Rapid identification and confirmation of unknown substances using Direct Insertion Probe – Exactive GC Orbitrap mass spectrometry

Significance of the Topic

In forensic and analytical chemistry rapid and confident identification of unknown substances is crucial for law enforcement and public safety. Illicit and emerging compounds often lack reference standards and present complex matrices. High resolution mass spectrometry combined with direct insertion probe analysis streamlines investigation of powders liquids and thermally labile samples. It enhances detection selectivity and reduces analysis time.

Objectives and Study Overview

This study evaluates a fast method for identifying unknown suspicious substances using a direct insertion probe coupled to an Exactive GC Orbitrap mass spectrometer. The aim was to demonstrate a simple workflow achieving high confidence through both electron ionization and chemical ionization data.

Methodology and Instrumentation

• Instrument Used
• Exactive GC Orbitrap mass spectrometer operated at 60 000 resolution FWHM at mz 200
• Direct Insertion Probe for direct sample introduction via vacuum probe interlock
• Ionization Modes
• Electron Ionization at 70 eV
• Positive and negative chemical ionization with methane reagent gas
• Probe Temperature Program
• Initial 80 C hold 20 s ramp 100 C min to 350 C hold 40 s
• Sample Preparation
• Solid morphine and methadone standards at 1 mg/ml in methanol 0.5 µl loaded into quartz crucible

Main Results and Discussion

• Electron ionization spectra matched NIST library with high similarity index scores above 830 and match probability above 87 percent for morphine and methadone
• High resolution accurate mass measurements delivered sub ppm mass error facilitating elemental composition assignments. Isotopic pattern comparisons yielded 100 percent fidelity for identified compounds
• Chemical ionization provided molecular ion confirmation through M+H M+C2H5 and M adducts enhancing confidence when chromatographic separation and standards are unavailable

Benefits and Practical Applications

• Rapid analysis bypassing chromatographic steps minimizes time to result
• Versatile sample introduction accommodates liquids solids polymers and thermally labile analytes
• High resolution mass accuracy and isotopic fidelity enhance selectivity and reduce false positives
• Combined EI and CI data provides comprehensive structural and molecular weight confirmation

Future Trends and Applications

• Integration of automated library searching with machine learning for unknown identification
• Expansion to broader compound libraries including novel psychoactive substances and synthetic biomarkers
• Coupling DIP Orbitrap with ambient ionization methods for real time field analysis
• Development of miniaturized high resolution systems for on site forensic screening

Conclusion

Direct insertion probe analysis on a high resolution Orbitrap platform provides a powerful rapid and reliable workflow for identifying unknown suspicious substances. The combination of EI spectra library matching and CI molecular ion confirmation achieves high confidence in elemental composition and structure assignment without the need for chromatographic separation.

References

1. Baron M Elie M Elie L Analysis of legal highs do they contain what it says on the tin Drug Testing and Analysis 2011 3 576 581
2. Thermo Fisher Scientific WP10456 The Power of High Resolution Accurate Mass Using Orbitrap Based GC MS
3. Thermo Fisher Scientific DEP DIP User Guide Direct Probe User Guide