Development of a methodology for the simultaneous determination of inorganic and organolead compounds using supercritical fluid extraction followed by gas chromatography–mass spectrometry and its application to environmental matrices

Abstract

A method for the extraction of triethyl lead (TEL +), trimethyl lead (TML +), and Pb 2+ from sand was developed using supercritical modified CO 2–CH 3OH extraction and in situ complexation with sodium diethyldithiocarbamate (NaDDTC) using a 2 5 factorial exploratory design is described. The screened variables were (i) pressure (69–193 bar), (ii) temperature (40–150 °C), (iii) ligand amount (0–100 mg), (iv) methanol volume (0.0–0.5 mL) and (v) static time (0–45 min). The optimum extraction conditions found were as follow: pressure, 193 bar; temperature, 40 °C; amount of NaDDTC, 100 mg; methanol volume, 0.5 mL; static time 45 min; and CO 2 flow rate, 1 mL min −1. Under these conditions the following recoveries were obtained (TML + 97 ± 2%, TEL + 70 ± 5%, and Pb 2+ 100 ± 4%). The presence of NaDDTC is not necessary for the extraction of TML + and TEL +, but it is a very significative parameter for Pb 2+. A second experimental design 2 2 + star for temperature and pressure was realized, but the results were not better than those of the first model. SFE extract derivatization was achieved with pentylmagnesium bromide, and target analyte determination was carried out by gas chromatography–mass spectrometry. Detection limits in the full-scan mode were 4, 10, and 39 pg as lead for TMPeL, TEPeL and PbPe 4, respectively. The method was validated with urban dust containing TML + (CRM 605. Pb 7.9 ±1.2 μg kg −1) and river sediment containing inorganic lead (GBW08301. Pb 79.0 ± 12.0 mg kg −1) as reference materials. The proposed method was applied to lead analysis in sand collected from an oil-polluted beach in Chile.