58 May / June 2019
of the terminal functional groups by using accurate mass and MS/MS spectra of thermal desorption products (Figure 15). KMD and RKM plots [5] are also helpful (Figure 16).
Conclusions
Figure 13. TIC and Mass Spectrum at Thermal Desorption Region of PBA Using TDP/DART-MS
Py-GC/MS disables observation of molecular weight distribution since the target analytes are pyrolysis products.
MALDI-MS enables observation of absolute molecular weight distribution, if the sample has quite a narrow distribution. However, this PBA sample has a distribution that is too wide to determine average molecular weight (Figures 11a, 11b). In that case, SEC/ MALDI-MS is effective (Figure 12)
TDP/DART-MS enables measurement of molecular weight distribution of thermal desorption compounds (Figure 13).
Terminal functional groups
TDP/DART-MS is useful for direct analysis of otherwise difficult samples like oils and polymers. In the case of oils, TDP/DART-MS enables detection of additives and base oil in lubricating oils by applying a heat gradient, without any pre-treatment or sample preparation. Thus, it is suitable for evaluating the degradation degree of lubrication oils, which has not been characterised by FT-IR analysis. TDP/DART-MS is also a useful method to analyse the change in chemical structure (e.g. oxidation state, molecular weight, etc.). Therefore, this analytical method is expected to contribute to advances in R&D, forensic analysis, and quality control in the oil and gas field.
Figure 14. KMD and RKM Plots of PBA Using MALDI-MS Spectrum (reflector mode)
For polymer samples, both Py-GC/MS and TDP/DART-MS enables measurement of polymer materials such as vulcanised rubbers and crosslinked resins, but information regarding molecular weight distribution is limited. On the other hand, MALDI-MS enables measurement of absolute molecular weight distribution, but only if the samples are soluble and have narrow distribution (Mw / Mn < 1.2). TDP/DART-MS enables individual measurement of low molecular weight pyrolysis products and oligomeric thermal desorption products, since it utilises a DART soft ionisation technique combined with thermal desorption. Therefore, it provides valuable clues to elucidate the chemical structure of unknown compounds (for example, compounds not listed in spectral libraries, degraded products, reacted products, etc). Thus, TDP/DART-MS can contribute to further development of polymer analysis technology.
References
1.C.Takei,
K.Kinoshita,
T.Nishiguchi,
h.Shimada,
K.Maeno,
Y.Shida; 63rd ASMS Annual Conference, Poster ThP74 (2015)
Figure 15. MS/MS Spectrum of m/z 257.17 Using TDP/DART-MS
2.R.B.Cody, C.Takei,
H.Shimada,
Y.Shida, A.Kusai; 64th ASMS Annual Conference, Poster MP545(2016)
3.C.Takei, K.Yoshizawa, H.Ohtani; 65th ASMS Annual Conference, Poster WP605(2017)
4.S.Tsuge, H.Ohtani, and C.Watanabe; Pyrolysis-GC/MS Data Book of Synthetic Polymers, Elsevier (2011) p. 92-93
Figure 16. KMD and RKM Plots of PBA Using TDP/DART-MS Spectrum at Thermal Desorpton Region
Py-GC/MS disables identification of terminal functional groups of unknown polymer samples. However, quantitative analysis is possible for known terminal functional groups.
MALDI-MS enables analysis of the number of terminal functional groups. KMD analysis is helpful, since the number of terminal functional groups are clearly visualised (Figure 14).
TDP/DART-MS enables not only analysis of how many terminal functional groups exist, but also elucidation of the chemical structure
5.H.Sato,
S.Nakamura, K.Teramoto,
T.Sato; JASMS, 2014, 25(8), 1346- 1355
Acknowledgements
We would like to acknowledge Chikako Takei and Kenichi Yoshizawa, BioChromato Inc for providing poster content from the 2017 Gulf Coast Conference Poster Lubricating Oils Analysis Using Thermal Desorption and Pyrolysis / Direct Analysis in Real Time-Mass Spectrometry and the 2018 American Society for Mass Spectrometry Poster Analysis of Poly(butyl acrylate) by Py-GC/MS, MALDI-MS and Thermal Desorption and Pyrolysis combined with DART-MS
†DART is a registered trademark of JEOL USA
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