Mass spectroscopic and some optical spectroscopic studies ontrace element analysis in solids

Abstract

This thesis deals with certain aspects of the chemical analysis of solids, viz., the accuracy and precision of measurements and phenomena connected with RF?spark and other discharge processes. Results have been obtained on: a) Matrix effects (sensitivity of impurities in a variety of matrices) b) Examination of Local Thermodynamic Equilibrium (LTE) in RF?spark and vibrator?arc plasmas c) A study of molecular ions in a variety of ionic and covalent solids and metallic alloys Relative Sensitivity Coefficients (RSCs), based on singly charged ions (with Fe as standard), for 11 alloying elements in 2 iron?base, 3 aluminium?base, and 1 titanium?base spectroscopic standard alloys have been measured with an AEI MS702 mass spectrometer. These indicate no detectable matrix effects — as the relative standard deviations (RSDs) in RSCs for many elements in these matrices are within 20%, comparable with the RSD in individual measurements (15–20%). However, RSCs calculated for doubly and triply charged ions indicate matrix effects, as the RSDs in RSCs for many elements are 40–60%. An examination of LTE in RF?spark plasma has been made using Saha–Eggert ionisation plots. The progressive increase in electron?temperature (Te) values, calculated from the slopes of such plots for n?/n? and n?/n?, indicates lack of LTE in RF?spark plasma. LTE conditions in vibrator?arc plasma have been examined using Boltzmann?distribution temperature (Tp) obtained from optical spectra and mass?spectrometric measurements (Tg) of Ti and Al. The inconsistency between Tp and Tg shows that LTE conditions do not prevail in vibrator?arc plasma. A study of the various molecular ions observed in RF?spark mass spectra of a variety of solids indicates: a) a series pattern X?Y? with a monotonic decrease in intensities, b) alternation of intensities in several series, and c) evidence supporting vapour/plasma?phase formation rather than extraction (“plucking”) from the lattice.