Determination of (ultra)trace amounts of lead in biological materials by on-line coupling flow injection microcolumn separation and preconcentration to electrothermal atomic absorption spectrometry using a macrocycle immobilized silica gel sorbent

Abstract

A fully automated procedure was developed for the determination of (ultra)trace lead in biological materials by on-line coupling flow injection (FI) microcolumn separation and preconcentration with electrothermal atomic absorption spectrometry (ETAAS) using a macrocycle immobilized silica gel sorbent (Pb-02). The analyte was selectively and efficiently collected on a conically shaped column (50 µl) packed with Pb-02 over a wide range of sample acidity (0.08-≥3 mol l^–1 HNO₃). Quantitative elution of the retained analyte from the column was achieved with 46 µl of 0.03 mol l^–1 ethylenediamine tetraacetic acid (EDTA) solution at pH 10.5. The eluate was driven with an air flow into the graphite tube preheated to 110 °C. No precise timing was needed during analyte elution and eluate introduction. When 0.15 mol l^–1 HNO₃ was used as the wash medium and the residual solution was removed from the column and connecting tubes by air before elution, the only potential interferents were found to be Ba(II), Sr(II) and K(I) due to their competition for the cavity of the macrocyclic compound because their ionic radii are similar to that of Pb(II). Nevertheless, these potential interferences were eliminated or minimized by a proper increase of eluent volume and/or EDTA concentration. Under the optimized conditions, the tolerated concentrations of Ba(II), Sr(II) and K(I) were at least 10, 100 and 5000 mg l^–1 in the digest, respectively. With a sample loading rate of 3 ml min^–1 and a 20-s preconcentration time, an enhancement factor of 23 and a sampling frequency of 23 h^–1 with a collection efficiency of 70% were obtained. The detection limit (3s) was found to be 2 ng l^–1. The relative standard deviation (n=9) was 2.9% at the 500 ng l^–1 Pb level. The results for a number of standard reference materials (rice flour, blood and urine) demonstrated the applicability of the proposed method to the analysis of biological materials with simple aqueous standards for calibration.

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