Sample preparation for GC-MS analysis
1.
Prepare a standard curve each time samples are being analyzed. Set up 9 tubes
containing 1ml of methanol and the following:
Tube 1
Tube 2
Tube 3
Tube 4
Tube 5
Tube 6
Tube 7
Tube 8
Tube 9
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Spike 1: 12μL
Spike 2: 30μL
Spike 3: 60μL
Spike 4: 120μL
Spike 5: 300μL
Spike 6: 600μL
Spike 7: 1.2mL
LQ: 48μL
HQ: 48μL
(0.05 mg/L)
(0.125mg/L)
(0.250mg/L)
(0.5mg/L)
(1.25mg/L)
(2.50mg/L)
(5mg/L)
(0.20mg/L – From a 0.5mg/L LQ stock)
(4mg/L - From a 10mg/L HQ stock)
Note: All volumes of THC used come from a standard stock with a concentration of
0.5mg/L (Please refer to appendix for making the THC stock).
2.
Add 200μL of the internal standard to all tubes. Vortex all tubes and centrifuge
them at 43°C for 1hr.
3.
Make up a mixture of Hexane:BSTFA (4:1) and add 120μL to all tube. Vortex
and cap all tubes.
4.
Incubate all tubes for 20 minutes in a 70°C oil bath and then allow the samples to
cool down at 4°C for 5 minutes.
5.
Transfer all the samples to GC analysis vials and load them onto the GC-MS.
Appendix
Before each analysis, the following must be available:
1. 0.5mg/L stock of THC and 0.5mg/L stock of D3 – THC (internal std). To make
up stock add 50μL of THC or D3 – THC into 9.95mL of methanol.
2. 0.5mg/L LQ and 10mg/L HQ stock of THC which is to be made up in methanol
and water (1:1).
3. Hexane, Methanol (both being HPLC grade) and BSTFA.