A Unified Method for the Analysis of Aromatic Solvents Using the Agilent 6820 Gas Chromatography System

Importance of Topic

Analyzing the purity of aromatic solvents is critical for quality control in petrochemical production, ensuring product performance, safety, and regulatory compliance. Traditional practice relies on multiple ASTM GC methods, each targeting specific compounds. This approach requires extensive instrumentation, time, and resources.

Objectives and Overview

The study aims to consolidate ten ASTM GC methods for aromatic solvent analysis into a unified procedure using a single Agilent 6820 GC system with nitrogen as carrier gas. This unified method is designed to maintain chromatographic performance while reducing complexity and cost.

Methodology

A calibration mixture containing 24 aromatic compounds in n-hexane was prepared. GC separations were performed on an Agilent 6820 system equipped with a split/splitless inlet and FID detector. Key parameters:

• Carrier gas: Nitrogen at 7.6 psi, inlet at 75 °C
• Injection: 1 µL, split ratio 100:1
• Column: HP-Innowax (60 m × 0.32 mm × 0.5 µm)
• Oven program: 75 °C (23 min), 1.3 °C/min to 100 °C, 4.4 °C/min to 145 °C, hold, post-run at 220 °C

Used Instrumentation

• Agilent 6820 Gas Chromatograph with split/splitless inlet and FID
• Agilent Cerity Networked Data System for QA/QC
• Split liner (Agilent p/n 19251-60540) and green septa (Agilent p/n 5183-4759)
• HP-Innowax capillary column (Agilent p/n 19091N-216)
• 10 µL manual syringe for injections

Main Results and Discussion

The unified method achieved baseline separation for 24 aromatic components with minor coelution of p- and m-ethyltoluene, which was significantly improved compared to individual ASTM protocols. Application to specific standards (o-xylene, p-xylene, ethylbenzene, styrene) confirmed adequate resolution and compliance with ASTM criteria, e.g., valley points below 50% of contaminant peaks for p-xylene and appropriate peak shapes under nitrogen.

Benefits and Practical Applications

• Reduces the number of instruments and columns required
• Enhances laboratory efficiency and flexibility
• Lower operational costs by using nitrogen instead of helium
• Facilitates instrument redundancy and minimizes downtime

Future Trends and Applications

Potential developments include faster temperature programs, use of alternative carrier gases, miniaturized columns for high-throughput testing, and integration with advanced data analytics platforms to extend this unified approach to other solvent classes.

Conclusion

The Agilent 6820-based unified GC method offers a robust, cost-efficient, and simplified solution for aromatic solvent purity analysis, consolidating ten ASTM methods into one protocol without compromising performance.

Reference

• ASTM Annual Book of Standards, Vol. 6.04, Paint - Solvents; Aromatic Hydrocarbons, ASTM International.
• McCurry JD. A Unified Gas Chromatography Method for Aromatic Solvent Analysis. Agilent Technologies, publication 5988-3741EN.
• ASTM D3798: Standard Test Method for Analysis of p-Xylene.
• ASTM D3797: Standard Test Method for Analysis of o-Xylene.
• ASTM D5060: Standard Test Method for Determining Impurities in High-Purity Ethylbenzene.