1.1 ,This test method covers the determination of total p-tertiary-butylcatechol inhibitor added to polymerization and recycle grades of butadiene or to other C₄ hydrocarbon mixtures containing no phenolic material other than catechol or no oxidized phenolic material other than that derived from oxidation of catechol. In general, all phenols and their quinone oxidation products are included in the calculated catechol content. Small amounts of polymer do not interfere. This test method is applicable over the range of TBC from 50 ,mg/kg to 500 ,mg/kg.