Spectrophotometric determination of manganese(II) with tetrasodium 25, 26,27,28-tetrahydroxycalix[4]arene-5,11,17,23-tetrasulfonate

Complex formation of manganese(II) with tetrasodium 25,26,27,28-tetrahydroxy-calix[4]arene-5,l 1,17,23-tetrasulfonate (CALX-S4) and its application to the spectrophotometric determination of manganese(II) in solution were studied. Manganese(II) reacted with CALX-S4 to form a 1: 1 red-purple complex in aqueous alkaline solution. The color intensity increased with the increase in pH, approaching a maximum at pH 10.4 ~ pH 11.3. The absorption peak appeared at 495 nm, and the molar absorption coefficient was 9.19 × 103 M-1 cm-1 at the peak. This color reaction was highly selective for manganese(II); except for manganese(II), only cerium(III) formed a colored complex with CALX-S4 under the conditions recommended for the determination of manganese(II). Chromium(III) caused negative errors, and a large amount of iron(III) also interfered by forming a colored species. Interferences due to the presence of those ions could be eliminated by removing them as their thiocyanate complexes using a column packed with an anion exchange resin. The proposed (CALX-S4) method was applied successfully to the determination of manganese(II) in an artifical sample solution and in the sludge formed in a tube which was used to pump up ground water.