A 0.32 mm ID Capillary Column Approach to Contract Laboratory Program (CLP) Pesticides Analysis

Importance of the topic

The determination of trace-level organochlorine pesticides is a cornerstone in environmental contract laboratories, where high throughput and reliable results are essential for competitiveness and regulatory compliance. Advances in gas chromatography configurations, including medium-bore capillary columns and innovative splitters, can significantly reduce analysis time and instrument downtime, translating into increased sample capacity and operational efficiency.

Study Objectives and Overview

This work aims to present a robust gas chromatographic method for simultaneous primary and confirmatory analysis of 22 organochlorine pesticides at trace levels using 0.32 mm ID capillary columns. By employing hydrogen as carrier gas, flow programming, and a reusable Capillary Flow Technology (CFT) two-way splitter without makeup gas, the study evaluates method performance, linearity, sensitivity, and maintenance benefits in a contract laboratory context.

Methodology and Instrumentation

Sample Preparation:

• Standard mixes (CLP-023R-160X and CLP-024R-160X) diluted in 2,2,4-trimethylpentane to yield a six-level calibration range (3.2–80 ng/mL).
• Volumetric glassware and class A pipettes ensured gravimetric accuracy; 2,2,4-trimethylpentane served as blank and syringe-wash solvent.

Chromatographic Conditions:

• Instrument: Agilent 7890A GC with dual µECDs and 7683B autosampler (5 µL syringe, 0.5 µL splitless injection).
• Carrier gas: Hydrogen with flow programming (79.7 cm/s ramped from 3.76 to 5.77 mL/min).
• Oven program: 180 °C (0.5 min) to 240 °C at 20 °C/min, hold 1.3 min; 20 °C/min to 265 °C; 120 °C/min to 320 °C, hold 3 min.
• Inlet: Pulsed splitless at 250 °C; pulse 40 psi for 0.2 min; purge 15 mL/min at 1 min.
• Detection: µECD at 325 °C with N₂ makeup (total flow ≈62 mL/min).

Instrumentation:

• Agilent 7890A Gas Chromatograph with dual µECD detectors.
• Agilent 7683B autosampler (5 µL syringe, p/n 5181-1273).
• Agilent Capillary Flow Technology two-way splitter without makeup gas (p/n G3181B).
• Retention gap: 1 m × 0.32 mm Hi-Temp deactivated fused silica (p/n 160-2855-5).
• Columns: Agilent J&W DB-17ms (30 m × 0.32 mm × 0.25 µm, p/n 123-4732) and DB-XLB (30 m × 0.32 mm × 0.5 µm, p/n 123-1236).
• Inlet liner: Deactivated dual taper direct connect (p/n G1544-80700); ferrules: SilTite® metal ferrules (p/n 5188-5362/5361).

Main Results and Discussion

The method achieved complete separation of all 22 target pesticides in under eight minutes, with sharp, symmetrical peaks and excellent repeatability. Dual-column analysis using the CFT splitter enabled simultaneous primary (DB-17ms) and confirmatory (DB-XLB) detection from a single injection. On-column loadings down to 0.8 pg yielded clear chromatograms with resolution (Rs) of 1.4 between critical pairs (e.g., α-chlordane/endosulfan I). Calibration curves across 3.2–80 ng/mL demonstrated R² ≥ 0.9993 for all analytes on both columns, and %RSD values below 5%, confirming linearity and precision at trace levels.

Benefits and Practical Applications

• High throughput: Analysis and confirmation in less than eight minutes per sample supports rapid turnaround.
• Enhanced capacity: Larger bore (0.32 mm) columns allow increased sample loading versus 0.18 mm formats.
• Reduced downtime: Reusable CFT splitter isolates inlet and columns, simplifying maintenance and decreasing instrument offline time.
• Carrier gas efficiency: Hydrogen reduces run times with no compromise in resolution; method translation software facilitates conversion from helium methods.

Future Trends and Potential Applications

As demand for rapid and reliable pesticide monitoring grows, future developments may include:

• Integration with mass spectrometry detectors for expanded analyte panels and confirmation strength.
• Automated method translation and optimization tools to facilitate gas selection and flow programming.
• Miniaturized splitters and smart diagnostics to further minimize dead volumes and maintenance interventions.
• Green analytical chemistry approaches, leveraging hydrogen carrier and reduced solvent usage.

Conclusion

This study demonstrates a fast, sensitive, and dependable method for trace organochlorine pesticide analysis using 0.32 mm ID capillary columns, hydrogen carrier gas, and a reusable CFT splitter. The approach delivers sub-8-minute separations, excellent linearity (R² ≥ 0.9993), low detection limits (0.8 pg on-column), and streamlined maintenance—enabling contract laboratories to increase billable hours and maintain high data quality.

Reference

1. Agilent G3181B Two-Way Splitter Kit Without Makeup Gas Installation and Operation Guide, Agilent Technologies.
2. Agilent Method Translation software download page, Agilent Technologies.