Characteristics of a Controlled Atmosphere ac Arc

Abstract

A study was carried out to determine the characteristics of the ac arc when using various controlled atmospheres. This research was instigated because our laboratory makes extensive use of the ac arc for the analysis of air particulate matter and of body tissues and fluids. Although controlled atmosphere sources have been widely investigated, they have generally been with the dc arc. The atmospheres were evaluated by measuring the background, precision, and sensitivity of various elements using 3 matrices (graphite, lithium carbonate—graphite, and lithium fluoride—graphite). The conclusions reached were (1) the limit of detection for 21 elements was determined for each matrix. In each case, 7 elements were more sensitive by a factor of two or better in the oxygen—argon mixture than in air. The other elements showed no improvement: (2) the standard deviations obtained on 30 or more repeat analyses on each of 6 elements showed the precision of analysis of the 2 lithium—graphite matrices to be better by as much as a factor of three than the graphite matrix in both air and the oxygen—argon mixture. (3) Only the lithium carbonate—graphite matrix showed any improvement in precision when using the oxygen—argon mixture, but the results were not appreciably better than those of the lithium fluoride—graphite mixture in air.