Determination of Chloride and Sulfate in Gasoline-Denatured Ethanol

Importance of the Topic

Ethanol derived from biomass is a key renewable fuel that reduces reliance on fossil sources. Ensuring the purity of denatured ethanol is critical because chloride and sulfate impurities form corrosive deposits that can damage engine parts and distribution infrastructure. Sensitive and accurate quantification of these anions is required to comply with industry standards such as ASTM D4806 and to preserve fuel system integrity.

Objectives and Study Overview

This work evaluates a direct injection ion chromatography method for measuring total chloride, total sulfate, and potential sulfate in gasoline-denatured ethanol. The study adapts an eluent generation approach with carbonate and bicarbonate reagents to meet ASTM D7319-12 requirements. Ruggedness testing and method qualification were performed using fuel samples containing natural gas condensate and corrosion inhibitors.

Methodology and Analytical Conditions

The analysis employed a Dionex ICS-2100 system equipped with an IonPac AG22 guard column and IonPac AS22 analytical column. A carbonate eluent generator cartridge and an electrolytic pH modifier produced a continuous 4.5 mM K2CO3 / 1.4 mM KHCO3 eluent at 1.2 mL per minute. Samples were directly injected in 25 µL volumes and detected by suppressed conductivity using an AMMS-300 suppressor with chemical regeneration. Calibration standards ranged from 0.3 to 50 mg/L for chloride and 0.3 to 20 mg/L for sulfate.

Used Instrumentation

• Dionex ICS-2100 ion chromatography system with pump, degasser, injector valve, column heater, and conductivity detector
• Dionex AS-DV autosampler with 5 mL PolyVial trays
• Dionex EGC III K2CO3 carbonate eluent generator cartridge and EPM III electrolytic pH modifier
• IonPac AG22 guard column and IonPac AS22 analytical column
• Dionex AMMS-300 anion suppressor in external regeneration mode
• Chromeleon chromatography data system version 7.1

Main Results and Discussion

The method demonstrated high ruggedness with over 400 injections of both undiluted and fivefold diluted gasoline-denatured ethanol without column degradation. Retention time RSD values were below 0.25 percent and peak area RSD values were below 1.6 percent. Calibration curves exhibited linearity with r² values above 0.999. Limits of detection were 6.5 µg/L for chloride and 21.8 µg/L for sulfate, well below fuel quality limits. Sample analysis of two industry sources revealed native chloride and sulfate levels below 2 mg/L. Spike recoveries ranged from 92 to 97 percent for chloride and 100 to 104 percent for sulfate.

Benefits and Practical Applications

• Direct injection eliminates complex sample pretreatment
• Automated eluent generation reduces reagent handling and enhances reproducibility
• High sensitivity meets regulatory requirements for fuel grade ethanol quality control
• Robust performance supports routine analysis in QC and research laboratories

Future Trends and Possibilities

Advances may include integration of inline oxidation for comprehensive sulfur speciation, higher throughput systems with multiplexed columns, coupling to mass spectrometry for enhanced selectivity, and portable IC platforms for on-site monitoring of renewable fuel production processes. Continued development of greener eluent generation and fully automated workflows will improve efficiency and sustainability.

Conclusion

A direct injection ion chromatography method using carbonate eluent generation and suppressed conductivity detection provides accurate and precise measurement of chloride and sulfate in gasoline-denatured ethanol. The approach delivers low detection limits, strong linearity, and excellent column robustness, fulfilling industry standards and supporting fuel quality assurance.

Reference

• Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark Ignition Engine Fuel D4806 ASTM International
• Standard Test Method for Determination of Total and Potential Sulfate and Inorganic Chloride in Fuel Ethanol by Direct Injection Suppressed Ion Chromatography D7319 ASTM International
• Perati P P, De Borba B M, Rohrer J S. Determination of Chloride and Sulfate in Gasoline-Denatured Ethanol. Thermo Fisher Scientific Application Note 1052 (2013).