An insight into the solution equilibria of magnesium(II) with purpurin andspectrophotometric determination of magnesium

The complexation equilibria of magnesium(II) with purpurin (PURP) are studi ed spectrophotometrically as a function of pH in 50% (v/v) ethanol-water me dium at 20 degreesC. The uncharged complex formed at pH 9.5 allows precise and accurate determination of magnesium over the concentration range 0.8-4. 3 mug ml(-1). The molar absorptivity of the Mg-PURP complex at 540 nm and d etection limit for Mg are 9.2 x 10(3) 1 mol(-1) cm(-1) and 75 ng ml(-1), re spectively. The proposed method is rapid and possesses reasonable selectivi ty. Under the optimum conditions, the use of first-derivative spectrophotom etry has the advantage of high sensitivity than normal spectrophotometry an d allows the determination of 0.2 mug ml(-1) of magnesium. The validity of the method is examined by analysing several SRM Portland cement samples and a variety of cement materials of variable magnesia content., (C) 2001 Else vier Science B.V. All rights reserved.