15 Chromogen/Metal Indicator



Metal Indicator

  • Product code
    C010  Chlorophosphonazo-III
  • CAS No.
  • Chemical name
    2,7-Bis(4-chloro-2-phosphonophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid
  • MW
Unit size Price Item Code
100 mg $57.00 C010-10
1 g $329.00 C010-12
Quantity may be adjusted within the cart.

Product Description

Chlorophosphonazo-III is a colorimetric reagent for thorium, uranium, lanthanoids, actinoids, and alkaline earth metals. This reagent is readily soluble in water and is violet at pH 4 or lower, blue in NaOH solution, and brilliant green in acids such as H2SO4, HCl and diluted HNO3 (it decomposes in concentrated HNO3). Its proton dissociation constants are reported to be -1.1, -1.1, 0.6, 0.8, 1.5, 2.5, 5.47, 7.20, 12.15 and 15.13 (μ=0.1, 20ºC). Chlorophosphonazo-III is used as a selective colorimetric reagent for calcium in a mixed Ca/Mg sample in the pH range of 2-3. It is also a useful indicator for the precipitation titration of SO42- using Ba2+ as a standard solution.


Chemical Structure



Technical info

Table 1 Metal Detection Conditions Using Chlorophosphonazo-III


Open References

1) K. Ueno, T. Imamura and K. L. Cheng, "Handbook of Organic Analitical Reagents 2nd Edition", CRC Press1992.
2) L. R. Snyder and B. E. Buell, "Characterization and Routine Determination of Nonbasic Nitrogen Types in Cracked Gas Oils by Linear Elution Adsorption Chromatography", Anal. Chem., 196436(4), 767.
3) J. W. Ferguson, J. J. Richard, J. W. O'laughlin and C. V. Banks, "Simultaneous Spectrophotometric Determination of Calcium and Magnesium with Chlorophosphonazo-III", Anal. Chem., 196436, 796.
4) D. S. Howell, J. C. Pita, J. F. Marquez, "Ultramicro Spectrophotometric Determination of Calcium in Biologic Fluids", Anal. Chem., 196638, 434.
5) T. Yamamoto, "Extraction-photometric Determination of Uranium(IV) with Chlorophosphonazo-III", Anal. Chim. Acta1973, 65, 329.
6) M. Zenki, T. Masutani and T. Yokoyama, "Repetitive Determination of Calcium Ion and Regeneration of a Chromogenic Reagent Using Chlorophosphonazo III and an Ion Exchanger in a Circulatory Flow Injection System", Anal. Sci., 200218, 1137.

Handling and storage condition

Appearance: Reddish brown to black purple crystalline powder
Solubility in water: To pass test (clear, reddish purple)
Absorbance: ≧ 0.530 (around 550 - 570 nm)
Sulfated ash: ≦ 20.0 %
IR spectrum: Authentic
Handling and storage condition
Ambient temperature

Product Classification

Product Classification

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