Direct Methods of Estimation in the Spectrographic Analysis of Cobalt in Soil Concentrates

Abstract

THE relationship which forms the basis of the internal standard method of Spectrographic analysis may be written : where I T, I S are the respective intensities of the analysis and internal standard lines; C T, C S are the respective concentrations of the analysis and internal standard elements ; and a, n are constants dependent on the general conditions of excitation. In its application to the determination of trace constituents in biological concentrates1, the internal standard, which is iron, varies in content, and the calibration involves three steps : (a) obtaining plots of log I T/I S (background-corrected) against log C T for sets of standard mixtures K, L, M, N, … containing increments of the internal standard element from one set to the next ; (b) selecting one of these as the standard working curve, for example, the plot from the M set ; and (c) deriving a correction graph for the C S value of the sample. The calibration curves for cobalt, namely, log I T/I S versus log C T (10–1,000 p.p.m.) and log I S/I S(M) versus log C S (2.0–50.0 per cent Fe2O3), are obtained as straight lines of unit gradient.