Highly selective chromogenic ionophores for the recognition of chromium(III) based on a water-soluble azocalixarene derivative

A new water-soluble chromium-selective chromogenic azocalix[4]arene had been synthesized from diazo coupling reaction between calix[4]arene and diazonium salts, and characterized by 1H NMR, IR,UV and element analysis. It possesses an absorbance maximum at 365 nm in buffered aqueous environment, but addition of chromium(III) ion induced a weak blue shift to 350 nm and a new absorption peak at 520 nm (bathochromic shift of 155 nm), exhibited an isosbestic point at 470 nm. It is more noticeable that the absorbance at 520 nm increases along with the augment of the concentration of chromium(III) ion. Based on this, a simple and selective spectrophotometric method was developed for the determination of chromium(III), in the range of 9.35 × 10-4 to 4.45 × 10−3 mol L−1 of chromium(III) the linear regression equation was determined to be: absorbance (A) = 0.001 × C (10−4 mol L−1 chromium(III)) + 0.2379, r = 0.998, n = 6.