Determination of Sulfate and Chloride in Ethanol by Ion Chromatography

Significance of the Topic

Ethanol blending in gasoline can carry chloride and sulfate impurities that form corrosive deposits in engines and contravene ASTM D4806 fuel specifications.
Accurate determination of these anions at mg/L levels ensures fuel quality and engine reliability.

Objectives and Study Overview

This work presents a straightforward, direct injection ion chromatography (IC) method for measuring chloride and sulfate in ethanol within 15 minutes.
The approach was validated through an ASTM interlaboratory study to establish precision and bias for fuel analysis.

Methodology

Direct injection of ethanol samples filtered through 0.2 μm membranes avoids extensive pretreatment.
Two IC approaches were developed:

• AS18 column with 30 mM KOH eluent (eluent generation or manual), 1 mL/min, 15 min run.
• AS14A column with 8 mM carbonate/1 mM bicarbonate eluent (eluent generation or manual), 1.2 mL/min, 35 min run.

Continuous suppression was achieved using the AMMS III suppressor with 50 mN H₂SO₄ regenerant at 5–8 mL/min.

Instrumental Setup

• Dionex IC system (ICS-3000/2000/1500/1000/90) with autosampler.
• Eluent Generator (EGC II KOH or K₂CO₃) and Carbonate Mixer kit.
• AMMS III membrane suppressor in pressurized regenerant mode.
• Chromeleon 6.8 chromatography data system.

Main Results and Discussion

Both methods achieved baseline separation of chloride and sulfate from common anions and ethanol oxidation products (formate, acetate).
Limits of detection were below 0.1 mg/L; calibration was linear up to 20 mg/L (chloride) and 10 mg/L (sulfate) with correlation coefficients >0.998.
Precision for sub-10 mg/L levels showed RSDs below 1% (n=7).
Real ethanol samples, denatured or spiked, demonstrated accurate quantitation and reproducible retention times.

Benefits and Practical Applications

• Direct injection minimizes sample handling and risk of contamination.
• Fast analysis (15–35 min) supports high sample throughput.
• Flexible eluent preparation: eluent generation or manual mixing.
• Robust suppression with AMMS III across eluent strengths.
• Applicable to quality control in fuel production and regulatory compliance.

Future Trends and Applications

Advancements may include inline matrix elimination, coupling IC with mass spectrometry for enhanced selectivity, and automated monitoring in production lines.
Development of more stable suppressor materials and microfluidic IC devices can further reduce analysis time and reagent use.

Conclusion

The described Dionex IC methods deliver rapid, sensitive, and reproducible determination of chloride and sulfate in ethanol, fulfilling ASTM D4806 requirements and streamlining fuel quality assessment.

References

• ASTM D 4806, Standard Specification for Ethanol Fuel.
• ASTM WK9828, Test Method for Inorganic Chloride and Sulfate by Direct Injection IC.
• ASTM WK9829, Test Method for Inorganic Chloride and Sulfate in Fuel Ethanol.
• Application Note 85, Determination of Trace Anions in Organic Solvents, Dionex 2004.