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Direct Complexometric Determination of the Calcium and Magnesium in Milk (Eriochromeblack T Method)

Department of Food Science, University of Illinois, Urbana

ABSTRACT

A method was developed to determine the total calcium and magnesium in diluted milk by direct titration with ethylenediamine tetraacetate (EDTA). The method yields complete recovery of the added calcium (99.86–100.02%) and values for total calcium and magnesium close to those obtained by the methods of Jenness and Bird et al. The test is not significantly affected by changes in dilution of the milk with water from a ratio of 1:10 to 1:30 or by differences in the amount of indicator added in the range of 0.025 to 0.075 ml. It was found that variations in the pH of the system from 8.5 to 10.0 did not significantly affect the results. Also, the test can be performed over a broad range of buffer strength (0.5 to 1.5 ml per 50-ml sample). The presence of the phosphates and proteins does not influence the results. The method is convenient, rapid, and reproducible, with a standard deviation of 0.20 meq/liter of milk or 0.264% of the total calcium and magnesium in the milk, which indicates sufficient precision for most purposes.