To those who are interesting in toxicology,

I have postmortem urine and blood samples, both are initially positive for THCA using EIA and ELISA techniques respectively. The THCA in blood has been confirmed and quantified by SPE extraction using GC-MS. However, I could not confirm the result of urine. I repeat the extraction more than about four times. We usually counter like this situation and we extract the urine sample using wash ether (in-house method) prior acidic hydrolysis and SPE and it works. But it does not work with this sample. The urine sample is also positive for other medications, which might mask the THCA and make the extraction difficult.

Any help or comment is really appreciated.