Analysis of Cresol Positional Isomers

Importance of the Topic

Accurate separation and quantification of cresol isomers (o-, m-, and p-cresol) is critical in environmental monitoring, petrochemical processing, and quality control of phenolic compounds. These structural isomers exhibit similar chemical properties but different toxicological profiles and reactivities. Reliable chromatographic methods ensure that each isomer can be individually detected, improving safety assessments and regulatory compliance.

Objectives and Overview of the Study

This application note evaluates two reversed-phase liquid chromatography methods for the analysis of cresol positional isomers. The primary goal is to compare performance on a phenyl-bonded phase versus a C18-bonded phase regarding separation efficiency, analysis time, and sensitivity when using a Nexera™-i system with UV detection at 254 nm.

Methodology and Instrumentation

Two column chemistries were tested under isocratic conditions:

• Shim-pack GIST Phenyl (100 mm × 3.0 mm I.D., 2 μm) with water/methanol (80/20 v/v), flow rate 0.4 mL/min, column temperature 40 °C, injection volume 5 μL.
• Shim-pack GIST C18 (100 mm × 2.1 mm I.D., 2 μm) with water/methanol (70/30 v/v), flow rate 0.2 mL/min, column temperature 40 °C, injection volume 2.5 μL.

The Nexera-i system with UV-VIS detection at 254 nm provided reproducible retention times and peak shapes for each isomer at 20 mg/L concentration.

Results and Discussion

The phenyl-bonded phase achieved baseline separation of o-, m-, and p-cresol within a short runtime, leveraging π–π interactions for enhanced selectivity. The retention order observed was p-cresol < m-cresol < o-cresol. Resolution values exceeded 1.8 for critical peak pairs. The C18 phase also separated the isomers effectively but required a longer analysis time to achieve comparable resolution.

Benefits and Practical Applications

• Rapid and robust analysis suitable for routine QC in industrial laboratories.
• High selectivity on phenyl columns improves identification in complex matrices.
• Isocratic operation simplifies method implementation and reduces equilibration time.

Future Trends and Opportunities

Emerging developments include coupling phenyl and C18 chemistries in tandem columns for multidimensional separations and integrating mass spectrometric detection for lower detection limits and structure confirmation. Advances in sub-2 μm particle columns and ultra-high-performance LC systems will further shorten runtimes and enhance throughput.

Conclusion

This study demonstrates that a phenyl-bonded reversed-phase column on a Nexera-i system provides superior speed and selectivity for cresol isomer analysis, while a C18 column offers an alternative with solid overall performance. Both methods support efficient quality control and environmental analysis workflows.

References

1. Application News L549 (JP, ENG), Shimadzu Corporation, First Edition: Dec. 2021.