Determination of drugs of abuse in oral fluid using dried oral fluid spot assisted by 24-well plate and LC-MS/MS.

Background: Oral fluid has proven to be an excellent matrix for drug testing. Several analytical techniques are available, including the use of dried spots, which have gained increasing recognition in recent years. In this study, a new method was developed and validated using dried oral fluid spot (DOFS) assisted by a 24-well plate for the simultaneous determination of thirteen drugs of abuse and metabolites in oral fluid by LC - MS/MS.

Methods: Samples were collected by expectoration and diluted with water. A 100 μL aliquot of sample was applied onto the spot, dried for 60 min, and extracted with 250 μL of acetonitrile:methanol (3:1). The method was validated according to the ANSI/ASB Standard 036 guideline, and 86 oral fluid samples were analyzed.

Results: The limits of quantification ranged from 1 to 5 ng/mL, and all calibration curves were linear. Precisions ranged from 2.0 to 13.0% and Bias fluctuated from -19.7 to 9.6%. Ionization suppression or enhancement was noted at -16.2 to 16.6%. Among the analyzed samples, 86% tested positive for at least one substance.

Conclusions: The findings confirm that the proposed method was successfully validated, providing a new bioanalytical approach for the detection of drugs of abuse in oral fluid.