Single Quad LC/MS Analysis of Organic Acids Using an Agilent Hi‑Plex Column

Importance of the Topic

Accurate measurement of organic acids is vital in food testing, environmental monitoring and clinical analysis due to their roles in metabolism, spoilage and fermentation processes. Traditional reversed-phase LC struggles with highly hydrophilic acids, leading to poor retention and coelution. Combining ion exclusion chromatography with single quadrupole mass spectrometry offers enhanced separation and sensitivity.

Objectives and Study Overview

This application note evaluates an ion exclusion method using an Agilent Hi-Plex H column coupled to a single quadrupole MS. The goals were to achieve baseline separation of a panel of organic acids, assess sensitivity and linearity, and demonstrate applicability to a real food sample (yogurt whey).

Methodology and Used Instrumentation

The method employed:

• Agilent 1290 Infinity II LC system
• Agilent 6120 Single Quadrupole LC/MS
• Agilent Hi-Plex H column, 250 × 4.6 mm, 8 µm

Chromatographic conditions:

• Mobile phase A: 0.01 % formic acid in water/ACN 80/20
• Post-column additive: 0.01 % NH₄OH in water/ACN 80/20 at 0.1 mL/min
• Flow rate: 0.2 mL/min; temperature: 50 °C; injection: 10 µL
• MS detection: ESI negative mode, SIM acquisition targeting [M–H]⁻ ions with optimized fragmentor voltages

Main Results and Discussion

Twenty organic acids were separated with distinct retention times ranging from ~5.9 min (oxalic acid) to ~13.1 min (butyric acid). Signal-to-noise ratios at 1 ppm exceeded 50 for all analytes and reached over 2,500 for some (e.g., gluconic, fumaric acids). In yogurt whey diluted 100×, key acids were detected with clear peaks. A malic acid spike (0.1 ppm) yielded a 93 % recovery. Linearity was demonstrated from 0.01 to 0.25 ppm (R² = 0.9991).

Benefits and Practical Applications

• High sensitivity down to 10 ppb enables trace-level quantitation.
• Robust baseline separation minimizes matrix interferences.
• Suitable for routine QA/QC in food, beverage and environmental labs.
• Direct MS detection eliminates need for post-column derivatization.

Future Trends and Opportunities

Advances may include coupling with tandem MS for higher selectivity, faster UHPLC gradients for increased throughput, and integration into automated workflows. Applications could expand to clinical metabolomics, fermentation monitoring and environmental screening of organic acids.

Conclusion

The combination of ion exclusion chromatography on an Agilent Hi-Plex H column with single quadrupole MS provides efficient, sensitive analysis of a broad panel of organic acids. The method delivers excellent separation, low detection limits, accurate recovery in complex matrices and strong linearity, making it well suited for diverse analytical laboratories.