A single-valve sequential injection manifold (SV-SIA) for automation of air-assisted liquid-phase microextraction: stopped flow spectrophotometric determination of chromium(VI)

A single-valve sequential injection setup is suggested for automation of an air-assisted liquid-phase microextraction. In order to eliminate parasitic signals, the stopped flow detection mode was employed. The aqueous phase (1.5 mL), containing chromium(VI), chloride ions (0.6 mol L-1), sulphuric acid (0.07 mol L-1) and dimethyl indocarbocyanine dye (1.33 x 10(-4) mol L-1), was dispensed into the extraction chamber and was followed by moderate injection of a 250 mu L organic phase and intense mixing by multiple air bubbling. The extraction phase was then submitted for stopped flow UV-Vis spectrophotometric detection at 560 nm wavelength. The calibration plot was linear up to 104 mu g L-1 of chromium(VI). The limit of detection, calculated as 3s of a blank test (n = 10), was found to be 4.5 mu g L-1. The developed procedure was applied for the determination of Cr(VI) in various water samples.