GC/MS and DART-MS as complementary methods for investigating the effects of weathering on chemical profiles of ignitable liquids: A case study for paint thinner

Abstract

In this study, gas chromatography/mass spectrometry (GC/MS) and direct analysis in real time mass spectrometry (DART-MS) were used to analyze paint thinner samples weathered under different conditions. As GC/MS total ion chromatograms (TIC) of weathered paint thinner samples varied significantly due to the disparate evaporation rates of organic compounds in the mixture, DART-MS spectra have shown more consistent profiles among different samples. The distinctive ion clusters identified in the DART-MS spectra were attributed to the less volatile glycol ethers and polymeric compounds with alkyl chains in the paint thinner samples. Analysis of variance-principal component analysis (ANOVA-PCA) was applied to study the contributions of weathering degree and temperature factors to the total variance of GC/MS TIC and DART-MS spectral datasets and found that both factors played significant roles in the weathering process (p < 0.05), though weathering degree contributed to considerably more total variance to GC/MS TIC profiles (i.e., 93.4%). The paint thinner GC/MS and DART-MS profiles were compared with those from other common ignitable liquids, such as gasoline, torch fuel, lighter fluid, and Japan drier. The partial least squares discriminant analysis (PLS-DA) models were constructed to classify the ignitable liquids with the classification rates of 99.97 ± 0.02% and 99.80 ± 0.08% for models based on GC/MS and DART-MS data, respectively. Our study has shown that DART-MS can provide discriminative information for distinguishing ignitable liquid samples and complement the existing GC/MS method by the detection of less volatile compounds.