Development and evaluation of a glow discharge emission source for the breath-by-breath determination of oxygen
Abstract
The development of a glow discharge emission source is described and its ability to quantitate oxygen is evaluated. The emission source consisted of a flow cell containing two hollow metallic cylinders which served as electrodes. This cell was operated under vacuum and the intensity of the emission lines was measured using a commercially available UV/Vis spectrophotometer. An RF excitation source was originally employed; however, the 778-nm emission line, corresponding to atomic oxygen, was poorly resolved. Increased resolution was obtained through the use of a DC excitation source. The application of constant-voltage, constant-current, and constant-power excitation was studied and it was found that the best results were obtained with constant-power excitation. Calibration plots for 10-100% O$\sb2$ in nitrogen were obtained at a pressure of 0.40 Torr and a constant power of 300 mW using tungsten wire electrodes. The device was found to have a within-run precision (relative standard deviation, RSD) of $\pm$1.6% or less, a run-to-run RSD of $\pm$2% or less, and a day-to-day pooled standard deviation of $\pm$2.5-3.2 counts. The oxygen resolution was found to be in the range of 0.12-0.67% and the absolute accuracy was 1-2% O$\sb2.$ A plot of computed oxygen concentration (%) versus prepared oxygen concentration (in the range of 10 to 100% oxygen) for four replicate trials resulted in a least-squares fit having the equation: y = (1.0000 $\pm$ 0.0092)x $-\ (6.4\times10\sp{-6}\pm 0.56)$ %O$\sb2$ with a standard error of the estimate of 1.43% O$\sb2$ and an R$\sp2$ value of 0.9982.
Degree
Ph.D.
Advisors
Pardue, Purdue University.
Subject Area
Analytical chemistry|Biomedical research
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