Application: Alkaline earth metals detection, colorimetric

ChemicalName: 2,7-Bis(4-chloro-2-phosphonophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid

Appearance: Reddish brown or black purple crystalline powder
Absorbance (0.018 mmol/l): ≥0.530 (around 550  E570 nm)
MW: 757.37
, C22H16Cl2N4O14P2S2

Storage Condition: ambient temperature, protect from metal
Shipping Condition:
ambient temperature

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

1. L. R. Snyder, et al., Characterization and Routine Determination of Nonbasic Nitrogen Types in Cracked Gas Oils by Linear Elution Adsorption Chromatography. Anal Chem. 1964;36:767-773.
2. J. W. Ferguson, et al., Simultaneous Spectrophotometric Determination of Calcium and Magnesium with Chlorophosphonazo-III. Anal Chem. 1964;36:796-799.
3. D. S. Howell, et al., Ultramicro Spectrophotometric Determination of Calcium in Biologic Fluids. Anal Chem. 1966;38:434-438.
4. T. Yamamoto, Extraction-photometric Determination of Uranium(IV) with Chlorophosphonazo-III. Anal Chim Acta. 1973;65:329-334.
5. M. Zenki, et al., 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. 2002;18:1137-1140.
Table 1 Metal Detection Conditions Using Chlorophosphonazo-III

Code# Unit Size Ships in* Price Quantity
100 mg
8-14 business days $42.00
1 g
8-14 business days $246.00

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