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- Posts: 7
- Joined: Fri Apr 12, 2019 6:47 am
My first post.
Hope someone can give me some tips on issue i have with LCMS analysis of THC-COOH in urine.
I am doing alkaline hydrolysis with ammoniumhydroxide 25% (60uL amhyd, 120 uL IS (THCA-d9 in water), 240 uL urine or spiked urine calibrator). So no SPE, dilute and shoot method.
I have done ion suppression and I had 40% suppression compaird to blank prepparation (ie water instead of urine) and THCA and THCAd9 behaves similar.
However when i spike THCA and IS to urine and check revovery agains blank prepparation THCA and IS do not behave similar between urines from different co-workes (subj healthy, meds and no meds, not using cannabis).
For exampel matrix X IS respons down 41% THCA only 17% and matrix P IS down 34% and THCA 27%.
Compairing the different urine matrixes to each other shows that for one matrix the IS can be higher but THCA can be lower than for an other urine matrix.
This affects the slope of my calibration curve. I have noted a slope difference of 30% which off course will affect my results proportionally and I get very high LOT to LOT variations.
Has anyone seen this effect or have any tips or ideas that could help me? SPE off cours could be one tip but trying to sett up method performed at several labs in Sweden.
Appologies for any misspellings or grammar errors since English is not my first language.
Sincerly
Pär