FLOW-INJECTION ONLINE ACID DIGESTION AND PRE-REDUCTION OF ARSENIC FOR HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY - A FEASIBILITY STUDY

A flow injection (FI) manifold is described which makes possible on-line microwave-assisted acid digestion, followed by pre-reduction of As(V) to As(III) and its determination by hydride generation atomic absorption spectrometry. The merging zone technique is used in order to reduce acid consumption for digestion. The efficiency of acid digestion is increased by pressure which is built up in-line by a flow restrictor. Flows for sample pretreatment and hydride generation can be optimized independently. L-cysteine was found superior to potassium iodide as the pre-reductant because much lower reagent and acid concentrations are required, much harsher conditions can be tolerated for acid digestion, and the integrated absorbance signals for arsenic in blood and standards are essentially identical, making possible the use of the standard calibration procedure. The sampling frequency is 7-10/hr, depending on the conditions chosen, and the limit of detection, i.e. the concentration giving a signal equal to three times the standard deviation of the signal of the blank solution, is 0.25 mug/l for a 500 mul sample volume. The recovery of 10 mug/l As(V) added to a blood sample was 94 +/- 2 and 98 +/- 2% (n = 3) in absorbance and integrated absorbance, respectively.