Reversible intermittent flow-injection determination of mercury in sediments and vinasses by cold vapor atomic absorption spectrometry

A reversible intermittent pow-injection procedure is proposed for the autom ated determination of mercury in sediments and vinasses by cold vapor atomi c absorption spectrometry, CVAAS. Solutions of sample and stannous chloride are carried by two air streams and sequentially injected into the generato r/separator chamber in a segmented asynchronous merging zone configuration. The intermittent flow in the forward direction carries the mercury vapor t hrough the flow cell, and in the backward direction, if aspirates the the r emaining solution from the vessel to waste. We investigated composition and concentration of reagents, pow rates, commutation times, reactor configura tion, and conditions for mercury release. The accuracy was checked by mercu ry determination in a certified sediment and spiked vinasses and river wate rs. The system handles about 100 samples per hour (0.50-5.00 mu g L-1), con suming ca. 2.5 mL of sample and 50 mg of SnCl2 per determination; Good reco veries (92-103%) were obtained with spiked samples. Results are precise (RS D <3% for 2.5 mu g Hg L-1, n = 12) and in agreement with values for certifi ed reference material at 95% confidence level. (C) 1999 John Wiley & Sons, Inc.