Reduced Ion-suppression in Bioanalysis by Liquid Chromatography Mass Spectrometry Applying Specially Treated Solid Phase Extraction

Significance of the Topic

A major hurdle in LC-MS bioanalysis is ion suppression caused by endogenous compounds co-eluting with target analytes. This phenomenon compromises sensitivity, quantitative accuracy, reproducibility and increases instrument maintenance. Developing sample preparation techniques that minimize non-specific binding of matrix components is critical for reliable bioanalysis.

Objectives and Study Overview

This study evaluates specially hydroxylated solid-phase extraction (SPE) sorbents—Agilent Bond Elut Plexa (non-polar interaction) and Bond Elut Plexa PCX (cation exchange)—for their ability to reduce ion suppression and improve assay performance for basic drug compounds in human plasma.

Methodology and Instrumentation

Sample Preparation:

• Dilute human plasma 1:3 with 2% aqueous ammonia (Plexa) or 2% H₃PO₄ (PCX).
• Condition sorbent with MeOH and water.
• Load sample, wash with low-strength organic and aqueous phases.
• Elute analytes with MeOH:ACN or ammonia in organic solvent.

Post-column Infusion Experiment:

• Blank plasma injections with continuous infusion of analytes to map ion suppression zones.

LC-MS Conditions:

• LC: Agilent 1260 Infinity with Poroshell 120 EC-C18 column (2.1×50 mm, 2.7 µm).
• Mobile phases: A = 0.1% formic acid in water; B = 0.1% formic acid in methanol; gradient 10→90% B in 4 min.
• MS: Agilent 6460 triple quadrupole, ESI+ JetStream, gas temp 350°C, sheath gas temp 400°C, capillary 4000 V.

Results and Discussion

Comparison to Competitor SPE:

• LOD ranged from 0.01 to 0.05 ng/mL; LOQ from 0.05 to 0.5 ng/mL across analytes.
• Recovery 90–120% with RSD ≤3.9% (n=6).
• Calibration curves linear with R² ≥0.995.
• Lipid monitoring via m/z 184→184 transition showed significantly lower lipid signal for Plexa and PCX than competitors, confirming reduced matrix interferences.
• Bond Elut Plexa PCX delivered highest MS area for propranolol (~9708), outperforming Competitor A (8112) and B (6974).

Benefits and Practical Applications

Applying hydroxylated SPE sorbents yields:

• Enhanced sensitivity and lower detection limits.
• Improved reproducibility and accuracy in quantitation of basic drugs.
• Reduced ion suppression and instrument maintenance.
• Straightforward integration into routine bioanalytical workflows for QC, PK studies and therapeutic drug monitoring.

Future Trends and Opportunities

Advancements may include:

• High-throughput 96-well SPE formats for large sample batches.
• Automation and integration with online SPE-LC-MS platforms.
• Custom sorbent chemistries for broader metabolomics and lipidomics applications.
• Expansion to additional biological matrices (urine, tissue homogenates).

Conclusion

Hydroxylated Agilent Bond Elut Plexa and Plexa PCX SPE sorbents significantly reduce ion suppression in LC-MS bioanalysis of basic drug compounds. They deliver excellent sensitivity, linearity and recovery, outperforming conventional SPE materials and simplifying method robustness.

Reference

• Agilent application note: 5990-8388EN
• Agilent application note: 5990-8400EN