FI/SI on-line solvent extraction/back extraction preconcentration coupled to direct injection nebulization inductively coupled plasma mass spectrometry for determination of copper and lead

Abstract

An automated sequential injection on-line preconcentration procedure for determination of trace levels of copper and lead via solvent extraction/back extraction coupled to ICP-MS is described. In citrate buffer of pH 3, neutral complexes between the analytes and the chelating reagent, ammonium pyrrolidinedithiocarbamate (APDC), are extracted into isobutyl methyl ketone (IBMK). The organic phase is separated from the aqueous one by means of a dual-conical gravitational phase separator, and stored in a PTFE holding coil. Afterwards, the organic phase is propelled and mixed with an aqueous back extractant of nitric acid containing Pd(II) ions as stripping agent, thereby facilitating a rapid metal exchange reaction with the APDC ligand and transfer of the analytes back into the aqueous phase. The aqueous phase is separated in a second dual-conical gravitational phase separator, and 30 µl is entrapped in a sample loop, the content of which is subsequently introduced into the ICP-MS, via a direct injection high efficiency nebulizer (DIHEN), for quantification. Enrichment factors of 29.6 (Cu) and 23.3 (Pb), detection limits of 17 ng l⁻¹ (Cu) and 11 ng l⁻¹ (Pb), along with a sampling frequency of 13 h⁻¹ were obtained at a sample flow rate of 6.0 ml min⁻¹. The precisions (RSD) at the 0.2 µg l⁻¹ level were 4.4% (Cu) and 4.8% (Pb), respectively. The applicability of the procedure is demonstrated for the determination of copper and lead in three certified reference materials and a urine sample.