Microspectrophotometry in Forensic Science

Abstract

Infrared microspectrophotometry is a combination of two techniques – optical microscopy and infrared (IR) spectrometry – which supply specific information about the composition and structure of a given material. The equipment used is a Fourier transform infrared (FTIR) spectrometer connected on line with an optical microscope. The microscope allows observation of a sample in white light at relatively high magnification; this allows its morphology and microstructure to be established, and facilitates selection of the area which will subsequently be subjected to IR spectrometric analysis. The microscope also permits use of polarized light in investigations. The spectrometer enables analysis of a sample with a chosen measuring technique – transmission or reflection – with the aim of determining the chemical composition of the sample. It also supplies information about its microstructure and orientation. This method is particularly useful in the analysis of trace amounts of various substances secured as material evidence in court cases, and in analysis of the homogeneity of the sample, identification of inclusions and contaminants on the surface, and detection of structural defects. A specific advantage of this method is its ability to unambiguously photograph and record marked and measured areas of the sample and minimize the process of preparing the sample for analysis. Furthermore, IR microspectrophotometry gives the rare opportunity of studying small crystals or areas in the oriented materials by using polarized IR radiation, both by the transmission and the reflection technique. Its fundamental drawback is that the physical nature of the microsample may influence the precision of the photometric measurements and cause distortion of the spectra (artefacts) obtained. Furthermore, because only a small area is studied the heterogeneity of the sample and the amount of contaminants may significantly influence the results of spectrometric measurements. Microspectrophotometry in the ultraviolet/visible (UV/VIS) range is a combination of photometric measuring techniques and optical microscopy. It allows comparison of the color of very small samples of various materials, such as single fibers, tiny amounts of paint, traces of ink or ball‐point pen ink on a forged document in an objective way, independently of the sharpness and quality of the observers's vision. It yields immediate information about spectral differences existing between two samples of similar color, which are indistinguishable by use of the optical microscope. Additionally, using appropriate software to analyze the results of microspectrometric measurements, it enables precise measurement of a color, and – applying the theory of colors – gives a color a defined numerical value; this facilitates communication between experts working with this method. The equipment consists of an optical microscope with a spectrometer for analysis in the visible and ultraviolet range, connected to a microcomputer via an analog‐to‐digital converter.

Evaluation of the evidential value of physicochemical data by a Bayesian network approach

“…It allows a screening of the often numerous items at the scientist's disposal and the selection of those that should be analysed further by instrumental methods. These include the characterisation of the polymer composition by FTIR spectroscopy [18,19] and, in case the fibres were dyed, a microspectrophotometric comparison of colour [20,21]. Since microspectrophotometry in the UV-VIS or VIS range has been used as a part of the analysis of coloured textile fibres in forensic fibre examination, the results have been generated in the form of transmission and absorbance spectra.…”

Supramolecular interaction of transition metal complexes with albumins and DNA: Spectroscopic methods of estimation of binding parameters

“…In particular, the evidence of weak binding is important in the study of bioorthogonal reactions, the processes occurring in living systems without participation of any their components. [27,28] Moreover, state-of-the-art spectroscopy methods are developing towards microspectroscopy, [29][30][31] involving new methods of absorption and laser spectroscopy, and other methods for solving complicated problems. [32] Comprehension of the scope of the methods applied in the study of supramolecular interaction and approaches to the calculation of constants would enable to enlarge essentially the scope of the methods used.…”

Rapid, Nondestructive Denim Fiber Bundle Characterization Using Luminescence Hyperspectral Image Analysis

“…6,10,19 However, two dyes having similar chemical structures could exhibit indistinguishable UV–Vis absorption spectra. Single-point microspectrophotometry 19,20 is another technique that can be used for fiber bundle dye discrimination. While this method may yield immediate information about spectral differences between two samples, the inherent issue lies with the actual sample being analyzed.…”

“…As an example, opaque and pale samples often yield broad and indistinct electronic absorbance spectra. 20…”