Hydrocarbons, C6 – C7, aromatic hydrocarbons, C6 – C8 - Analysis of impurities in benzene

Importance of the topic

Rapid and accurate analysis of trace impurities in benzene is critical for ensuring product quality, regulatory compliance and safety in industrial and laboratory settings. The ability to detect contaminants at low ppm levels supports environmental monitoring, pharmaceuticals, petrochemical manufacturing and materials testing.

Objectives and study overview

This application note demonstrates a gas chromatographic method employing a narrow‐bore capillary column and flame ionization detection to quantify C6–C8 impurities in benzene at concentrations ranging from 1 to 200 ppm. The goal is to achieve high sensitivity, reproducibility and short analysis times suitable for routine quality control.

Methodology

• Column: 0.15 mm id × 25 m, 1.2 μm CP-Sil 5 CB thick film
• Injection: Split mode, 2 μL sample volume at 250 °C
• Carrier gas: Hydrogen at 150 kPa (1.5 bar)
• Temperature program: 70 °C (2 min) to 200 °C at 20 °C/min, hold 5 min
• Detector: FID at 250 °C

Used Instrumentation

• Agilent capillary gas chromatograph configured for split injection
• Agilent CP-Sil 5 CB WCOT fused silica column (Part no. CP7693)
• Flame ionization detector
• Hydrogen supply for carrier gas
• Standard autosampler capable of 2 μL injections

Main results and discussion

The method separates key C6–C8 impurities within 10–15 minutes with high peak efficiency (~150,000 plates per 25 m). Reproducibility is better than 3% RSD for compounds between 5 and 500 ppm, and detection limits reach 1–5 ppm under split injection conditions. Identified impurities and typical concentrations in a benzene sample include:

1. Unknown impurity: 5 ppm
2. Methylcyclopentane: 37 ppm
3. Cyclohexane: 96 ppm
4. Methylcyclohexane: 427 ppm
5. Toluene: 49 ppm
6. Ethylbenzene: 11 ppm

Benefits and practical applications

• High sensitivity and precision for trace impurity quantification
• Short turnaround times support high-throughput quality control
• Wide applicability across chemical, petrochemical and pharmaceutical industries
• Robust method using readily available GC/FID instrumentation

Future trends and opportunities

Advancements may include microfluidic GC platforms, alternative detector technologies such as micro-FID or vacuum ultraviolet detectors, and automated data processing workflows. The adoption of greener carrier gases and miniaturized columns could further reduce analysis time and environmental impact.

Conclusion

The presented GC-FID method with a 0.15 mm id CP-Sil 5 CB column provides a reliable, fast and sensitive approach for analyzing C6–C8 impurities in benzene. Its reproducibility and low detection limits make it suitable for routine QA/QC and research applications.

References

• No external references were specified in the original document.