Flow Injection On-line Reductive Precipitation Preconcentration With Magnetic Collection for Electrothermal Atomic Absorption Spectrometry

Abstract

A flow injection on-line preconcentration system coupled to an electrothermal atomic absorption spectrometer for the determination of trace metals in saline media is described. The filterless, magnetic collection of coprecipitated analytes is based on the tetrahydroborate reductive precipitation of added iron and palladium in alkaline medium at a sample flow rate of 1.7 ml min^–1. The precipitate is dissolved in a 20 µl volume of mixed acid and transported direct to the graphite furnace. With the exception of Cr (33% recovery in seawater), recoveries of Ag, As, Bi, Cd, Co, Cu, Mn, Ni, Pb, Sb and Tl averaged 84% from deionized water and 67% from coastal seawater with a frequency of 12 measurements h^–1. The sensitivity of the graphite furnace technique can be enhanced over 400-fold (for an 11 ml sample volume) compared to a standard 20 µl injection volume. Detection limits in the low pg (absolute) or pg ml^–1 (relative) range can be reached. Results, presented for the determination of As, Cd, Cr, Cu, Mn and Ni in 1 ml volumes of CASS-3 NRCC Certified Reference Material seawater, are not statistically different (t-test, 95% confidence limit) from the certified values for these elements.