Gas chromatographic-mass spectrometric analysis of mercaptan odorants in liquefied petroleum gas and liquefied natural gas

Abstract

A gas chromatographic-mass spectrometric method for the determination of mercaptan odorants (dimethyl sulfide, tert.-butylmercaptan, tetrahydrothiophene) in natural gas has been developed. The gas sample filled in a 5 l Tedlar bag was introduced into the 0.5 ml volume of a sampling loop, separated on a 50 m capillary column coated with 5 % phenylmethylsilicone and detected by a mass spectrometer. Natural gas samples collected from 124 sites were analyzed and the concentration of added odorants was found to be between 9.7 and 66.2 ppm (w/w). The detection limit of each odorant was below 1 ppm (w/w). The advantages of the developed technique were lower detection limits, elimination of interference peaks by introducing into the sampling loop system and selected-ion monitoring mode, and reduced total analysis time. The intra-day and inter-day precision of the established method was R.S.D. < 5% (n = 5). (C) 1997 Elsevier Science B.V.