Semi-automated determination of arsenic and selenium in river water by hydride generation atomic absorption spectrometry using a gas collection device

Abstract

A hydride generation system was assembled with a mixing coil and a gas-liquid separator, and was operated with electromagnetic solenoid pinch valves and variable speed peristaltic pumps by manipulating electromagnetic relays and timers. Thus hydrides evolved in the coil were stored in the separator and then swept automatically into an electrically heated quartz furnace. A decrease in sensitivity with deterioration of the furnace was not observed, as the amount of water introduced into the furnace was minimal. The sensitivity for arsenic(III) was ca. 50% higher than that for arsenic(V), nonetheless arsenic was determined in its pentavalent state. The sensitivities for peak-height measurement were 0.01 and 0.005 A ng^–1 for arsenic(V) and selenium(IV), respectively. The sampling rate was 15 samples h^–1. Accuracies checked with biological standard reference materials obtained from the National Bureau of Standards (NBS) were within the certified values. The proposed system was used to determine both arsenic and selenium in river water. The water was concentrated after the addition of nitric, sulphuric and perchloric acids. Siliceous residues deposited during the concentration procedure were removed as silicon tetrafluoride on heating.