shimadzu UV-1700 spectrophotometer. Standard curve technique was used to find out the concentrations of both MG and PEG. The concentrations of PEG and MG were determined at 280 and 620 nm, respectively. In order to eliminate the interference of PEG micelles to the determination, the dilute phase was diluted to ensure that the PEGs concentrations were lower than their critical micelle concentrations (CMC). The quantities of MG and PEG in coacervate phase were calculated by material balance, respectively. The extraction
This section is divided into three parts. In first part, the effects of different factors such as concentration of (NH4 )2 SO4 , pH of the solution, temperature and equilibration time, on the extraction efficiency of MG were discussed. The values of adsorption capacity (m) and energy of adsorption (n) were defined in the second part. In last part, the expression of feed surfactant concentration (Cos) as a function of feed MG concentration (Co) was obtained and verified by application experiments. 3.1. Partition behaviors of MG in CPE procedure This part described the adsorption phenomena of MG in PEG10000, PEG6000, PEG2000 and PEG600 systems, respectively. In the four systems, the concentrations of PEGs and MG were 40 g L−1 and 6.85 × 10−5 mol L−1 , respectively. 3.1.1. Effect of pH In order to prevent the discolor of MG, MG must be kept in acid solution [12]. Fig. 1 shows the influence of pH on the extraction efficiency of MG. Changing the pH from 2.0 to 6.5, the extraction efficiencies of MG had no significant change in the four PEG systems. 3.1.2. Effect of concentration of (NH4 )2 SO4 The salting out effect made water molecular into the dilute phase, and addition of salt can accelerate phase separation and fall the cloud point of surfactant solution. (NH4 )2 SO4 is a stronger phase separation salt. The amount of salt used increased with the hydrophilicity of surfactant, the hydrophilicity of PEGs was followed an order of PEG600 > PEG2000 > PEG6000 > PEG10000. As shown in Fig. 2, in the four PEG systems, for phase separation, more amount of (NH4 )2 SO4 was required, the lower PEG molecular
Fig. 1. Effect of pH on the extraction of malachite green.
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
233
Fig. 2. Effect of salt concentration on the extraction of malachite green.
Fig. 3. Effect of temperature on the extraction of malachite green.
mass. When recovery of 95% was obtained, amounts of (NH4 )2 SO4 required were 1.1 g for PEG10000, 1.3 g for PEG6000, 1.5 g for PEG2000, and 1.9 g for PEG600.
alteration in the four PEG–MG systems. CMC of non-ionic surfactant decreases at higher temperature [13], which leads to an increase of the micelle amounts, therefore, the extraction efficiency of solute shall be increased with increasing temperature. In the following experiments, the temperature was selected at 60 ◦ C.
3.1.3. Effect of temperature The influence of temperature on the extraction efficiencies of MG was investigated in the four PEG systems. Fig. 3 shows the effect of temperature on the extraction of MG. The extraction efficiencies of MG increased with temperature in the range of 20–60 ◦ C, and beyond 60 ◦ C, the extraction efficiencies had no significant
3.1.4. Effect of equilibration time In CPE process, the equilibration time was much shorter than that of solid adsorbents in common use [14,15]. For all the
Fig. 4. Adsorption isotherms of MG over PEGs: (a) PEG10000–MG, (b) PEG6000–MG, (c) PEG2000–MG, (d) PEG600–MG.
234
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
Table 1a Mean values of slope and R.S.D. of different PEGs. PEG10000
a
PEG2000 −5
(3.592 ± 0.024) × 10 0.66
Mean R.S.D.b (%) b
PEG6000 −5
a
PEG600 −4
(6.488 ± 0.091) × 10 1.39
(3.172 ± 0.060) × 10 1.86
(3.009 ± 0.062) × 10−3 2.06
Mean value for five calculations. Standard deviation for five calculations.
Table 1b Mean values of intercept and R.S.D. of different PEGs.
Meana R.S.D.b (%) a b
PEG10000
PEG6000
PEG2000
PEG600
44.464 ± 8.422 18.94
63.216 ± 3.534 5.59
(2.240 ± 0.139) × 102 6.22
(1.299 ± 0.094) × 103 7.21
Mean value for five calculations. Standard deviation for five calculations.
four PEG systems, the extraction efficiencies increased with time and the extraction equilibrium was attained during a shorter time. The extraction efficiencies were found to be constant beyond 10 min. Therefore, the equilibrium time of 10 min was selected. 3.2. Adsorption isotherm 3.2.1. Langmuir isotherm In order to determine adsorption capacity and energy of adsorption of the different PEG–MG systems, the data of concentrations and adsorption amounts from CPE procedures of the four PEG–MG systems were applied to obtain Langmuir isotherm. The CPE procedures were carried out as described in Section 2.2.1 at pH 4.5. If an adsorption process is the formation of monolayer of adsorbate on the outer surface of adsorbent, and after that no farther adsorption takes place, this type of adsorption can be expressed as the well-known Langmuir model (Eq. (1)). q=
mnCe 1 + nCe
(1)
where q is the amount of adsorbate adsorbed per mol of adsorbent at equilibrium (mol mol−1 ), Ce is the equilibrium concentration of adsorbate in dilute phase (mol L−1 ). The constants m and n are the Langmuir constants, m signifies the adsorption capacity (mol mol−1 ) and n is related to the energy of adsorption (L mol−1 ) [16]. In this study, the adsorption behavior of MG in PEG solutions was investigated as following steps: the concentrations of MG in the feed were 6.85 × 10−5 , 1.37 × 10−4 , 2.05 × 10−4 , 2.74 × 10−4 and 5.48 × 10−4 mol L−1 , and the concentrations of PEG in the feed were varied as 40, 60, 80, 100 and 120 g L−1 for each concentration level of MG, and all experiments were carried out at (60 ± 1) ◦ C. After phase separation, the volumes of coacervate phase and the concentrations of PEG and MG in dilute phase were measured. The amounts of PEG and MG in coacervate phase were calculated by material balance. Fig. 4(a) (b), (c) and (d) shows the adsorption isotherms of PEG10000–MG, PEG6000–MG, PEG2000–MG and PEG600–MG systems, respectively, which is illustrated by plotting q vs. Ce.
Fig. 5. Plotting 1/q vs. 1/Ce for m and n calculations.
3.2.2. Evaluating the values of m and n The Langmuir equation can be linearized into the following form: 1 1 1 = + q m mnCe
(2)
According to Eq. (2), a plot of 1/q vs. 1/Ce gives a straight line with slope 1/mn and intercept 1/m. The data of m and n are determined by using slope and intercept of the linear form (Eq. (2)) of the Langmuir model. In order to accurately calculate the values of m and n, five replications were carried out for each of the PEG–MG systems. The values of slope and intercept are calculated and are tabulated in Tables 1a and 1b. The values of m and n of each PEG–MG system are calculated by the mean values of these slopes and intercepts, which are tabulated in Table 1c. The linear plots of 1/q vs. 1/Ce are shown in Fig. 5, and the solid lines were plotted with mean values of m and n. The chain length of surfactant can affect its hydrophobicity. The chain length increases with surfactant molecular mass, which leads to an increase of hydrophobicity and adsorption ability. This tendency can be observed in Table 1c. Values of adsorption capacity (m) and energy of adsorption (n) are obviously increase with PEG molecular mass and follows an order, PEG10000 > PEG6000 > PEG2000 > PEG600.
Table 1c Calculated m and n of different PEGs. PEG10000 a
−1
m (mol mol na (L mol−1 ) a
)
PEG6000 −2
(2.324 ± 0.445) × 10 (1.239 ± 0.240) × 106
Calculated by mean values of slope and intercept.
PEG2000 −2
(1.586 ± 0.079) × 10 (0.975 ± 0.055) × 106
PEG600 −2
(0.448 ± 0.026) × 10 (0.707 ± 0.048) × 106
(0.770 ± 0.047) × 10−3 (0.432 ± 0.031) × 106
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
235
Table 2 Determination results of recovery in water samples. Malachite green added (mol L−1 )
PEG
PEG addeda (mol L−1 )
Malachite green (n = 5) found (mol L−1 ), R.S.D. (%)
10000
2.74 × 10 1.37 × 10−6 2.74 × 10−6
−4
3.23 × 10 3.66 × 10−4 4.19 × 10−4
2.29 × 10 (2.50) 1.15 × 10−6 (2.44) 2.44 × 10−6 (2.25)
83.66 84.03 89.15
6000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
5.98 × 10−4 6.60 × 10−4 7.38 × 10−4
2.48 × 10−7 (2.19) 1.25 × 10−6 (2.10) 2.53 × 10−6 (1.83)
90.47 91.45 92.41
2000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.90 × 10−3 3.12 × 10−3 3.39 × 10−3
2.31 × 10−7 (3.60) 1.13 × 10−6 (3.23) 2.47 × 10−6 (2.66)
84.46 82.66 90.17
600
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.73 × 10−2 2.86 × 10−2 3.01 × 10−2
2.35 × 10−7 (3.86) 1.13 × 10−6 (3.03) 2.38 × 10−6 (3.14)
85.74 82.16 86.80
a
−7
Recovery (%)
−7
Added by the calculated concentration.
3.3. Determination of correlation between the initial surfactant concentration required and the feed solute amount
(2) The volume of dilute phase is so large that Vd can be approximate to the volume of initial solution before CPE (Vo).
3.3.1. Calculation of the surfactant concentration required for the extraction of solute up to a desire level Using Eq. (2), a calculation procedure is outlined to determine the amount of surfactant required for the extraction of solute up to a desired level. The amount of adsorption is defined as,
According to the above assumptions, combining Eqs. (2)–(5) leads to:
q=
Qd Gs
(3)
where Qd and Gs are the amount of solute and surfactant in coacervate phase, respectively. Qd E= Qo
(4)
where E is the extraction efficiency and Qo is the feed amount of solute.
1 Vo Go = + EQo m mnQo(1 − E)
(6)
Go = Cos Vo
(7)
Qo = Co Vo
(8)
where Cos and Co are the concentrations of surfactant and solute in the feed, respectively. Combining Eqs. (6)–(8) leads to: Cos =
E ECo + m mn(1 − E)
(9)
where Vd is the volume of dilute phase. For determining the correlation between the initial surfactant concentration required and the feed solute amount, some assumptions were made:
Cos is as a function of Co. The values of m and n were calculated for a forementioned four PEG–MG systems. Therefore, using the concentration of MG in feed and a desired level of extraction efficiency (E), Eq. (9) can be solved to obtain PEG concentration required (Cos). Fig. 6 shows variation of required PEG concentrations for different feed MG concentrations at (60 ± 1) ◦ C in the CPE processes when the desired extraction efficiency of 90%.
(1) The concentration of surfactant in coacervate phase is thousand times than that in dilute phase [17] and the surfactant CMC is so small in dilute phase that it can be neglected in material balance [18]. Thus Gs can represent the amount of surfactant used in the feed (Go).
3.3.2. Analysis of real samples In order to test the reliability of the proposed correlations between surfactant concentration required and the feed MG concentration, MG concentrations in the range 2.74 × 10−7 to 2.74 × 10−6 mol L−1 were spiked to aqueous samples and shrimp
Ce =
Qo(1 − E) Vd
(5)
Table 3 Determination results of recovery in shrimp samples. PEG
Malachite green added (mol kg−1 )
PEG addeda (mol L−1 )
Malachite green (n = 5) found (mol kg−1 ), R.S.D. (%)
10000
2.74 × 10 1.37 × 10−6 2.74 × 10−6
−4
3.23 × 10 3.66 × 10−4 4.19 × 10−4
2.19 × 10 (2.56) 1.12 × 10−6 (3.02) 2.35 × 10−6 (2.88)
80.19 81.64 85.75
6000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
5.98 × 10−4 6.60 × 10−4 7.38 × 10−4
2.34 × 10−7 (2.50) 1.15 × 10−6 (2.26) 2.37 × 10−6 (2.18)
85.31 84.19 86.54
2000
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.90 × 10−3 3.12 × 10−3 3.39 × 10−3
2.27 × 10−7 (3.00) 1.08 × 10−6 (3.81) 2.24 × 10−6 (3.44)
82.86 78.55 81.61
600
2.74 × 10−7 1.37 × 10−6 2.74 × 10−6
2.73 × 10−2 2.86 × 10−2 3.01 × 10−2
2.31 × 10−7 (3.50) 1.07 × 10−6 (3.45) 2.35 × 10−6 (3.22)
84.30 78.16 85.77
a
Added by the calculated concentration.
−7
Recovery (%)
−7
236
J. Chen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 345 (2009) 231–236
(3) The relationship between the feed concentration of MG and the PEG concentration required is linearity, which may be useful to design a CPE procedure. (4) When the spiked aqueous samples are treated with the calculated PEG concentrations in CPE process, the extraction efficiencies of MG are approximately equal to the desired level. However, the extraction efficiencies of MG in the shrimp samples are less than that desired. The reason may be due to the fact that adsorption equilibrium is affected by matrix of samples. Therefore, if the solute is extracted in the complicated matrix, the surfactant concentration used shall be greater than that calculated. References
Fig. 6. Variation of required PEG concentrations for different feed concentrations of MG at 60 ◦ C with the desired extraction efficiency of 90%.
samples, respectively. Using Eq. (9), the PEG concentrations were calculated and used in the CPE processes. The determined mean recoveries were the ranges of 82.16–92.41% with the relative standard deviation (R.S.D.) of 1.83–3.86% (n = 5) in aqueous solutions and 78.16–86.54% with the R.S.D. of 2.18–3.81% (n = 5) in shrimp samples. The results are shown in Tables 2 and 3. 4. Conclusions We have applied a serial of PEGs as adsorbents for the extraction of malachite green. The result of present investigation shows that PEG have satisfactory adsorption capacity for the molecules of malachite green, and MG was successfully extracted to the desired level of recovery in CPE process by using the calculated PEG concentrations. On the bases of the experiment data obtained and results calculated, the following conclusions were made: (1) The adsorption of MG on to the micelles of PEG follows Langmuir isotherm. (2) The critical micelle concentration of PEG solutions increase with decreasing PEG molecular mass, therefore, amount of micelle in PEG solutions of same concentration increase with increasing PEG molecular mass, which leads to increase of the adsorption area in PEG systems, and adsorption capacity and energy of adsorption increase with increasing PEG molecular mass, which follows an order, PEG10000 > PEG6000 > PEG2000 > PEG600.
[1] A. Stammati, C. Nebbia, I.D. Angelis, A.G. Albo, M. Carltti, C. Rebecchi, F. Zampaglioni, M. Dacasto, Effects of malachite green (MG) and its major metabolite, leucomalachite green (LMG), in two human cell lines, Toxicol. In Vitro 19 (2005) 853. [2] L. Papinutti, N. Mouso, F. Forchiassin, Removal and degradation of the fungicide dye malachite green from aqueous solution using the system wheat bran—Fomes sclerodermeus, Enzyme Microb. Technol. 39 (2006) 848. [3] K.V.K. Rao, Inhibition of DNA synthesis in primary rat hepatocyte cultures by malachite green: a new liver tumor promoter, Toxicol. Lett. 81 (1995) 107. [4] S. Srivastava, R. Sinha, D. Roy, Toxicological effects of malachite green, Aquat. Toxicol. 66 (3) (2004) 319. [5] S.P. Bjergaard, K.E. Rasmussen, Electrical potential can drive liquid–liquid extraction for sample preparation in chromatography, Trends Anal. Chem. 27 (2008) 934. [6] M. Miró, S.K. Hartwell, J. Jakmunee, K. Grudpan, E.H. Hansen, Recent developments in automatic solid-phase extraction with renewable surfaces exploiting flow-based approaches, Trends Anal. Chem. 27 (2008) 749. [7] J.X. Wang, L. Tuduri, M. Mercury, M. Millet, O. Briand, M. Montury, Sampling atmospheric pesticides with SPME: laboratory developments and field study, Environ. Pollut. 157 (2009) 365. [8] C. Yi, J. Shi, S.J. Xue, Y. Jiang, D. Li, Effects of supercritical fluid extraction parameters on lycopene yield and antioxidant activity, Food Chem. 113 (2009) 1088. [9] E.K. Paleologos, D.L. Giokas, M.I. Karayannis, Micelle-mediated separation and cloud-point extraction, Trends Anal. Chem. 24 (2005) 426. [10] K. Kandori, R.J. Megreevy, R.S. Schecher, Solubilization of phenol in polyethoxylated nonionic micelles, J. Colloid Interf. Sci. 132 (1989) 395. [11] O. Hamdaoui, Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick, J. Hazard. Mater. B135 (2006) 264. [12] N. Pourreza, Sh. Elhami, Spectrophtometric determination of malachite green in fish farming water samples after cloud point extraction using nonionic surfactant Triton X-100, Anal. Chim. Acta 596 (2007) 62. [13] J.H. Clint, Surfactant Aggregation, Blackie, Glasgow, 1992, p. 154. [14] Y.S. Ho, G. McKay, Sorption of dye from aqueous solution by peat, Chem. Eng. J. 70 (1998) 115. [15] M.S. Chiou, H.Y. Li, Equilibrium and kinetic modeling of adsorption of reactive dye on cross-linked chitosan beads, J. Hazard. Mater. B93 (2002) 233. [16] M.K. Purkait, D.S. Gusain, S. DasGupta, Adsorption behavior of chrysoidine dye on activated carbon and its regeneration characteristics using different surfactants, Sep. Sci. Technol. 39 (10) (2004) 2419. [17] M.K. Purkait, S. DasGupta, S. De, Performance of TX-100 and TX-114 for the separation of chrysoidine dye using cloud point extraction, J. Hazard. Mater. B137 (2006) 827. [18] Z. Wang, F. Zhao, D. Li, Determination of solubilization of phenol at coacervate phase of cloud point extraction, Colloids Surf. A 216 (2003) 207.