Determination of Organochlorine Pesticides Using GC-MS with a Helium-conserving Injector

Significance of the topic

Organochlorine pesticides are among the most persistent and toxic synthetic compounds in the environment, requiring sensitive and reliable methods for monitoring their residues. Gas chromatography coupled with mass spectrometry (GC-MS) remains a gold standard for trace-level analysis, but traditional injectors can consume large volumes of helium, impacting operational costs and sustainability.

Objectives and study overview

This application note evaluates the analytical performance of the Thermo Scientific ISQ LT GC-MS system equipped with an Instant Connect Helium Saver injector and Chromeleon 7.2 Chromatography Data System for the identification and quantification of a suite of 20 organochlorine pesticides. The focus is on method sensitivity, precision, and cost-effective gas consumption.

Methodology

A splitless injection (1 µL) of standard mixtures was performed with a TRACE 1310 GC using a TG-5MS column (30 m × 0.25 mm, 0.25 µm). Initial full-scan acquisitions (50–350 amu) established retention windows and target ions, followed by single-ion monitoring (SIM) for quantitation. Calibration covered six concentration levels (1–100 ppb) and data processing was conducted with Chromeleon CDS.

• Oven program: 100 °C (2 min), 15 °C/min to 160 °C (5 min), 5 °C/min to 270 °C (2 min).
• Injector: 225 °C splitless for 2 min, split ratio 50:1, helium delay 0.1 min.
• Column flow: constant 1 mL/min helium carrier gas.

Instrumentation

• TRACE 1310 GC with Instant Connect Helium Saver injector (splitless liner with glass wool).
• Thermo Scientific TraceGOLD TG-5MS column (30 m, 0.25 mm ID, 0.25 µm film).
• ISQ LT single quadrupole mass spectrometer (source and transfer line at 270 °C).
• Chromeleon 7.2 Chromatography Data System for acquisition and processing.

Main results and discussion

Full-scan chromatograms at 1 ppm confirmed retention times for all analytes, which were then quantified in SIM mode. Calibration curves exhibited excellent linearity (R² > 0.995) across six levels. Area repeatability over ten injections showed RSDs below 3% for most compounds, except DDT (RSD 8.3%). Retention time precision was high, with RSDs generally below 0.4%. The Helium Saver injector demonstrated performance equivalent to a conventional split/splitless injector while significantly reducing helium usage by employing nitrogen for split and purge flows.

Benefits and practical applications

• Substantial helium savings reduce operational costs and dependency on helium supply.
• Maintained analytical performance without modifying established methods.
• High precision and reproducibility support routine environmental monitoring and regulatory compliance.
• Modular injector design allows flexibility in maintenance and system upgrades.

Future trends and potential applications

As helium availability fluctuates, gas-conserving injectors will become increasingly important. Integration with automated sampling and data processing workflows can further improve throughput. Potential extensions include multi-residue analysis, high-throughput environmental screening, and coupling with high-resolution mass spectrometry for enhanced selectivity.

Conclusion

The Thermo Scientific ISQ LT GC-MS with an Instant Connect Helium Saver injector delivers robust, reproducible analysis of organochlorine pesticides while minimizing helium consumption. This approach offers a cost-effective, sustainable solution for routine environmental laboratories, aligning analytical performance with resource conservation.