Determination of Counterions (Cations) by Ion Chromatography

Typically, a variety of counterions are used to selecting the optimum salts in the development stage of a pharmaceutical product because the physicochemical and pharmacokinetic properties associated with the active pharmaceutical ingredients (API) will vary depending on differences in counterions. Furthermore, as inorganic substances such as catalysts and ions used during synthetic process may affect such properties as solubility and stability, it is very important to conduct analysis of ionic contaminants. High-sensitivity analysis of these ionic contaminants, even when present at trace levels in pharmaceutical products, can be conducted using ion chromatography. Further, by adding an organic solvent to the eluent, the principle component can be eluted more quickly, thereby shortening the analysis time.
Here, we introduce examples of analysis of sodium, potassium, magnesium and calcium as the principal counter cations found in pharmaceuticals.

Analysis of Trace Amounts of Cations

We conducted low-concentration analysis of a standard solution of sodium, potassium, magnesium and calcium. Table 1 shows the area reproducibility and retention time (n = 6), and Table 2 shows the analytical conditions used. The results of analysis of the cation standard solution are shown Fig. 1.

Table 1 Repeatability

Table 2 Analytical Conditions

Fig. 1 Chromatogram of a Four-Cation Standard Mixture

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