The determination of calcium and magnesium in milk and milk diffusate

Abstract

Classical methods and methods based on the use of disodium ethylenediaminetetra-acetate (EDTA) for the semi-micro determination of calcium and magnesium in milk and milk diffusate are described. With both types of method satisfactory accuracy and precision are attainable. The use of the EDTA methods leads to greater speed and convenience but practice in recognizing the correct titration end-points is necessary.Over the past few years the classical methods for the determination of calcium and magnesium in biological fluids have been replaced to a considerable extent by procedures using disodium ethylenediaminetetra-acetate with metal-complexing indicators. The principal reason for this change, to which the analysis of milk has been no exception, is that the EDTA methods are quicker but in addition some authors have adversely criticized the accuracy and convenience of the classical methods (Maclntyre, 1957; Henly & Saunders, 1958).The classical method for the determination of calcium in milk and milk sera involves the precipitation of calcium as calcium oxalate followed by titration of the oxalate with potassium permanganate solution. Magnesium is then usually determined in the calcium-free supernatant liquid by precipitation as ammonium magnesium phosphate (NH 4 MgPO 4 .6H a O) followed by colorimetric determination of the phosphorus. Although these methods are undoubtedly time-consuming, especially that for magnesium, it will be shown that provided the correct conditions are used, they are accurate and precise (cf. Pyne, 1943).The EDTA methods for calcium and magnesium which have been, or could be, applied to milk and milk sera show considerable diversity. This is attributable to several factors. Thus, the EDTA titrations have to be done at a high pH where there is the possibility that phosphate will interfere through the precipitation of calcium and magnesium phosphates. This difficulty can be overcome, in the determination of calcium in milk for example, by the removal of phosphate from a suitable filtrate by an ion-exchange resin (Jenness, 1953) or by the simultaneous removal of protein and phosphate with a potassium metastannate precipitant (Ling, 1958) followed in each case by a direct EDTA titration, or by the direct addition of an excess of EDTA at a relatively low pH followed by back-titration with a standard calcium solution at a high pH (Kamal, 1960). Also, in the development of EDTA methods, the nonspecificity of EDTA has to be considered. This requires the separation of calcium

Influence of calcium fortification on sensory, physical and rheological characteristics of fruit yogurt

“…Calcium in yogurt samples was measured by complexometric method of Davies and White (1962) using disodium salt of ethylenediamine tetra-acetic acid (EDTA).…”

Changes in milk composition and processing properties during the spring flush period

“…Total divalent cations (TDC) in milk samples were measured by titration against ethylenediaminetetra-acetic acid (EDTA) disodium salt, by the method of Davies and White [5]. The EDTA sequesters all divalent ions within milk and therefore will account for both the calcium and magnesium present.…”

Heat stability and calcium bioavailability of calcium-fortified milk

“…The dissolved proportion of calcium was determined in rennet whey while total concentration of calcium was determined in the same sample of cow milk from which rennet whey was prepared. Calcium was estimated simultaneously in milk, whey, faeces and urine by complexometric method of Davies and White (1962) using disodium salt of ethylenediamine tetra-acetic acid (EDTA). Total phosphorus was determined according to the method of Kahovcova and Odavic (1969).…”