Reducing Sample Volume and Increasing Sensitivity for the Quantification of Human Insulin and 5 Analogs in Human Plasma Using ionKey/MS

Importance of the topic

Recombinant human insulin and its analogs are cornerstone biotherapeutics for diabetes management. Accurate quantification of these peptide drugs in plasma at low concentrations is critical for pharmacokinetic studies, pediatric dosing strategies and biosimilar development. Conventional ligand binding assays offer high sensitivity but suffer from matrix effects, variability and limited multiplexing. Advances in LC-MS/MS with microflow and integrated sources can address these challenges.

Objectives and Study Overview

The study aimed to transfer a high-sensitivity insulin assay to the integrated microfluidic ionKey/MS System and to reduce plasma volume requirements while enhancing detection limits. Key goals included:

• Reducing sample volume from 250 µL to 100 µL or 50 µL
• Decreasing injection volume from 30 µL to 10 µL
• Improving lower limit of quantification (LLOQ) to 25–50 pg/mL
• Validating performance across six insulin analogs

Methodology

Sample preparation combined protein precipitation with mixed-mode solid-phase extraction using a 96-well μElution plate, enabling analyte concentration and minimization of peptide losses. A trap/back-elute strategy accommodated injections of high-organic eluates and focused analyte bands prior to microflow separation. Chromatographic separation employed sub-2 µm C18 particles in a microfluidic channel under 2.5 µL/min flow at 75 °C.

Instrumentation Used

• Waters ionKey/MS System with 150 µm iKey Separation Device
• ACQUITY UPLC M-Class system with trap valve manager
• Oasis MAX 96-well µElution plates
• Xevo TQ-S triple quadrupole mass spectrometer
• MassLynx 4.1 and TargetLynx data processing software

Main Results and Discussion

The ionKey/MS System delivered a cumulative ~15-fold sensitivity gain over traditional 2.1 mm assays by combining a 2.5-fold sample reduction, 3-fold lower injection volume and at least 2-fold improved LLOQ. Standard curves for six insulin variants spanning 25–10 000 pg/mL showed excellent linearity (R2>0.99) using 1/x weighting. Quality controls at four levels achieved mean accuracies of 94–109% and precision (%CV) of 3.4–8.8%, satisfying FDA bioanalytical criteria. Chromatographic peak widths were 3–4.2 seconds, and closely related species such as human insulin and lispro achieved baseline resolution under microflow conditions.

Benefits and Practical Applications

• Substantial reduction in plasma volume and solvent consumption (≈60-fold)
• High specificity from mixed-mode SPE and efficient microflow chromatography
• Improved throughput with 13.5-minute run times and 96-well format
• Multiplexed quantification of six insulin forms in a single injection
• Ideal platform for PK studies, pediatric dosing and biosimilar comparison

Future Trends and Opportunities

Microflow LC-MS with integrated sources is poised to expand in peptide bioanalysis, enabling sub-50 pg/mL quantification with minimal sample volumes. Further miniaturization and automation may facilitate routine therapeutic monitoring, immunogenicity studies and rapid biosimilar screening. Integration with ion mobility or high-resolution MS could enhance specificity and enable comprehensive metabolite profiling.

Conclusion

The ionKey/MS System method offers a robust, sensitive and sample-sparing platform for simultaneous quantification of human insulin and its analogs in plasma. By reducing sample consumption and solvent usage while achieving LLOQs as low as 25 pg/mL, it outperforms conventional LC-MS/MS workflows and meets stringent regulatory validation criteria.

References

1. Chambers EE, Fountain KJ. Multidimensional LC-MS/MS Enables Simultaneous Quantification of Intact Human Insulin and 5 Recombinant Analogs in Human Plasma. Anal Chem 2014;86(1):694–702.
2. Chambers EE et al. Development of a Fast Method for Direct Analysis of Intact Synthetic Insulins in Human Plasma: The Large Peptide Challenge. Bioanalysis 2012;5(1):65–81.
3. FDA. Guidance for Industry Bioanalytical Method Validation. Rockville, MD; 2001.
4. Bansal S, DeStafano A. Key Elements of Bioanalytical Method Validation for Small Molecules. AAPS J 2007;9(1):E109–E114.