Chemometric-assisted microextraction based on an ionic liquid as ion-pairing agent for the determination of chromium species in environmental samples

BERTON, PAULA; VERA-CANDIOTI, LUCIANA; GOICOECHEA, HECTOR C.; WUILLOUD, RODOLFO G.

Baltimore

Simposio; ITP 2012-19th INTERNATIONAL SYMPOSIUM, EXHIBIT & WORKSHOPS ON ELECTRO- AND LIQUID PHASE-SEPARATION TECHNIQUES; 2012

ITP 2012-19th INTERNATIONAL SYMPOSIUM, EXHIBIT & WORKSHOPS ON ELECTRO- AND LIQUID PHASE-SEPARATION TECHNIQUES

Ionic liquids (ILs), defined as liquid salts at room temperature, have been proposed, among other applications, for separation processes due to their specific and unique properties. The hydrophobic long-chain quaternary phosphonium IL trihexyl(tetradecyl)phosphonium chloride (CYPHOS® IL 101) has been employed as extraction solvent in Liquid-Liquid Microextraction (LLME) for metal preconcentration. Recently, the use of CYPHOS® IL 101 has been investigated as a potential novel ion-pair reagent dissolved in conventional organic solvents for metal extraction from aqueous phases. In most of these methods, metal anionic chloro- or iodo-complexes are formed before ion-pair formation with CYPHOS® IL 101.In the present work, an IL is proposed for the first time as direct ion-pair reagent for Cr speciation analysis, without the need of an extra ligand reagent. The speciation analysis was developed with initial ion-pair formation between Cr(VI) and CYPHOS® IL 101 followed by a simple and rapid microextraction procedure named ultrasound-assisted emulsification-microextraction (USAEME) for Cr species separation and preconcentration. Determination of Cr was performed by direct injection of the organic phase into an electrothermal atomic absorption spectrometer (ETAAS). A Plackett?Burman screening design and a central composite design were used to optimize the operational conditions for the procedure. The multiple response criterion was successfully used to optimize the extraction of Cr(VI). The combination of microextraction and chemometrics significantly simplify sample processing, and also addresses problems related to improvement in detectability and method validation. Under optimum conditions, the analyte extraction efficiency was higher than 99% and yielded a preconcentration factor of 250 with only 10 mL of sample. The limit of detection obtained was 2.4 ng L−1 and the relative standard deviation was 4.8%, calculated at peak areas. A correlation coefficient of 0.9983 was achieved.The two oxidation states of chromium (Cr) most commonly present in aqueous solution, i.e. Cr(III) and Cr(VI), differ drastically in its physiological and toxicological effects, its chemical transformations as well as its distribution and transport in the environment. Therefore, considerable emphasis has been given to the development of analytical methodologies for Cr species separation and determination. The proposed method was successfully applied to the determination of Cr species at trace levels in natural and drinking water samples.