ISSN: 0022-1198
CODEN: JFSCA
Page Count: 20

Comparative Examination of Inks by Using Instrumental Thin-Layer Chromatography and Microspectrophotometry
Aginsky, VN
Senior Research Chemist, Forensic Science Center, Ministry of the Interior,

(Received 8 September 1992; accepted 24 March 1993)

Abstract

It is well-known that in thin-layer chromatographic (TLC) densitometry and reflectance microspectrophotometry (MSP) the relationship between signal output and content of substance(s) absorbing light is neither a directly, nor reciprocally proportional one. For this reason, the discriminating power of the widespread signal-to-signal ratio technique is not high in relation to similarly colored materials, especially to those having subtle differences of same colored components.

In this paper the modified signal-to-signal ratio approach applicable for both, TLC and MSP methods, is proposed. The approach includes transforming (by using the recommended equations and iterative procedure) the values of the signals obtained for compared materials, in such a manner that the ratios of these transformed signals become less mass-dependent in compared with the ratios obtained by using the signal-to-signal ratio technique. As a result of applying this approach, the discriminating power of densitometric TLC and MSP methods has been enhanced significantly. The value and limitations of the proposed techniques are considered

Keywords:
questioned documents microspectrophotometry, thin-layer chromatography, densitometry, signal, content, relationship, signal-to-signal ratio, iterative procedure, comparison, dyes, inks

Paper ID: JFS13515J
DOI: 10.1520/JFS13515J
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