[Contrastive study of two methods("programmed temperature vaporization with back flushing" and "head space") for light hydrocarbon analysis].

Abstract

Light hydrocarbon analytical method of "PTV with Back Flushing" presented here is characterized as follows: a) with "PTV" inlets temperature programmed; b) with gas line system of "Back Flushing"; c) with direct injection of oil samples. After oil sample injection, "Back Flushing" is on when light hydrocarbon components enter into analytical chromatographic column. At the same time, the temperature of inlet increases. The high temperature and "Back Flushing" blow the heavy components in the oil samples out of the analytical system. Besides, the analytical method of "Head Space" was established. Both "PTV with Back Flushing" and "Head Space" have the advantages of long column life and short analysis time. The resolution for lighter components < C9 meets the criterion of ASTM D5134-98, with the good repeatability. Ten oil samples from 6 oil areas were analysed by using the two methods. The relative deviations between the two analytical results represented by 19 geochemistry parameters were about +/- (1%-25%). The reasons for the deviation are discussed. It is pointed out that in geochemistry study it is not acceptable to combine the data obtained from two analytical methods. The analytical results obtained by injecting crude oil directly into injector are more reliable. The results obtained in "Head Space" analytical method should be calibrated when used in geochemistry study.