Evaluating the capabilities of DART-MS compared to FTIR spectroscopy and SEM-EDS for the analysis of architectural paint mixtures

Abstract

Architectural paint is a type of transferred trace material typically encountered by forensic laboratories, mostly in cases of forced entry. Forensic analysis of architectural paint generally consists of bright field microscopy followed by Fourier transform infrared (FTIR) spectroscopy. Further characterization can be achieved using additional techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This study aimed to evaluate the effectiveness of DART-MS compared to FTIR spectroscopy and SEM-EDS for the analysis of architectural paint analysis, as well as investigate how DART-MS could be incorporated into a paint analysis workflow. A total of 45 architectural mixed paint samples were obtained by preparing combinations of five base color paints as binary mixtures in known proportions. DART-MS detected multiple organic compounds, including tributyl citrate (TBC), polyethylene glycol (PEG), dioctyl maleate (DOM), and tert-butyldiethanolamine (TBDEA) which are common plasticizers, additives, and solvents in architectural paints. DART-MS also showed the ability to identify the black paint in mixed paints above 10 % at both 350 °C and 500 °C, unlike FTIR and SEM-EDS. Meanwhile, FTIR spectroscopy identified several organic and inorganic compounds in each of the base color paints, including binders, pigments, and extenders, and was generally able to determine which base color paints were present in a mixture. In addition to supporting the identification of the inorganic compounds detected using FTIR, SEM-EDS also demonstrated greater sensitivity for small concentrations of inorganic compounds in the mixed paints. Overall, the compounds detected through DART-MS analysis were not found with either FTIR or SEM-EDS, highlighting the complementary nature of these techniques. Furthermore, DART-MS demonstrated the capability to identify and monitor ions specific to the black base paint within mixed paint samples, supporting the adoption of a combined approach for enhanced architectural paint discrimination.