THE USE OF GC×GC-NCI-QTOF FOR THE QUANTITATIVE ANALYSIS OF ORGANOCHLORINE PESTICIDES (OCPs) AND POLYCHLORINATED BIPHENYLS (PCBs)

Importance of the Topic

Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) remain persistent organic pollutants with significant environmental and human health risks even at trace levels. Their widespread historical use and chemical stability demand robust analytical methods for accurate monitoring in soil, water, food, and other complex matrices.

Study Objectives and Overview

This preliminary investigation evaluates a comprehensive two-dimensional gas chromatography system (GC×GC) with thermal modulation coupled to a quadrupole time-of-flight mass spectrometer (QTOF) operating in negative chemical ionization (NCI) mode. The goals are to assess separation performance, sensitivity, linearity, repeatability, and mass accuracy for quantitative analysis of OCPs and PCBs at low concentrations.

Methodology and Instrumentation

Standard mixtures of OCPs and PCBs (150–300 ng/mL) were serially diluted in n-hexane to 2–300 ng/mL. Analyses were performed on an Agilent 7890B GC with split/splitless injection and a Zoex ZX2 cryogen-free thermal modulator. An Agilent 7200B QTOF MS in NCI mode (methane reagent gas, 50 Hz EDR) acquired data. GC Image HR software facilitated visualization and processing of the two-dimensional chromatograms.

Instrumentation

• Agilent 7890B gas chromatograph with split/splitless inlet
• Zoex ZX2 thermal modulator
• Agilent 7200B QTOF mass spectrometer in NCI mode
• GC Image HR data processing software

Main Results and Discussion

• Separation and Identification: GC×GC afforded enhanced resolution and peak capacity, minimizing co-elution. Identification relied on molecular ions, elution pattern, and complementary EI data via a removable ion source.
• Repeatability: Retention time RSDs were <0.2% (first dimension) and <1.2% (second dimension). Quantifier ion responses showed RSDs <6% (average 3.1%).
• Linearity: Calibration over 3–300 ppb yielded coefficients of determination (R²) between 0.99977 and 0.99999 (average 0.99991).
• Sensitivity: Signal-to-noise ratios at 2.5 ppb ranged from 33 to 186, indicating detection limits in the mid-ppt range for injected solution. Splitless injection and targeted NCI tuning could further improve sensitivity by an order of magnitude.
• Mass Accuracy: High-resolution spectra showed mass errors <0.8 ppm for pentachlorobenzene. Stability tests across eight runs reported errors <4 ppm (average <2.2 ppm). Isotopic patterns matched theoretical distributions, enhancing confidence in compound confirmation.

Benefits and Practical Applications

The GC×GC-NCI-QTOF approach delivers superior resolution to reduce matrix interference and co-elution, while high-resolution accurate mass detection supports both targeted quantification and untargeted screening. Rapid EI/CI switching and mass accuracy tools provide analytical flexibility, making it suitable for environmental monitoring, food safety, and quality control laboratories.

Future Trends and Opportunities

Further improvements may include optimized NCI parameters for ultra-trace detection, adoption of splitless injection protocols, and integration with automated data analysis algorithms for high-throughput screening. Expanding untargeted fingerprinting workflows can deepen understanding of complex environmental samples.

Conclusion

GC×GC with thermal modulation coupled to NCI-QTOF demonstrates robust, sensitive, and accurate quantification of OCPs and PCBs. The method’s high resolution, repeatability, linearity, and mass accuracy make it a powerful tool for persistent pollutant analysis.

References

Peroni D. The Use of GC×GC-NCI-QTOF for the Quantitative Analysis of Organochlorine Pesticides and Polychlorinated Biphenyls. JSB Application Note, 2017.