Determination of organic acids in animal feeds using two ion chromatography methods

Significance of the Topic

The inclusion of organic acids in animal feeds serves multiple functions: pH regulation, antimicrobial activity in the gut, enhanced nutrient digestibility, and modulation of microbial populations. Accurate quantification of these additives—such as citric, malic, formic, lactic, acetic, propionic, fumaric, succinic, malonic, and quinic acids—is essential for feed quality control, regulatory compliance, and optimization of animal performance.

Study Objectives and Overview

This application note compares two high-performance ion chromatography (IC) methods for organic acid analysis in animal feeds. Method A employs anion-exchange separation on a Dionex IonPac AS11-HC-4 µm column with a KOH gradient generated by an eluent generator. Method B uses ion-exclusion on a Dionex IonPac ICE-AS6 column with heptafluorobutyric acid eluent and organic-acid-compatible suppression. Both methods were assessed for resolution, calibration linearity, sensitivity, accuracy, precision, and applicability to dog, rabbit, and chicken feed samples.

Methodology and Instrumentation

Feed samples were ground (<1 mm), extracted with water (sonication or stirring), centrifuged or filtered, and diluted prior to IC injection. Method A used a Thermo Scientific Dionex ICS-5000+ HPIC system with DP pump, EG eluent generator, DC conductivity detector, and AS-AP autosampler. A KOH gradient (1–60 mM) in water/methanol separated ten acids plus inorganic anions, detected via a 2 mm suppressed conductivity cell. Method B ran on the same HPIC platform with HFBA eluent (0.32 mM) and a 9 mm suppressor regenerated with 5 mM tetrabutylammonium hydroxide, separating nine acids under ion-exclusion conditions.

Main Results and Discussion

Method A achieved baseline resolution of ten acids and seven common anions; fumarate partially coeluted with sulfate. Calibration curves (1–100 mg/L) required quadratic fitting (r2>0.9997); LODs ranged 0.08–0.22 mg/L. Method B resolved nine acids excluding inorganics; citric–malonic and malic–quinic overlaps were noted. Linear calibration (2–100 mg/L) gave r2=1.000; LODs 0.14–0.39 mg/L. Precision CVs were <10% for both methods. Recoveries for spiked malic, lactic, and acetic acids in feeds were 90–105%. Analysis of dog, rabbit, and chicken feeds showed expected acid profiles, with citric and malic as major components.

Benefits and Practical Applications

• Method A offers comprehensive separation of organic acids and inorganic anions in a single gradient run.
• Method B eliminates inorganic interferences and simplifies quantitation of key acids.
• Both methods deliver reliable sensitivity, reproducibility, and accuracy for feed QC laboratories.

Future Trends and Applications

Emerging directions include coupling IC to mass spectrometry for structural confirmation, further miniaturization for high-throughput screening, automated on-line sample cleanup (e.g., carbonate removal), and expansion to novel feed additives and metabolite profiling in precision livestock farming.

Conclusion

Two complementary IC approaches enable robust determination of organic acids in animal feeds. Anion-exchange IC provides broad separation capabilities including coeluting inorganics, while ion-exclusion IC offers rapid exclusion of inorganic matrix components. Both deliver high sensitivity, linearity, and accuracy suitable for routine feed analysis.

References

1. Animal feed collaborative study instruction CEN/TC 327 Version 7 (2017).
2. Grilli E. Impact of dietary organic acids and botanicals on intestinal integrity and inflammation in weaned pigs. Veterinary Research. 2015;11:96.
3. Thermo Scientific Dionex IonPac AS11-HC-4 µm Column Product Manual (2013).
4. Thermo Scientific Dionex IonPac ICE-AS6 Analytical Column Product Manual (2005).
5. Thermo Scientific Application Note 1068: Determination of Organic Acids in Fruit Juices and Wines by High-Pressure IC (2016).
6. Thermo Scientific Application Note 1157: Determination of Organic Acids in Kombucha Using a High-Pressure IC system (2016).
7. Thermo Scientific Application Note 291: Determination of Organic Acids in Wastewater Using Ion-Exclusion Chromatography (2011).
8. Thermo Scientific Technical Note 126: Determination of Organic Acids in Beer Samples Using High-Pressure IC (2013).