Forensic Dye Analysis by Direct Analysis in Real Time Mass Spectrometry and Raman Spectroscopy

Abstract

Differentiating similarly colored dyes is important in suspect-to-trace evidence connection. The thermal desorption/pyrolysis-direct analysis in real time-mass spectrometry (TD/Py-DART-MS) and the surface-enhanced Raman scattering (SERS) methods were developed to analyze dyes on textile fibers. Five blue dyes on different polymer matrices of fibers, including cotton, silk, and nylon, were analyzed. The mass spectra were collected from the dye standards and dyed fibers, with no prior extraction solvent step. A profile of desorption time and mass spectra was compared. The characteristic ions of dyes and polymers were identified. Dispersive Raman spectroscopy was used as a secondary method with an aqueous silver colloid to improve the signal-to-noise ratio and minimize the contribution of background polymer signal on Raman spectra. The TD/Py-DART-MS method requires a single fiber and no extraction, but it offers a multidimensional profile within 7 minutes. The method is simple and has high sample throughput potential, which may significantly contribute to the forensic identification of dyed fibers.