Simultaneous Quantification of 15 Drugs of Abuse in Oral Fluid and Plasma by Ultra High Performance Liquid Chromatography/Tandem Mass Spectrometry

Significance of the Topic

The accurate detection of psychoactive substances in biological fluids plays a pivotal role in forensic toxicology, road-side drug screening, workplace testing, and clinical monitoring. Oral fluid sampling offers non-invasive collection reflecting recent intake, while plasma provides systemic exposure data. A robust, high-throughput method capable of simultaneous multi-drug quantification at trace levels addresses the growing need for comprehensive drug surveillance.

Objectives and Study Overview

This work aimed to develop and validate an ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for the simultaneous quantification of 15 commonly abused drugs in oral fluid and plasma. Target analytes included opioids (morphine, codeine, dolantin, tramadol, methadone), stimulants (MDMA, ketamine, deoxyephedrine), and benzodiazepines (diazepam, nitrazepam, clonazepam, alprazolam, estazolam, triazolam, midazolam). The goal was to achieve low detection limits, wide dynamic range, and high precision suitable for real-world applications under regulatory standards.

Methodology and Instrumentation

• Sample Preparation: 50 µL of oral fluid or plasma underwent protein precipitation with 200 µL acetonitrile, vortex mixing, centrifugation (4500 rpm, 5 min), and direct injection of the supernatant.
• Chromatographic Separation: Shimadzu Nexera UHPLC system equipped with LC-30AD pumps, CTO-30A oven, DGU-30A5 degasser, and SIL-30AC autosampler. Separation on an Inertsil ODS-4 column (100 mm×3.0 mm, 2 µm) at 40 °C using gradient elution of water/0.1% formic acid/10 µM ammonium acetate (A) and acetonitrile (B) at 0.6 mL/min.
• Mass Spectrometry: Shimadzu LCMS-8080 triple quadrupole with ESI positive mode. Optimized source parameters: 4.5 kV ionization voltage, nebulizing gas 5 L/min, heating gas 12 L/min, probe 400 °C, HSID 300 °C. MRM transitions and collision energies were tailored for each compound.

Main Results and Discussion

Calibration curves for all 15 analytes displayed excellent linearity (r>0.998) over 0.5–500 ng/mL. Limits of quantification (LOQs) in oral fluid ranged from 0.16 to 0.32 ng/mL, with limits of detection (LODs) between 0.04 and 0.08 ng/mL. In plasma, LOQs were 0.075–0.239 ng/mL and LODs 0.019–0.060 ng/mL. Repeatability assessed at 0.5, 2.5, and 50 ng/mL levels yielded %RSDs below 4.4% in oral fluid and below 4.0% in plasma. These performance metrics confirm the method’s suitability for trace-level multi-drug quantification in complex matrices.

Benefits and Practical Applications

This UHPLC-MS/MS approach offers:

• High sensitivity and selectivity for simultaneous multi-class drug analysis.
• Minimal sample volume requirement facilitating non-invasive testing.
• Rapid throughput and robust performance for forensic and clinical laboratories.
• Compatibility with regulatory guidelines for roadside screening and workplace drug testing.

Future Trends and Potential Uses

Advancements may include expansion of analyte panels to novel psychoactive substances, integration with automated on-site sampling devices, and incorporation of high-resolution mass spectrometry for untargeted screening. Miniaturized and portable UHPLC-MS/MS platforms could enable in-field confirmation, while coupling to data-driven analytics will enhance real-time decision support.

Conclusion

The validated UHPLC-MS/MS method demonstrates high linearity, sensitivity, and precision for the simultaneous quantification of 15 drugs of abuse in oral fluid and plasma. Its low detection limits, minimal sample preparation, and robust performance make it well-suited for forensic toxicology, clinical monitoring, and roadside drug screening.