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The Analysis of Trace Contaminants in High Purity Ethylene and Propylene Using GC/MS

Abstract: A new product (Application 460-00) from Wasson-ECE utilizes an HP GC/MSD (gas chromatograph/mass selective detector) for the determination of trace levels of impurities that are moderate-to-low carbon-content such as oxygenates, mercaptans, sulfides, ammonia, arsine, and phosphine in ethylene and propylene. This work describes the performance of Application 460-00 with respect to linearity, repeatability, and limits of detection (for most compounds, low parts-per-billion). Compared to determinations with GC/FID (flame ionization detection) or GC/TCD (thermal conductivity detection), the use of GC/MSD demonstrates comparable performance with respect to linearity and repeatability: for example, for mercaptans and sulfides (40-100 ppb) in the ethylene assay, correlation coefficients for calibration curves range from 0.992 to 1.000 and relative standard deviations range from 1.95 to 9.31% RSD. Compared to GC/FID for the range of contaminant analytes studied here, the sensitivty is increased 50-fold; compared to GC/TCD, the sensitivity is increased 5000-fold. While the sensitivity of MS detection is comparable to that of sulfur chemiluminescence detection for sulfur-containing compunds, MS has the same sensitivity for a broader range of compound types. Moreover, the use of MS detection provides specificity for positive identification of anlytes. In Application 460-00, the multipart assays are automated via "composite methods." The result is a tool that provides higher productivity and more key information about feedstock materials - both of which aid the polymer industry.

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