On-line sorption preconcentration of chromium(VI) and its determination by flame atomic absorption spectrometry

A method was developed for the determination of Cr(VI) by flame atomic absorption spectrometry (FAAS) after on-line sorption preconcentration. The solution containing Cr(VI) was reacted with ammonium-pyrrolidinedithiocarbamate (APDC) in a flow injection manifold system designed for this purpose and the non-water soluble chromium complex formed was adsorbed in a sorption reactor. The commercial PEEK (polyether ether ketone) loop used in liquid chromatography (LC) was introduced instead of a knotted reactor recommended for preconcentration of other trace elements in the literature. The Cr-PDC complex was retained by the PEEK loop, from which the chromium complex could be eluted rapidly by methyl isobutyl ketone into the flame. The PEEK loop is cheaper than the LC column used previously for preconcentration of Cr(VI), it can easily be inserted into the system and it is practically of unlimited lifetime. The preconcentration could also be done at much greater flow rates than that for columns because of the little hydrodynamic resistance of the loops. Thus the duration of the determination could considerably be reduced. The preconcentration of 5 ml of Cr(VI) sample and FAAS determination could be carried out within 2 min. The enrichment factor was 65. The detection limit (3σ) was 2.0 ng ml−1. The relative standard deviation was 2.1% for 50 ng ml−1 and 6.8% for 5 ng ml−1 Cr(VI) (N=5). The proposed method was applied for determination of Cr(VI) in various water and cigarette ash samples.