15 Chromogen/Metal Indicator



Metal Indicator

  • Product code
    H007  HNB
  • CAS No.
  • Chemical name
    2-Hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3,6-naphthalenedisulfonic acid, trisodium salt
  • MW
Unit size -- --
1 g Please inquire distributors about price.


HNB is a metal indicator for calcium, and a colorimetric reagent for alkaline earth metal ions, rare earth metal ions, and uranium ions. HNB is readily soluble in water and alcohol. Aqueous solution of HNB is blue at pH 7-12, red above pH 13, and pink in the presence of calcium at pH 10. The detection range of alkaline earth metal ions and rare earth metal ions are 1-600 ppm and 1-300 ppm, respectively. The maximum wavelength of the complex is 650 nm. HNB is also used for UO2(II) detection. The proton dissociation constants of HNB are reported to be pKa4=6.44 and pKa5=12.91(μ=0.1, 24ºC).

Chemical Structure


Open References

1. 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.
2. M. Sugawara, et al., Catalytic Decomposition of the Excess Reagent in the Spectrophotometric Determination of Copper(II) with O,O EDihydroxyazo Compounds. Bull Chem Soc Jpn. 1977;50:3206-3208.
3. M. M. Ferris, et al., Examination of Metallochromic Indicators and Water-soluble Reagents for Metals by Planar Electrophoresis. Analyst. 1986;111:351-354.

Handling and storage condition

Appearance: Black purple powder
Solubility in water: To pass test (clear, red or deep reddish purple)
Absorbance: ≧ 0.600 (around 647 nm)
Absorbance (Calcium complex): ≧ 0.310 (around 562 nm)
Sulfated ash: ≦ 35.0 %
Sensitivity: To pass test
IR spectrum: Authentic
Handling and storage condition
Ambient temperature

Product Classification

Product Classification

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