On-line solid-phase chelation for the determination of six metals in sea-water by inductively coupled plasma mass spectrometry

An automated low pressure flow analysis method with on-line column pre-concentration/inductively coupled plasma mass spectrometry (ICP-MS) was developed for the simultaneous determination of cobalt, chromium, cadmium, manganese, zinc and nickel in aqueous environmental samples. The system is based on cationic retention of the analytes onto a mini-column filled with silica gel functionalised with 1-(di-2-pyridyl)methylene thiocarbonohydrazide placed in the injection valve of a simple flow manifold. The effects of chemicals and flow variables were investigated. The optimized operating conditions, selected as a compromise between sensitivity and analytical frequency were: sample pH 8.6, sample flow rate of 1.4 mL min−1, eluent flow rate of 1.3 mL min−1, and eluent (HNO3) concentration of 2% (m/m). The relative standard deviation (n = 5), enrichment factor and linear working range were 0.3–4.0%, 2.3–32.9 and 0.02–60 μg L−1, respectively. Detection limits (3 min sample loading time) were between 0.006 and 0.530 μg L−1. The accuracy of the proposed method was checked with two certified reference materials (CRMs) of sea water SLEW 3 and NASS-5 and with two natural waters SLRS-4 and TMDA-54.4. Values obtained were in accordance with those reported for the certified materials. Recovery was found to be in the range of 93–110% for a suit of water samples with variable matrices (seawater and river water) collected in Málaga, Spain.