3,5-DiBr-PAESA is an excellent colorimetric reagent for Cu(II) and Ag(I) detection. : 4-(3,5-Dibromo-2-pyridylazo)-N-ethyl-N-(3-sulfopropyl)aniline, monosodium salt, monohydrate. Molar absorptivity >124,000 around 637 nm (Cu complex).
The maximum wavelength and molar absorptivity of the Ag(I) complex are 618 nm and 80,000, respectively. The maximum wavelength and molar absorptivity of Cu(I) are 639 nm and 1.34x105, respectively. The absorption maximum of the complex shifts to longer wavelengths and the molar absorptivity increases in the presence of anionic surfactants such as sodium dodecylsulfate.