Determination of trace metals in high-salinity petroleum produced formation water by inductively coupled plasma mass spectrometry following on-line analyte separation/preconcentration

Abstract

A procedure is detailed for the determination of trace metals in high salinity petroleum produced formation water (PFW) by inductively coupled plasma mass spectrometry (ICP-MS) coupled with flow injection (FI) on-line matrix separation and preconcentration. High salinity PFW waters present complex composition containing various organic and inorganic substances. Mini-columns packed with Toyopearl AF-Chelate-650M iminodiacetate resin were used for the analyte separation/preconcentration of Cd, Pb, Ni, Zn, V, Co and U; Toyopearl 8-hydroxiquinoline resin for Fe, and silica immobilized 8-hydroxyquinoline resin for Mo. A Doehlert matrix and desirability function was used to generate response surfaces to optimize the column separation/preconcentration parameters. Using 7.5 mL aliquots of PFW, method limits of detection of 0.0007, 0.009, 0.017, 0.024, 0.0002, 0.047, 0.058, 0.002, 0.013 and 0.041 ng ml⁻¹ were obtained for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively. Vanadium, Co and Mn were determined by the method of standard additions whereas Cd, Pb, Ni, Zn, Mo, Fe and U were quantitated using isotope dilution. CASS-4 (coastal seawater) certified reference material was used for method validation and high-salinity PFW (39–120‰) from Brazilian offshore platforms examined. The concentration ranges found in these waters were 0.013–1.47, 0.057–0.80, 0.229–5.1, 0.096–3360, 0.001–0.081, 0.244–69, 0.84–1419, 0.004–3.5, 0.088–0.85 and 4.2–6230 ng ml⁻¹ for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively.