Modified approximate quantitative spectral analysis of rocks

Abstract

Two main methods of approximate quantitative atomic emission spectral analysis have traditionally been developed in the Central Laboratory of the Karpinsky All-Russian Research Geological Institute (VSEGEI): evaporation from the channel of carbon electrodes and a more efficient spill method. When comparing these two methods for introducing a sample into the arc discharge, two factors should be taken into account: the amount of material entering the discharge and the completeness of evaporation of chemical elements. A sample weighing about 40 mg is almost completely evaporated from the channel of a carbon electrode. The spill-injection method provides a uniform supply of a large powder sample (400 – 500 mg) into the arc discharge. The first method of analysis is well suited for determination of volatile and nonvolatile elements, whereas the second method provides stable conditions for evaporation and excitation during all the time when the sample is supplied into the discharge. The spill-injection method is more sensitive to changes in the bulk composition of the sample and the particle size of the sample material compared to evaporation from the electrode channel. These are the main factors affecting the magnitude of the systematic error in determining the concentrations of semi-volatile elements. The errors that make up the total error of approximate quantitative atomic emission spectral analysis are systematically analyzed in spectral laboratories. Comparison of the results of analysis of the same samples (state standard samples) with the results of chemical methods over a period of several years revealed that the maximum contribution to the total error is attributed to the visual assessment of the content and visual interpolation, as well as to a discrepancy in interpretation of results after a long time, etc. The impact of various errors has been reduced through the use of the MAES analyzer and the wide capabilities of the Atom software, which offer a correct consideration of the background with the option of individual settings, the use of coefficients accounting for the interference effect, and the possibility of analysis by several analytical lines of each chemical element thus allowing the use of constant calibration curves for a wide range of rock compositions.