The spectrographs determination of trace elements in the cathode layer ARC by the variable internal standard method

Abstract

The use of iron as the variable internal standard for the determination of trace elements in the cathode layer are, when the iron varies from two to one hundred per cent of ferric oxide, is discussed. Davidson and Mitchell's method, which requires one trace element working curve of fixed iron content and a correction curve for variation of iron content, is examined. Straight line working curves, of slope approximately unity up to at least five hundred parts per million, are obtained for most of the trace element lines when log intensity ratio, corrected for background, is plotted against log concentration, the curves for different iron contents being parallel but vertically displaced. Straight line correction curves are obtained by plotting this separation of the working curve, due to variation in iron content, against log concentration of iron. Two shortened methods for the derivation of the curves are proposed: in the first, the working and correction curves fan be prepared from a standard material by a single determination of the log intensity ratio of the trace element and internal standard lines, corrected for background; the second employs an observed working curve and an arbitrary correction curve. In the concentration ratio method, in which the working curve itself makes allowance for the variation in internal standard content, the log intensity ratio is plotted against the log concentration ratio and this method has similar limitations to the first shortened method.