Forensic discrimination of polyester fibers using gel permeation chromatography

Gel permeation chromatography (GPC)/size exclusion chromatography was developed for the forensic discrimination of polyester fibers. Fibers were dissolved with 1,1,1,3,3,3-hexafluoro-2-propanol and chloroform, and applied to liquid chromatography (LC) using tandemly coupled two styrene-divinylbenzene co-polymer GPC columns, chloroform mobile phase, 254 nm light absorbance monitoring, and using the polystyrene standards as molecular weight (MW) calibration reference compounds. Polyester polymers were eluted as the main tailing peaks followed by small low-MW peaks that included cyclic ethylene terephthalate trimer, which was assigned by LC-mass spectrometry and Fourier transform infrared spectroscopy. Fibers were discriminated using the GPC parameters of weight average MW (Mw), Mw/number average MW (polydispersity index, PDI), and percentage peak area of low-MW peak (PPAL). Reproducible GPC was achieved through controlled injection amount (3-16 mu g fiber). Inter-sample coefficient of variance (CV) in Mw, PDI, and PPAL for one poly(ethylene terephthalate) (PET) fiber was measured as 0.01, 0.02 and 0.016, respectively, and used as configurated CV for the discrimination between fiber pairs. The normalized variances for Mw, PDI, and PPAL were summed, and the square root was calculated. A value exceeding 2 indicated significant discrimination in the three-dimensional 2 s criteria. A comparison of 37 PET fibers (Microtrace Forensic Fiber Reference Collection, commercial polyester shirts, in-house manufactured PET yarns) was executed for GPC. Only 5.1% of the combinations could not be discriminated between the two different fibers. Site differences in the commercial PET shirts were found, where fibers taken from the neck sites were significantly different from those of the chest and sleeve.