Superior Sample Capacity for Basic Compounds with a Formic Acid Mobile Phase - A comparison of the Agilent InfinityLab Poroshell 120 CS-C18 to traditional C18 columns

Importance of the Topic

The analysis of basic pharmaceutical compounds often suffers from poor peak shape, limited loading capacity, and the need for harsh mobile phase additives. Improved chromatographic performance under simple formic acid conditions enables better quantitation of drug substances and impurities without risking system contamination or signal suppression.

Objectives and Overview

This study compares a charged surface superficially porous C18 column to traditional superficially and totally porous C18 phases. Key aims include evaluation of peak shape, sample loading capacity, and sensitivity for six basic drug compounds using a universal formic acid mobile phase.

Methodology and Instrumentation

An Agilent 1290 Infinity II LC system fitted with an Ultivo triple quadrupole mass spectrometer was used. A binary gradient of water with formic acid and acetonitrile provided weak ionic strength conditions. Columns tested: the InfinityLab Poroshell 120 CS­-C18 (2.1×100 mm, 2.7 µm), three superficially porous traditional C18 phases, and one totally porous C18 phase. Key instrument components included:

• Agilent 1290 Infinity II pump, sampler, column compartment
• Agilent Ultivo LC/TQ with Jet Stream ESI source
• InfinityLab Poroshell 120 CS­-C18 and traditional C18 columns

Main Results and Discussion

Under formic acid conditions, the charged surface column delivered significantly narrower and more symmetric peaks for all six basic analytes compared to the traditional C18. The traditional column required trifluoroacetic acid to approach similar peak shapes, introducing ion suppression and cleaning challenges. Loading capacity tests with amitriptyline revealed that the CS­-C18 phase maintained peak integrity at high on-column loads, whereas traditional phases exhibited marked broadening and tailing. In impurity studies, larger injections on the CS­-C18 enabled detection of low-level impurities without distortion of the main peak.

Benefits and Practical Applications

Key advantages of the charged surface CS­-C18 column include:

• Improved peak symmetry under mild formic acid conditions
• Enhanced sample loading capacity, supporting ultra-trace impurity detection
• Elimination of trifluoroacetic acid, reducing system contamination and ion suppression
• Universal method transferability across LC and LC/MS platforms

Future Trends and Opportunities

Expansion of charged surface phases to a wider range of ionizable analytes could benefit pharmaceutical, proteomic, and metabolomic applications. Integration into high-throughput workflows and further miniaturization may accelerate drug development and quality control. Ongoing phase chemistry innovations will likely deliver even greater selectivity and robustness for challenging basic compounds.

Conclusion

The Agilent InfinityLab Poroshell 120 CS­-C18 column outperforms traditional C18 phases for basic pharmaceutical analysis under a simple formic acid mobile phase. It offers superior peak shape, higher loading capacity, and increased sensitivity for impurity profiling, all while avoiding the drawbacks of trifluoroacetic acid.

Reference

• Gratzfeld-Hugsen A and Naegele E Maximizing Efficiency Using Agilent InfinityLab Poroshell 120 Columns Agilent Technologies application note 5990-5602EN 2016
• Meyer V R Practical High­Performance Liquid Chromatography Fourth Edition Wiley 2004 p 34