Gary S. Groenewold

Contaminant characterization on hair and fiber surfaces using imaging TOF-SIMS

Imaging time-of-flight secondary ion mass spectrometry (SIMS) was used to evaluate the detection of contaminant chemicals on the surfaces of single synthetic textile and canine hair fibers. The results of the study showed that a variety of chemical classes can be detected. Both cocaine and heroin could be easily observed as intact protonated molecules ([M + H]+) in the cation spectra acquired from textile fibers. Two organophosphates were evaluated: malathion, which is a common pesticide, and pinacolyl methyl phosphonic acid (PMPA), which is the principal degradation product of the nerve agent soman (a close relative of sarin). Malathion could be observed as (CH3O)2P(equalsS)S-, which is formed by thiophosphate cleavage of the intact malathion. PMPA is observed as the conjugate base ([PMPA - H]-). Surfactant chemicals found in hair care products were successfully detected on single hair fibers. Specifically, alkyl sulfates, ethoxylated alkyl sulfates, silicones, and alkylammonium compounds could be readily identified in spectra acquired from single hair fiber samples exposed to shampoo and/or conditioner. Generally, the results of the study show that imaging SIMS is applicable to single fiber analysis, for a range of adsorbed compound types. The forensic application of this instrumental approach has not been widely recognized. However, the ability of the technique to acquire specific chemical information from trace samples clearly points to applications where the need for chemical analysis is great, but the amount of sample is limited.

Static secondary ion mass spectrometry characterization of nail polish and paint surfaces

A variety of paint and fingernail polish samples, which were visually similar, but had different chemical compositions, were analyzed using three static secondary ion mass spectrometry (SIMS) techniques. These techniques included: (1) high spatial resolution/high mass resolution imaging time-of-flight SIMS; (2) analysis of stabilized high mass secondary ions with an ion trap SIMS capable of MS/MS; (3) qualitative characterization using a quadrupole SIMS with `pulsed extraction charge compensation. In some cases, distinguishing between different coatings was easily achieved because of the presence of dominant ions derived from the components of the coating materials in the SIMS spectra. In other instances, coating distinction was difficult within a product group because of spectral complexity; for this reason, multivariate statistical techniques were employed, which allowed meaningful classification of spectra. Partial Least Squares and Principle Component Analysis were applied to quadrupole SIMS data. When using Partial Least Squares analysis reasonably accurate coating identification was achieved with the preliminary data with overall correct identifications at greater than 90% sensitivity.