Isocratic HPLC method for the purity determination of hymecromone (CAS 90-33-5; synonyms beta-methylumbelliferone, 4-MU, Coumarin 4; formula 7-Hydroxy-4-methyl-2H-chromen-2-one), a choleretic and antispasmodic drug. The method uses an ARION(R) Plus C18 column, 10 um, 250 mm x 4.0 mm as printed, part number ARI-5720-PM46, with a mobile phase of methanol : phosphate buffer pH 7.0 (46.5 : 53.5 V/V), isocratic elution. Flow rate 1 ml/min, temperature 30 C, injection volume 20 ul, UV detection at 270 nm. Analytes: 1 hymecromone, 2 impurity A, 3 impurity B. The system suitability test on the reference standard is met with a large margin: the required resolution of hymecromon and impurity B (>= 3.0) is reached at 6.5 and the required resolution of impurity A and impurity B (>= 2.0) at…