Application of a macrocycle immobilized silica gel sorbent to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace lead in biological and environmental samples

A simple and highly selective now injection on-line preconcentration and se paration-name atomic absorption spectrometric method was developed for rout ine analysis of trace amounts of lead in biological and environmental sampl es. The selective preconcentration of lead was achieved in a wide range of sample acidity (0.075 to greater than or equal to 3 mol L-1 HNO3) on a micr ocolumn (145 mu L) packed with a macrocycle immobilized on silica gel. The lead retained on the column was effectively eluted with an EDTA solution (0 .03 mol L-1, pH 10.5), Three kinds of potential interferences, i.e., precon centration interferences from metal ions with an ionic radius similar to th at of Pb(II) due to their competition for the cavity of the macrocycle, elu tion kinetic interferences from ions which form stable complexes with EDTA due to their competition for EDTA, and interferences in the atomizer from r esidual matrix, were evaluated and compared in view of the read-out mode of the analyte response (peak area vs peak height), column wash step (with vs without), column capacity (50 vs 145 mu L), and column shape (conical vs c ylindrical). The results showed that a combination of increase in column ca pacity, quantitation based on peak area, and use of dilute nitric acid for column wash before elution efficiently avoid the above-mentioned potential interferences. With the use of a 145 mu L column the present system tolerat ed up to 0.1 g L-1 Ba(II), 1 g L-1 Sr(II), and at least 10 g L-1 Fe(III), C u(II), Ni(II), Zn(II), Cd(II), Al(III), K(I), Na(I), Ca(II), and Mg(II) in the sample digest. Further improvement of the interference tolerance can be achieved by increasing column capacity if more complicated samples need to be analyzed. At a sample loading rate of 3.9 mt min(-1) with 30-s preconce ntration, an enrichment factor of 52, a detection limit (3s) of 5 mu g L-1 Pb in the digest and a sampling frequency of 63 h(-1) were obtained. The pr ecision (RSD, n = 11) at the 200 mu g L-1 level was 1.9%, The enrichment fa ctor and the detection limit can be further improved by increasing sample l oading rate without degradation in the efficiency due to the favorable kine tics and low hydrodynamic impedance of the present system, The analytical r esults obtained by the proposed method for a number of biological and envir onmental standard reference materials were in good agreement with the certi fied and recommended values.