Effects of Ramp Rate and Starting Temperature on Gas Chromatography-Mass Spectrometric Analyses of Petroleum Hydrocarbons

Abstract

The quest for better GC-MS/FID starting temperature and ramping conditions for the quantification of hydrocarbons in our environment necessitated this study. A surrogate n-alkane standard was screened using nine GC-MS conditions involving the alteration of ramp rates and/or initial temperatures. There was observed increase in the TIC chromatogram or ionic mass unit as the ramp rate or initial temperatures were increased. The peak areas of the analytes were significantly affected. The R2 and response factor values of the eight standard calibration curves (each for a modified method) varied from 0.9224 – 0.9971 and 0.0034 – 0.0045 respectively. Consequently, the quantification of the diesel concentration in diesel spiked water and soil by using the eight methods was different from each other and from the standard method. Average differences of 11.5 and 15 % from the theoretical values were observed for the water and soil analyses respectively. Increasing ramp rates or initial temperatures led to shorter throughput but less data accuracy. The use of 60 oC as starting temperature and ramp at 5 oC/minute was better for quantification of the diesel range organics.