Improved Complexometric Determination of Calcium in Cheese

Accuracy and repeatability of complexometric methods for measuring calcium in cheese are limited by titration endpoints that are difficult to recognize. Much of this difficulty results from turbidity during titration. An alternative procedure is described in which 2 to 3 g of cheese are ashed, dissolved in dilute acid, and added calcium chloride is back titrated with ethylenediaminetetraacetic acid using hydroxy naphthol blue as indicator. Samples remain free of turbidity, and the titration endpoint is recognized easily.Recovery of calcium from solutions containing magnesium and phosphate was 100.9 ± .3%, indicating that a portion of sample magnesium (about 12%) also was measured. Error caused by magnesium recovery represented less than 1% of true calcium content.Analyses of 10 Cheddar cheese samples by the proposed method and by atomic emission differed by an average of .010% calcium. Mean values of the 10 samples did not differ significantly (P>.05) between methods. Duplicate analyses of 67 Cheddar cheese samples differed by an average of .008 ± .006% calcium. Similar repeatability was achieved by several inexperienced analysts. The method is applied readily to other dairy products.