Micellar-Sensitized Spectrophotometric Determination of Magnesium in Drinking Water

Abstract

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,Ntrimethylammonium 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 mol L-1 EDTA, 0.01 mol L-1 triethanolamine and 5000 µg NaF 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