Spectrophotometric Determination of Calcium in Foodstuffs with DBM-Arsenazo

The optimum experimental conditions of the color reaction between DBM-arsenazo and calcium were studied. Calcium(Ⅱ) reacts with DBM-arsenazo to produce a blue complex with a molar ratio of 1:2(M:R) in NH3-NH4Cl buffer solution medium at pH 10.4. The maximum absorption wavelength of the complex locates at 628 nm. The apparent molar absorptivity of the method is e 628nm = 3.92 × 104 L/mol·cm. Beer’s law is obeyed over the range of 2 ～ 10 μg of calcium in 10 ml of solution. The method was used in the determination of calcium in rice, wheat flour and potato foodstuff samples and the obtained results are in excellent agreement with those obtained by atomic absorption spectrometry. The relative standard deviations of six replicate determinations are 0.62 % ～ 1.03 % and the recoveries of the standard addition are 98.0%～100.5%.