主题：Journal of Forensic Sciences

Journal of Forensic Sciences
Volume 51 Issue 4 Page 771  - July 2006
doi:10.1111/j.1556-4029.2006.00155.x
High-Performance Liquid Chromatography–Ultraviolet–Visible Spectroscopy–Electrospray Ionization Mass Spectrometry Method for Acrylic and Polyester Forensic Fiber Dye Analysis*
Lauren M. Petrick, M.S.1; Trevor A. Wilson, B.S.2; and W. Ronald Fawcett, Ph.D.1

ABSTRACT: A critical point of comparison between a fiber collected from a crime scene and a fiber from a known source is the color. Fiber dye analysis using thin-layer chromatography or ultraviolet (UV)–visible (Vis) microspectrophotometry provides useful, although limited, data for comparison. High-performance liquid chromatography–electrospray ionization mass spectrometry (LC/MS) overcomes these limitations by integrating chromatography, ultraviolet–visible spectroscopy, and mass spectrometry into a single instrument. In order to evaluate the applicability of the LC/MS to forensic fiber dye analysis, a multi-stage chromatographic method using acidified water and acidified acetonitrile was developed that separated and identified a mixture of 15 basic and 13 disperse dye standards. The LC/MS also detected and analyzed dyes extracted from individual 0.5 cm acrylic and polyester fibers, demonstrating its applicability to this type of analysis. With regard to the analysis of disperse dyes in polyester fibers, the replacement of pyridine with acetonitrile in the extraction system allowed direct injection of the extracts into the LC/MS. The advantage of the LC/MS over other instrumental methods of textile dye analysis is demonstrated by the analysis and differentiation of three black acrylic fibers: two fibers had similar UV–Vis spectra but were differentiated with chromatography and two had similar UV–Vis spectra and chromatograms but were differentiated using the mass spectrometer.
The forensic analysis of fiber evidence involves the evaluation and comparison of the physical and chemical characteristics of the submitted fibers, one of which is color. The color of a fiber is imparted by dyes that are added during the manufacturing process. Each type of fiber, such as acrylic or polyester, differs in the chemical structure of its polymer chain. Therefore, different dye classes have been developed to maximize the dyeability (ability to accept the dye) and color fastness (resistance to fading) of the fiber. The main difference between these dye classes is the chemical processes used to bind the dye molecules to the polymer, resulting in covalent bonds, ionic bonds, or Van der Waals attractions. By virtue of their application, all dyes within a particular class are removed from the fiber using the same general extraction system that typically has no effect on other classes (e.g., the solvent system for basic dyes does not remove disperse dyes). These resulting extraction solutions are then analyzed and compared to determine whether or not the dyes are similar.
Current methods of analyzing the dye in a fiber, such as ultraviolet (UV)–visual (Vis) microspectrophotometry and thin-layer chromatography (TLC), have demonstrated their ability to be highly discriminating. However, both of these methods have some limitations that the high-performance liquid chromatograph (HPLC) coupled with a mass spectrometer overcomes. The UV–Vis
Current methods of analyzing the dye in a fiber, such as ultraviolet (UV)–visual (Vis) microspectrophotometry and thin-layer chromatography (TLC), have demonstrated their ability to be highly discriminating. However, both of these methods have some limitations that the high-performance liquid chromatograph (HPLC) coupled with a mass spectrometer overcomes. The UV–Vis microspectrophotometer objectively characterizes the color of a fiber by generating an absorbance spectrum. The main advantage of the microspectrophotometer is that analysis can be performed directly on the fiber—no extraction is required. UV–Vis microspectrophotometry alone fails in its ability to differentiate dye isomers, discriminate between fibers of the same color but comprised of different dye mixtures (metamerism), or to analyze deeply colored items (1). Unlike the microspectrophotometer, TLC requires extraction of the dye from the fiber and selection of an appropriate mobile phase for chromatography. The dyeing mechanism (viz. dye class) is determined using a system of extraction solvents and evaluating which one successfully removes the color from the fiber. TLC suffers from a lack of reproducibility between laboratories and difficulty in comparing lightly colored items (including shades of yellow) (1). High-performance liquid chromatography–electrospray ionization (ESI) mass spectrometry (LC/MS) offers the same dye class information as TLC (via extraction and chromatography) and yet the spectroscopic information of UV–Vis microspectrophotometry is not restricted by either lightly or deeply colored fibers. LC/MS is sufficiently sensitive in detecting all dyes, even those in relatively low concentrations found in lightly colored fibers. Likewise, LC/MS is sufficiently selective in detecting dyes in low concentrations where they might ordinarily be masked in deeply colored fibers by dyes in high concentrations. Additionally, the LC/MS generates mass information that discriminates between coeluting compounds and can be used to confirm the identity of the dye. This means that the instrument can compare all colors (including custom blending), tints, and hues present in fiber evidence and differentiate between dyes of similar color, including isomers. The only limitation of the LC/MS is that the dye must be able to be extracted from the fiber in order to be analyzed. Forensic applications of LC/MS exist for the analysis of controlled substances (2), explosives, poisons, toxins, biologicals (http://www.lcgceurope.com/lcgceurope/article/articleDetail.jsp?id=36,589), and inks (3,4). However, the application of this instrumental technique to textile dye identification and characterization has not been investigated until recently.