Development and validation of an analytical method for hydrocarbon residues using gas chromatography-mass spectrometry

Abstract

This work outlines the development of a gas chromatographic mass spectrometric (GCMS) method for the analysis of hydrocarbon residues such as those encountered in the examination of fire debris. The work compares favourably against an existing ASTM E-1618-06 method for ignitable liquid analysis currently used for the development of the National Centre for Forensic Science (NCFS) ignitable liquid database. A test mixture comprising fourteen hydrocarbons as recommended by the ASTM-1618-06 method was used to evaluate and validate the separation conditions together with a matrix matched ignitable liquid mixture diluted to 2 µL mL⁻¹ in dichloromethane. Optimised conditions were as follows: injection volume of 1 µL with split ratio 50 to 1 at inlet temperature 280 °C, carrier gas flow rate was set as 1.0 mL min⁻¹, the column temperature was maintained at 40 °C for 3 minutes, then increased at a rate of 12.5 °C min⁻¹ to 290 °C, and held for 4 minutes. Undiluted ignitable liquid samples (50% gasoline : diesel) were also analysed with a high split ratio (300 : 1) and low injection volume (0.2 µL) to avoid column overloading and to eliminate any difficulties associated with solvent masking. This method provided improved separation and sensitivity compared to the ASTM method. Excellent precision both intra-day and inter-day (<3% RSD for peak area) was also obtained. The stability of ignitable liquid storage was also investigated over a two week period for various types of vials and septa.