• Manual determination
Add 1 ml of ascorbic acid (reagent 4) and 1 ml of mixed reagent (reagent 6) to 50 ml of sample. Mix thoroughly after each reagent addition.
The absorbance of the blue phosphorus complex reaches a maximum in a few minutes and stays almost constant for many hours. However, the absorbances should be read wihin 10-30 min,using a wavelength of 880 nm. This determination, on an unfiltered sample, gives the amount of dissolved inorganic phosphate ions in true solution and probably also includes a small fraction of those ions that are adsorbed onto particles and subsequently dissolved by the acid in the mixed reagent. The latter fraction is not included when a filtered sample is analysed.
No salt correction is required