Analysis of Organic acids by Conductive detector

Importance of the Topic

Accurate separation and quantification of organic acids is essential in food and beverage quality control, pharmaceutical research, environmental monitoring and metabolic profiling. Ion-exclusion liquid chromatography with conductivity detection provides a robust and selective approach to analyze a wide range of organic acids, ensuring high sensitivity and reproducibility.

Objectives and Overview

This application note presents a post-column conductivity detection method for simultaneous analysis of 14 organic acids using Shimadzu’s Nexera™ ion-exclusion system and Shim-pack™ SCR-102H column. The study aims to demonstrate baseline separation, precise detection and potential uses of this method in routine analysis.

Methodology

The method employs ion-exclusion chromatography under isocratic conditions. Key parameters include:

• Mobile phase: 5 mmol/L p-toluenesulfonic acid buffered with 20 mmol/L Bis-tris and 0.1 mmol/L EDTA
• Flow rate: 1.0 mL/min
• Column temperature: 40 °C
• Injection volume: 10 μL
• Detection: post-column conductivity detector

The sample consisted of 14 organic acids (1,000 mg/L each), including phosphoric, citric, malic, lactic and valeric acids. Separation was achieved within 50 minutes based on their ion-exclusion behavior.

Used Instrumentation

• Nexera™ organic acid analysis system
• Shim-pack™ SCR-102H column (300 mm × 8.0 mm I.D., 7 μm, P/N: 228-17893-91)
• Shim-pack™ guard column SCR-102H (50 mm × 6.0 mm I.D., P/N: 228-17924-91)
• Conductivity detector with post-column mixer (piping unit J, P/N: S228-21747-91)
• 1.5 mL polypropylene vials

Main Results and Discussion

The chromatogram shows baseline separation of 14 organic acids, with clear peak resolution and uniform peak shape. Early eluters such as phosphoric and citric acids are well separated, while short-chain aliphatic acids (e.g., acetic, propionic, butyric) elute later with distinct resolution. The conductivity detector provided stable background and high signal-to-noise ratios, supporting reliable quantitation across the concentration range.

Benefits and Practical Applications

This analytical approach offers:

• High reproducibility and robustness for routine QA/QC
• Wide dynamic range for low-level and high-level acids
• Minimal sample preparation and straightforward isocratic conditions
• Applicability to food, fermentation broths, clinical and environmental samples

Future Trends and Opportunities

Advancements may include faster throughput via shorter columns or elevated flow rates, integration with mass spectrometric detection for structural confirmation, and automated data processing using AI-based algorithms. Miniaturized systems and environmentally friendly mobile phases are also emerging trends.

Conclusion

The Shim-pack SCR-102H ion-exclusion method coupled with conductivity detection delivers reliable separation of multiple organic acids in a single run. Its simplicity and versatility make it suitable for diverse analytical needs in industry and research.

References

Application News L578 (JP, ENG), Shimadzu Corporation, First Edition Dec. 2021