Fast Determinations of Phosphate and Citrate in Carbonated Beverages Using On-Line Degassing with the Carbonate Removal Device (CRD) and a Reagent-Free™ Ion Chromatography System

Significance of the Topic

Phosphoric and citric acids are common acidulants and preservatives in carbonated beverages. They contribute to flavor profile and shelf life but require reliable quantification. Carbon dioxide interference and bubble formation can compromise ion chromatography analysis. Effective carbonate removal is therefore essential to ensure accurate and precise measurement of these anions.

Objectives and Study Overview

This work aimed to implement an on-line degassing approach using a Carbonate Removal Device (CRD) integrated into a reagent-free ion chromatography (RFIC) system to streamline phosphate and citrate analysis in colas. The study compared performance metrics against a conventional off-line degassing method and extended the method to a variety of commercial cola products.

Methodology and Instrumentation

A Dionex ICS-2000 reagent-free IC system equipped with an EluGen KOH eluent generator and CR-ATC cartridge was used. Separation employed an IonPac Fast Anion III column with guard at 1.0 mL/min and 30 °C, with 20 mM KOH eluent. A 4 mm CRD was installed between the AS40 autosampler and injection valve to remove dissolved carbonate on-line. Samples were injected via a calibrated 1.1 μL PEEK loop. Suppressed conductivity detection in recycle mode (70 mA) provided quantitation. Standards ranging from 50 to 600 mg/L were prepared, and linearity and noise were assessed over extended runs.

Main Results and Discussion

On-line CRD degassing produced retention times of approximately 2.78 min for phosphate and 3.73 min for citrate, matching off-line methods. Quantitation precision was better than 0.3 %RSD, with linearity coefficients greater than 0.999. The CRD functioned reliably for up to 950–2660 injections, with typical service life determined by leak testing. Application to additional commercial colas yielded phosphate concentrations between 221 and 523 mg/L and citrate between 43 and 172 mg/L, demonstrating method robustness across sample matrices.

Benefits and Practical Applications

On-line carbonate removal reduces sample preparation time by eliminating 20-minute off-line degassing steps and minimizes manual handling. The approach enhances laboratory throughput while maintaining analytical performance. It can be readily applied to quality control of beverages and other acidic carbonated products where interference from carbonate is problematic.

Future Trends and Applications

Further development may focus on extending the on-line degassing concept to a broader range of analytes and sample types, including environmental and biological samples. Advances in membrane materials and degassing module design could improve lifetime and reduce maintenance. Integration with hyphenated techniques such as IC–MS may enable trace-level analysis in complex matrices. Automation of sample preparation workflows will continue to drive efficiency in high-throughput laboratories.

Conclusion

The integration of a Carbonate Removal Device into a reagent-free ion chromatography system offers a fast, reliable, and user-friendly method for determining phosphate and citrate in carbonated beverages. Comparable analytical figures of merit to traditional off-line degassing are achieved, with significant gains in throughput and simplicity. This approach supports routine quality control and research applications in beverage analysis.

References

1. Dionex Corporation. Rapid Determination of Phosphate and Citrate in Carbonated Soft Drinks by Reagent-Free Ion Chromatography. Application Note 169, 2005.
2. Dionex Corporation. Reducing Carbonate Interference in Anion Determinations with the Carbonate Removal Device (CRD). Technical Note 62, 2005.
3. Dionex Corporation. ICS-2000 Ion Chromatography System Operator’s Manual. 2003.
4. Dionex Corporation. Quickstart Procedure for the ASRS ULTRA II Anion Self-Regenerating Suppressor. Application Note 031951, 2005.
5. Dionex Corporation. Product Manual for IonPac Fast Anion III Guard Column and Analytical Column. 2004.
6. Dionex Corporation. Application of Eluent Generation for Trace Analysis of Borated Waters. Application Note 166, 2004.
7. Dionex Corporation. Quickstart Instructions for Carbonate Removal Device (CRD). 2005.
8. Dionex Corporation. Product Manual for the Carbonate Removal Device. 2005.
9. Dionex Corporation. AS40 Automated Sampler Operator’s Manual. 2004.
10. Dionex Corporation. ICS-2000 Ion Chromatography System Operator’s Manual: Connecting an AS40 Automated Autosampler. 2003.
11. Dionex Corporation. Product Manual for Carbonate Removal Device. 2005.