U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Flow-Injection-ICP-MS Method Applied to Benthic Flux Studies of San Francisco Bay

By Brent R. Topping and James S. Kuwabara

This paper is available in pdf format: Topping.pdf

ABSTRACT

An automated low-pressure flow-injection (FI) sample introduction method for use with an inductively-coupled plasma mass spectrometer (ICP-MS) has been applied to determine trace-element benthic fluxes in the San Francisco Bay. Due to metal concentrations of the order of 10 nM and lower, dilution is not an applicable method for circumventing the high ionic-strength (up to 0.7M) of the samples, which inhibits accurate analysis. Due to low volume constraints (as low as 60 ml per sample) presented by the design of the benthic flux experiment, high-throughput concentration methods are not viable. Using the FI method, small (~4 ml) aliquots are buffered on-line to pH 5.2 and are passed through a chelating resin. Following a deionized water flush, the sorbed metals are eluted with 1M quartz-distilled HNO₃, and carried into the plasma. This process represents advancement over the previously employed method involving off-line preconcentration followed by graphite furnace atomic absorption spectroscopy (GFAAS) analysis. Improvements are observed in detection limits, confidence intervals, viable analytes, reduction of contamination sources, and analysis time. For copper and nickel, metals whose estuarine transport mechanisms in the Bay are presently of much interest, detection limits are <0.2 nM, which are less than those for similar samples by GFAAS (<2 nM). Whereas GFAAS allows for effective analysis of only copper and cadmium under our experimental constraints, the FI method has thus far been found appropriate for analysis of Cu, Cd, Ni, Zn, Pb, Mn, Co and V. The FI-ICP-MS method, while still in its relative infancy, represents an invaluable addition to our analytical capabilities, and could benefit any study requiring multi-element analysis in low-volume samples of high ionic strength.