Flow injection determination of selenium by successive retention of Se(IV) and tetrahydroborate(III) on an anion-exchange resin and hydride generation electrothermal atomization atomic absorption spectrometry with in-atomizer trapping - Part 1. Method development and investigation of interferences

A sample solution was passed at 20 mi min(-1) through a column (150 x 4 mm(2)) of Amberlite IRA-410Stron anion-exchange resin for 60 s. After washing, a solution of 0.1% sodium borohydride was passed through the column for 60 s at 5.1 mi min(-1) Following a second wash, a solution of 8 mol l(-1) hydrochloric acid was passed at 5.1 mi min(-1) for 45 s. The hydrogen selenide was stripped from the eluent solution by the addition of an argon flow at 150 mi min(-1) and the bulk phases were separated by a glass gas-liquid separator containing glass beads. The gas stream was dried by passing through a Nafion(R) dryer and fed, via a quartz capillary tube, into the dosing hole of a transversely heated graphite cuvette containing an integrated L'vov platform which had been pretreated with 120 mu g of iridium as trapping agent. The furnace was held at a temperature of 250 degrees C during this trapping stage and then stepped to 2000 degrees C for atomization. The calibration was performed with aqueous standards solution of selenium (selenite, SeO32-) with quantification by peak area. A number of experimental parameters, including reagent flow rates and composition., nature of the gas-liquid separator, nature of the anion-exchange resin, column dimensions, argon flow rate and sample pH, were optimized. The effects of a number of possible interferents, both anionic and cationic were studies for a solution of 500 ng l(-1) of selenium. The most severe depressions were caused by iron (III) and mercury (II) for which concentrations of 20 and 10 mg l(-1) caused a 5% depression on the selenium signal. For the other cations (cadmium, cobalt, copper, lead,. magnesium, and nickel) concentrations of 50-70 mg l(-1) could be tolerated. Arsenate interfered at a concentration of 3 mg(-1), whereas concentrations of chloride, bromide, iodide, perchlorate, and sulfate of 500-900 mg l(-1) could be tolerated. A linear response was obtained between the detection limit of 4 ng l(-1), with a characteristic mass of 130 pg. The RSDs for solutions containing 100 and 200 ng l(-1) selenium were 2.3% and 1.5%, respectively. (C) 1998 Published by Elsevier Science B.V.