Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

Sub-Department

Chemistry

First Advisor

Stephen L Morgan

Abstract

Methodology for the microextraction of basic dyes on acrylic, acid dyes on nylon, disperse dyes on polyester, and reactive dyes, direct dyes, and indigo on cotton textile fibers is reported. Although these processes are destructive to the fiber evidence, the ability to analyze dye extracts from sub-millimeter fiber lengths of single fibers, coupled with detection limits in the hundred picogram range by ultra-performance liquid chromatography (UPLC) with both diode array detection (DAD) and tandem mass spectrometry (MS-MS) makes routine forensic characterization feasible.

Microextraction, followed by UPLC, can often distinguish similar fibers containing different, but similar, dyes with the combination of retention time matching, UV/visible spectral comparison, and structural analysis by mass spectrometry. This work focuses on determining the optimum extraction conditions for each dye class and developing chromatographic methods with suitable resolution and sensitivity for trace analysis. Analysis of fibers as small as 1 mm in length is the target sample size to minimize destruction of fiber evidence. Analytical figures of merit and validation statistics, including extraction reproducibility, linearity, limits of detection and quantitation, and UPLC precision, are reported.

The analysis of cotton fibers is challenging because they can be dyed with three different classes of dye, each requiring a different method for extraction and analysis. Reactive dyes present a unique challenge because they are chemically bound to the cellulose structure of the fiber. Release of these dyes from cotton requires breaking of the covalent bond using hot sodium hydroxide. The resulting hydrolysis reactions can also cleave amide bonds and possibly other chemical bonds in the dye molecule. The various structural changes that can take place leads, in many cases, to production of multiple reaction products from a single dye. We demonstrate successful extraction of reactive dyes from single 1 mm cotton fibers with detection limits as low as 3.3 pg. Systematic experiments at varying reaction conditions, with product analysis by mass spectrometry, were also performed to characterize the degradation of reactive dyes under hydrolysis, and to facilitate interpretation of reactive dye extractions.

The concept of the sensitivity ratio as an analytical performance characteristic was introduced by John Mandel of the National Bureau of Standards in 1954, but has been not been widely applied in analytical chemistry. The basis for Mandel sensitivity is reviewed here, along with examples of its use. Because the sensitivity ratio is independent of the scale in which measurements are expressed, it is a useful tool for comparisons of variability between different analytical methods.

Rights

© 2013, Scott James Hoy

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