Utilizing the Mixed-Mode Atlantis PREMIER BEH C18 AX Column for the Analysis of Cationic Surfactants Under Reversed-Phase Conditions

Importance of the Topic

Cationic surfactants, particularly quaternary ammonium compounds (QACs), play critical roles in cosmetic, pharmaceutical, and agricultural applications due to their antimicrobial and antistatic properties. Their amphiphilic nature poses analytical challenges in reversed-phase liquid chromatography, often resulting in poor peak shapes and retention issues. Developing robust methods for reliable quantitation of these compounds is essential for quality control, regulatory compliance, and environmental monitoring.

Objectives and Study Overview

This study demonstrates a streamlined reversed-phase approach for separating a mixture of three cationic surfactants—1-dodecylpyridinium chloride, benzyldimethyldodecyl ammonium chloride, and benzyldimethylhexadecyl ammonium chloride—using the mixed-mode Atlantis PREMIER BEH C18 AX column. The goal was to achieve baseline resolution, satisfactory retention, and sharp peak shapes within a short runtime without derivatization or ion-pair reagents.

Methodology and Instrumentation

The separation exploited mixed hydrophobic and anion-exchange interactions on a hybrid organic/inorganic particle stationary phase packed into MaxPeak High Performance Surfaces column hardware. Key method parameters included:

• Column: Atlantis PREMIER BEH C18 AX, 2.1 × 100 mm, 1.7 µm
• Mobile phase A: 0.1 mM ammonium formate, pH 4.0
• Mobile phase B: acetonitrile; linear gradient from 25 % to 85 % B over 8.34 min
• Flow rate: 0.4 mL/min; column temperature: 30 °C; injection volume: 0.3 µL

Instrumentation:

• UPLC system: ACQUITY UPLC H-Class PLUS
• Detector: Evaporative light scattering detector
• Data system: Empower 3 chromatography data software

Results and Discussion

The three QACs were baseline resolved within a 10 min run. Retention factors (k) were 3.8, 5.1, and 7.8 for 1-dodecylpyridinium chloride, benzyldimethyldodecyl ammonium chloride, and benzyldimethylhexadecyl ammonium chloride, respectively. Tailing factors remained below 1.4, indicating excellent peak symmetry. These results confirm effective mixed-mode retention and minimal peak distortion under reversed-phase conditions.

• 1-Dodecylpyridinium chloride: t_R = 3.59 min, k = 3.8, tailing = 1.16
• Benzyldimethyldodecyl ammonium chloride: t_R = 4.56 min, k = 5.1, tailing = 1.33
• Benzyldimethylhexadecyl ammonium chloride: t_R = 6.58 min, k = 7.8, tailing = 1.39

Practical Benefits and Applications

This method eliminates the need for time-consuming derivatization or ion-pair additives, providing fast equilibration, high reproducibility, and broad pH stability. It is suitable for routine quality control in formulation development, contamination screening, and environmental sample analysis.

Future Trends and Potential Applications

Potential developments include:

• Extension to broader classes of ionic surfactants and polar analytes
• Integration with mass spectrometric detection for enhanced sensitivity
• Automation of sample preparation and high-throughput screening workflows
• Application in environmental monitoring and biodegradation studies

Conclusion

The mixed-mode Atlantis PREMIER BEH C18 AX column delivers a robust, efficient reversed-phase solution for challenging cationic surfactants. Its combined hydrophobic and anion-exchange characteristics ensure rapid, high-resolution separations without auxiliary reagents, streamlining analytical workflows in diverse industrial and research settings.

References

1. Olkowska E, Ruman M, Kowalska A, Polkowska Z. Determination of surfactants in environmental samples; Part 1 cationic compounds. Ecol. Chem. Eng. S. 2013;20:331–342.
2. Zhang K, Liu X. Mixed-mode chromatography in pharmaceutical and biopharmaceutical applications. J. Pharm. Biomed. Anal. 2016;130:19–34.
3. Walter TH, Alden B, Boissel C, Field J, Lawrence N, Osterman D, Patel A. A new mixed-mode reversed-phase/anion-exchange stationary phase based on hybrid particles. Waters Corp. Application Note;2020.