Two Dimensional HPLC using a High pH Stable Superficially Porous Column

Importance of the topic

The analysis of trace impurities in complex mixtures is a cornerstone of pharmaceutical, environmental, and chemical process development. Two-dimensional liquid chromatography (2D-LC) extends conventional HPLC by combining orthogonal separation mechanisms to resolve co-eluting analytes. High-pH-stable superficially porous columns open new possibilities for orthogonality and selectivity by enabling robust separations under both low and elevated pH conditions.

Goals and overview of the study

This work evaluates a novel Agilent Poroshell High-pH (HPH) superficially porous C18 stationary phase in a heart-cutting 2D-LC configuration using the Agilent 1290 Infinity system. The study aims to:

• Demonstrate column stability at pH 10 over extended usage.
• Assess pH-driven orthogonality between high-pH and low-pH gradients.
• Illustrate improved impurity resolution for structurally related compounds.

Methodology and instrumentation

A heart-cutting 2D-LC approach was employed. Samples were first separated at high pH on a Poroshell HPH C18 column, with targeted peak fractions transferred via a loop and switching valve to a second-dimension low-pH gradient. Key instrumentation modules on the Agilent 1290 Infinity 2D-LC included:

• G1311A Quaternary Pump (400 bar) and G4220A 1290 Infinity Pump
• G1316C Thermostatted Column Compartment with 2-position/4-port valve
• G1329A Auto-sampler for reproducible injections
• G1315C and G4212A Diode Array Detectors for 1st and 2nd dimensions
• OpenLab control software with dedicated 2D-LC interface

Main results and discussion

Column stability tests confirmed that the Poroshell HPH stationary phase retained performance after 40 000 column volumes at pH 10. Correlation plots of retention times between pH 3 vs. pH 4.8 on conventional EC-C18 showed high R² values (>0.94), whereas comparisons of pH 3 vs. pH 10 on HPH C18 yielded R² ≈ 0.46 (methanol) and R² ≈ 0.35 (acetonitrile), indicating strong orthogonality. Heart-cut experiments separated a minor impurity peak from a major component, uncovering a third compound not resolved in 1D. Applications to amphetamine mixture and acidic, basic, and neutral drugs demonstrated enhanced retention and peak shape at high pH using ammonium bicarbonate buffer, improving selectivity and sensitivity.

Benefits and practical applications

• Expanded pH range (2–10) maintains column lifetime under harsh buffer conditions.
• Orthogonal selectivity from pH modulation facilitates method development without changing stationary phase.
• Heart-cutting workflow integrates seamlessly in standard 2D-LC setups, requiring no additional software.
• Improved peak shape for basic analytes at high pH enhances quantitation and resolution of trace impurities.

Future trends and opportunities

As multidimensional chromatography continues to evolve, high-pH-stable superficially porous columns will enable more robust and automated workflows. Emerging trends include:

• Integration of high-throughput 2D-LC in pharmaceutical QC laboratories.
• Development of new buffer systems and mobile phases tailored for high-pH separations.
• Coupling 2D-LC with mass spectrometry for enhanced characterization of impurities.
• Software-driven optimization of cut timing and gradient parameters to maximize orthogonality.

Conclusion

The adoption of Poroshell HPH superficially porous columns in 2D-LC heart-cutting workflows delivers significant gains in orthogonal separation and impurity profiling. High-pH stability broadens method development flexibility, while streamlined instrumentation and software support enable rapid optimization of complex sample analyses.

References

1. Long W, Wang X, Chen W, Link J, Buckenmaier S. Two Dimensional HPLC using a High pH Stable Superficially Porous Column. HPLC 2014, New Orleans, USA.