51
Table 1. MS data acquisition parameters for THC and THCA. (a) SRM transitions and conditions. Compound Polarity
Precursor (m/z)
THCA Negative
THCA-d3 Negative THC
THC-d3
Positive Positive
(b) Ion source parameters.
Parameter Name Parameter Value Spray Voltage
3500 V (+) 2500 V (-)
Vaporiser Temperature
Ion Sweep Gas Pressure
Capillary Temperature
330°C
Sheath Gas Pressure 35 arb 5 arb
Aux Gas Pressure 25 arb 270°C
Collision Pressure 1.5 mTorr
criteria, the limit of quantitation was 10 pg/ mL for THCA and 0.5 ng/mL for THC in oral fluid. Linearity was determined from 0 to 1000 pg/mL for THCA and 0 to 1000 ng/mL for THC. Calibration curves and chromatograms of the lowest standard are shown in Figure 3a,b for THCA and Figure 4a,b for THC, and both compounds displayed linear response over the concentration range.
Recovery was determined by spiking 50 pg/mL of THCA and 5 ng/mL THC into five
donor samples before and after SPE. These samples showed an average recovery of 98.1% for THCA and 61.6% for THC.
Samples for determining the precision of the sample preparation and analytical procedure were prepared by spiking oral fluid with THCA and THC at three different concentration levels (25, 100, and 500 pg/ mL for THCA and 2.5, 10, and 50 pg/mL for THC). Four replicates were analysed in three separate batches. The %RSD across these samples was less than 8.5% for THCA and less than 3.2% for THC for all three concentration levels (Table 2), indicating the reliability of the method to produce precise analyte concentrations.
Conclusions
In this report, we have demonstrated a sample preparation method for urine and oral fluid based on micro-elution SPE. This method enables rapid analyte extraction from the sample with high recoveries and precision. More importantly, the method requires fewer steps and less time than method using conventional
Table 2. Analytical precision for the analysis of THCA and THC in oral fluid based on four replicate samples analysed in three separate batches (n = 12).
Sample Low Mid
High
[THCA] (pg/mL) % RSD 25
100 500
8.4 7.7 6.3
[THC] (ng/mL) %RSD 2.5 10 50
3.2 2.4 2.2
343.2 346.2 315.3 318.3
Product (m/z)
245.1 302.2 193.1 196.1
Collision Energy (V)
30 22 24 25
87 85 58 59
RF Lens (V)
SPE formats. Extracts can be analysed without evaporation and reconstitution prior to LC-MS/MS analysis, instead only requiring dilution. This approach has been demonstrated to be suitable for achieving the very low detection limits required for analysing THCA in oral fluid.
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