Talanta 85 (2011) 891–896 Contents lists available at ScienceDirect Talanta j ourna l ho me page: www.elsevier.com/locate/talanta Development of cloud point extraction using pH-sensitive hydrogel for preconcentration and determination of malachite green Morteza Bahram ∗ , Foroogh Keshvari, Peyman Najafi-Moghaddam Department of Chemistry, Faculty of Science, Urmia University, Urmia, Iran a r t i c l e i n f o Article history: Received 2 January 2011 Received in revised form 27 April 2011 Accepted 28 April 2011 Available online 6 May 2011 Keywords: Hydrogel Preconcentration Central composite design Malachite green a b s t r a c t A novel and sensitive cloud point extraction procedure using pH-sensitive hydrogel was developed for preconcentration and spectrophotometric determination of trace amounts of malachite green (MG). In this extraction method, appropriate amounts of poly(styrene-alt-maleic acid), as a pH-sensitive hydrogel, and HCl were added respectively into the aqueous sample so a cloudy solution was formed. The cloudy phase consists of hydrogel particles distributed entirely into the aqueous phase. Organic or inorganic compounds having the potential to interact with polymer particles (chemical interaction or physical adsorption) could be extracted to cloudy phase. After centrifuging, these particles of hydrogel were sedi- mented in the bottom of sample tube. The sedimented hydrogel-rich phase was diluted with acetonitrile and its absorbance was measured at 617 nm ( max of malachite green in hydrogel). Central composite design and response surface method were applied to design the experiments and optimize the exper- imental parameters such as, concentration of hydrogel and HCl, extraction time and salting out effect. Under the optimum conditions, the linear range was 1 × 10 −8 –5 × 10 −7 mol L −1 malachite green with a correlation coefficient of 0.992. The limit of detection (S/N = 3) was 4.1 × 10 −9 mol L −1 . Relative standard deviation (RSD) for 7 replicate determinations of 10 −7 mol L −1 malachite green was 3.03%. In this work, the concentration factor of 20 was reached. Also the improvement factor of the proposed method was 23. The advantages of this method are simplicity of operation, rapidity and low cost. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Generally in the analytical process especially in the extraction procedures, the main step is sample preparation and pretreatment (e.g. the extraction of an analyte of interest to an organic phase) that eventuates in the isolation and enrichment of interest from a sample matrix [1]. The main direction in recent researches is towards the devel- opment of efficient, economical, simple, rapid and clean sample preparation methods. Liquid–liquid extraction (LLE) is one of the oldest preconcentration methods in analytical chemistry [2]. This technique is time consuming and needs large amount of expen- sive and toxic organic solvent(s). Other methods like supercritical fluid extraction (SFE) and solid-phase extraction (SPE) are relatively expensive methods [3]. Solid-phase microextraction (SPME) [4–6] includes extraction and preconcentration of analyte(s) from aque- ous samples or from headspace of the samples is also expensive and at most time the reproducibility of the results is low. In addition, the fiber which is used in SPME is fragile and has a limited lifetime [7]. Single drop microextraction (SDME) is inexpensive and very ∗ Corresponding author. Tel.: +98 441 2972143; fax: +98 2776707. E-mail address: m.bahram@urmia.ac.ir (M. Bahram). little solvent is used [8,9]. However, several disadvantages for this method have been reported; fast stirring would tend to break up the organic drop, air bubbles are formed [3]; extraction is time- consuming and equilibrium cannot be attained, even after a long time in most cases [9]. Cloud point extraction procedure is an easy, safe, rapid and inexpensive method which has been designed for the separation, purification and preconcentration of a variety of substances includ- ing metal ions and organic compounds [10–12]. This technique [13–15] is based on a property of most non-ionic surfactants in aqueous solutions, i.e., forming micelles and becoming turbid when being heated to the particular temperature (T c ). When the tem- perature is higher than T c , the micellar solution will be separated into a surfactant-rich phase of a small volume and a diluted aque- ous phase, in which the surfactant concentration is close to the critical micellar concentration (CMC). Depending on the surfac- tants property, the hydrophobic, amphiphilic or even ionic solutes can be extracted to the surfactant-rich phase. The advantage of CPE is the preferable use of water as the solvent, in compari- son to other preconcentration procedures that still use toxic and flammable organic solvents. Also, the anionic surfactants which have been used as effective extracting agents in the cloud point extraction methods often require salt addition and adjustment of pH [16–18]. 0039-9140/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2011.04.074