You are here:
Identifying Plastics-related Compounds using Mass Spectrometry. Coverage, Applications and Web Resources
Citation:
Simon-Manso, Y., T. Mak, X. Liang, E. Erisman, W. Wallace, S. Stein, C. Lowe, A. Williams, S. Wickramasekara, K. Nahan, AND B. Oktem. Identifying Plastics-related Compounds using Mass Spectrometry. Coverage, Applications and Web Resources. American Society for Mass Spectrometry Meeting, Minneapolis, MN, June 05 - 09, 2022.
Impact/Purpose:
N/A
Description:
The NIST Mass Spectrometry Data Center is working on a comprehensive approach to the chemical analysis of plastics-related compounds (PRC) using mass spectrometry as a contribution to the NIST circular economy program (https://www.nist.gov/circular-economy). Due to the versatility of plastics, many manufactured products and environmental pollutants are associated with PRC. 10,547 compounds including monomers, additives, and processing aids of the plastics industry (Environ. Sci. Technol. 2021, 55, 9339-9351) and three types of ionizations has been used in this work to obtain mass spectra and build standard libraries of PRC. Furthermore, this study includes performance comparisons of the different type of ionizations, fundamentals of ionizations, solvent-effect, careful curation, and registration of chemical structures in the EPA CompTox Chemicals Dashboard and several other applications. Multiple MS2 spectra of each neat PRC were recorded at 12 different collision energies by direct infusion using both, an APCI source on a QTOF-6530 and ESI source on a FUSION-LUMOS-Orbitrap. EI spectra were recorded using Agilent 5977-GC/MSD and 8890-GC systems. Chromatographic conditions were adjusted according to the chemical nature of the compounds. In-house software was used for clustering, annotating, and building the three libraries. Different solvents, such as methanol, acetonitrile, isopropanol, and tetrahydrofuran were used to optimize acquisition conditions and study the APCI ionization process. LC runs were performed using reversed-phase, half-an-hour gradients, MPA: water (0.1% FA), MPB: methanol (0.1% FA). Human urine, drinking water and polymer extracts from medical devices samples were prepared following previous publications (Anal.Chem.,2019,91,18,12021, and Talanta,212(2020),1204643). First, we demonstrate that electron impact (EI), electrospray ionization (ESI), and atmospheric-pressure chemical ionization (APCI) ionizations provide full coverage for the chemical analysis of PRC. This is followed by the comparison of the three types of ionization regarding their appropriateness or effectiveness for the analysis of specific compounds. The PRC set contains molecules of very different sizes, polarities, acid-base character, and hydrophobicity, so it is very appropriate to investigate responses to the three types of ionizations. At this point the NIST/EPA/NIH GC/MS Mass Spectral Library (EI) includes 5,921 PRC and about 700 to be added soon. LC-ESI/MS is generally less appropriate for PRC; however, the tandem mass spectral library already contains many plasticizers and processing aids (~ 500) and about a hundred more are in the process to be added. The LC-APCI/MS library will contain about a thousand PRC for the next delivery of the library. Further work is in progress to include spectra of all reported PRC in our libraries. The PRC set contains molecules of very different sizes, polarities, acid-base character, and hydrophobicity, so it has been very appropriate for revisiting the fundamentals of APCI ionization. APCI is recommended for low polarity and molecular weight compounds, but it was found that aromatic and branched hydrocarbons, polyenes, PAHs and other non-polar compounds, frequently with masses over ~500 Da, produce strong signals even using low concentration solutions. To our best knowledge, most PRC spectra in the APCI library have been recorded by the first time using this type of ionization. Four solvents were tested, acetonitrile, methanol, isopropanol, and tetrahydrofuran. Overall, the best results were obtained using methanol. It is known that APCI typically produces the [M+H]+ and M+. ions, however, a variety of uncommon or infrequently observed ions were also observed and studied in terms of signal strength, and solvent dependence. (Abstract too long for this section, please view attached document for remainder)