Stability of drugs of abuse in synthetic oral fluid investigated using a simple "dilute and inject" method of analysis.

Human oral fluid is well established as a matrix for drug screening, particularly in the workplace. The need to synthesise synthetic oral fluid (SOF) has been recognised in order to overcome human oral fluid's composition variability. We have used SOF spiked with six common drugs of abuse or their primary metabolites: morphine, amfetamine, benzoylecgonine, cocaine, diazepam, and (-)-Δ9 -tetrahydrocannabinol (THC) in order to assess the suitability of this matrix for quality assurance purposes. For confirmation of a drug screening test, controls and spiked standards are normally required. All our analytes were detected by LC-MS/MS using a quick and easy "dilute and inject" sample preparation approach as opposed to relatively slower solid-phase extraction. The limit of detection (LOD) was 10 ng/ml for diazepam and THC and 5 ng/ml for morphine, amfetamine, benzoylecgonine and cocaine. Validation results showed good accuracy as well as inter- and intra-assay precision (CV [%] < 5). Our work highlighted the importance of adding Tween® 20 to the SOF and calibrants to reduce losses when handling THC. Furthermore, drug stability was tested at various temperatures (5°C, 20°C and 40°C), for a number of days or after freeze-thaw cycles. Recommendations regarding storage are provided, the spiked SOF being stable at 5°C for up to 1 week without significant drug concentration loss.

Artificial oral fluid characterisation: Potential for use as a reference matrix in drug testing.

Quality assurance schemes for drug-screening programmes require access to large quantities of biological matrices for reference or control samples. This presents problems when the availability of a matrix, such as oral fluid (OF) for screening or for confirmatory purposes, limits the collection of large volumes. In such cases, synthetic alternatives of OF may provide a solution. The preparation of an artificial (synthetic) oral fluid (AOF) was conducted by dissolving its components (salts, surfactant, antimicrobial agent and mucin) in water. We characterised the physical properties of AOF to determine its suitability as a matrix for quality assurance purposes. The evaluation of pH, specific gravity (SG), conductivity (mS cm-1 ), freezing point depression (°C), light-scattering and kinematic viscosity (mm2 s-1 ) showed AOF to be a stable, reliable matrix. Synthetic OF was prepared using components (mucin, surfactants and so on) obtained from different suppliers and a comparison was performed. Our results suggest that AOF is a feasible matrix for the preparation of quality assurance samples for confirmatory or drug screening programmes.