DETERMINATION OF SELENIUM BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY .1. CHEMICAL MODIFIERS

The effect of various chemical modifiers, including nitrates of palladium, nickel, magnesium, calcium, lanthanum, europium and aluminium, on the analytical signal of selenium in a graphite furnace was studied. The signals of various selenium compounds, such as selenite, selenate and organic compounds representing different types of selenium forms in body fluids (selenomethionine and trimethylselenium iodide), were evaluated. The shape of the transient signal appears to be influenced not only by the chemical reactions in the graphite-selenium-modifier system, but also very strongly by vaporization effects connected with the physical character of the charred residue. It follows that successful chemical modification involves the application of a considerable excess (higher than 1000-fold) of some metal nitrates, which produce refractory oxides and no thermally stable carbides, and are at the same time capable of quantitative conversion of the analyte into a single form. An integral part of the modifier action is trapping of the resulting compound by the modifier residue.