Practical determination and validation of instrument detection limit for the Thermo Scientific ISQ 7000 Single Quadrupole GC-MS system with Advanced Electron Ionization source

Significance of the topic

The ability to detect analytes at ultra-trace levels is a critical requirement in environmental monitoring, pharmaceutical analysis, food safety, and forensic investigations. Enhancing sensitivity in gas chromatography–mass spectrometry (GC-MS) enables reliable identification and quantification of compounds present at femtogram amounts. The Advanced Electron Ionization source integrated into the Thermo Scientific ISQ 7000 Single Quadrupole GC-MS addresses these challenges by substantially improving ionization efficiency and lowering detection limits.

Objectives and study overview

This study aimed to evaluate and validate the instrument detection limit (IDL) of the ISQ 7000 GC-MS equipped with the AEI source. Key goals included:

• Determining the lowest detectable amount of octafluoronaphthalene (OFN) on-column
• Assessing repeatability across multiple injections and different laboratory sites
• Comparing performance against conventional EI sources

Methodology and instrumentation

The IDL was calculated at the 99 percent confidence level using repeat injections and precision data following the formula IDL = t × Amount × %RSD. OFN at 5 fg/µL in iso-octane served as the standard. Experiments were conducted on nine ISQ 7000 systems worldwide under identical conditions.

• Autosampler AS 1310 with 10 µL syringe, 1 µL injection volume, three sample rinses
• TRACE 1310 GC: TraceGOLD TG-SQC column (15 m × 0.25 mm × 0.25 µm), splitless mode, 220 °C inlet, He carrier at 1.2 mL/min, oven ramp from 45 °C to 190 °C
• ISQ 7000 GC-MS: AEI ion source at 200 °C, electron energy 45 eV, emission current 50 µA, SIM acquisition of m/z 272, dwell time 0.1 s

Key results and discussion

Repeated injections demonstrated stable peak areas over 16 runs. An eight-injection SIM overlay yielded an IDL of 0.46 fg for OFN. Across nine instruments in diverse labs, IDLs ranged from 0.46 fg to 0.87 fg, with an average of 0.64 fg. These results confirm consistent sub-femtogram detection capability and superior sensitivity compared to conventional EI sources.

Benefits and practical applications

The enhanced sensitivity of the AEI source on a single quadrupole platform enables:

• Reliable screening of trace contaminants in environmental water and soil samples
• Quality control of trace-level impurities in pharmaceutical manufacturing
• Detection of ultra-low-level residues in food and beverage analysis
• Routine forensic screening for trace evidence

Future trends and applications

Advances likely to build on this work include:

• Automation of ultra-trace workflows for high throughput laboratories
• Application of AEI technology to a broader range of analytes and sample types
• Integration with software for real-time detection limit monitoring
• Further design refinements to maximize ion yields and reduce background noise

Conclusion

The Thermo Scientific ISQ 7000 GC-MS with the Advanced Electron Ionization source consistently achieves instrument detection limits below 1 fg for OFN. This groundbreaking performance on a robust single quadrupole platform opens new opportunities for ultra-trace analysis in research and routine laboratories.

References

1. Koontz SL Low-energy electron impact ionization source design and characterization Ph.D. Dissertation University of Arizona 1983
2. American Petroleum Institute Analytical Detection and Quantification Limits Survey of State and Federal Approaches Publication 4721 2002
3. Thermo Fisher Scientific Technical Note 10494 Practical Determination and Validation of Instrument Detection Limit of Thermo Scientific ISQ 7000 GC-MS with ExtractaBrite EI Source 2018