FLOW INJECTION-FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF TRACE LEVELS OF CADMIUM WITH ONLINE PRECONCENTRATION BY MEANS OF COPRECIPITATION

Flow injection systems for determination of trace metal ions are described, which comprize on-line preconcentration by coprecipitation with ensuing dissolution and detection by flame atomic absorption spectrometry. Exemplified for the assay of cadmium, which is coprecipitated with iron(II) by means of hexamethylene ammonium hexamethylene dithiocarbamate in an incorporated knotted reactor and subsequently eluted by an organic solvent of methyl isobutyl ketone, two optional FI-approaches for accomplishing this feat are compared and discussed in respect to performance. While one, which is based on a previously published procedure, employs continuous pumping of the eluting agent, the approach suggested herein relies on dissolution of the collected precipitate within a small, discrete organic zone. Because the concentration of analyte thus is increased in the eluent, this concept allows an increased sensitivity, a lower limit of detection (0.074 mu g l(-1); 3 sigma), and an extended dynamic measuring range (0.5-20 mu g l(-1)), albeit implying an increased sample consumption per assay and hence a decreased sampling frequency.