Gas chromatographic analysis of trace metals isolated from aqueous solutions as diethyldithiocarbamates.

Abstract

While the determination of trace levels of metal ions in sea waters and other marine samples can be accomplished by spectroscopic means (atomic absorption or inductively coupled plasma) recent publications describing the determination of metal ions as diethyldithiocarbamate derivatives has raised the possibility of using gas chromatographic techniques. A study was undertaken to establish optimum procedures both for the isolation of trace metals as diethyldithiocarbamates from aqueous media and for their quantitation by gas chromatography. The diethyldithiocarbamate standards required for this study [ i.e. those of Ni(II),Cu(II), Zn(II), Cd(II), Pb(II), Hg(II) and Co(III)] were prepared and characterized. A gas chromatographic method was developed, involving the use of the mixed stationary phases QF-1 and OV-101 at low concentrations, which gave a highly efficient separation of mixtures of up to five of the metals studied. Contrary to other reports in the literature dealing with the gas chromatography of some metal diethyldithiocarbamate or other, the use of glass tubing to pack columns was found to be critical for obtaining successful separations, and elimination of possible degradation of the metal diethyldithiocarbamates on the columns. Linear responses were the rule in the nanogram concentration range investigated for each metal. Accuracy of analyses of ppm concentrations of the metals was in the order of ± 5% or better, with relative standard deviations of 5% or less. Low ppb (ng/ml) detection was feasible starting with metals dissolved in either dis tilled water, or in synthetic sea water. Theoretical principles have been proposed to account both for the nature of the gas chromatographic separation observed and for the degradation problems encountered and overcome.