磷含量的测定范围为0001%（m/m）至0025%（m/m）。铬（III）和二氧化硅会产生干扰，干扰被消除。其原理是在硝酸和盐酸的混合物中溶解试验部分，用硫酸发烟，将Cr（III）氧化为Cr（VI），沉淀Fe（III）磷酸盐并重新溶解沉淀物，添加硼酸、酒石酸和氨基磺酸，形成和提取磷钼酸，将杂多酸还原为钼蓝并反萃取至水相，在700 nm处测量水溶液的吸光度。

Phosphorus content can be determined in the range of 0,001 % (m/m) to 0,025 % (m/m). Cr(III) and silica cause interference which is eliminated. The principle is dissolution of a test portion in a mixture of nitric and hydrochloric acids, fuming with sulfuric acid, oxidation of Cr(III) to Cr(VI), precipitation of Fe(III) phosphate and redissolution of the precipitate, addition of boric, tartaric and sulfamic acids, formation and extraction of molybdophosphoric acid, reduction of the heteropoly acid to molybdenum blue and back-extraction into an aqueous phase, measurement of the absorbance of the aqueous solution at 700 nm.