Volume 12, Issue 4 (July 1984)
Principles on Analysis by Spark Sampling and Plasma Excitation as Applied to Super Alloys
During the last two years, a new concept of metal spectrochemical analysis has emerged. Fundamental to the concept is separating the process of sampling a material from the process of causing the eroded material to emit light. During the analysis sequence, a spark source samples a metal rapidly and precisely. The atom clusters eroded from the sample are introduced into an inductively coupled argon plasma (ICAP) source. The ICAP atomizes the clusters and excites the atoms with minimal matrix effects. It causes the resultant atoms and ions to emit light linearly over four to five orders of magnitude in concentration. Secondary to the evolution of this method of analysis is the identification, quantitation and control of four parameters: (1) the amount of sample eroded per unit time (sample uptake), (2) the influence of an interfering species on the signal measured at the detector of another species (interelement effect), (3) contamination from the residue of a previous sample (sample cross talk), and (4) change in the amount of sample eroded by spark sampling over time (sampling time dependence). It is important to the method that the following assumptions prove to be correct: (1) the atom clusters erode from the sample and have the same composition as the sample itself and (2) all of the elements in the sample are determined during the analysis. The analytical method that results from the separation of sampling and excitation, the control of the four parameters, and the validity of the two assumptions are capable of minimizing matrix effects in optical emission metals analysis. By using the method, an analyst can calibrate or standardize with one kind of material, such as low alloy steel, and analyze another, such as Waspaloy. The utility of this form of metals analysis, separate sampling and excitation analysis (SSEA), will be demonstrated by examining the methodology and results of low alloy steel, Waspaloy, and Rene analysis.