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THC-COOH Detected!  ∆-8 or ∆-9?

13 Apr 2021

Urine testing for cannabis metabolites is a routine analysis for drug testing labs, but what metabolite is actually being observed when a positive result is detected? Cannabis is a very complex matrix composed of many different constituents, some illegal and some legal in the United States. Delta-9-THC is the main psychoactive component in cannabis, but this compound has over 30 different isomeric forms! Some of which are discussed in more detail in the following blog: Analyzing THC Concentrates? Look for Isomers!

For the purpose of this blog, I’ll only be talking about delta-9-THC and delta-8-THC. Delta-9-THC is illegal for recreational use in most states but the legality of it is growing. Delta-8-THC, which has some diluted psychoactive effects, is legal on a federal level but has been banned in a few states.

So what happens when delta-8-THC is ingested and a urine screen for delta-9-THC is performed? The metabolites for delta-8-THC and delta-9-THC are structurally similar isobars and are only differentiated by the location of a singular double bond. Both compounds will produce a carboxylated metabolite requiring chromatographic separation in order to differentiate between the two isomers which may not occur in most routine testing methods.

Here, a method has been developed to detect delta-9-THC-COOH (11-nor-9-carboxy-9-THC) and delta-8-THC-COOH (11-nor-9-carboxy-8-THC) in 3.5 mins by LC-MS/MS. This method utilizes isocratic mobile phase conditions for high throughput, has simple mobile phase additives, and produces baseline resolution.

Column Raptor FluoroPhenyl (cat.# 9319A12)
Dimensions: 100 mm x 2.1 mm ID
Particle Size: 2.7 µm
Pore Size: 90 Å
Guard Column: Raptor FluoroPhenyl EXP Guard Column Cartridge 5 mm, 2.1 mm ID, 2.7 µm (cat.# 9319A0252)
Temp.: 30 °C
Sample (±)11-Nor-9-carboxy-D9-THC (cat.# 34068), other compound obtained separately
Diluent: 30/70 Water/Methanol, 0.1% formic acid
Conc.: 2.5 ng/mL
Inj. Vol.: 2 µL
Mobile Phase  
A: Water, 0.1% formic acid
B: Methanol, 0.1% formic acid
Time (min) Flow (mL/min) %A %B
0.00 0.4 30 70
3.5 0.4 30 70
Detector MS/MS
Ion Source: Electrospray
Ion Mode: ESI+
Instrument UHPLC
Peaks tR (min) Conc. (ng/mL) Precursor Ion Product Ion 1 Product Ion 2
Δ-8-THC-COOH 2.842 2.5 345.2 299.3 327.2
Δ-9-THC-COOH 3.237 2.5 345.1 327.1 299.2


By using this method of analysis, drug testing labs are able to resolve the two metabolite isomers with a 3.5 minute cycle time, allowing for rapid differentiation between the two compounds. Is your lab currently running or interested in this analysis? Let us know about it in the comments below!