Determination of Chloride and Sulfate in Gasoline-Denatured Ethanol

Significance of the Topic

The use of ethanol as a renewable fuel additive requires careful control of inorganic anion contamination. Chloride and sulfate impurities can form corrosive deposits that damage engine and pipeline components. Reliable, sensitive and robust analytical methods are essential to ensure that denatured gasoline ethanol meets strict quality limits defined by international standards.

Goals and Study Overview

This work evaluates a direct injection ion chromatography method for total chloride, total sulfate and potential sulfate in gasoline denatured ethanol. It adapts a previously described method for methanol denatured ethanol to natural gasoline condensate with corrosion inhibitors. Key objectives include method ruggedness, accuracy, precision and compliance with ASTM D4806 and D7319 standards.

Methodology and Instrumentation

The analysis employs a Thermo Scientific Dionex ICS-2100 system with electrochemical eluent generation using an EGC III K2CO3 cartridge and EPM III pH modifier. Separation is achieved on an IonPac AG22 guard column and AS22 analytical column. Suppressed conductivity detection is performed with an AMMS 300 suppressor in chemical regeneration mode. A 25 microliter direct injection is used with a 4.5 mM potassium carbonate 1.4 mM potassium bicarbonate eluent at 1.2 milliliters per minute and 30 degrees Celsius. Calibration covers 0.3 to 50 milligrams per liter for chloride and 0.3 to 20 milligrams per liter for sulfate.

Main Results and Discussion

The method demonstrated excellent column ruggedness over more than 400 sample injections with no observable degradation. Retention time RSD was under 0.3 percent and peak area RSD under 1.6 percent. Calibration curves were linear with r2 greater than 0.999 for both analytes. Limits of detection were 6.5 micrograms per liter for chloride and 21.8 micrograms per liter for sulfate. Recoveries of spiked samples ranged from 92 to 97 percent for chloride and 100 to 104 percent for sulfate. Two industry samples showed native chloride and sulfate levels below regulatory limits. Potential sulfate was determined by oxidation with hydrogen peroxide and measured without interference.

Benefits and Practical Applications

• Direct injection minimizes sample handling and risk of contamination
• Electrochemical eluent generation ensures reproducible eluent composition
• High sensitivity supports compliance well below specification limits
• Robust column performance reduces maintenance and downtime
• Method aligns with established ASTM international standards

Future Trends and Opportunities

Analytical innovations may include integration with mass spectrometric detection for broader analyte coverage and automated online sampling to enhance throughput. Expanded application of direct injection IC in biofuel production QA QC will support more diverse feedstocks and denaturant mixtures. Advances in suppressor technology and column chemistries may further improve sensitivity and reduce analysis time.

Conclusion

This study confirms a fast and reliable direct injection IC method for the determination of chloride and sulfate in gasoline denatured ethanol. The approach delivers excellent precision accuracy and column robustness, meeting stringent fuel quality standards and offering a practical solution for routine biofuel testing.

Instrumentation Used

• Thermo Scientific Dionex ICS-2100 or equivalent ICS series system
• EGC III K2CO3 carbonate eluent generator cartridge
• EPM III electrolytic pH modifier
• IonPac AG22 guard column and AS22 analytical column
• AMMS 300 chemical regeneration suppressor

References

1. Renewable Fuels Association historic US fuel ethanol production statistics
2. Biofuels the promise and the risks world bank report
3. Patil Tran Giselrod sustainable production of biofuels microalgae Int J Mol Sci 2008 9 1188 1195
4. ASTM D4806 specification for denatured fuel ethanol for blending with gasolines
5. ASTM D7319 test method for total and potential sulfate and inorganic chloride by direct injection IC
6. Dionex application note 290 determination of sulfate and chloride in ethanol according to ASTM D7319