Determination of basic constituents in petroleum products by potentiometric titration with perchloric acid in glacial acetic acid. The total base number (TBN) is the quantity of perchloric acid, expressed in terms of equivalent number of milligrams of potassium hydroxide (or alternatively in milli-equivalents of hydroxide per gram), that is required to neutralize all basic constituents present in 1 g of sample when titrated under the prescribed conditions.