7
very narrow mass differences between isobars, eg, C3 vs SH4 (0.0034 Da), CH2 vs N (0.0126 Da), and CH4 vs O (0.0364 Da) (required resolving power at m/z 300 of 89 000, 24 000, 8400, respectively). It is highly unlikely that such isobars occupy the same 2D time space in GC×GC; thus, resolving power requirement would be much lower. GC×GC‐PI‐HRMS with prominent molecular ions can add several other dimensions on top of two‐dimensional chromatographic separation. Added dimensions could be: 1) near unambiguous mass determination; 2) detection of heteroatom classes; 3) degree of unsaturation; 4) carbon number characterisation; and 5) elemental compositions. These could be used for improved visualisation and characterisation of petrochemicals. As shown in Figure 5, a significant retention of molecular ions could be achieved in PI compared to EI. Cumulative spectra achieved through PI- HRMS could further be treated to generate
Kendrick Mass Defect (KMD) plot to reveal and compare the distribution of alkyl series and abundances of classes with different degrees of saturation. In addition, m/z to C:H ratio, carbon number to C:H ratio, or m/z to DBE etc. could be plotted for improved visualisation of data.
In conclusion, PI plays a greater role in isomeric species identification of paraffinic and heteronate compounds as it generates molecular ions as well as structurally important fragment ions. However, for bicyclic, or polycyclic naphthenic, and monoaromatic compounds, EI still remains advantageous. GC×GC‐Soft-ionisation (PI) followed by high‐resolution MS analysis enables confirmation of structures/ formulae as well as improved visualisation of data.
References 1. C.V. Mühlen, C.A. Zini, E.B. Caramão
and P. Marriott, Applications of comprehensive two-dimensional gas chromatography to the characterisation of petrochemical and related samples, J. Chromatogr. A 1105(2006), 39-50.
2. A. Giri, M. Coutriade, A. Racaud, K. Okuda, C. Cody and J-F. Focant, Molecular characterization of volatiles and petrochemical base oils by photo‐ ionization GC×GCTOF‐MS, Anal. Chem. 89(2017), 5395‐5403.
3. M.S. Alam, C. Stark and R.M. Harrison, Using variable ionization energy time‐of‐flight mass spectrometry with comprehensive GC×GC to identify isomeric species, Anal. Chem. 88(2016), 4211‐4220.
4. L. Hanley and R. Zimmermann, Light and molecular ions: the emergence of vacuum UV single‐photon ionization in MS, Anal. Chem. 81(2009), 4174‐4182.
160 min 3,285 56 L ACN 800 kWh USD 3,400 USD 114,400 *** ** *
1 2
3 4 5
6
Analysis Time Number of Analyses per Instrument p.a. Organic EluentWaste ** Electric Power Consumption ** Costs of Organic Solvents ** Lab Costs **,***
For Ebastinumacc. to
Ph.Eur. Per 1,000 analyses Assuming daily costs of USD 1,000 per instrument and operator
www.molnar-institute.com
-98% +4,000% -98% -98% -99% -98%
3+1 min 131,400 1.05 L ACN:IPA 20 kWh USD 44 USD 2,844
In-silico RejuvenatedMethod
Pharmacopoeia Method *
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