Computer-assisted SIMPLEX optimisation of an on-line preconcentration system for determination of nickel in sea-water by electrothermal atomic absorption spectrometry

Abstract

An original on-line preconcentration system for the determination of nickel by electrothermal atomic absorption spectrometry is achieved by replacing the sample tip of the autosampler arm by a microcolumn packed with a silica gel chelating resin functionalised with 1-(di-2-pyridyl)methylene thiocarbonohydrazide. The modification of the autosampler in the tubing line and circuit allowed either the flow of the sample through the column or the operation of the autosampler in the normal mode, where microlitres of HNO 3 2 M, which acts as the elution agent, pass through the microcolumn, eluting Ni(II), which is directly deposited in the graphite tube as a drop of a precisely defined volume. Optimum graphite furnace operating conditions were sought by software which integrates the SIMPLEX optimisation method and quality requirements such as sensitivity and precision. The optimised method has two linear calibration ranges, between 0 and 1 ng ml –1 and between 1 and 5 ng ml –1 , with a detection limit of 0.06 ng ml –1 and a throughput of 36 samples h –1 for 60 s of preconcentration time. The accuracy of the method was examined by the analysis of a certified reference material and by determining the analyte content in spiked sea-water and synthetic sea-water. The results show sufficiently high recoveries.