MULTIELEMENT TRACE-METAL DETERMINATION BY ELECTRODEPOSITION, SCANNING ELECTRON-MICROSCOPIC X-RAY-FLUORESCENCE, AND INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

Multielement analysis of multicomponent metallic electrodeposits is described, based on scanning electron microscopy with energy dispersive X-ray fluorescence [EDXRF] detection, followed by dissolution and inductively coupled plasma mass spectrometry [ICP-MS] detection. Application of the method is described for determination of trace elements in seawater, including Zn, Mn, Co, Cu, Cr, Ni, Fe, Cd, Pb, and Hg. These elements are simultaneously electrodeposited onto a niobium wire working electrode at -1.40 V vs an Ag/AgCl reference and subjected to EDXRF analysis. Internal standardization is practical for quantitative calibration at the 1 ppm analyte concentration level in an analyte:internal standard concentration ratio range of 0.02-50. Detection limits for EDXRF range from 1.9 ppb for Fe to 50 ppb for Cd. The deposit is dissolved for subsequent ICP-MS determination. Significant reduction in ICP-MS matrix interferences by Na, Ca, Mg, K, and Cl ions is achieved by deposition at potentials more positive than their very negative reduction potentials. Measurement of elemental isotope ratios is achieved with 0-8 % relative error. ICP-MS detection limits for all elements except Zn and Fe are superior to those of EDXRF. Mn, Ni, Cd, Pb, and Hg can easily be determined in the range of 13-86 parts per trillion with ICP-MS. © 1990, American Chemical Society. All rights reserved.