Simultaneous Measurement of Anions and Cations: Method Validation

The use of HILIC chromatography and the Corona® Detector with HPLC offers an alternative technique for the analysis of ions. This applications note discusses the validation of this method of analysis.

Dedicated instrumentation, multiple columns and time-consuming changeovers are required in order to measure both anions and cations with ion chromatography.

A new method for ion analysis has been introduced (1) that measures both anions and cations in a single analysis using standard HPLC. This application note describes aspects of method validation.

Materials

A standard HPLC system with a Corona® CAD Detector.

Column: Sequant ZIC®-pHILIC 5 μm, 4.6 × 150 mm, 30 °C

Mobile Phase and Gradient: see reference 2.

Corona: 100 pA, no filter

Flow Rate: 0.5 mL/min.

Injection Volume: 10 μL

Figure 1

Results

In Figure 1, overlays of eight concentrations of anions and cations are illustrated. The reproducibility and intermediate precision of the analysis was examined for peak areas and retention times of standards using one concentration (~12.5 μg/mL of each ion salt) over the length of the study. Five injections of standard 4 were made on days 1 and 2; six injections on days 4 and 7. The peak area reproducibility, as well as the retention time reproducibility, was examined over the 22-point data set for the six ions. The inter-and intra-day reproducibility results are listed in Table I.

Table I: Inter-and intra-day reproducibility results

Conclusion

The data collected during this study demonstrates that the analysis of ions using the Corona detector can be performed accurately and reproducibly to low nanogram levels. All major validation parameters were tested for chloride, sulfate, sodium, and potassium with only reproducibility reported here. (The analysis did not include all robustness levels according the FDA Q7A). For complete validation information see reference 2. These data illustrate intermediate precision of the detector and method. The validation of this analysis along with the versatility of this ion method makes a viable alternative to traditional approaches.

References

(1) ESA Application note 70-8290 Simultaneous Measurement of an Anion and Cation.

(2) Evaluation of Methods for the Simultaneous Analysis of Cations and Anions Using HPLC with Charged Aerosol Detection and a Zwitterionic Stationary Phase, J. Chromatogr. Sci., 47, 534–539.

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