Dual sample injection for gas chromatographic determination of sulfur species with flame photometric detection

Abstract

on the graphite tube than we had feared and it is possible to make more than 50 measures with the same tube.But the results are very dependent on the quality of the graphite tubes, and quality can vary in the same batch of pyrolytic tubes. Sometimes replacing peak height by peak area mode can improve reproducibility and linearity.The results obtained by electrothermal atomic absorption spectrometry are in good accordance with those obtained by inductively coupled plasma spectrometry using the conditions described in a previous paper (2), modified for a simultaneous spectrometer, JY 48, with background correction by automatic displacement of the entrance slit.In conclusion, in our experience, addition of a high concentration of nitric acid dramatically improved aluminum determination in concentrates used to obtain dialysis fluid.Registry No. Aluminum,; nitric acid, 7697-37-2. LITERATURE CITED(1) Alfrey, A. C.; Le Gendre, G. R.; Kaehny, W. D. New Engl.The processing of oil shale whether by in situ or surface retorting generates gaseous sulfur products. During the development of near production-size processes, the release of these products needs to be monitored not only for compliance with air quality standards but also as a data base for input into the design or selection of a product gas cleanup system.The need for continuous monitoring demands that the system be fully automated and reliable.The use of a flame photometric detector (FPD) in gas chromatography (GC) lends itself nicely to the analysis of sulfur gases because the sensitivity for sulfur-containing compounds is in the subnanogram range. The detector has a major drawback in that the dynamic range of the detector only encompasses about 2 decades of sulfur concentrations, which is considerably less than the differences between the major sulfur species (hydrogen sulfide) and the minor species (carbonyl sulfide, methyl and ethyl mercaptan, carbon disulfide, and thiophene) observed in previous monitoring of oil shale retorts (I, 2).Gangwal and Wagner (3) overcame limitations imposed by the small dynamic range of the detector by evacuating the sample loop to an appropriate pressure. However, this technique requires precise vacuum control to evacuate to the same pressure each time and does not eliminate the problem of handling largely different component concentrations in the same gas sample. For this reason we connected two sample valves in series, one with a small sample loop for components present in high concentrations and one with a large sample loop to handle components in lower concentrations. Samples from both valves were sequentially injected during the same determination. EXPERIMENTAL SECTIONA Hewlett-Packard 5840 gas chromatograph equipped with a single FPD and conventional six-port gas sampling injection valve was used for the analysis. Modification in the sample injection system was made in order to accommodate a small sample size as well as dual injection by adding a Rheodyne sample valve, type 50. This valve was modified as shown in Figure 1 by r...