A New Kind of Amide free Polymer for Simplified, Improved SPE

Importance of the Topic

A robust and selective sample cleanup procedure is essential for reliable bioanalysis by liquid chromatography–mass spectrometry (LC–MS). Matrix components such as proteins and phospholipids can suppress ionization, reduce sensitivity and compromise quantitation. Innovations in solid-phase extraction (SPE) sorbent chemistry aim to improve analyte recovery and reduce matrix effects in complex biological samples.

Objectives and Study Overview

This study introduces and evaluates a new amide-free, water-wettable polymeric SPE sorbent (Bond Elut Plexa) designed to exclude proteins and lipophilic interferents via a hydrophilic surface. The aims are:

• Compare Plexa performance against a conventional polymeric SPE sorbent for recovery and cleanliness.
• Develop and validate quantitative LC–MS methods for metoprolol and propranolol in human plasma.
• Assess matrix removal efficiency through ion suppression experiments.

Methodology and Instrumentation

Sample Preparation and SPE Workflow:

• Human plasma (100 µL) was diluted 1:3 with aqueous buffer.
• SPE cartridges conditioned with methanol and water.
• Samples loaded, washed with 95:5 water:methanol to eliminate interferences.
• Analytes eluted with methanol, evaporated to dryness and reconstituted in mobile phase.

Chromatography and Detection:

• Column: Agilent Pursuit C18, 2.0 × 50 mm, 3 µm particle size.
• Mobile phase A: 0.1% formic acid aqueous; B: methanol; gradient from 80:20 (A:B) to 20:80 in 3 min; total run time 4.5 min.
• Injection volume: 10 µL.
• Mass spectrometry: Electrospray ionization, argon collision gas; MRM transitions m/z 268.2 → 116.0 for metoprolol and 260.0 → 116.0 for propranolol.

Main Results and Discussion

Recovery and Linearity:

• Plexa achieved absolute recoveries >90% across a calibration range of 1–1,000 ng/mL for both analytes.
• Calibration curves were linear (R2 ≥ 0.9995), with precision ≤ 6% RSD and accuracy within ±10%.

Matrix Cleanliness and Ion Suppression:

• Plexa extracts showed minimal protein co-elution compared to the conventional polymer, resulting in substantially lower ion suppression.
• Metoprolol experienced negligible signal loss, whereas propranolol exhibited moderate suppression with the conventional sorbent but was protected by Plexa’s hydrophilic barrier.

Comparative Performance:

• Conventional polymer recoveries ranged from 53–81%, while Plexa recoveries were 81–98%.
• Ion suppression studies confirmed that signal loss originates from residual matrix components in the injection rather than extraction inefficiency.

Benefits and Practical Applications

• Simplified SPE workflow with a single sorbent chemistry for diverse drugs, reducing method development time.
• Enhanced sensitivity and reproducibility in LC–MS bioanalysis by effective protein and lipid exclusion.
• Compatibility with high-throughput workflows and automation formats (96-well plates).

Future Trends and Applications

The development of tailored polymer chemistries with integrated polarity gradients may further optimize analyte retention while excluding matrix components. Future directions include:

• Adaptation to other biological matrices (urine, tissue homogenates).
• Integration with ultra-fast LC–MS and microflow systems.
• Expansion of sorbent formats for on-line SPE and automated workstations.

Conclusion

The amide-free, water-wettable polymer (Bond Elut Plexa) delivers superior analyte recovery, excellent linearity and markedly reduced matrix effects compared to conventional polymeric SPE. Its unique hydrophilic surface chemistry simplifies bioanalytical cleanup and enhances LC–MS sensitivity and robustness.

Reference

• Agilent Technologies, Inc. Application Note 5990-8756EN, Bond Elut Plexa: A new amide-free SPE sorbent for simplified, improved bioanalysis. Lake Forest, CA; July 2011.