Sample Preparation Method for Determination of Mycophenolic Acid in Plasma Using ISOLUTE® SLE+

Significance of the Topic

Mycophenolic acid is a key immunosuppressive metabolite monitored to guide dosing in organ transplant patients. Reliable quantitation in plasma ensures therapeutic efficacy while minimizing rejection risks.

Objectives and Overview

The presented study develops and validates a sample preparation workflow using ISOLUTE SLE+ for extraction of mycophenolic acid from plasma. The method is compatible with both UV detection and LC–MS/MS, offering a streamlined alternative to traditional liquid–liquid extraction.

Methodology and Sample Preparation

The procedure involves:

• Spiking 200 µL plasma with indomethacin internal standard and 2% formic acid.
• Loading the acidified sample onto a 400 µL ISOLUTE SLE+ column.
• Eluting analytes twice with 900 µL methyl tert-butyl ether under gravity or gentle pressure.
• Evaporating the organic extract under nitrogen and reconstituting in water:methanol (1:1, 2 mL).
• Optional concentration or dilution steps tailored for UV or LC–MS/MS analysis.

Used Instrumentation

The analytical setup comprised:

• UHPLC: Shimadzu Nexera LC-30AD with ACQUITY UPLC BEH C18 (2.1×50 mm, 1.7 µm).
• Mobile phases: 0.1% formic acid (A) and acetonitrile (B), gradient elution at 0.4 mL/min.
• MS detection: Shimadzu LCMS-8060 in positive ESI mode with SRM transitions m/z 321→207 for mycophenolic acid and m/z 358→139 for indomethacin.

Main Results and Discussion

Calibration in SRM mode was linear from 0.1 to 200 ng/mL (r2≥0.999), covering the therapeutic window (0.5–20 µg/mL). Recovery tests at 0.5, 5.0, and 20 µg/mL yielded >98% with negligible matrix effects. Acidification to 2% formic acid markedly improved extraction efficiency to ~101%. Appropriate sample volumes ensured reproducible retention on the diatomaceous earth bed.

Benefits and Practical Applications

The ISOLUTE SLE+ method offers high analyte recovery, reduced emulsions, and minimal matrix interference, enhancing throughput and reliability in therapeutic drug monitoring laboratories. It is adaptable for both UV assays and sensitive LC–MS/MS quantitation.

Future Trends and Opportunities

Opportunities include integrating SLE workflows into automated platforms, extending the approach to other acidic drugs, exploring greener solvents, and coupling with high-resolution mass spectrometry for expanded bioanalytical applications.

Conclusion

The described SLE-based sample preparation delivers a robust, high-throughput solution for accurate determination of mycophenolic acid in plasma, supporting precise therapeutic management in transplant medicine.