Analysis for Cd, Cu, Ni, Zn, and Mn in estuarine water by inductively coupled plasma mass spectrometry coupled with an automated flow injection system Original Research Article

A flow injection inductively coupled plasma magnetic sector mass spectrometry (FI-ICP-MS) method was developed for the analysis of Cd, Cu, Ni, Zn, and Mn in estuarine waters. The method uses just greater than 3 ml sample, and employs an automated on-line preconcentration step using a metal chelating resin (Toyopearl AF-Chelate 650 M). Acidified samples for the analysis of Cd, Cu, Ni, and Zn were buffered on-line to pH of 5.6±0.2 with ammonia acetate just prior to loading onto the chelating resin, while samples for Mn analysis were adjusted to pH of 9.0±0.2 prior to concentration. Limits of detection were: Cd=1.4 ng l−1 (0.013 nM), Cu=17 ng l−1 (0.27 nM), Ni=28 ng l−1 (0.48 nM), Zn=46 ng l−1 (0.70 nM), and Mn=86 ng l−1 (1.6 nM). The blank concentrations were less than 1.5% of the SLEW-2 concentrations for each element analyzed, except Ni, which had a significant, but very constant blank from the Ni cones used. The detection limits were less than 5% of the concentrations observed in the San Francisco Bay estuarine samples, with the exception of Zn where the detection limit was 10% of the concentration of lowest San Francisco Bay sample analyzed. Using the FI preconcentration technique, we conducted medium resolution scans of potential isobaric interferences (mass units 55–66) using a magnetic sector ICP-MS to identify a number of interferent complications with evaluating certain isotopes, especially, 59Co, and 60Ni. Investigations of potential interferents illustrate the importance of appropriate isotope selection and, in some instances, the need to perform blank corrections with both an instrumental and a matrix blank. The method was verified by the analysis of an estuarine water standard reference materials (SLEW-2), and San Francisco Bay samples with previously reported values. Six estuarine samples run in triplicate generated the following average precision (presented as % R.S.D.); Cd=4.2%, Cu=3.2%, Ni=3.3%, Zn=4.4%, and Mn=2.2%.