Determination of Total and Potential Sulfate and Total Chloride in Fuel-Grade Butanol Per ASTM D7319-09

Importance of the Topic

This application note addresses the need for rapid, reliable detection of inorganic contaminants in fuel-grade butanol, an emerging biofuel additive. Sulfate and chloride impurities can accelerate engine corrosion and impair fuel quality. By meeting or exceeding established ethanol specifications, analytical methods for butanol ensure safe blending, regulatory compliance, and consistent performance in spark-ignition engines.

Study Objectives and Overview

The aim of the study was to develop a direct-injection ion chromatography (IC) procedure for determining total and potential sulfate, and total chloride in butanol per ASTM D7319-09. Rather than evaporate and reconstitute samples, the method employs a 5 µL injection of untreated butanol or butanol–hydrogen peroxide mixtures, offering faster sample throughput and reduced preparation.

Methodology

The procedure uses suppressed conductivity detection following separation of anions on a Dionex IonPac AS22 column with carbonate/bicarbonate eluent. Potential sulfate is quantified by oxidizing sulfur species with 30% hydrogen peroxide in a 10% aqueous dilution before injection. Linearity, limits of detection (LOD) and quantification (LOQ), precision, and accuracy (via spike-recovery) were evaluated across the ranges specified by ASTM standards.

Used Instrumentation

• Thermo Scientific Dionex ICS-2100 Ion Chromatography System (isocratic pump, vacuum degasser, high-pressure injector, column heater, conductivity detector)
• Thermo Scientific Dionex IonPac AS22 Analytical Column (2 × 250 mm) with AG22 Guard Column (2 × 50 mm)
• Chemical-regeneration suppressor (Dionex AMMS 300, 2 mm)
• Thermo Scientific Dionex Chromeleon CDS Version 6.8 or higher
• Thermo Scientific Dionex AS-DV Autosampler (5 mL vials)
• Reagent-grade hydrogen peroxide, sulfuric acid, sodium carbonate/bicarbonate eluents

Main Results and Discussion

The method achieved linear calibration for chloride (0.3–50 mg/L, r² ≥ 0.9999) and sulfate (0.3–20 mg/L, r² ≥ 0.9993). LODs were 0.03 mg/L for chloride and 0.1 mg/L for sulfate; LOQs were 0.1 mg/L and 0.3 mg/L, respectively—well below ASTM D4806-11A limits (40 mg/L Cl⁻, 4 mg/L SO₄²⁻). Precision across triplicate injections showed retention time RSD ≤0.08% and area RSD ≤0.73%. Spike-recovery tests yielded 88–90% for chloride and 103–104% for sulfate, confirming method accuracy. Direct injection of peroxide-treated samples produced stable baselines and consistent responses for potential sulfate determination.

Benefits and Practical Applications

• Eliminates lengthy evaporation and reconstitution steps
• Reduces solvent consumption and risk of analyte loss
• Delivers high sensitivity and precision for low-level inorganic analytes
• Complies with ASTM D7319-09 and meets ethanol quality benchmarks
• Suitable for routine quality control in fuel laboratories

Future Trends and Potential Applications

Advances may include coupling IC to mass spectrometry for improved specificity, miniaturized or portable IC instruments for in-field analysis, and automated sample-preparation modules. Broader applications could target other organosolv biofuels, mixed-matrix samples, or multi-analyte panels addressing organic and inorganic contaminants.

Conclusion

The presented direct-injection IC method offers a rapid, robust, and accurate approach to quantify total and potential sulfate and total chloride in fuel-grade butanol. It meets stringent ASTM criteria and streamlines laboratory workflows, supporting biofuel quality assurance and regulatory compliance.

References

1. Huang H.; Liu H.; Gan Y.R. Genetic Modification of Critical Enzymes and Involved Genes in Butanol Biosynthesis from Biomass. Biotechnol. Adv. 2010, 28, 651–657.
2. Rowe D.W. Meeting the Analytical Requirements for Sulfate in Ethanol. Ethanol Producer Magazine. 2006.
3. Nexant Chemical Strategies. Biobutanol: The Next Big Biofuel. White Plains, NY, 2009.
4. Law L. Production of Biobutanol from White Grape Pomace by Clostridium saccharobutylicum. MAppSc Thesis, Auckland University of Technology, 2010.
5. Hess G. BP and DuPont Plan ‘Biobutanol’. Chem. Eng. News 2006, 84, 9.
6. BP Biobutanol Fact Sheet, 2006.
7. ASTM D7328-07. Standard Test Method for Determination of Total and Potential Inorganic Sulfate and Total Inorganic Chloride in Fuel Ethanol by Ion Chromatography. ASTM Int., 2007.
8. ASTM D4806-11A. Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines. ASTM Int., 2011.
9. ASTM D7319-09. Standard Test Method for Determination of Total and Potential Sulfate and Inorganic Chloride in Fuel Ethanol by Direct Injection Suppressed Ion Chromatography. ASTM Int., 2009.