by Eric Chi and Jason Cole, Thermo Fisher Scientific, Austin, TX

In forensic toxicology, the analysis of oral fluid is becoming a popular alternative to the use of urine or blood to test for abuse of drugs, such as marijuana. Unlike urine and blood, oral fluid samples can be taken from a subject without causing pain or embarrassment and without the need for extensive training.

The marijuana plant contains a pharmacologically active compound—?9-tetrahydrocannabinol (THC)—known to have mind-altering properties. Since marijuana is one of the most commonly used illegal drugs, THC analysis in oral fluid is becoming increasingly important, however this type of analysis can be particularly challenging due to the low concentration of THC typically found in oral fluid, as well as the low volumes of oral fluid that are generally available for analysis. Like many biological fluids, the chemical background from the oral fluid matrix can limit the low detection levels required for this analysis.

The use of gas chromatography coupled with a triple quadrupole mass spectrometer overcomes many of these challenges. To demonstrate the capabilities of this technique, a method for the detection of THC in an oral fluid matrix was fully validated for linearity, precision and carryover. A Thermo Scientific TSQ Quantum GC analyzer was selected over a single quadrupole due to its ability to detect analytes to very low quantitation limits in complex matrices. Thermo Scientific ToxLabs Forms 2.5.1 software was used for sample analysis and quantitation, as well as method validation.

Experimental tests

Table 1. The sequence noted in this table summarizes the sample preparation, extraction, and derivatization steps used prior to loading the sample onto an autosampler for GCMS analysis. Click to enlarge.

Sample preparation plays a critical role in method validation since many certifying bodies recommend or require method validation performed in matrix. In this case, solid phase extraction was used due to its ease of use and the cleanliness of the resultant extracts. After extraction, the samples were derivatized with bis (trimethylsilyl) trifluoroacetamide (BSTFA). The silylated reaction products were analyzed using the TSQ Quantum GC triple stage quadrupole GC-MS-MS system using multiple reaction monitoring (MRM). Known negative oral fluid calibration standard was spiked and extracted at 0.2, 2, and 20 ng/mL for use as calibrators.