Time-of-Flight Secondary Ion mass Spectrometry (TOF SIMS) can be used to obtain accurate mass spectra and mass spectral imaging of the longitudinal surface and/or cross-sectional area of dyed fibers. These data, when coupled with an analytical dye database, can be used to unambiguously identify commercial textile dyes collected from crime scenes. In this study, a method has been developed using TOF SIMS to provide an advanced dyed fiber analysis protocol that: 1) is effective at relatively low concentrations of dye in the fiber and can be applied to the cross section of a single fiber; 2) enables location dependent two dimensional mass spectral based chemical imaging of dyed fibers on the fiber surface and/or on a fiber cross section; 3) enables dye analysis with minimal destruction/consumption of fiber. As an example, TOF SIMS was employed to identify C.I. Acid Blue 25 with only 0.1% dye by weight of fiber on nylon 6.6 fiber surfaces and cross sections. In this method, a C60 ion beam was used as a �soft cleaning� method to remove surface contamination and any Bi ion beam induced damaged materials from previous scans. This method enabled increased integration of molecular ion signal which results in significant improvement in signal-to-noise and thus improved mass spectral resolution of the dye. An example showing the identification of dyes from one single fiber cross sections will be presented to demonstrate that positive identification is feasible with minimal destruction of fiber trace evidence.            This project was supported by NIJ Grant # 2009-DN-BX-K216. The opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect those of the Department of Justice.

Improvement of detection limit of acid dyes in nylon fibers via time-of-flight secondary ion mass spectrometry

247th National Meeting (2014)

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