We are performing testing on several lots of Ammonium Citrate, Dibasic following the ACS Reagent Chemicals monograph. For the Phosphate analysis, we need clarification on the preparation of the standard solution. On the following section: Colorimetry and Turbidimetry - Procedure for Phosphate, Method 1, it states: "Any blue color should not exceed that produced by 0.02 mg of phosphate ion in an equal volume of solution containing the quantities of reagents used in the test."
We are not sure if this refers from "Add 1 mL of ammonium molybdate-sulfuric acid solution (5%)..." forward, or if we have to also add the reagents stated in the Phosphate portion of the monograph (magnesium nitrate hexahydrate, nitric acid) including the ignition and evaporation to dryness.
Any help with clarification will be greatly appreciated.
