Stable isotope analysis of safety matches using isotope ratio mass spectrometry–a forensic case study

Abstract

Isotope ratio mass spectrometry (IRMS) was used to assess what contribution the technique could make towards the comparative analysis of matchstick samples within the 'normal' framework of a forensic investigation. A method was developed to allow the comparison of samples submitted as a result of an investigation, with the added advantage of rapid sample turn-around expected within this field. To the best of our knowledge this is the first time that wooden safety matches have been analysed using IRMS. In this particular case, bulk stable isotope analysis carrried out on a 'like-for-like' basis could demonstrate conclusively that matches seized from a suspect were different from those collected at the scene of crime. The maximum delta13C variability observed within one box was 2.5 per thousand, which, in conjunction with the error of measurement, was regarded to yield too wide an error margin as to permit differentiation of matchsticks based on 13C isotopic composition alone given that the 'natural' 13C abundance in wood ranges from -20 to -30 per thousand. However, from the delta2H values obtained for crime scene matches and seized matches of -114.5 per thousand and -65 per thousand, respectively, it was concluded that the matches seized were distinctly different from those collected at the crime scene.

Forensic utility of isotope ratio analysis of the explosive urea nitrate and its precursors

“…This approach has been applied in a forensic context to manufactured materials such as matches [7], paint [8], adhesive tapes [9], and plastic bags [10], as well as non-UN explosives [11][12][13][14][15]. Variations in the carbon or nitrogen isotope ratios have been used to show a possible link between starting reagents and the final explosive product molecules, such as RDX [14].…”

Forensic analysis of wooden safety matches — A case study

“…Preliminary work regarding the feasibility of Stable Isotope Profiling (SIP) of matchsticks was previously published [1]. The case study presented here, however, not only includes additional SIP data but also presents SIP data in conjunction with the data from established forensic analytical techniques, in virtually the same way they were reported to the senior investigating officer.…”

“…In addition the internationally recognised standard, IAEA-CH-7, was used for quality assurance purposes [1,6]. Measured δ 2 H-values were normalised according to the method described by Coplen [7] with Z-factors (or 'stretch' factors) typically being of the order of 1.02 to 1.03.…”

Stable isotope analysis of white paints and likelihood ratios

“…Two certified standards of known isotopic composition were used to quality control samples, coumarin (δ 18 O-VSMOW =15.83‰, δ 2 H VSMOW =62.56‰) and glucose penta-acetate (δ 18 O-VSMOW =23.94‰, δ 2 H VSMOW =−98.48‰), which have been calibrated against internationally recognised reference materials by Iso-Analytical (Sandbach, Cheshire, UK). Polyethylene (IAEA-CH-7) was also used for quality assurance purposes [9][10][11][12]. The principle was to use span standards which cover the range expected from the samples analysed.…”

“…Raw data obtained were blank corrected and calibrated against the REF samples by the proprietary instrument software. If necessary, δ-values were drift corrected according to the deviation of measured δ-values from known δ-values of the quality controls [9][10][11][12].…”