USING HYBRID ORGANIC/INORGANIC SURFACE TECHNOLOGY TO MITIGATE ANALYTE INTERACTIONS WITH METAL SURFACES IN UPLC SEPARATIONS OF SMALL MOLECULE PHARMACEUTICALS

Importance of the Topic

The performance of ultra-performance liquid chromatography (UPLC) can be compromised by unwanted interactions between analytes and metal surfaces in instrument and column hardware. These surface interactions lead to peak tailing, lower signal intensity, increased variability, and on-column reactions that generate spurious peaks. For pharmaceutical analysis of small molecules, ensuring accuracy and reproducibility is critical for quality control, method validation, and regulatory compliance.

Objectives and Study Overview

This study evaluates a novel hybrid organic/inorganic surface technology (HST) applied to metal components in UPLC systems and columns. The aim is to compare standard UPLC hardware versus HST-coated hardware (branded ACQUITY Premier System and Column) for separations of three small molecule pharmaceuticals: hydrocortisone sodium phosphate, deferoxamine mesylate, and clozapine. Key performance indicators include peak shape, peak area sensitivity, reproducibility, and prevention of on-column oxidation.

Methodology and Instrumentation

Separations were performed under consistent chromatographic conditions using acetonitrile gradients and ammonium formate or hydroxide mobile phases. Two hardware configurations were compared:

• Standard UPLC system with BEH C18 1.7 µm columns
• ACQUITY Premier System and Column featuring ethylene-bridged siloxane HST coating

Detection methods included UV absorbance for hydrocortisone and clozapine, and electrospray ionization mass spectrometry for deferoxamine mesylate. Mass injections ranged from 2 ng to 200 ng for hydrocortisone, 2 ng to 60 ng for deferoxamine, and a fixed 10 ng load for clozapine variability studies.

Key Results and Discussion

The HST hardware consistently outperformed the standard configuration:

• Hydrocortisone sodium phosphate: HST produced narrower, more symmetric peaks, higher calibration slopes, and lower relative standard deviations (RSD) at low mass loads (2, 20, 50 ng).
• Deferoxamine mesylate: At 10 ng, peak area RSD was reduced from 16.8% (standard) to 2.1% (HST), with average peak areas increasing from ~3.01×10^6 to ~4.89×10^6 intensity units.
• Clozapine: Repetitive injections on standard hardware generated an N-oxide by-product representing 2.05% of total area after 13 runs. HST reduced this oxidation product to just 0.06% under identical conditions.

These findings confirm that HST effectively suppresses metal-analyte interactions, stabilizes peak areas, and minimizes artifact formation.

Benefits and Practical Applications

Implementing HST in UPLC instruments and columns offers several advantages for pharmaceutical analysis:

• Improved accuracy and linearity of calibration curves at low analyte concentrations
• Enhanced reproducibility of peak areas across injections
• Reduced peak tailing and sharper chromatographic profiles
• Prevention of on-column oxidation and artifact generation

These benefits support more reliable quantitation in method development, quality control, and bioanalysis workflows.

Future Trends and Opportunities

Further expansion of surface modification technologies may address interactions with a broader range of pharmaceutical compounds, including highly polar or metal-chelating analytes. Integration with emerging stationary phase chemistries and automated manufacturing of coated hardware could streamline adoption. Additionally, combining HST with high-throughput and multi-omics platforms has potential to enhance analytical robustness in both research and industrial settings.

Conclusion

The use of hybrid organic/inorganic surface technology on UPLC metal components significantly improves chromatographic performance for small molecule pharmaceuticals. By reducing surface interactions, HST delivers more accurate, reproducible, and artifact-free separations, addressing critical challenges in pharmaceutical analysis.

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