Characterisation of forensic glass samples using inductively coupled plasma mass spectrometry

Abstract

The analytical technique of inductively coupled plasma mass spectrometry (ICP-MS) was evaluated for its applicability to the characterisation of window glass fragments, having identical refractive indices, and of the type that are frequently presented as physical evidence to a forensic laboratory. Minute glass fragments, weighing as little as 500 µg, were digested with acid in specially designed poly(tetrafluoroethylene) vials using an ultrasonic bath. The solutions were then analysed directly by aspirating into an ICP-MS system. The concentrations of 48 elements could be accurately determined with a relative standard deviation of equal to or less than 4%. Analysis by ICP-MS provides an elemental fingerprint of a glass sample. By using an initial discriminating group of 15 elements the uniqueness of a fragment can be established. By determining a further 25 elements, the results of the discrimination test can then be considered unquestionable. Australian window glasses were found to be readily distinguishable from window glasses from the USA. Tests performed produced successful discrimination levels of no less than 85% for the USA samples and no less than 90% for the Australian window glass samples investigated.