Determination of sulfate and chloride in denatured ethyl alcohol according to ASTM D 7319

Importance of the Topic

Ethanol fuel is contaminated with inorganic ions such as chloride and sulfate which can clog filters, corrode engine components and reduce performance. Reliable quantification of these anions is essential for quality control and compliance with fuel standards such as ASTM D 4806 and the recent ASTM D 7319 method specification.

Study Objectives and Overview

This work presents a direct injection ion chromatography method with suppressed conductivity detection for simultaneous determination of total and potential sulfate and inorganic chloride in denatured ethyl alcohol. The approach aligns with the newly approved ASTM D 7319 and meets the sulfate and chloride limits defined in ASTM D 4806-06c.

Methodology and Instrumentation

Samples are analyzed by injecting 20 muL of ethanol directly into a compact ion chromatograph. Potential sulfate is quantified after adding hydrogen peroxide to convert sulfur species to sulfate. Key system components include:

• 861 Compact IC system
• MSM II trichamber suppressor module
• 838 advanced sample processor
• Metrosep A Supp 5 – 150 column with guard
• Conductivity detector after suppression

Eluent consists of 3.2 mmol/L sodium carbonate and 1.0 mmol/L sodium bicarbonate at 0.7 mL per minute and column temperature of 35 °C.

Key Results and Discussion

Calibration curves show linear response from 0.625 to 50 ppm for chloride and 0.25 to 20 ppm for sulfate with correlation coefficients above 0.9998. Detection limits are 0.6 ppm for chloride and 0.2 ppm for sulfate. Reproducibility and repeatability remain high even after 1500 injections containing organic denaturants and hydrogen peroxide. Both conductivity and mass spectrometric detection deliver accurate results across blank, standard and sample measurements with relative standard deviations below 3% for chloride and 4% for sulfate.

Benefits and Practical Applications

The direct injection IC method offers fast, solvent compatible analysis with minimal sample preparation. It ensures robust, precise monitoring of anion contamination in fuel ethanol for QA/QC laboratories, blending facilities and regulatory compliance.

Future Trends and Opportunities

Further developments may include coupling the IC system with mass spectrometry for multi-anion screening, automating inline process monitoring, miniaturizing systems for field use and extending methodology to trace analytes in biofuels and other solvent matrices.

Conclusion

The described suppressed ion chromatography method fulfills ASTM D 7319 requirements, providing a reliable, high-throughput approach to determine sulfate and chloride levels in denatured ethanol, supporting engine protection and regulatory standards compliance.

References

1. Rowe DW Meeting the analytical requirements for sulfate in ethanol Ethanol Producer Magazine 2006 issue 152-154
2. Metrohm Application Work AW-US6-0110-072005 Determination of sulfate in denatured ethyl alcohol by direct injection ion chromatography and suppressed conductivity
3. Gandhi J Benton R Rowe DW Determination of bromide and sulfate in flame retardants by ion chromatography LC GC Application Notebook February 2005
4. ASTM D 4806-06c Standard specification for denatured fuel ethanol for blending with gasoline for spark-ignition engines
5. ASTM D 7319-07 Standard test method for determination of total and potential sulfate and inorganic chloride in fuel ethanol by direct injection suppressed ion chromatography