Solvents - Analysis of impurities in ethanol

Importance of the Topic

The rapid and reliable determination of trace impurities in ethanol is vital for quality control across chemical, pharmaceutical and fuel industries. Ensuring ethanol purity prevents downstream process issues and meets regulatory and safety standards. High-throughput methods are especially valuable for manufacturers and testing laboratories that analyze large sample loads.

Objectives and Study Overview

This application note investigates the performance of a narrow-bore (0.15 mm i.d.) capillary column coated with a thick film of CP-Sil 5 CB for the quantitative analysis of impurities in ethanol. The study assesses chromatographic efficiency, reproducibility, detection limits and typical analysis times under split-injection, flame ionization detection (FID) conditions.

Methodology and Instrumentation

Gas chromatographic separation was carried out using a 25 m × 0.15 mm fused-silica WCOT column with 1.2 μm CP-Sil 5 CB stationary phase. A temperature program ramped from 70 °C (2 min hold) to 200 °C at 20 °C/min, followed by a 5 min hold. Hydrogen carrier gas at 150 kPa ensured the shortest possible run times, although helium is also suitable. Samples (2 μL of ethanol spiked with impurities) were introduced via split injection at 250 °C, and analytes were detected by FID at 250 °C.

Main Results and Discussion

The method delivered high efficiency (≈150 000 plates per 25 m) and reproducibility, with standard deviations below 3 % for compounds present at 5–500 ppm. Despite split injection, detection limits down to 1–5 ppm were achieved. Typical total run times ranged from 10 to 15 minutes, supporting high sample throughput. Nine common impurities—methanol, acetone, isopropanol, diethyl ether, t-butanol, propanol isomers, methyl ethyl ketone and isobutanol—were fully resolved and quantified, with an additional impurity peak detected at low concentration.

Benefits and Practical Applications

• Single-column approach capable of addressing approximately 85 % of routine impurity analyses in chemical manufacturing.
• Trace-level quantification (1–5 ppm) suitable for stringent quality control.
• Fast cycle times (10–15 min) streamline laboratory workflows and increase throughput.
• Robust reproducibility ensures reliable results across multiple batches and operators.

Future Trends and Potential Applications

Advances in carrier gas automation, alternative detection schemes (e.g. MS coupling) and faster temperature programming will further reduce analysis times and enhance sensitivity. Emerging stationary phases tailored for polar or reactive impurities may expand the method’s applicability. Integration with online sampling and data analytics will support continuous monitoring and real-time process control in industrial settings.

Conclusion

The use of a 0.15 mm × 25 m CP-Sil 5 CB column with thick film coating enables rapid, sensitive and reproducible analysis of ethanol impurities. This approach offers a versatile, high-throughput solution for quality assurance laboratories, reducing the need for multiple column types and accelerating decision-making in production environments.

References

Agilent Technologies, Inc. Application Note: Solvents – Analysis of Impurities in Ethanol, 2011.