Higher Resolution Separation of Organic Acids and Common Inorganic Anions in Wine

Significance of the Topic

The composition of organic acids and inorganic anions plays a critical role in defining the flavor, acidity, and quality of wine.
High-resolution separation and sensitive detection of acids such as tartaric, malic, citric, and acetic acids enable monitoring of fermentation, aging, and malolactic conversion.
Accurate profiling supports quality control, product consistency, and identification of off-flavors in both red and white wines.

Objectives and Overview of the Study

This application note presents an improved ion chromatography method for simultaneous separation and quantitation of 16 organic acids and common inorganic anions in wine.
The method employs a novel OmniPac PAX-100 column with gradient elution using sodium hydroxide and organic solvents to achieve enhanced resolution compared to conventional AS11-based columns.
Quantitative performance is demonstrated through calibration, analysis of four commercial wines, and recovery studies.

Methodology and Instrumentation

Reagents and Standards:

• DI water (18 MΩ·cm), sodium hydroxide (0.1 M and 1.0 M), methanol/ethanol mix (12/16 %), sulfuric acid solutions (1 N and 20 mN).
• Stock standards prepared for 16 analytes including fluoride, acetate, lactate, formate, shikimate, chloride, nitrite, bromide, nitrate, succinate, malate, tartarate, sulfate, oxalate, phosphate, and citrate.

Sample Preparation:

• Wine samples diluted 1:100 with DI water and cleaned using OnGuard II RP cartridges to remove hydrophobic interferences.
• Spiking with multi-analyte standards for recovery assessment.

Chromatographic Conditions:

• Column: OmniPac PAX-100 analytical (4×250 mm) with guard (4×50 mm) and IonPac ATC-HC trap (9×75 mm).
• Eluent gradient: DI water, 12 % methanol/16 % ethanol, 0.1 M NaOH, and 1.0 M NaOH over 35 min.
• Flow rate 1.0 mL/min, column temperature 30 °C, injection volume 25 µL.
• Detection by suppressed conductivity using an AMMS 300 suppressor regenerated with 20 mN H₂SO₄.

Used Instrumentation

• Dionex ICS-3000 or ICS-5000 ion chromatography system with DP or SP pump and DC detector/chromatography module.
• 6-port injection valve and dual temperature zones.
• AS autosampler and AXP pump.
• Chromeleon® CDS software version 6.80 SR9 or higher.

Main Results and Discussion

• Conventional AS11 and AS11-HC columns failed to resolve key organic acids (acetate, lactate, shikimate, succinate, malate) under tested conditions.
• OmniPac PAX-100 column achieved baseline separation of 9 organic acids and 7 inorganic anions in 35 min.
• Calibration linearity was excellent for all analytes (r² ≥ 0.997), with reliable slopes and offsets across the selected ranges.
• Analysis of four commercial wines (two reds, two whites) yielded reproducible quantitation (RSD < 3.5 % for most analytes), covering concentrations from trace fluoride to high tartarate levels.
• Spike recovery studies showed acceptable accuracy (76–120 %), demonstrating method robustness in complex matrices.

Benefits and Practical Applications

• Simultaneous analysis of organic and inorganic anions reduces analysis time and sample handling.
• High resolution and sensitivity support detailed profiling of wine acidity and flavor-contributing species.
• Method is suitable for routine quality control, monitoring of fermentation progress, and detection of off-flavors in enology laboratories.
• Compatibility with Reagent-Free IC configurations offers simplified operation by eliminating external eluent preparation.

Future Trends and Opportunities

• Integration of mass spectrometric detection for enhanced selectivity and structural confirmation of organic acids.
• Automation of sample cleanup and dilution to further increase throughput in high-volume laboratories.
• Extension of the method to other fermented and non-fermented beverages, fruit juices, and food quality applications.
• Development of miniaturized columns and microflow systems to reduce solvent consumption and waste.

Conclusion

An optimized ion chromatography method using the OmniPac PAX-100 column provides superior resolution and quantitation of 16 organic acids and inorganic anions in wine.
The approach delivers robust performance, accurate results, and practical applicability for quality control and research in the wine industry.

Reference

1. Dionex Corporation. Organic Acids in Wine. Application Note 21, LPN 03205-02, 1997, Sunnyvale, CA.
2. Masson P. Influence of Organic Solvents in the Mobile Phase on the Determination of Carboxylic Acids and Inorganic Anions in Grape Juice by Ion Chromatography. J Chromatogr A. 2000;881:387–394.
3. Dionex Corporation. Determination of Organic Acids in Fruit Juices. Application Note 143, LPN 1415, 2003, Sunnyvale, CA.
4. Dionex Corporation. Determination of Organic Acids in Cranberry and Bilberry Extracts. Application Brief 112, LPN 2560, 2010, Sunnyvale, CA.
5. Dionex Corporation. OnGuard II Cartridges Product Manual. Document No. 031688-06, 2004, Sunnyvale, CA.