Standard Guide for Microspectrophotometry in Forensic Fiber Analysis

Importancia y uso:

5.1 The comparison of color is one of the key steps taken in a fiber comparison, as color is one of the most important discriminating characteristics of fibers. Microspectrophotometers allow for an objective measurement of the color (based upon selective light absorption) of small samples, which can be complementary to, and more discriminating than, microscopical color comparisons.

5.2 Microspectrophotometric spectral comparison is one part of a multi-analytical comparative approach. It is used in conjunction with techniques that identify the fiber composition, such as polarized light microscopy (PLM) and Fourier transform infrared spectroscopy (FTIR). For the identification of the dye components, other techniques such as thin layer chromatography (TLC), Raman spectroscopy, or liquid chromatography mass spectrometry (LC-MS) can be employed and are complementary to the information provided by microspectrophotometry. For more detailed information regarding PLM, FTIR, and TLC refer to Guides E2228, E2224, and E2227 respectively.

5.3 This guide is designed to assist a FSP in the selection of appropriate sample preparation methods and instrumental parameters for the microspectrophotometric analysis and comparison of fibers. When used for comparison purposes, the goal is to determine whether any exclusionary differences exist between the samples (1-9).4

5.4 Limitations to the value of MSP data and comparisons include:

5.4.1 Absorption can be impacted by environmental factors, physical damage, or sample handling. For example, a fiber or textile that has been exposed to environmental factors that irregularly alter the color (for example, photofading) can exhibit spectral differences to a fiber or textile that has not been similarly exposed.

5.4.2 Spectral data collected in the visible region from very dark or very light fibers could be of limited value.

5.4.3 Certain fiber types naturally absorb in the UV region (for example, wool, polyester), limiting data collection and interpretation.

5.4.4 MSP is not a practical technique to identify the individual dyes in a fiber.

5.5 Fiber sample spectra are measured using transmittance spectroscopy. The emission of fluorescence by fiber samples is also measurable using an MSP with microspectrofluorimetry capability (9-12).

Subcomité:

E30.15

Volúmen:

14.02

Número ICS:

07.140 (Forensic science)

Palabras clave:

forensic fiber analysis; microspectrophotometer; microspectrophotometry; MSP;