Sensitive determination of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol in wastewater by solid-phase extraction with pre-column derivatization and liquid chromatography-tandem mass spectrometry.

As the dangers of cannabis abuse draw attention worldwide, it is necessary to assess the level of consumption in the community. The analysis of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (THC-COOH) excreted in wastewater can provide information for a defined catchment area. Due to its hydrophobic nature and absence of ionizable groups, its detection is challenging. In this study, a highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantitative determination of THC-COOH in urban wastewater. The derivatization reagent 6-methylpyridine-3-sulfonyl chloride (MPS) with analyte-specific fragmentation was proven to be the most effective for improving sensitivity. Samples were extracted by solid-phase extraction (SPE) and satisfactory recovery was achieved (>79%) by adding acetonitrile to the samples for ultrasonic-assisted extraction before filtration. The limit of detection (LOD) and limit of quantification (LOQ) was 0.03 ng L and 0.1 ng L, respectively, from a 40 mL sample. The established methodology was applied to profile the presence of THC-COOH in influent wastewater samples. It was shown that 20 out of the 252 samples contained THC-COOH and the concentrations were all below 1 ng L.