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Method Development and Validation of Comparative Finished Fiber Analysis Using Nano-Sampling Cryomicrotomy and Time-of-Flight Secondary Ion

NCJ Number
Date Published
January 2014
70 pages
This project achieved its goal of developing an unprecedented, comprehensive, repeatable, and reproducible analytical method for characterizing dyed and finished fibers; the method has an insignificant adverse impact on evidence preservation while reducing or eliminating cross-contamination.
Sub-micron level sample removal of fibers was achieved using cryomicrotomy, followed by time-of-flight secondary ion mass spectrometry (TOF SIMS) analysis of the surface and cross-section of dyed fibers. The data collected was validated using high performance liquid chromatography - quadrupole time-of-flight mass spectrometry (LC-Q-TOF) following microextraction of dye from the fibers. The cryomicrotome-based fiber cross-sectioning method and its utility has been compared to the Analytical Instrumentation Facility's conventional microtome method for fiber cross-sectioning. Experiments to date have shown that the cryo-based method is key to obtaining consistent and effective cross-sectioning of fibers. The cryomicrotome method has been successfully used to make cross-sections of a single fiber for TOF SIMS analysis. A TOF SIMS method has been developed for analyzing disperse dyes in polyester and acetate and acid dyes in nylon. A revised TOF SIMS method that uses C60 ion beam has improved the detection limit for acid dyes in nylon cross-sections. The cryomicrotome and TOF SIMS method was validated via comparison of data with more conventional micro extraction LC-Q-TOF mass spectrometry. Methods were developed for extracting dyes from polyester, acetate, and nylon fibers. The isocratic and gradient elution methods developed for LC analysis of a series of disperse dyes and acid dyes have shown excellent repeatability for single dye analysis, which is sufficient for a searchable database. Using the optimized methods for LC analysis, a reference set of known fibers dyed with the most commercially important dyes for apparel and automotive polyester (73 dye samples, acetate (19 dye samples), and residential nylon carpet (6 dye samples) was established. 22 figures, 24 references, and a listing of media through which the research has been disseminated

Date Published: January 1, 2014