其原理是通过硫酸或高氯酸蒸馏将氟从试样中分离出来。以茜素磺酸钠和亚甲基蓝为指示剂，用硝酸钍溶液滴定。或者，硝酸钍滴定可单独使用茜素磺酸钠作为指示剂，终点在仔细定义的条件下通过分光光度法测定。525 nm波长处的吸光度应达到0.6的任意值。也得到了IUPAC的批准。

The principle consists in separation of the fluorine from a test portion by distillation with sulphuric acid or perchloric acid. Titration with thorium nitrate solution using sodium alizarinsuphonate and methylene blue as indicators. Alternatively the thorium nitrate titration may be carried out using sodium alizarinsuphonate alone as indicator, the end-point being determined spectrophotometrically under carefully defined conditions. The absorbance at a wavelength of 525 nm shall reach the arbitrary value of 0.6. Has also been approved by the IUPAC.