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Abstract-A significant problem with flow injection chemical vapor generation atomic absorption spectrometry is a loss of sensitivity and blockage of transfer lines due to excessive moisture transported to the atom cell or lodged in the transfer line. A Nafion dryer tube was used to remove moisture from the wet carrier gas stream. The hygroscopic Nafion membrane removed water at 1.7 mg/min at an efficiency of 95 ± 4% when SnCl 2 was used as the reductant. When 0.4% (m/v) borohydride was used as the reductant, 2.3 mg/min of water was removed at an efficiency of 91 ± 3%. No measurable change in precision was observed and a 5% reduction in peak height sensitivity (vs. PTFE) was seen for mercury when using the Nafion transfer line. At 60°C the Nafion dryer removed 4.9 mg/min of water vapor at an efficiency of 93 ± 3%. The loss of mercury vapor through the Nafion membqme was no more than 0.04%. Only a 3% reduction in peak height sensitivity was observed for the determination of arsenic and selenium. Detection limits for mercury, calculated from calibration data, were 77 ppt, 20 ppt and 150 ppt for the PTFE tube, the model MD-250 dryer and the model MD-125 dryer, respectively.

Following digestion of the sample in a mixture of bromate and hydrobromic acid, the inorganic selenium produced was quantified by trapping hydrogen selenide, formed when a 500 ml sample volume injected into a hydrochloric acid carrier stream merged with a stream of sodium borohydride solution, on the iridium-pretreated interior of a graphite furnace atomizer. A number of parameters relating to the digestion, flow injection manifold and trapping in the atomizer were investigated, including a study of factors affecting the detection limit. It was found necessary to heat the digest under reflux at a temperature of 150ЊC for 2 h. Quantitative recoveries, from a human urine matrix, of selenite, selenate, trimethylselenium, selenocystine, selenopurine and selenomethionine spikes were obtained. The efficiency of hydride generation, transport and trapping was 75%. The major factors affecting the detection limit were the reagent purity and the volume injected. For high-purity hydrobromic acid and borohydride free of caking agent, the detection limit, based on three times the standard deviation of the blank, was 0.06 mgl − 1 for a 1000 ml injection volume corresponding to a detection limit of 3 mgl − 1 for a urine sample. The method was validated by the accurate analyses of Standard Reference Material 2670 from the National Institute of Standards and Technology, and urine samples from an interlaboratory comparison program. The procedure avoids the need for perchloric acid and produces selenium in the + 4 oxidation state and thus no reduction is needed prior to generation of the hydrogen selenide. The use of a graphite furnace atomizer avoids the need for frequent reconditioning of the atomizer surface and the need for the standard additions method, both of which are drawbacks of procedures which make use of the quartz tube atomizer. All sample handling procedures following the digestion were automated by the use of flow injection technology.

In the determination of arsenic and selenium by flow injection hydride generation ETAAS, the presence of up to 20% sodium chloride enhanced the signals for 20 mg l 21 arsenic and selenium by up to 28%. The enhancement was obtained with a variety of gas-liquid separators. A systematic study of the possible causes of the signal enhancement in the determination of selenium was undertaken, from which it was concluded that the effect originated in the processes responsible for the distribution of the hydrogen selenide between the solution and gas phases. Processes related to the transport of the analyte from the gas-liquid separator and the trapping of the analyte on the interior of the atomizer were not affected by the presence of dissolved salts. As sodium was found to be transported to the atomizer, it was deduced that aqueous aerosol was deposited in the atomizer, although the quantities were irreproducible. The enhancement could be eliminated by increasing the borohydride concentration. However, with the small volume gas-liquid separator, this latter approach was limited because of carry-over of liquid to the atomizer. The effect could be compensated for by adding up to 40% m/v of salt to the borohydride reagent.

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