Group-type analysis of Crude Oil using GC/FI-TOFMS - Reproducibility of group-type analysis results

Importance of the Topic

Accurate characterization of crude oil composition is essential for refining, quality control and process optimization. Determining molecular weight distributions and grouping hydrocarbons by structural type informs decisions in petroleum processing and environmental monitoring.

Objectives and Study Overview

This study evaluated the reproducibility of group-type analysis of crude oil using gas chromatography coupled with field ionization time-of-flight mass spectrometry (GC/FI-TOFMS). Ten replicate analyses were performed to assess variation in molecular weight parameters across five hydrocarbon classes.

Methodology and Instrumentation

The crude oil sample underwent solid-phase extraction on a C18 cartridge and was eluted sequentially with hexane, toluene and a chloroform/methanol mixture. The extract was concentrated and reconstituted in hexane. GC/FI-TOFMS analysis conditions:

• Gas chromatograph: Agilent 6890N with DB-5ms column (30 m × 0.25 mm × 0.25 µm)
• Oven program: 50 °C hold, 15 °C/min ramp to 280 °C, 5 min hold
• Injection: split 1:200 at 280 °C, 1 µL injection volume
• Carrier gas: helium at 1 mL/min
• Mass spectrometer: JEOL JMS-T100GC “AccuTOF GC” with field ionization (–10 kV), m/z 35–500, 0.3 s/spectrum
• Data processing: Polymerix™ group-type analysis software

Main Results and Discussion

Group-type analysis provided number-average (Mn), weight-average (Mw) and z-average (Mz) molecular weights, polydispersity (PD) and corresponding degrees of polymerization for paraffins, naphthenes, olefins, aromatics and total hydrocarbons. Across ten replicates:

• Average Mn: 205.4; Mw: 215.6; Mz: 226.9
• Polydispersity: 1.050 (CV 0.42%)
• Degree of polymerization: DPn 8.67 (CV 2.64%), DPw 9.37 (CV 2.83%), DPz 10.18 (CV 3.21%)

Coefficients of variation were below 3% for all parameters, demonstrating excellent method precision. The low variability of PD highlights reliable assessment of distribution breadth.

Benefits and Practical Applications

This GC/FI-TOFMS approach enables soft ionization with minimal fragmentation, delivering intact molecular ion distributions critical for complex hydrocarbon mixtures. It supports:

• Quality control in petroleum refining
• Monitoring feedstock consistency
• Environmental assessment of hydrocarbon contamination

Future Trends and Applications

Emerging developments may include coupling with multidimensional chromatography for enhanced class separation, use of ultrahigh-resolution mass analyzers to resolve isobaric species, and integration with chemometric tools for automated pattern recognition. Applications may extend to synthetic polymer characterization and biofuel analysis.

Conclusion

Group-type analysis of crude oil by GC/FI-TOFMS on the JMS-T100GC system combined with Polymerix™ software exhibits high reproducibility and precision. The methodology provides reliable molecular weight distributions and supports diverse applications in petrochemical analysis.

Instrumental Setup

• JEOL JMS-T100GC “AccuTOF GC” mass spectrometer with field ionization
• Agilent 6890N gas chromatograph and DB-5ms column
• Polymerix™ group-type analysis software