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

Abstract

A sample solution was passed at 20 ml min −1 through a column (150×4 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 ml min −1. Following a second wash, a solution of 8 mol l −1 hydrochloric acid was passed at 5.1 ml min −1 for 45 s. The hydrogen selenide was stripped from the eluent solution by the addition of an argon flow at 150 ml 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® 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 μg of iridium as trapping agent. The furnace was held at a temperature of 250°C during this trapping stage and then stepped to 2000°C for atomization. The calibration was performed with aqueous standards solution of selenium (selenite, SeO 3 2−) 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 1 −1 of selenium. The most severe depressions were caused by iron (III) and mercury (II) for which concentrations of 20 and 10 mg 1 −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 1 −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 1 −1, with a characteristic mass of 130 pg. The RSDs for solutions containing 100 and 200 ng 1 −1 selenium were 2.3% and 1.5%, respectively.