I have a question regarding the Hydroxy Naphthol Blue Indicator. My current understanding from the instructions is to mix 0.2g of Hydroxy Naphthol Blue with 30g of sodium chloride. For the 0.1M EDTA volumetric solution titration, 300mg of this mixture is used.
However, for the suitability testing of Hydroxy Naphthol Blue for calcium determination, it states that 300mg of the neat chemical is used.
Given that the indicator used in the EDTA titration is a 150-fold dilution, I would like to clarify if a clear color change is expected during the EDTA titration.
There is also a note in the monograph of Hydroxy Naphthol Blue stating that "This reagent is deposited on crystals of sodium chloride. The small blue crystals are freely water-soluble. In the pH range between 12 and 13, the solution of the indicator is reddish pink in the presence of calcium ion and deep blue in the presence of excess (ethylenedinitrilo)tetraacetate.". I would like to clarify on the purpose of this note.
