GC-TOFMS Application: Ethylene Propylene Diene Monomer Rubber Analysis by using Pyrolysis-GCxGC-MS

  • Summary

MSTips No.273

Introduction

 Recently, we developed a new gas chromatography/high resolution time-of-flight mass spectrometer (GC/HR-TOFMS) system which allows using multiple ionization techniques not only electron ionization (EI) but also field ionization (FI) and photo ionization (PI).
FI is a soft ionization technique that is well suited for hydrocarbons analysis because it generates molecular ions with minimal fragmentation for all compounds, including saturated hydrocarbons. PI is an also soft ionization technique that provides high sensitivity and molecular ion information for compounds with ionization energies below the maximum practical photon energy (10.8 eV) of the deuterium lamp used in our current design.
In this study, pyrolysis(Py)/GCxGC/HR-TOFMS system was applied to investigate the pyrolysis products of Ethylene-propylene–diene rubber (EPDM).

Result and discusion

To evaluate the potential of Py/GCxGC, we compared the chromatographic peak separation between regular 1DGC and 2DGC (Fig.1) measured by EI. In the 1DGC data, a lot of co-elute components were observed and they were difficult to identify clearly. In the 2DGC data, these compounds were separated with 2nd GC dimensions and we observed approximately 1,023 compounds in the EPDM sample using an automatic peak search function for the GCxGC/EI data.

Table 1 Measurement condition

[Pyrolysis condition]
Pyrolysis Temp. 650°C
[GCxGC condition]
1st column BPX5(SGE), 30m x 0.25mm, 0.25um
2nd column BPX50(SGE, 2m x 0.1mm, 0.1um
Oven temp. 50°C (1 min) → [5°C/min] → 320°C (10 min)
Inj. Temp. 300°C
Inj. Mode. Split mode (100:1)
Column flow 1.8 mL/min
Modulation period 5 sec
[MS condition]
Ion source EI/PI combination ion source
EI/FI combination ion source
Ionization EI+, 70 eV, 300 uA
PI+, D2 lamp: 115-400 nm
(10.8 eV@115 nm)
FI+, -10 kV, 8mA/10sec
Mass range m/z 35-650
Comparison of the 1DGC and 2DGC TICCs

Fig.1 Comparison of the 1DGC and 2DGC TICCs

We got excellent chromatographic separations not only EI method but also soft ionization methods, PI and FI (Fig.2). We identified pyrolysis products using NIST EI database search (Fig.3).
On the other hand, there were many un-known components which cannot be identified using EI database with lower match factor. In this case, we estimated these chemical formulas from the accurate m/z values of these molecular ions in FI and PI mass spectra. For example, we showed accurate mass analysis about compound A. We got 6 candidate for the molecule formula. The measured m/z and isotopic pattern is most similar with C23H26N2. So, we suspected that this compounds is Polymerized 2,2,4-trimethyl-1,2-dihydroquinoline which is used as Rubber Antioxidant TMQ

GCxGC/EI , PI and FI TICCs

Fig. 2 GCxGC/EI , PI and FI TICCs

GCxGC/EI qualitative analysis result

Fig. 3 GCxGC/EI qualitative analysis result

Mass spectra and accurate mass analysis for the compound A on the 2DGC TICC.

Fig.4 Mass spectra and accurate mass analysis for the compound A on the 2DGC TICC.

Conclusion

  • We can get excellent GCxGC separations for EI and soft ionizations, PI and FI.
  • EI database search is still first step for the GC/MS qualitative analysis.
  • Soft ionizations and accurate mass analysis is useful for the compound identification.
The combination of PY/GCxGC/HRTOFMS and multiple ionization technique is a quite useful for qualitative analysis of the pyrolysis products of rubbers.
TMQ

TMQ

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