HG/T 4440-2012 "Spinning & weaving dyeing and finishing aids, determination of phosphorus content" standard specifies a method for the determination of phosphorus content in Spinning & weaving dyeing and finishing aids by nitric acid-perchloric acid digestion method. The standard is applicable to the determination of trace phosphorus content in Spinning & weaving dyeing and finishing aids. After the sample is digested with nitric acid-perchloric acid, phosphorus is completely converted into normal phosphoric acid salt. Under acidic conditions, the normal phosphoric acid salt reacts with ammonium molybdate to form phosphomolybdenum heteropolyacid, which is then reduced to a blue complex by ascorbic acid. Absorbance of the complexes was determined by UV-Visible Spectrophotometer, and the phosphorus content in the samples was calculated according to the standard working Linear dispersion. The standard also details the reagents and materials required to ensure the accuracy and Reliability of the analysis.