LC/MS/MS Separation of Cholesterol and Related Sterols in Plasma on an Agilent InfinityLab Poroshell 120 EC‑C18 Column

Significance of the Topic

Cholesterol and structurally related sterols play key roles in human physiology and pathology. Accurate quantitation of these compounds and their metabolites in plasma supports clinical research into lipid metabolism, cardiovascular risk assessment, and biomarker discovery. High chromatographic resolution and sensitive detection are critical for distinguishing isobaric sterols without chemical derivatization.

Study Objectives and Overview

This study evaluates the performance of Agilent InfinityLab Poroshell 120 EC-C18 and SB-C18 columns for the separation of 12 sterols in plasma by LC/MS/MS with atmospheric pressure chemical ionization (APCI). It compares column selectivity and resolution at different particle sizes (2.7 μm vs. 1.9 μm) and demonstrates method sensitivity, reproducibility, and applicability to spiked plasma samples.

Methodology and Instrumentation

• Sample Preparation: Sterol standards and human plasma extracts spiked at 10–100 ppb levels.
• Chromatography: Agilent InfinityLab Poroshell 120 EC-C18 (3.0 × 100 mm, 1.9 μm) operated at 15 °C, flow rate 0.60 mL/min, injection volume 20 μL. Gradient elution from 92–100% methanol over 16 minutes, 2-minute post time.
• Column Comparison: EC-C18 vs. SB-C18 phases, both 3.0 × 100 mm, 2.7 μm, and EC-C18 in 1.9 μm format to enhance resolution of positional isomers.
• Detection: Agilent 6460A triple quadrupole LC/MS in positive APCI mode. Optimized parameters include capillary voltage 2000 V, drying gas at 325 °C/4 L/min, vaporizer 350 °C, nebulizer pressure 30 psi, and specific MRM transitions for each sterol.

Instrumentation

• Agilent 1290 Infinity II high-speed pump, multisampler, and column thermostat.
• Agilent InfinityLab Poroshell 120 EC-C18 and SB-C18 columns.
• Agilent 6460 triple quadrupole mass spectrometer with APCI source.
• Agilent MassHunter LC/MS data acquisition and qualitative analysis software.

Key Results and Discussion

• The EC-C18 phase exhibited superior selectivity and baseline resolution for critical isobaric pairs such as cholesterol and lathosterol, which coelute on SB-C18.
• Reducing particle size to 1.9 μm further improved peak capacity and resolved challenging isomers under identical chromatographic conditions.
• Optimized APCI capillary voltage of 2000 V prevented signal suppression and ensured stable MRM response at trace levels (10 ppb).
• Method reproducibility was validated by overlaying ten consecutive injections of 100 ppb standards, showing consistent retention times and peak areas.
• Spiked plasma analysis demonstrated effective quantitation of low-abundance sterols despite a 2,000:1 cholesterol to lathosterol concentration ratio.

Benefits and Practical Applications

• Enables highly sensitive detection of diverse sterols and metabolites in complex biological matrices without derivatization.
• Provides baseline separation of isobaric compounds, critical for clinical and pharmaceutical research.
• Robust and reproducible platform suitable for routine QA/QC and biomarker studies in healthcare and biotechnology labs.

Future Trends and Applications

• Combining Poroshell technology with high-resolution MS to further distinguish structural isomers and oxidized derivatives.
• Expanding the sterol panel to include novel biomarkers for metabolic disorders and neurodegenerative diseases.
• Implementing automated sample preparation and microflow LC/MS workflows for high-throughput clinical screening.

Conclusion

The optimized LC/MS/MS method using a 1.9 μm Agilent InfinityLab Poroshell 120 EC-C18 column and APCI detection on the 6460A triple quadrupole system delivers exceptional resolution and sensitivity for sterol analysis in plasma. It resolves critical isobaric sterol pairs and achieves reproducible quantitation, making it a powerful tool for clinical research and routine lipid profiling.

References

1. McDonald JG, et al. A comprehensive method for extraction and quantitative analysis of sterols and secosteroids from human plasma. Journal of Lipid Research. 2012;53(7):1399–1409.