Prepare the mixed labeled isotope working solution diluting the contents of one ampoule (5 mL) into acetonitrile such that 125 μL of labeled isotope in 1.0 mL of urine results in the concentration between 15 ppb to 30 ppb. Store the working mixed labeled isotopes at -10°C or below.
Add 125μL of the mixed labeled working solution to a 1 mL urine sample via the
Gilson Liquid Handler.