Spectrophotometric determination of magnesium in the presence of polyvinyl alcohol

Abstract

The optimum conditions of complex color reaction between Mg²⁺ and arsenazo-III (ASA-III) in the presence of polyvinyl alcohol were studied. In the medium of pH 10.0 ammonia-ammonium chloride, Mg²⁺ and ASA-III form a 1:2 purple complex and the maximum absorption peak is at 574 nm. At this wavelength, the absorbance (A) is linearly related with the concentration of Mg²⁺ over the range of 0.1–2.5 μg/mL and its equation: A = 0.4969 C (μg/mL)+0.0634, with a regression coefficient of 0.9993. The apparent molar absorption coefficient of method is 1.35×10⁴ L·mol^–1·cm^–1 and its detection limit is 76 ng/mL. Appropriate amount of polyvinyl alcohol can make sensitivity of the determination of magnesium increase 10.1%. The method was used to determine magnesium in potato and salt samples. The recovery of the standard addition was 99.6%–100.5%. The relative standard deviation was less than 5% for thirteen replicate determinations. The reliability of this method has been certified by parallel determination against atomic absorption spectrometric method.