Phosphorus content can be determined in the range of 0,000 5 % (m/m) to 0,05 % (m/m). As, Cr, Hf, Nb, Si, Ta, Ti, W interfere, but the interferences can be avoided. The principle is dissolution of a test portion in a mixture of nitric and hydrochloric acids, fuming with perchloric acid, removal of chromium, complexation of silicon, conversion of phosphorus to phosphovanadomolybdic acid, extraction of this compound.