Simultaneous Separation of an Acidic Drug Substance and its Counterion on a Weak Cation-Exchange/Reversed-Phase Mixed-Mode HPLC Column

Xiaodong Liu and Christopher Pohl, Dionex Corporation

The separation and quantitation of drug substances and counterions are two important determinations in the pharmaceutical industry (1). Drug substances and counterions are determined by HPLC (often on reversed-phase columns) and by ion chromatography (IC), respectively. IC is the preferred method for selective and sensitive screening of both cationic and anionic pharmaceutical counterions (2). To increase the analysis throughput, it is desirable that for analysis of drug formulation both drug substance and counterions can be determined within a single run. Naproxen is a non-steroidal anti-inflammatory drug commonly used for treating moderate to severe pain, fever, inflammation, and stiffness. Naproxen sodium was approved by the U.S. Food and Drug Administration (FDA) as an over-the-counter drug. No reports were found describing one technique for the simultaneous determinations of both naproxen and the counterion (Na⁺ ).

Experimental

Acclaim® Mixed-Mode WCX-1 columns (4.6 × 150 mm, dp = 5 μm, P/N 068353, Dionex, Sunnyvale, California) were used. Separations were performed on a modular UltiMate® 3000 HPLC System (Dionex) equipped with a LPG 3600 gradient pump, WPS-3000 Autosampler, TCC-3200 column oven, and a Sedex-85 evaporative light scattering detector (Sedere, Alfortville, France). Chromeleon® 6.70 Chromatography Management Software (Dionex) was used for system control and data processing. Naproxen sodium standard was purchased from Sigma (St. Louis, Missouri).

Figure 1

Results and Discussion

The Acclaim Mixed-Mode WCX-1 column contains new silica packing material that features a hydrophobic alkyl chain with a carboxylate terminus (Figure 1). As a result, it provides both reversed-phase and weak cation-exchange properties. While conventional reversed-phase (RP) columns fail to retain Na⁺ ion, the Acclaim Mixed-Mode WCX-1 not only retains Na⁺ , but also acidic drug substances (naproxen) in the same analysis, providing effective determination of both analytes (Figure 2). Moreover, the elution order can be adjusted by changing the buffer concentration in the mobile phase.

Figure 2

Conclusion

The Acclaim Mixed-Mode WAC-1 features unique and adjustable selectivity, good peak shapes, and efficiency for various basic analytes. Its multi-mode retention mechanism allows analysis in HILIC mode (3). Therefore, it can be used as a complementary column to conventional RP columns by providing different selectivity and as a specialty column for simultaneous determination of acidic drug substances and counterions.

References

(1) Y. Kazakevich, R. Lobrutto, "HPLC for Pharmaceutical Scientists," Wiley-Interscience, New Jersey, 2007.

(2) Dionex Corporation website: www.dionex.com/en-us/webdocs/4642_an106.pdf.

(3) Dionex Corporation website: www.dionex.com/en-us/columns_accessories/spec/cons65659.html.

Acclaim, Chromeleon and UltiMate are registered trademarks of Dionex Corporation.

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