Standard HG/T 4740-2014 "Determination of phosphoric acid salt content in Spinning & weaving dyeing and finishing aids" specifies the method for the determination of total phosphoric acid salt content in Spinning & weaving dyeing and finishing aids by using the Spectrophotometric method, spectrophotometry. This standard applies to the conversion of all phosphorus in the sample to orthophosphoric acid salt by wet digestion, and then the content of phosphoric acid is determined by the Spectrophotometric method, spectrophotometry. During the determination process, the sample reacts with phosphoric acid in the presence of acidic medium and antimony salt to form phosphoric acid heteropolyacid, which is then reduced to phosphoric acid by ascorbic acid and determined by spectrophotometer at 890nm. This standard ensures accurate determination of total phosphoric acid content in Spinning & weaving dyeing and finishing aids to meet quality control and regulatory requirements.