Five liquid chromatographic methods were developed for the forensic examination of non ball pen inks from questioned documents.
Using a simple isocratic HPLC system with a highly sensitive Spectra Physics system, each of the 17 groups of ink tested were readily separated, and representative chromatograms were obtained. The technique was reproducible by repeated extraction and analysis of each sample several times. Out of the 113 samples examined, a group of 32 samples were not distinguishable from other inks in the group and required examination of the ultraviolet and visible spectra to determine differences in the composition of the inks. With this approach, 108 of 113 inks in the collection, the majority of which had not been previously distinguished by thin layer chromatography, were distinguished. The main advantage of this technique over traditional methods is that complete chromatographic and spectral data can be collected simultaneously using a sample size of a few nanograms. Those inks which cannot be immediately differentiated on the basis of their chromatographic data can be further examined by comparison of their ultraviolet or visible spectra and, if required, the derivative spectra of individual peaks. The two advantages over thin layer chromatography are increased sensitivity and increased resolution which produce detailed information for comparison of samples. 7 figures and 6 references (Author abstract modified)
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