Improved SPE for LC-MS Determination of Ractopamine in Porcine and Bovine Liver: The Oasis MCX Method Using Otto SPEcialist

Significance of the Topic

Trace-level monitoring of veterinary drug residues such as ractopamine in animal tissues is critical for food safety and regulatory compliance. Sensitive and selective analytical workflows are needed to detect compounds at parts-per-billion levels, support export requirements, and ensure public health. Automated cleanup strategies further enhance laboratory efficiency and data precision in high-throughput testing environments.

Study Objectives and Overview

This application note evaluates a streamlined sample preparation and cleanup approach for quantifying ractopamine and its glucuronide metabolites in porcine and bovine liver. The study replaces a manual vacuum-based SPE protocol with semi-automated positive pressure processing using an Otto SPEcialist manifold in conjunction with Oasis MCX 96-well plates, prior to UPLC-MS/MS analysis. Key goals include improving recovery, reproducibility, throughput, and reducing cross-contamination risks.

Methodology and Instrumentation

Homogenized liver samples (5 g) undergo triplicate methanolic extractions, combining supernatants and evaporating to near dryness. Samples are enzymatically hydrolyzed with β-glucuronidase before SPE cleanup. Oasis MCX 96-well plates are conditioned with methanol, loaded with extract, washed, and eluted with 5 % ammonium hydroxide in methanol under controlled positive pressure. Eluates are directly transferred to UPLC-MS/MS without filtration.

Used Instrumentation

• Otto SPEcialist positive pressure manifold
• Waters ACQUITY UPLC I-Class PLUS system
• ACQUITY UPLC BEH 1.7 µm, 2.1 × 50 mm column
• Xevo TQ-XS triple quadrupole mass spectrometer
• MassLynx v4.2 data management software

Main Results and Discussion

The Otto SPEcialist workflow achieved quantitative recoveries of ractopamine at 0.1 ng/g with relative standard deviations less than half those of the manual cartridge method. Automated processing delivered an 87 % increase in chromatographic peak area and improved signal-to-noise ratios, facilitating reliable integration at trace levels. Direct injection of plate eluates eliminated filtration and evaporation steps, accelerating turnaround.

Benefits and Practical Applications

• Enhanced cleanup efficiency and high recovery for ractopamine in liver matrices
• Reduced variability and cross-contamination risk in 96-well format
• Increased throughput and analyst productivity
• Cost savings through elimination of filters and extra consumables

Future Trends and Potential Applications

Emerging trends include integration of fully automated sample prep platforms with online SPE-LC-MS workflows to further reduce manual intervention. Advancements in sorbent chemistries and micro-elution formats may enable higher sensitivity and lower solvent consumption. The approach can be extended to other veterinary drugs, mycotoxins, and environmental contaminants in various food matrices.

Conclusion

The semi-automated positive pressure SPE method using Oasis MCX 96-well plates and Otto SPEcialist provides robust cleanup and reliable quantification of ractopamine at 0.1 ng/g in porcine and bovine liver. Compared to traditional vacuum cartridge workflows, this strategy delivers superior reproducibility, signal enhancement, and operational efficiency, supporting high-throughput food safety testing.

Reference

AOAC Official Method 2011.23. Determination and Confirmation of Parent and Total Ractopamine in Bovine, Swine, and Turkey Tissues.