Diatrizoic Acid (Amidotrizoic acid) is an organic, iodinated radiopaque X-ray contrast medium used in diagnostic radiography.

Radiochemical enzyme assays for COX-1 and COX-2: 10 μL of purified COX-1 (0.7-0.8 μg) or COX-2 (3.0 units, 0.3μg) is activated with 50 μL of cofactor solution [l-epinephrine (1.3 mg/mL), reduced glutathione (0.3 mg/mL), and hematin (1.3 mg/mL) in oxygen-free Tris-HCl buffer (pH 8.0)]. The enzyme solution (60 μL) is added to Ibuprofen solutions or DMSO (20 μL) after [14C]arachidonic acid is added in 0.2 mL eight-strip test tubes and preincubated 10 minutes on ice. Samples are incubated for 15 minutes at 37 °C, after which the reaction is terminated by addition of 10 μL of 2 M HCl and 5 μL of carrier solution (PGE2 and PGF2α, 0.2 μg/mL of each in EtOH). The unmetabolized arachidonic acid is separated from the prostaglandin products by column chromatography and eluted with n-hexane-dioxane-glacial acetic acid (70:30:1). The prostaglandin products are then eluted with EtOAc-MeOH (85:15), and the samples are counted in a Packard scintillation spectrometer. IC50 values are obtained by linear regression analysis.