Direct-reading d.c. arc spectrometry for rapid geochemical surveys

Abstract

A technique developed for the rapid quantitative analyses of metals in large suites of silicate materials is described. A direct-reading emission spectrometer interfaced to a dedicated minicomputer is used with d.c. arc excitation. Sample, buffer and arc parameters were chosen to promote reproducible selective volatilization. By partial integration of the line emission for the volatile metals, the spectrum background contribution is reduced, improving line to background ratios and permitting both “volatile” and “nonvolatile” metals to be determined in one burn. Preformed electrode cups are used in a specially designed arc chamber which incorporates a gas jet for controlled atmosphere and arc stabilization, and permits automatic electrode alignment as well as rapid and efficient cleaning between samples. No adjustment of the electrodes is made during the burn. One standard only is required for calibration since the working curves are linear over the concentration ranges of interest and a method of background correction using this same standard is described. A high rate of analysis as well as good accuracy and precision is achieved for 21 metals.