86 Journal of Membrane and Separation Technology, 2014, 3, 86-90 E-ISSN: 1929-6037/14 © 2014 Lifescience Global Maltodextrins Based Solid Membranes for the Enantioanalysis of L-Cysteine Raluca-Ioana Stefan-van Staden * and Luxolo Holo Laboratory of Electrochemistry and PATLAB Bucharest, National Institute of Research for Electrochemistry and Condensed Matter, 202 Splaiul Independentei Str., 060021, Bucharest, Romania Abstract: Three enantioselective membranes based on maltodextrins with different values of dextrose equivalent (DE) were proposed for the enantioanalysis of L-cysteine. The membranes were used for the design of potentiometric sensors. The slopes of the sensors were near-Nernstian (higher than 58.00mV/decade of concentration) with limits of detection of magnitude order of 10 -11 and 10 -12 mol/L. The surfaces of the membranes were stable for more than 6 months of continuous use. They can be renewed by polishing on alumina paper. Keywords: L-cysteine, solid enantioselective membrane, maltodextrin, enantioselective, potentiometric membrane electrode. 1. INTRODUCTION L-Cysteine (L-Cys) is a sulphur-containing amino acid R-SH and one of the twenty basic proteins [1]. It can be used as a prospective radiation protector and cancer indicator [2-5]. The electrochemical study of cysteine has been reported [6-9]. The development of chemically modified amperometric electrodes for detection of cysteine is a growing field [10-16]. Fluorescence was also employed for the assay of cysteine [17]. Chiral recognition is an area of considerable research interest due to its importance in biological, chemical and pharmaceutical sciences [18]. Tech- niques, which are intensively used for chiral recognition are: chromatography, capillary zone electrophoresis, mass spectrometry and electrochemistry. Utilization of electrochemical techniques will make the enantioanalysis highly reliable [19]. Maltodextrins represents a class of very powerful chiral selectors [20-22]. Variations in DE values result in maltodextrins with varying physico-chemical properties: solubility, hydroscopicity, osmolality and their effectiveness to reduce the freezing point increase with increasing DE, while viscosity, cohesiveness and coarse-crystal prevention increase as DE decreases [23, 24]. Maltodextrins were used as chiral selectors for enantiomeric separations by capillary zone electro- phoresis [21, 22, 25-29], and they were also used for the design of enantioselective, potentiometric membr- ane electrodes [19, 30-33]. Although, the HPLC *Address correspondence to this author at the Laboratory of Electrochemistry and PATLAB Bucharest, National Institute of Research for Electrochemistry and Condensed Matter, 202 Splaiul Independentei Str., 060021, Bucharest, Romania; Tel: +40751507779; E-mail: iustinavanstaden@yahoo.com (standard method) method, and fluorescence based method are highly used for biomedical analysis, they cannot always be high reliable especially for urine samples, when the complexity of the sample is very high. This paper proposed three solid enantioselective membranes used in the design of enantioselective, potentiometric membrane electrodes (EPMEs) for the enantioanalysis of L-cysteine. The membranes were based on maltodextrins with different DE. 2. EXPERIMENTAL 2.1. Reagents and Materials L- and D-Cysteine were bought from Sigma-Aldrich (St. Louis, MO, USA). Maltodextrins (DE 4.0-7.0, 13.0- 17.0, 16.5-19.5) and graphite powder (1-2 μm, synthetic) were bought from Aldrich (Milwaukee, WI, USA). Deionised water was obtained using a Modulab system (Continental Water Systems, San Antonio, TX, USA). The L- and D-cysteine solutions necessarily in the characterization of the enantioselective, potentiometric membrane electrodes were prepared from standard L- and D-cysteine solutions (10 -2 mol/L), respectively, by serial dilutions. All solutions were buffered with phosphate buffer (pH 2.40, 0.1mol/L) from Merck (Darmstadt, Germany) (1:1, v/v, buffer: deionised water). 2.2. Apparatus The potentiometric measurements were done using a system comprising a 663 VA stand (Metrohm, Herisau, Switzerland), a PGSTAT 20 (Eco Chemie,