ChemicalName: 2-Hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthoic acid MW: 438.41, C21H14N2O7S
Appearance: Black purple powder
Absorbance (0.046 mmol/l, in MeOH): 0.600 E0.800 (around 555 nm)
Storage Condition: ambient temperature, protect from light
Shipping Condition: ambient temperature
NN is a colorimetric and chelatometric reagent for calcium (pH 12, λmax=470 nm) and UO22+ (λmax=570 nm, ε=1.36x105). Although NN is soluble in water, the solution is unstable and decomposes in a few minutes, especially in the presence of oxidative ions. Its proton dissociation constants are reported to be pKa2=9.26 and pKa3=13.67 (μ=0.1, 24ºC). An NN solution of 0.1% w/v in 50% aqueous methanol is stable for one week if stored in a cool and dark place. Ascorbic acid is used as a stabilizer of the NN stock solution. Al, Cu, Fe(III), and Ni interfere with the determination of calcium by NN and should be masked by KCN or triethanolamine.
1. J. Patton, et al., New Indicator for Titration of Calcium with (Ethylenedinitrilo) Tetraacetate. Anal Chem. 1956;28:1026-1028.
2. A. Itoh, et al., Evaluation of 2-Hydroxy-1-(2-Hydroxy-4-Sulpho-1-Naphthylazo)-3-Naphthoic Acid and Hydroxynaphthol Blue as Metallochromic Indicators in the EDTA Titration of Calcium. Analyst. 1970;95:583-589.