Low and High pH Stability of an Agilent Poroshell HPH C18

Importance of the Topic

Effective RPLC column performance heavily depends on chemical robustness when operating under extreme mobile phase conditions. Expanding the operational pH range enables improved chromatographic selectivity and greater method development flexibility.

Objectives and Study Overview

This study aimed to evaluate the lifetime and selectivity stability of an Agilent Poroshell HPH C18 column under low and high pH conditions using gradient elution with acetonitrile. Two mobile phase regimes were compared:

• 0.1% trifluoroacetic acid (TFA) at pH ~2
• 10 mM ammonium bicarbonate buffer at pH 10

Methodology and Used Instrumentation

A series of 2,000 sequential injections of a mixed analyte sample was performed on an Agilent 1290 Infinity system. Key instrumentation and operating parameters included:

• Agilent 1290 Infinity Binary Pump (up to 1200 bar) with PEEK seals
• Thermostatted Column Compartment at 25 °C
• High-Performance Autosampler with PEEK rotor seal
• Diode Array Detector at 254 nm, 80 Hz, 10 mm path length
• Poroshell HPH C18 column, 2.1 × 50 mm, 4 µm

Sample mixtures comprised acidic, basic, and neutral compounds at 1 mg/mL in 50:50 water/acetonitrile. Gradient elution ranged from 5% to 95% acetonitrile over 5 minutes at 0.4 mL/min.

Main Results and Discussion

Low pH Stability:

• After 2,000 injections with 0.1% TFA, retention times and peak shapes for all analytes remained constant.
• The column delivered consistent performance over a ten-day period consuming approximately 5 L of each mobile phase.

High pH Stability:

• Using 10 mM ammonium bicarbonate at pH 10, retention times were stable over 2,000 injections for all compounds except minor drift in nortriptyline.
• Elution order shifted significantly compared to low pH, highlighting tunable selectivity.

These findings indicate that Poroshell HPH C18, featuring organically modified superficially porous particles, resists silica dissolution and maintains bonded phase integrity under both acidic and basic conditions.

Benefits and Practical Applications

• Extended column lifetime under extreme pH enhances laboratory throughput and reduces operating costs.
• Selectable elution profiles at low or high pH broaden method development options for complex mixtures.
• Compatibility with volatile buffers supports mass spectrometry detection without damaging the column.

Future Trends and Applications

Advances in particle engineering and bonding chemistries will further expand the pH stability window of RPLC columns. Emerging areas include:

• Hybrid particle supports combining core-shell design with organic modification.
• Novel buffer systems offering stronger pH control with minimal column wear.
• Integration with high-throughput and miniaturized platforms for pharmaceutical and biopharmaceutical analysis.

Conclusion

The Agilent Poroshell HPH C18 column demonstrates exceptional stability and consistent selectivity in both strongly acidic and alkaline mobile phases. This versatility enables more robust method development and extends column service life across diverse analytical applications.

References

1. J. J. Kirkland et al., J. Chromatogr. A 762 (1997) 97–112.
2. J. J. Kirkland et al., J. Chromatogr. A 691 (1995) 3–19.
3. J. J. Kirkland et al., Anal. Chem. 70 (1998) 4344–4352.
4. C. Ye et al., J. Pharmaceut. Biomed. 50 (2009) 426–431.
5. H. A. Claessens et al., J. Chromatogr. A 728 (1996) 259–270.
6. W. J. Long, Agilent Technologies Publication 5991-5022EN (2014).