Combating selective ionization in the high resolution mass spectral characterization of complex mixtures

Area of Science:

• Analytical Chemistry
• Petrochemical Science
• Environmental Science

Background:

• Direct "dilute and shoot" mass spectral analysis is standard but limited for complex mixtures.
• Selective ionization and aggregation affect comprehensive characterization of naturally-occurring samples.
• High-field Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) is required for accurate elemental composition assignment.

Purpose of the Study:

• To overcome limitations of direct mass spectral analysis for complex petroleum samples.
• To improve compositional coverage and detection of previously undetectable species.
• To enhance confidence in elemental composition assignment and optimize ionization.

Main Methods:

• Developed three chromatographic fractionation approaches for positive/negative electrospray ionization (ESI) and atmospheric pressure photo-ionization (APPI) FT-ICR MS.
• Targeted specific chemical functionalities (nitrogen, oxygen) and structural motifs (aromatic cores).
• Utilized FT-ICR MS for high-resolution mass spectral analysis and accurate mass measurement.

Main Results:

• Achieved a 2-10-fold increase in compositional coverage for petroleum samples.
• Exposed species undetectable by direct "dilute and shoot" analysis.
• Provided coarse selectivity in chemical functionalities, enhancing assignment confidence and optimizing ionization.

Conclusions:

• Chromatographic fractionation significantly enhances the comprehensive characterization of complex petroleum mixtures.
• These methods address selective ionization discrimination and aggregation issues inherent in direct analysis.
• The approach optimizes ionization conditions, maximizing compositional coverage and analytical insight.