GC Analysis of Tetrahydrocannabinol (THC) and Carboxytetrahydrocannabinol (THCCOOH) in Surface Water on SLB®-5ms after SPME using 50/30 μm DVB/Carboxen/PDMS Fiber, On-Fiber Derivatization
Materials
accessory
Headspace vial, screw top, rounded bottom (vial only)
volume 10 mL, clear glass vial, thread for 18, O.D. × H 22.5 mm × 46 mm, pkg of 100 eaMagnetic Screw Cap for Headspace Vials, 18 mm thread
PTFE/silicone septum (white PTFE/tranparent blue silicone), septum thickness 1.3 mm, pkg of 100 earelated product
N-Methyl-N-(trimethylsilyl)trifluoroacetamide
derivatization grade (GC derivatization), LiChropur™, ≥98.5%(−)-Δ9-THC-D3 solution
100 μg/mL in methanol, ampule of 1 mL, certified reference material, Cerilliant®(±)-11-nor-9-Carboxy-Δ9-THC-D3 solution
100 μg/mL in methanol, ampule of 1 mL, certified reference material, Cerilliant®(−)-trans-Δ9-THC solution
1.0 mg/mL in methanol, ampule of 1 mL, certified reference material, Cerilliant®used together
SPME Fiber Assembly
50/30µm DVB/CAR/PDMS, StableFlex (2cm), needle size 24 ga, Autosampler, pk of 3, notched gray hubCONDITIONS
sample preparation
SPME
sample/matrix
8 mL surface water in 10 mL vial, adjusted to pH 2 with HCl, spiked with THC and THCCOOH at 50 ng/L each compound
SPME fiber
StableFlex™ SPME Fiber, DVB/CARBOXEN-PDMS, 2 cm
extraction
immersion, 60 min, 60 °C
desorption process
260° C, 3 min
sample preparation
post-extraction derivatization: 500 μL MSTFA in 10 mL vial, headspace, 30 min, 60 °C
sample preparation
fiber post-bake: 10 min, 270 °C
column
SLB-5ms: 20 m x 0.18 mm I.D., 0.18 μm (28564-U)
oven
90°C (3 min), 20 °C/min to 200 °C, 3 °C/min to 300°C (5 min)
inj. temp.
260 °C
detector
MSD
MSD interface
325 °C
scan range
SIM:THC: m/z=303, 371(quant), 386;THCCOOH: m/z=371 (quant), 473, 488
carrier gas
helium, 1 mL/min constant flow
injection
splitless
liner
0.75 mm SPME
Description
Analysis Note
Cannabis is a Schedule 1 substance under US federal law. However, at the time of this writing, four US states have legalized it for recreational and medical use. The level of use by the general public is typically determined through questionnaires and crime statistics, but this approach may not give an accurate assessment. Sewage epidemiology seeks to correlate data from these surveys with actual levels found in wastewater. In the case of cannabis, this can be done by analyzing for the psychoactive substance, tetrahydrocannabinol (THC), and its major metabolite, carboxytetrahydrocannabinol (THCCOOH). THC can be analyzed by GC directly, but because THCCOOH contains an acid group in its structure it requires derivatization. Thus, if the two compounds are analyzed together, derivatization must be used. In this application, solid phase microextraction (SPME) with post-extraction, on-fiber derivatization was used for low level analysis of THC and THCCOOH from surface water prior to separation on an SLB®-5ms GC column. Cerilliant CRMs provided reliable quantification.
Legal Information
SLB is a registered trademark of Merck KGaA, Darmstadt, Germany, StableFlex is a trademark of Sigma-Aldrich Co. LLC