Examination of Firearms Review: 2007 to 2010 - Interpol

about forensic applications of ambient ionisation methods. The method is capable of
detecting compounds in a wide range with minimal sample workup, yet the time of
analysis is short. Also here the development of the technique(s) is crucial for it to
become widely used. 71
Another detection method using mass spectrometry is a proton transfer reaction,
PTR-MS. The technique has been developed almost exclusively for detection of
gaseous organic compounds in air, but the possibility of detecting fire accelerants
onsite has been shown. It is also possible to identify substances after a prolonged
storage of burnt material with a characteristic mass spectra coupled with principal
component analysis. 72
The high content of ethanol in motor fuels may produce problems in fingerprinting
samples. Especially aliphatic alcohols with the carbon number C3-C8 provide
challenges for the analytical method used. A flow switching GC x GC has been
demonstrated to generate high speed and high resolution separations as well as to
gain quantitative and accurate results. The fast runtime combined with separation
efficiency seems to surpass the compared ASTM methods. A drawback of the
method is that it is not capable to separate ethers from gasoline aliphatics, although
they are not normally added to the gasoline under study (E85). 73 The presence of
foreign material improperly mixed to samples can be detected by fingerprinting
applied to chromatographic data. In addition to multi-way calibration techniques
combined with GC x GC-FID can reveal complex mixtures being treated as a single
analyte. 59
Outside the scope of general analysis methods, a study about gasolines and their
modifications during evaporation and burning by normal phase HPLC has been made.
The task was to determine polycyclic aromatic hydrocarbons, because they are less
subjected to alterations during the fire. Arenes were identified not only by retention
time but also by distribution of absorption spectral lines at peak points. Relative
concentration of alkylarenes was experimentally obtained. 74
Another method not so common in arson analysis is stable isotope profiling of burned
matches. Burned matches may be recovered from fire scenes, but unfortunately the
isotope profile of matches with gasoline from mock fires were not significantly
different from the ones without fire accelerant. 75
3.3 Individualisation of ignitable liquids
Identification and classification of fire accelerants in arson residues, especially
ignitable liquids, has gained more efforts each year. The method used to obtain
distribution varies, although in many cases analysis is made by GC-MS combined
with different types of data handling. For example, comprehensive two-dimensional
gas chromatography combined with mass spectrometry has been a preferred
technique for analysis of complex volatile and semi-volatile mixtures. The use of two
different types of columns and a modulator offers an orthogonal separation system
and also provides the target compound’s carbon number and chemical structure. 76
Alteration of fire debris samples due to microbial degradation of sample matrices
might lead to differences in chromatographic profiles of ignitable liquids.
431