15 Chromogen/Metal Indicator



Metal Indicator

  • Product code
    P003  PAR
  • CAS No.
  • Chemical name
  • MW
Unit size Price Item Code
1 g $101.00 P003-10
5 g $371.00 P003-12
Quantity may be adjusted within the cart.

Product Description

PAR is a metal indicator and colorimetric reagent for heavy metal ions. The solubility of this reagent in water (5 mg per 100 ml at 10ºC) is higher than that of PAN. PAR is slightly soluble in alcohol. The aqueous solution is red at pH 5.5 or less, orange at pH 6-12.5, and red at pH 13 or higher. Its proton dissociation constants are reported to be pKa1(NH+)=3.1, pKa2(p-OH)=5.6 and pKa3(o-OH)=11.9 (m=0.2). PAR forms complexes with various metal ions that can be extracted with chloroform.

Chemical Structure


Chelate titration: Al, Bi, Cd, Cu, Ga, Hg, In, Mn, Ni, Pb, Zn
Precipitation titration: MoO4(II), WO4(II)
Colorimetry: Al, Au, Bi, Co, Cr, Cu, Fe, Hf, Ga, In, Nb, Ni, Pb, Pd, Sb, Sn, Ti, Tl, U, V, Zn

Technical info

Table 1 Photometric Detection Conditions Using PAR

M=metal ion, L=PAR, X=antipyrine, TPAC, Crystalviolet or Diphenylguanidine


Open References

1. W. J. Geary, et al., The Metal Complexes of Some and Azomethine Dyestuffs Part I. Spectra in Water, and in Dioxan/Water in the Wavelength Range 320-600 mμ. Anal Chim Acta. 1962;26:575-582.
2. R. M. Dagnall, et al., Determination of Lead with 4-(2-Pyridylazo)-resorcinol-I Spectrophotometry and Solvent Extraction. Talanta. 1965;12:583-588.
3. G. Pilloni, et al., Spectrophotometric Determination of Diethyllead and Diethyltin Ions with 4-(2-Pyridylazo)-resorcinol. Anal Chim Acta. 1966;35:325-329.
4. L. Sommer, et al., Complexation of Aluminium, Yttrium, Lanthanum and Lanthanides with 4-(2-Pyridylazo)Resorcinol (PAR). Talanta. 1967;14:457-471.
5. R. Sawyer, Determination of Dialkyltin Stabilisers in Aqueous Extracts from PVC and Other Plastics. Analyst. 1967;92:569-574.
6. Z. Kleckova, et al., Spectrophotometric Study of Complex Equilibria and Determination of Lead(II) with 4-(2-Pyridylazo)resorcinol. Collect Czech Chem Commun. 1978;43:3163-3178.
7. A. Rios, et al., New Configuration for Construction of pH Grandients in Flow Injection Analysis. Anal Chem. 1986;58:663-664.

Handling and storage condition

Appearance: Yellowish orange to orangish red powder
Solubility in NaOH solution: To pass test (clear, red)
Absorbance: ≧ 0.45 (around 385 nm)
Sulfated ash: ≦ 1.5%
Sensitivity: To pass test
IR spectrum: Authentic
Handling and storage condition
Ambient temperature

Product Classification

Product Classification

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