On-line simultaneous pre-concentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry

摘要

An on-line pre-concentration system for the sequential determination of cadmium and lead in drinking water by using fast sequential flame atomic absorption spectrometry (FS-FAAS) is proposed in this paper. Two minicolums of polyurethane foam loaded with 2-(6-methyl-2-benzothiazolylazo)-orcinol (Me-BTAO) were used as sorptive pre-concentration media for cadmium and lead. The analytical procedure involves the quantitative uptake of both analyte species by on-column chelation with Me-BTAO during sample loading followed by sequential elution of the analytes with 1.0molL~(-1) hydrochloric acid and determination by FS-FAAS. The optimisation of the entire analytical procedure was performed using a Box-Behnken multivariate design utilising the sampling flow rate, sample pH and buffer concentration as experimental variables. The proposed flow-based method featured detection limits (3σ) of 0.08 and 0.51 μgL~(-1) for cadmium and lead, respectively, precision expressed as relative standard deviation (RSD) of 1.63% and 3.87% (n = 7) for cadmium at the 2.0 μgL~(-1) and 10.0 μgL~(-1) levels, respectively, and RSD of 6.34% and 3.26% (n = 7) for lead at the 5.0 μgL~(-1) and 30.0 μgL~(-1) levels, respectively. The enrichment factors achieved were 38.6 and 30.0 for cadmium and lead, respectively, using a sample volume of 10.0 mL. The sampling frequency was 45 samples per hour. The accuracy was confirmed by analysis of a certified reference material, namely, SRM 1643d (Trace elements in natural water). The optimised method was applied to the determination of cadmium and lead in drinking water samples collected in Santo Amaro da Purificac.ao City, Bahia, Brazil.