SOLAμ SPE – achieve highly reproducible bioanalytical results with reduced sample volumes

Significance of the topic

In bioanalytical and clinical research workflows sample volume is often limited by ethical or practical constraints. Conventional SPE methods rely on large elution volumes and subsequent evaporation steps that can lead to analyte loss, especially for small volatile compounds and larger biomolecules. The SOLAµ microelution SPE format addresses these challenges by enabling highly reproducible extractions with minimal sample consumption and eliminating drying steps.

Objectives and study overview

The main goal of this application study was to demonstrate the performance of Thermo Scientific SOLAµ SPE for reducing sample volume by an order of magnitude while maintaining sensitivity and reproducibility. The method was illustrated using niflumic acid in diluted human plasma, with chromatographic separation on an Accucore RP-MS column and quantitative detection by a TSQ Vantage triple stage quadrupole mass spectrometer.

Methodology and used instrumentation

Sample preparation and SPE procedure:

• Human plasma diluted 1:1 with 4% phosphoric acid, 25 µL loaded onto SOLAµ WAX 96-well plate
• Plate conditioning: 200 µL methanol, followed by 200 µL water
• Sample loading at 0.5 mL/min, wash with 200 µL ammonium acetate buffer (pH 4) and 200 µL methanol
• Microelution: two aliquots of 12.5 µL methanol with 2% ammonia, direct injection of the combined 25 µL eluent

LC-MS/MS conditions:

• LC: Thermo Scientific Dionex UltiMate 3000 RSLC, Accucore RP-MS 50×2.1 mm, 2.6 µm column, gradient from 70:30 to 10:90 (A:B) in 2 min, flow rate 750 µL/min, run time 4 min
• MS: Thermo Scientific TSQ Vantage, HESI positive mode, MRM transitions m/z 283→265 for niflumic acid and 288.8→271.1 for the d5 internal standard

Main results and discussion

The method achieved a linear dynamic range of 1–1000 ng/mL (R² = 0.995), with the limit of quantitation at 1 ng/mL displaying adequate signal-to-noise. Accuracy across calibration standards and QC levels ranged within ±11% and precision (n = 18) was better than 8% RSD. Recovery exceeded 98% and matrix effects were below 5% at low and high QC concentrations. Comparison between conventional 2 mg SPE and 0.2 mg microelution SPE with ten-fold reduced sample volume showed equivalent assay performance.

Contributions and practical applications

• Reduced sample consumption by ten-fold without sacrificing sensitivity
• Elimination of evaporation and reconstitution steps, lowering analyte loss
• High reproducibility and robustness at low elution volumes
• Improved stability of labile analytes due to minimized adsorption
• Suitable for studies with limited biological samples or costly analyses

Future trends and applications

As microelution SPE formats become more widespread, potential developments include integration with automated platforms, expansion to other stationary phase chemistries for diverse analytes, and coupling with miniaturized chromatographic and mass spectrometric systems. This approach supports high-throughput workflows in clinical diagnostics, pharmacokinetics, and environmental monitoring where sample volume and throughput are critical.

Conclusion

Thermo Scientific SOLAµ SPE enables highly reproducible bioanalytical extractions with minimal sample volumes, delivering linearity, accuracy, precision, and recovery comparable to conventional SPE methods while avoiding drying steps. The microelution format is well suited for applications constrained by sample availability and for improving assay throughput and integrity.