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

Significance of the Topic

Butanol is gaining interest as a higher-energy, lower-volatility biofuel additive that can be blended into gasoline at higher proportions than ethanol without impairing engine performance or increasing emissions. Trace amounts of inorganic anions such as sulfate and chloride can form acid deposits, corrode engine components, and impair fuel quality. Reliable determination of total and potential sulfate and total chloride in fuel-grade butanol is therefore essential for quality control and to meet industry specifications.

Study Objectives and Overview

This work presents a direct injection ion chromatography method compliant with ASTM D7319-09 for measuring total and potential sulfate and total chloride in butanol. The method aims to meet or exceed the sensitivity requirements of ASTM D4806-11A (≤4 mg/L sulfate, ≤40 mg/L chloride) while reducing sample preparation time by eliminating evaporation and reconstitution steps.

Methodology and Instrumentation

The method uses a Thermo Scientific Dionex ICS-2100 (or ICS-1100/1600/5000) system equipped with:

• Dionex IonPac AG22 guard column (2×50 mm) and AS22 analytical column (2×250 mm)
• AMMS 300 anion micro-membrane suppressor in chemical regeneration mode with 50 mN sulfuric acid
• Suppressed conductivity detector
• AS-DV autosampler with 5 mL PolyVials

Chromatographic conditions:

• Eluent: 4.5 mM sodium carbonate/1.4 mM sodium bicarbonate
• Flow rate: 0.3 mL/min
• Injection volume: 5 µL
• Column temperature: 30 °C
• Run time: 20 min

Potential sulfate is measured by adding 0.5 mL of 30% hydrogen peroxide to 9.5 mL butanol, vortexing to mix, and injecting directly.

Main Results and Discussion

Calibration was linear over 0.3–50 mg/L for chloride (r2 > 0.9999) and 0.3–20 mg/L for sulfate (r2 > 0.9993). Estimated limits of detection were 0.03 mg/L (chloride) and 0.1 mg/L (sulfate) with limits of quantification at 0.1 mg/L and 0.3 mg/L, respectively. Retention time precision (n=3) was ≤0.08% RSD and peak area precision ≤0.73% RSD. Spike recovery studies in butanol yielded recoveries of 88–90% for chloride and 103–104% for sulfate, confirming method accuracy and reproducibility. Overlay chromatograms demonstrated stable baselines and consistent peak shapes across replicates.

Benefits and Practical Applications

The direct injection approach substantially reduces sample handling and turnaround time compared to evaporation/reconstitution methods. Its high sensitivity and precision support quality assurance in biofuel production, blending operations, and regulatory compliance testing. The method can be applied in laboratories performing routine analysis of fuel additives or monitoring inorganic contaminants in solvent matrices.

Future Trends and Potential Applications

• Integration with high-throughput autosamplers and online sample preparation to increase daily sample capacity.
• Extension to other oxygenated biofuels and blends such as n-propanol or mixed alcohol streams.
• Development of even lower-detection-limit suppressors and columns for ultra-trace analysis in advanced fuel formulations.
• Coupling with mass spectrometric detection for speciation of organic and inorganic anions in complex fuel matrices.

Conclusion

A direct injection ion chromatography method using suppressed conductivity detection provides accurate, precise, and rapid determination of total and potential sulfate and total chloride in fuel-grade butanol. The method meets ASTM D7319-09 and achieves detection limits well below industry specifications, offering a streamlined alternative to more laborious sample preparation protocols.

Reference

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• ASTM D7319-09; ASTM International, 2009.