Direct Analysis of Textile Fabrics and Dyes Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization Mass Spectrometry

Abstract

The forensic analysis of textile fibers uses a variety of techniques from microscopy to spectroscopy. One such technique that is often used to identify the dye(s) within the fiber is mass spectrometry (MS). In the traditional MS method, the dye must be extracted from the fabric and the dye components are separated by chromatography prior to mass spectrometric analysis. Direct analysis of the dye from the fabric allows the omission of the lengthy sample preparation involved in extraction, thereby significantly reducing the overall analysis time. Herein, a direct analysis of dyed textile fabric was performed using the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) source for MS. In MALDESI, an IR laser with wavelength tuned to 2.94 μm is used to desorb the dye from the fabric sample with the aid of water as the matrix. The desorbed dye molecules are then post-ionized by electrospray ionization (ESI). A variety of dye classes were analyzed from various fabrics with little to no sample preparation allowing for the identification of the dye mass and in some cases the fiber polymer. Those dyes that were not detected using MALDESI were also not observed by direct infusion ESI of the dye standard.

Forensic comparison of synthetic fibers

“…Those dyes that were not detected using MALDESI were also not observed by direct infusion ESI of the dye standard. [13] Direct analysis of textile fiber and dyes with IR-MALDESI is advantageous because no extraction is required. Fibers can be used for multiple analyses because a very small amount of fiber is sufficient for analysis.…”

“…Direct analysis of dyed textile fabrics in the identification of dye mass and in some cases the fiber polymer using infrared matrixassisted laser desorption electron spray ionization mass spectrometry. [13] This figure is available in colour online at wileyonlinelibrary. com/journal/pat Very recently, an HPLC-DAD-MS method has been used for the analysis of fiber dyes of different classes, such as neutral, positively charged, and negatively charged dyes; dyes with single charges; dyes with multiple charges; hydrophilic and hydrophobic dyes; and dyes in a wide range of size and molecular mass in a single analytical run.…”

“…The white square indicates the analyzed section displayed in the "after" image. [13] This figure is available in colour online at wileyonlinelibrary.com/journal/pat Figure 11. Chromatograms and absorbance spectra of (a, b) extracted Reactive Orange 16; (c, d) Reactive Orange 16 powder dye reference; (e, f) Disperse Blue 73; and (g, h) Basic Red 46.…”

Analysis of trace fibers by IR-MALDESI imaging coupled with high resolving power MS

“…These extraction and separation steps, however, can be time consuming, thus there have been investigations into the use of direct analysis techniques to allow for obtaining MS information with minimal sample preparation. Laser desorption photoionization (LD-PI) [9], direct analysis in real time (DART) [10], and matrix-assisted laser desorption electrospray ionization (MALDESI) [11] have each been used for direct sampling of dyestuffs from textile fabric/fibers. The unique attributes of direct analysis MS techniques has also found application in other areas of forensic science [12–14].…”

“…Some dyes, such as acid dyes, are anionic and thus observable in negative ionization mode, while basic dyes are cationic and observable in positive ionization mode [7]. Previous experiments demonstrated proof of principle for analyzing the dyes directly from fabric [11]; however, this manuscript pushes towards a more relevant single-fiber analysis.…”