Mixed-Mode, Weak Anion-Exchange, Solid-Phase Extraction Method for the Extraction of Niflumic Acid from Human Plasma

Significance of the Topic

Accurate quantification of strong acidic drugs such as niflumic acid in human plasma is essential for pharmacokinetic, clinical and bioanalytical studies. Mixed-mode solid-phase extraction (SPE) methods combine reversed-phase and ion-exchange interactions to improve matrix cleanup, enhance reproducibility and reduce matrix effects compared to traditional precipitation or single-mode SPE procedures.

Objectives and Study Overview

This application note evaluates a workflow for the extraction and quantification of niflumic acid from human plasma using Thermo Scientific SOLA WAX weak anion-exchange SPE cartridges, coupled with an Accucore RP-MS HPLC column and TSQ Vantage MS/MS detection. The study aims to demonstrate linearity, recovery, precision and matrix effect improvements over conventional approaches.

Methodology and Instrumentation

• Sample Preparation
  100 µL plasma diluted 1:1 with 2% phosphoric acid.
• SPE Procedure
  – Cartridge: SOLA WAX 10 mg, 1 mL
  – Conditioning: 500 µL MeOH, then 500 µL water
  – Loading: sample at 0.5 mL/min
  – Washing: 500 µL 25 mM ammonium acetate buffer, then 500 µL MeOH
  – Elution: 500 µL MeOH with 2% NH4OH at 0.5 mL/min
  – Dry under N2, reconstitute in 100 µL 2% formic acid in water
• LC-MS/MS Conditions
  – LC system: Dionex UltiMate 3000
  – Column: Accucore RP-MS, 2.6 µm, 50 × 2.1 mm at 30 °C, flow 750 µL/min, 3 min total run
  – Mobile phases: A=water+0.1% FA, B=MeOH+0.1% FA; gradient from 60:40 to 0:100 and back
  – Injection: 2 µL full-loop, wash solvents water and 45:45:10 IPA/ACN/acetone
• MS/MS Parameters
  – Instrument: TSQ Vantage, HESI positive, spray 3000 V
  – Vaporizer 475 °C, capillary 300 °C, sheath gas 50 arb, aux gas 60 arb, collision 1.5 mTorr
  – Q1/Q3 resolution 0.7 FWHM, scan time 0.02 s
  – Transitions: niflumic acid 283→265 (CE 21 V), niflumic acid D3 288→270.1 (CE 22 V)
• Data Analysis: LCQUAN software v2.6

Main Results and Discussion

Linearity was established over 1–1000 ng/mL with R2 = 0.999. At 3 ng/mL, average recovery was 86.6%. Precision for 20 replicates at 3 ng/mL yielded 6.3% CV (4.3% CV using internal standard), outperforming reported protein-precipitation CVs (~13.5%). Matrix effects were limited to 7.9%, compared to ~94% suppression in simple precipitation methods. Chromatographic peaks for niflumic acid at 3 ng/mL eluted in under 3 min with sharp, symmetric profiles.

Benefits and Practical Applications

• Robust recovery and low variability for acidic analytes in plasma
• Superior matrix cleanup that reduces ion suppression
• Reduced sample and solvent volumes for high-throughput workflows
• Fast analysis time (< 3 min) using standard pressure HPLC
• Improved data confidence in bioanalytical and clinical laboratories

Future Trends and Applications

Advances may include further miniaturization of mixed-mode SPE formats, integration with automated liquid-handling systems, development of greener solvent protocols, and coupling with ultrahigh-performance and high-resolution mass spectrometry for enhanced sensitivity and selectivity in complex sample matrices.

Conclusion

The combined SOLA WAX SPE and Accucore RP-MS LC-MS/MS workflow provides a rapid, reproducible and sensitive assay for niflumic acid in human plasma. High recovery, excellent precision and minimal matrix effects underscore its suitability for demanding bioanalytical applications.

References

1. Kang W. Determination of Talniflumate and Niflumic Acid in Human Plasma by Liquid Chromatography–Tandem Mass Spectrometry. Analytical Science. 2009;2:571–574.