Extraction of Amphetamines and Metabolites from Urine (including Elimination of Sympathomimetic Amine Interferences) Using ISOLUTE® SLE+ Prior to GC/MS Analysis

Importance of the Topic

The analysis of amphetamines and their metabolites in urine is crucial for forensic, clinical, and workplace testing. Reliable sample preparation and interference removal ensure accurate quantitation of target analytes, supporting diagnostic, regulatory, and research applications.

Objectives and Study Overview

This study aimed to develop and validate a streamlined workflow for the extraction of amphetamine, methamphetamine, MDMA, MDA, MDEA, and their stable isotope internal standard from human urine. A key objective was the selective oxidation of interfering sympathomimetic amines (ephedrine, pseudoephedrine) prior to supported liquid extraction using ISOLUTE SLE+ plates, followed by GC/MS analysis in SIM mode.

Methodology and Instrumentation

The sample preparation consisted of:

• Urine pretreatment with phosphate buffer (pH 6) and sodium periodate oxidation at 60 °C to degrade ephedrine and pseudoephedrine.
• Alkalinization with ammonium hydroxide and loading onto 1 mL ISOLUTE SLE+ columns.
• Extraction with dichloromethane/isopropanol (95/5, v/v) under gravity and assisted vacuum.
• Post-elution derivatization with heptafluorobutyric anhydride in methanol, heating at 75 °C, evaporation, and reconstitution in ethyl acetate.

Used Instrumentation:

• GC: Agilent 7890A with QuickSwap, DB-5 column (30 m × 0.25 mm × 0.25 μm), helium carrier (1.2 mL/min), splitless injection at 175 °C.
• MS: Agilent 5975C in SIM mode (source 230 °C, quadrupole 150 °C) targeting specific quantifier ions for each analyte.

Main Results and Discussion

Complete removal of ephedrine and pseudoephedrine was confirmed by comparing chromatograms before and after oxidation, eliminating interference in the methamphetamine SIM window. Calibration across 5–500 ng/mL yielded correlation coefficients above 0.997 for all analytes. The lower limit of quantitation was established at 5 ng/mL for amphetamine, methamphetamine, MDA, MDMA, and MDEA. Recovery was high and consistent, with no emulsion formation or significant matrix effects.

Benefits and Practical Applications

• Efficient removal of sympathomimetic interferences enhances specificity.
• Supported liquid extraction simplifies workflow and reduces solvent usage compared to traditional LLE.
• Low LLOQ and robust linearity support trace-level detection in forensic and clinical settings.
• The method is adaptable to high-throughput and automation platforms.

Future Trends and Applications

Emerging developments may include coupling SLE-based workflows with UHPLC-MS/MS for faster analysis and extending the approach to a broader panel of designer drugs. Miniaturized and automated SLE formats could further increase throughput and reproducibility in routine toxicology screening.

Conclusion

The optimized ISOLUTE SLE+ protocol with pre-oxidation provides a reliable, efficient, and sensitive method for the extraction and GC/MS analysis of amphetamines and metabolites in urine, with complete elimination of key interferences and robust quantitation performance.