Separation of Calcium from Magnesium by Oxalate Method

The determination of calcium and magnesium in milk and milk diffusate

“…In both the classical and EDTA methods the weight of calcium in the samples of TCA nitrate and diffusate taken for analysis usually exceeds 1 mg (range 1-3 mg) and therefore a period of 4 h at room temperature (about 20 °C) was adopted to ensure the complete precipitation of calcium oxalate (Marsden, 1941;A.O.A.C., 1945;Michaels, Anderson, Margen & Kinsell, 1949;Holth, 1949). However, precipitation periods of 1, 2, 4, 10 and 20 h were found to give values which agreed closely for both calcium and magnesium with both methods.…”

“…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.…”

“…Also, in the development of EDTA methods, the nonspecificity of EDTA has to be considered. This requires the separation of calcium 286 D. T. DAVIES AND J. C. D. WHITE and magnesium before each is determined (van der Have, 1954;Henly & Saunders, 1958), or that magnesium be determined as the difference between the calcium plus magnesium value and the calcium value (Jenness, 1953;Kamal, 1960;Bird, Weber, Cox & Chen, 1961) or that the calcium value be obtained by difference (Middleton, 1961). Another consideration in the use of EDTA is that indicators suitable for the direct titration of calcium, e.g.…”

Determination of Calcium and Magnesium with (Ethylenedinitrilo)tetraacetic Acid. Studies in Accuracy

“…The weighing of calcium as calcium oxide was used for certifying standards, and the method has since been termed an inferior method of determining calcium with respect to accuracy (8, Table III A review of the development of methods for calcium and magnesium revealed that emphasis has been placed on finding faster methods, with the result that methods evidently have been tailored to yield values that agreed with certificate values of standards. For example, Holth (8) has shown that a minimum of 4 hours is required for complete calcium oxalate precipitation. However, the popular calcium method based on a volumetric oxalate-permanganate procedure (10) specifically calls for a 20-to 30-minute precipitation period for the calcium oxalate.…”

Ferrous Metallurgy

“…Kolthoff has discussed amperometric titrations (53). Heyrovsk^h as given an optimistic but interesting discussion of modern trends of polarographic analysis (43). Stross has published a most interesting and valuable survey article on the polarographic analysis of light metals and alloys (103).…”