Extraction of Anabolic Steroids from Horse Urine Using ISOLUTE® SLE+ Prior to LC-MS/MS Analysis

Importance of the topic

The reliable detection of anabolic steroids such as ethylestrenol and stanozolol in horse urine is critical for anti-doping control in equine sports. Sensitive and reproducible sample preparation minimizes false negatives, supports regulatory compliance, and ensures animal welfare.

Objectives and Study Overview

This application note describes a streamlined Supported Liquid Extraction (SLE) workflow using ISOLUTE SLE+ for isolating ethylestrenol and stanozolol from horse urine. The extracted analytes are then quantified by LC-MS/MS. Protocols for 48-well plates, 96-well plates, and column formats are provided, aiming to maximize recovery and precision while reducing labor and solvent use.

Methodology and Instrumentation

Sample Pretreatment:

• Mix urine 1:1 with water.
• Load 800 µL onto 1 mL ISOLUTE SLE+ plate and allow absorption for 5 minutes under light vacuum or positive pressure.

Elution and Post-Processing:

• Elute with three 1 mL aliquots of MTBE (or DCM) by gravity, finishing with brief vacuum.
• Evaporate eluate to dryness at 40 °C under air or nitrogen.
• Reconstitute in 500 µL of 20/80 water/acetonitrile with 0.1% formic acid.

Instrumentation Used:

• UPLC: Waters Acquity with ACE Excel 2 µm C18 column (50 × 2.1 mm).
• Mobile phases: 2 mM ammonium acetate with 0.1% formic acid in water and methanol.
• Gradient: 25%→10% aqueous to 100% organic, 4 min cycle, 0.4 mL/min flow.
• MS/MS: Premier XE triple quadrupole with electrospray in positive MRM mode.
  Transitions monitored: Stanozolol 329.0→94.8, 329.0→106.8; Ethylestrenol 271.1→120.8, 274.1→146.8.

Main Results and Discussion

Recoveries for both analytes exceeded 85% across plate and column formats. Reproducibility (RSD) ranged from <3% for stanozolol to <16% for ethylestrenol depending on format. MTBE and DCM performed comparably. No significant matrix interferences or emulsions were observed. Recovery profiles remained stable across gelding and filly urine.

Benefits and Practical Applications

• High analyte recovery and low variability improve confidence in doping tests.
• SLE+ eliminates emulsion issues common to LLE and reduces solvent consumption.
• Compatibility with 48- and 96-well formats supports high throughput screening.
• Simple vacuum or positive-pressure operation allows seamless integration in automated workflows.

Future Trends and Opportunities

Advances may include further miniaturization of SLE, integration with robotic platforms, and expansion to other classes of performance-enhancing compounds. Coupling with high-resolution mass spectrometry could extend qualitative screening capabilities.

Conclusion

The ISOLUTE SLE+ protocol combined with LC-MS/MS offers a robust, reproducible, and high-throughput solution for detecting anabolic steroids in horse urine, supporting stringent anti-doping requirements.