Analysis of APIs in a Pain-Relief Medicine on a Thermo Scientific™ Acclaim™ Mixed-Mode WAX-1 Column

Importance of the Topic

Pain relief tablets often include multiple active ingredients whose analysis requires efficient separation and quantification. Mixed-mode chromatography, combining reversed-phase and ion-exchange interactions, offers high selectivity and resolution for such complex mixtures. Reliable analysis ensures drug safety, potency verification and quality control in pharmaceutical settings.

Study Objectives and Overview

The primary goal of this study was to develop a robust high-performance liquid chromatography method for simultaneous determination of five pain-relief APIs—caffeine, acetaminophen, salicylamide, acetylsalicylic acid and salicylic acid—in a single tablet formulation using mixed-mode stationary phase.

Methodology and Instrumentation

The separation was performed on a Thermo Scientific Acclaim Mixed-Mode WAX-1 column (4.6 × 150 mm, 5 µm particle size). A binary mobile phase consisting of 40 volume percent acetonitrile and 60 volume percent aqueous buffer (6.8 g KH2PO4 and 0.5 g sodium pyrophosphate decahydrate per liter, pH adjusted to 6.0) was used at a flow rate of 1 milliliter per minute. The column temperature was maintained at 30 °C and detection was carried out by UV absorbance at 220 nanometers. Sample preparation involved grinding a 500 mg tablet, dissolving 400 mg of powder in 40 grams deionized water, sonication for 5 minutes, filtration through a 0.45 µm membrane, and fourfold dilution with deionized water.

Benefits of pyrophosphate in the buffer included suppression of metal ion interferences, enhancing peak shape and reproducibility.

Results and Discussion

All five analytes were baseline-separated within a 20-minute run time. Retention order was caffeine followed by acetaminophen, salicylamide, acetylsalicylic acid and salicylic acid. The mixed-mode mechanism provided improved selectivity for acidic and basic compounds in a single analysis. Peak symmetry and resolution met typical system suitability criteria for pharmaceutical assays.

Benefits and Practical Applications

• Simultaneous quantification of multiple APIs in under 20 minutes
• Reduced sample preparation steps with simple aqueous buffers and direct injection
• Enhanced method robustness due to mixed-mode selectivity and pyrophosphate suppression of metal ion effects
• Suitable for routine quality control in pharmaceutical laboratories

Future Trends and Potential Applications

Advancements in mixed-mode stationary phases and buffer chemistries are expected to further improve analysis of complex formulations. Automation of sample preparation and integration with mass spectrometric detection can expand capabilities to trace-level impurity profiling. Application of similar strategies to other combination drugs and bioanalytical samples will grow in regulatory and clinical environments.

Conclusion

The developed mixed-mode HPLC method on a WAX-1 column demonstrated rapid, selective and reproducible separation of five active ingredients in a pain-relief tablet. Its simplicity and performance make it well-suited for pharmaceutical quality control workflows.

Used Instrumentation

• Chromatograph: High-performance liquid chromatography system
• Column: Thermo Scientific Acclaim Mixed-Mode WAX-1, 4.6 × 150 mm, 5 µm
• Detector: UV absorbance at 220 nm

References

• Thermo Fisher Scientific Inc. Application Note 23719, 2009