Hollow fiber liquid phase microextraction for cr(iii) and cr(vi) speciation

Abstract

A technique of hollow fiber liquid phase microextraction (HF-LPME) followed by diphenylcarbazide-based UV-Vis spectrophotometric method was developed for speciation of chromium in surface water samples. Aliquat 336 was used as the extraction solvent. A 2 cm-polypropylene hollow fiber membrane impregnated with Aliquat 336 was attached to a medical syringe needle tip and immersed into the sample solution. The method was based on the extraction of Cr(VI) anion into Aliquat 336 via anion-exchange mechanism. After extraction, the membrane was removed from the needle and Aliquat 336 enriched with Cr(VI) was eluted with a small volume of 1,5 diphenylcarbazide in ethanol solution. The violet complex was formed and determined by UV-Vis spectrometer at 548 nm. For the determination of Cr(III), Cr(III) was first oxidized to Cr(VI) by hydrogen peroxide in basic medium, extracted and determined as total chromium, then the amount of Cr(III) was obtained by subtracting of Cr(VI) from the total amount of chromium. Aliquat 336 concentration, extraction time, sample volume, stirring rate and matrix effect were studied and optimized. The enrichment factor about 15 and 5 were obtained for extraction of deionized water and surface water, respectively. The method evaluation showed good accuracy and precision for the determination of Cr(III) and Cr(VI) in surface water samples with recoveries ranging of 81.2-114.8 % and relative standard deviation of 4-11 %. The limits of detection were 3 and 10 µg L-1 for deionized water and surface water, respectively. The method is simple, cheap, and uses less organic solvent, which is environmental friendly.