Development of a High Sensitivity SPE-LC-MS/MS Assay for the Quantification of Glucagon in Human Plasma Using the ionKey/MS System

Significance of the Topic

Quantifying glucagon, a 29-amino-acid polypeptide hormone, is vital for understanding and managing conditions such as diabetes and severe hypoglycemia. High-sensitivity measurement in human plasma supports both clinical pharmacokinetic studies and research into endogenous hormone dynamics.

Objectives and Study Overview

The main goals of this work were to develop a robust SPE-LC-MS/MS assay capable of detecting glucagon at low pg/mL levels in human plasma and to leverage the ionKey/MS System to maximize sensitivity while minimizing solvent and sample consumption. The study evaluated sample preparation, chromatographic separation, and mass spectrometric detection to achieve a limit of detection (LOD) of 12.5 pg/mL and a linear dynamic range up to 1,000 pg/mL.

Methodology

Sample Preparation

• 200 µL human plasma treated with protease inhibitors and spiked with glucagon standards.
• Acidification (0.5% acetic acid) and dilution (5% ammonium hydroxide) to improve peptide solubility and disrupt protein binding.
• Mixed-mode SPE using Oasis® MAX 96-well µElution plates for selective extraction and concentration, with optimized wash and elution steps to minimize nonspecific binding and matrix effects.

Chromatography

• Trap-and-back-flush configuration on an ACQUITY UPLC M-Class system.
• iKey Peptide BEH C18 separation device (150 µm × 100 mm, 1.7 µm) at 2.0 µL/min and 75 °C, using a 15–45% acetonitrile gradient over 6 minutes.

Mass Spectrometry

• Xevo TQ-S triple quadrupole operated in positive ESI mode.
• MRM transitions selected for specificity: two high-m/z b-ion fragments and one ammonia-loss transition.
• Optimized cone voltages and collision energies to balance sensitivity and selectivity.

Used Instrumentation

• ionKey/MS System with ionKey Source
• ACQUITY UPLC M-Class System
• iKey Peptide BEH C18 Separation Device
• Xevo TQ-S Mass Spectrometer
• Oasis® MAX 96-well µElution Plate
• MassLynx® 4.1 and TargetLynx™ Software

Main Results and Discussion

The optimized assay achieved an LOD of 12.5 pg/mL and linearity (r2 > 0.99) from 12.5 to 1,000 pg/mL using 200 µL plasma. The ionKey/MS microflow approach provided a 10-fold sensitivity gain and 4-fold higher signal-to-noise compared to a conventional 2.1 mm I.D. system, with 5-fold reduction in injection volume. Mixed-mode SPE drastically reduced matrix effects (<15%) versus reversed-phase extraction. Selective b-ion transitions offered lower background than the more intense ammonia-loss transition, ensuring both sensitivity and specificity in complex plasma samples.

Benefits and Practical Applications

• Low sample and solvent requirements reduce cost and waste.
• High throughput compatibility with 96-well µElution format and potential automation.
• Sensitive detection of endogenous and pharmacological glucagon levels supports PK/PD studies and clinical diagnostics.
• Potential to multiplex large peptide assays using LC-MS/MS.

Future Trends and Opportunities

Advances in microfluidic LC-MS platforms will further enhance sensitivity for large biomolecules. Integration with automated sample processing and high-resolution MS may enable broader peptide panels and real-time biomarker monitoring. Continued refinement of mixed-mode sorbents and multidimensional chromatography can improve selectivity for challenging analytes.

Conclusion

This work demonstrates a highly sensitive, selective SPE-LC-MS/MS assay for glucagon quantification in human plasma. Utilizing the ionKey/MS System and optimized sample preparation, the method achieves low pg/mL detection with minimal matrix interference and efficient workflow.

Reference

1. Eli Lilly and Company. Glucagon for Injection United States Package Insert.
2. R&D Systems, Inc. Quantikine® ELISA Glucagon Immunoassay, DGCG0.
3. EMD Millipore. Glucagon Chemiluminescent ELISA Kit, EZGLU-30K.
4. Millipore. Glucagon RIA Kit, GL-32K.
5. ALPCO Diagnostics. Glucagon RIA, Plasma Quantification.
6. Lapko V et al. LC-MS/MS glucagon quantification. EBF Symposium 2010.
7. Lapko VN et al. Bioanalysis 2013;5(23):large peptide quantification.
8. Gerich JE et al. J Clin Invest. 1976 Apr;57(4):875–84.