Analysis of Tricyclic Antidepressants using Agilent Poroshell HPH C18

Significance of the Topic

Tricyclic antidepressants (TCAs) remain important both as therapeutic agents and as model analytes for chromatographic evaluation of column performance. Their three-ring structures and basic amine functionalities challenge stationary phases through ion-exchange interactions with residual silanols. High-pH stable superficially porous C18 columns offer an opportunity to improve separation efficiency and reproducibility for these ionizable compounds, especially when operating at mid to high pH where silica dissolution and tailing issues can arise.

Objectives and Overview of the Study

This study compares the chromatographic performance of Agilent Poroshell HPH C18 columns (2.7 µm and 4 µm particle sizes) against superficially porous columns from another vendor (2.6 µm and 5 µm) for the analysis of a mixture of TCAs and a neutral probe (uracil) at pH 7. Key metrics include peak shape, tailing factors, plate counts, retention order, and operating pressure.

Applied Methodology and Instrumentation

The separation was performed on an Agilent 1260 Infinity LC system comprising a binary pump (up to 600 bar), thermostatted column compartment, high-performance autosampler, and diode array detector with a 1 µL flow cell. Columns evaluated were 3 × 100 mm Agilent Poroshell HPH C18 (2.7 µm and 4 µm) and 3 × 100 mm columns from another vendor (2.6 µm and 5 µm). The mobile phase was 60:40 acetonitrile to 20 mM sodium phosphate buffer adjusted to pH 7, delivered at 1 mL/min and 25 °C, with detection at 254 nm. Analytes included uracil (50 µg/mL), doxepin HCl (250 µg/mL), nortriptyline HCl (500 µg/mL), amitriptyline HCl (250 µg/mL), and trimipramine maleate (500 µg/mL). Data acquisition and processing used Agilent ChemStation software.

Main Results and Discussion

At pH 7, all TCAs are protonated (pKa 8–10), making them susceptible to silanol interactions. The Poroshell HPH C18 columns exhibited symmetrical peaks with low tailing factors (1.05–1.96) and high plate counts (up to 15 679 for trimipramine on the 2.7 µm column). Operating pressures were 280 bar (2.7 µm) and 143 bar (4 µm). In contrast, the other vendor’s columns showed significant peak broadening and higher tailing (up to 3.22) with reduced efficiency. Retention order and selectivity remained comparable across columns, demonstrating method scalability.

Benefits and Practical Applications of the Method

• Robust peak shape for basic pharmaceuticals at mid-pH conditions.
• High efficiency and plate counts enable sharper separations and faster analysis.
• Lower solvent consumption using 3 mm ID columns reduces operating costs and waste.
• Compatibility with mass spectrometry due to reduced flow rates and solvent load.

Instrumentation Used

• Agilent 1260 Infinity Binary Pump SL (G1312B)
• Agilent 1260 Thermostatted Column Compartment (G1316C)
• Agilent 1260 High Performance Autosampler SL Plus (G1376C)
• Agilent 1260 Diode Array Detector with 10 mm flow cell (G4212A, p/n G4212-60008)

Conclusion

Agilent Poroshell HPH C18 columns demonstrate superior durability and performance for tricyclic antidepressant analysis under phosphate buffer at pH 7. Their high-pH stability, efficient separations, and low solvent usage make them a preferred choice for routine and advanced applications involving basic analytes.

Future Trends and Applications

Emerging trends include broader adoption of high-pH stable superficially porous phases for diverse basic compounds, integration with high-resolution mass spectrometry, and exploration of alternative buffer systems for extended column lifetime. Continued particle engineering may further enhance selectivity and robustness for pharmaceutical and environmental analyses.

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