This International Standard specifies a spectro-photometric method for the determination of phosphorus in steel and iron with the following limitations. The method is applicable to phosphorus contents between 0,001 0 % (m/m) and 1,0 % (m/m). Arsenic, hafnium, niobium, tantalum, titanium, and tungsten interfere in determining phosphorus, but the interferences can be partially overcome by formation of complexes and use of small quantities of test portion. Depending on the concentration of the interfering elements, the application ranges and test portions given in table 1 apply. The lower end of the application range can only be reached in test samples with low contents of the interfering elements.