Reproducibility of the 7400 Auto-Sampler for BTEX in Water

Significance of the Topic

The reliable quantification of volatile organic compounds such as benzene, toluene, ethylbenzene and xylene (BTEX) in water is critical for environmental monitoring and regulatory compliance. High reproducibility in autosampling workflows minimizes analytical uncertainty and supports consistent quality control in water analysis laboratories.

Objectives and Study Overview

This application note examines the precision of the CDS Model 7400 Auto-Sampler coupled to the Model 7000 Purge & Trap system for routine analysis of BTEX at a target concentration of 50 ppb in aqueous matrices. The study evaluates intra-run variability across multiple consecutive injections without intermediate blank runs.

Methodology and Used Instrumentation

The workflow follows these steps:

• Transfer of 5 mL water samples from autosampler vials to the purge vessel.
• Addition of internal standard solution.
• Purge at 35 mL/min He flow for 11 minutes at controlled temperature.
• Trapping volatiles on the 7000 trap, followed by thermal desorption into the GC.
• Vessel rinsing and trap baking between runs.

Used Instrumentation:

• CDS Model 7400 Auto-Sampler
• CDS Model 7000 Purge & Trap system
• Gas chromatograph with temperature-controlled valve oven and transfer line
• Mass spectrometer detector
• GC-IR hyphenated system (DiscovIR-GPC) for polymer additive characterization

Main Results and Discussion

Overlayed chromatograms for benzene and the internal standard demonstrated excellent run-to-run consistency. Relative standard deviations (RSD) over eight consecutive analyses were:

• Benzene: 1.2 %
• Toluene: 2.1 %
• Ethylbenzene: 2.6 %
• Xylene: 1.1 %

The average RSD of 1.8 % highlights the system’s robustness for low-level BTEX determinations. In a separate polymer study, GC-IR analysis successfully deconvoluted complex silver-ink binders and identified three principal polymeric constituents and a latent cross-linker additive by characteristic FT-IR bands.

Benefits and Practical Applications

The demonstrated reproducibility supports routine monitoring of trace volatile contaminants in drinking and environmental waters, enhancing confidence in compliance reporting. GC-IR hyphenation extends analytical scope to non-volatile polymer additives in industrial materials, aiding formulation development and forensic analysis.

Future Trends and Potential Applications

Advances in autosampler robotics, lower detection limits and integrated multi-detector platforms will further streamline trace analyses. Emerging GC-IR databases and chemometric tools promise deeper insight into complex mixtures such as ink formulations, polymer blends and food contact materials.

Conclusion

The CDS 7400 Auto-Sampler and 7000 Purge & Trap deliver highly reproducible BTEX analyses at regulatory levels in water. Combined GC-MS and GC-IR hyphenated systems offer comprehensive workflows for volatile and non-volatile component characterization in environmental and industrial matrices.

Reference

• T. A. Bellar and J. J. Lichtenberg, Journal of the American Water Works Association, 66(12), 739.