Micellar-Sensitized Spectrophotometric Determination of Magnesium in Drinking Water

摘要

A sensitive and relatively selective spectrophotometric method is proposed for the rapid determination of magnesium using Eriochrome black T (EBT) as a complexing agent in the presence of N-cetyl-N,N,N-trimethylammonium bromide (CTAB). The complex formation reaction between EBT and magnesium (II) is instantaneous in presence of NH3/NH4Cl buffer at pH 9.5 after CTAB adds as micellar-sensitized medium and the absorbance as analytical signal remains stable for over 6 h. N-cetyl N,N,N-trimethylammonium bromide as cationic surfactant and Triton X-100 as nonionic surfactant are used for improving the sensitivity and solubility of the analytical system, respectively. The surfactant-sensitizing method allows the determination of magnesium in the concentration range of 0.05-1.2 µg mL–1 with a molar absorption coefficient of 8928 L mol–1 cm–1 and Sandell’s sensitivity of 2.82 ng cm2-. The method has a detection limit of 0.012 µg mL–1 (DL=3Sb/m) and quantification limit of 0.054 µg mL–1 (QL=10Sb/m) at an analytical measurement wavelength of 640 nm with a bathochromic shift of 86 nm. The selectivity of chelating reagent was improved by the use of 1 mL masking agent solution containing 0.1 M EDTA, 0.01 M triethanolamine and 5000 µgNaF mL–1. The proposed method has been successfully applied to the determination of magnesium at trace levels in different drinking water samples. The precision (with CV of 2.35%) and the accuracy obtained were highly satisfactory.