Determination of Cr(VI) by flame atomic absorption spectrometry combined with flow-injection on-line sorption preconcentration.

A method was developed for the determination of Cr(VI) by flame atomic absorption spectrometry (FAAS) after on-line preconcentration by sorption. The solution containing Cr(VI) was reacted with ammonium-pyrrolidinedithiocarbamate (APDC) in the FI-manifold system designed for this purpose and the water insoluble chromium complex formed was adsorbed in a sorption reactor. The commercial PEEK loop used in HPLC-technique was introduced instead of a knotted reactor recommended in the literature for preconcentration of other trace elements. The precipitate was also retained quantitatively by the PEEK loop, from which the chromium complex could be eluted by MIBK at a high rate and could be rinsed into the flame. The PEEK loop of suitable length is cheaper than a HPLC column used so far for preconcentration of Cr(VI), and could be easily inserted in the system and it is a unit of practically unlimited lifetime. The preconcentration could be done also at a far greater flow rate than that allowed in the case of columns due to its low hydrodynamic resistance. Thus the time of the determination could be reduced considerably. The preconcentration of Cr(VI) could also be done from samples containing materials (acids, proteins and other organic materials) which might seriously damage HPLC columns. The preconcentration of Cr(VI) from a 5 mi sample and determination by FAAS could be carried out within 2 minutes. The enrichment factor was 65. The detection limit (3 sigma) was obtained as 2.0 mu g/l. The precision was 2.1 % RSD for 50 mu g/l Cr(VI) (N = 10).