Automated Dried Spot Analysis for Rapid Quantitation of Tramadol and Metabolites

Importance of the topic

Tramadol is a centrally acting analgesic commonly used to manage acute and chronic pain through a dual mechanism of neurotransmitter reuptake inhibition and weak opioid receptor activation. Its growing popularity among athletes and recent classification as a prohibited doping agent by the Union Cycliste Internationale highlight the need for reliable monitoring of tramadol intake.

Dried spot sampling (blood, serum, saliva, urine) offers a minimally invasive, stable approach for remote collection and long-term storage. Automating this workflow reduces manual handling, contamination risk, and turnaround time, making it highly relevant for clinical, forensic, and anti-doping laboratories.

Goals and study overview

This work demonstrates an end-to-end, automated platform for the rapid quantitation of tramadol and its primary metabolites (O- and N-desmethyltramadol) in various dried spot matrices. The objectives include:

• Integrating sample spotting, desorption, cleanup, separation, and detection in a continuous online process.
• Validating method performance across blood, serum, saliva, and urine with high throughput (8 minutes per sample) and capacity (96 cards per batch).
• Achieving linearity, precision, and accuracy compatible with clinical and anti-doping applications.

Methodology

Sample aliquots (6 µL) were spiked with analytes and internal standards, deposited onto dried blood spot cards, and dried at ambient temperature. The Transcend DSX-1 autosampler performed flow-through desorption with 0.1% formic acid at 1 mL/min and 100 °C HotCap for 30 seconds. Desorbed extracts passed through a TurboFlow column for on-line cleanup, removing salts and proteins, before transfer to the analytical column for separation and mass spectrometric detection.

Calibration ranged from 5 ng/mL to 400 ng/mL with weighting (1/x), yielding R²>0.99 across all matrices. Precision (%RSD) and accuracy (%CV) remained below 20% at low concentrations, meeting regulatory criteria for quantitative bioanalysis.

Instrumentation Used

• Thermo Scientific Transcend DSX-1 Dried Spot Autosampler with FTDTM flow-through desorption technology
• TurboFlow online extraction module coupled to UHPLC-MS/MS
• TSQ Altis™ MD triple quadrupole mass spectrometer
• Cyclone™-P and biphenyl analytical columns
• Thermo Scientific TraceFinder™ software for data acquisition and quantitation

Main results and discussion

The automated workflow achieved:

• Throughput of 8 minutes per dried spot with capacity for 96 samples per batch.
• Linearity (R²>0.99) across all matrices from 5 to 400 ng/mL.
• Precision and accuracy within ±20% at the lower limit of quantification.
• Reproducible internal standard responses over 70 consecutive injections (%RSD<15%).

Chromatograms at the lower limit of quantification demonstrated clear peak separation and consistent retention times, while pre- and post-run images ensured spot integrity and traceability.

Benefits and practical applications

This integrated approach provides:

• Minimal sample preparation and reduced manual intervention.
• High throughput suited for clinical pharmacokinetic studies and doping control.
• Robust quantitation in diverse biological matrices.
• Enhanced sample traceability through automated imaging.

Future trends and potential applications

Advancements may include further miniaturization of autosampler hardware, integration with point-of-care diagnostics, and coupling with high-resolution mass spectrometry for broader metabolite profiling. Implementation of IoT and cloud-based data platforms could enable real-time monitoring and remote result reporting.

Conclusion

The fully automated DSX-1 dried spot autosampler combined with TurboFlow UHPLC-MS/MS delivers a fast, reliable, and high-throughput solution for quantifying tramadol and metabolites in dried spot matrices. The method meets stringent performance criteria and offers a scalable workflow for clinical laboratories and anti-doping agencies.

References

1. Anesth Analg. 2017 Jan;124(1):44-51.
2. Union Cycliste Internationale. UCI Technical Regulations on Tramadol. 2019.
3. Drug Test Anal. 2020 Nov;12(11-12):1649-1657.