EVALUATING THE NOVEL UNISPRAY IONISATION SOURCE FOR THE ANALYSIS OF PETROLEUM SAMPLES

Importance of the topic

Mass spectrometric ionisation is a critical step in the analysis of complex petroleum samples. Efficient ionisation techniques expand molecular coverage, improve sensitivity for trace components, and support quality control and research across refinery, environmental, and industrial applications.

Study Objectives and Overview

This study evaluates a novel atmospheric pressure UniSpray ionisation source and compares its performance with established techniques (ESI, APCI, APPI, ASAP) for a variety of petroleum-derived samples, including vacuum residues, light crude fractions, polycyclic aromatic hydrocarbons (PAHs), and oilfield additive chemicals.

Methodology and Instrumentation

The UniSpray source employs a grounded capillary that emits an analyte solution aerosolized by high-velocity nitrogen. The spray impacts a stainless steel rod charged between 0.5 and 4.0 kV; ions form via the Coandă effect as the gas/liquid flow interacts with the curved surface.

Instrumentation

• SYNAPT G2-Si HDMS mass spectrometer for direct infusion and thermal desorption (ASAP).
• Xevo TQD tandem quadrupole MS coupled to UHSFC (UPC2) for oilfield additive separations.

Key Results and Discussion

• Vacuum residue analysis: UniSpray spectra were broadly similar to other sources, but did not show superior diesel component coverage under the conditions tested.
• Sensitivity dependence: Ion signal intensity varied strongly with spray impaction position on the rod and with rod voltage; optimal response was achieved at central impaction and 4.0 kV.
• PAH compounds: UniSpray failed to ionise PAHs effectively, confirming APPI as the preferred technique for nonpolar aromatic species.
• Oilfield additives: For imidazolines and quaternary ammonium salts, UniSpray coupled with UHPLC-MS/MS delivered substantially higher responses and improved calibration performance compared to ESI.

Benefits and Practical Applications

UniSpray extends the analytical toolbox for petroleum and related fields by:

• Enhancing detection of polar and semi-polar oilfield chemicals.
• Allowing rapid screening via direct infusion or thermal desorption.
• Providing tunable parameters (voltage, spray position) to optimize sensitivity for diverse crude fractions.

Future Trends and Applications

Potential developments include:

• Integration of UniSpray with advanced separation methods (e.g., UPLC, ion mobility).
• Design of hybrid ionisation sources combining UniSpray with photo- or chemical-ionisation approaches.
• Expanded use in petroleomics for comprehensive molecular profiling.
• Adaptation for environmental monitoring and emerging contaminants.

Conclusion

UniSpray ionisation demonstrates significant promise for targeted analysis of oilfield additives and complements existing ionisation methods. Careful optimization of operational parameters is essential to maximize performance across petroleum sample types.

Reference

1. Bajic S. An Aerodynamic Perspective on Impactor API Sources. Waters Poster PSTR134897766, ASMS 2016.
2. Nascimento HDL et al. A Universal Source for Ionization of Polar and Nonpolar Compounds: Testing its Applicability to Petroleomic Studies. ASMS Poster TP05-092, 2015.
3. Lubin A et al. Head-to-Head Comparison of ESI and UniSpray for Eicosanoid Analysis. Chromatographia A 2016;1440:260.