Calcium spectrophotometric titration

Complexometric titration where the initially formed red calcium-eriochrome black T color is replaced vrith the blue calcium-EDTA color at the end point Spectrophotometric titration of the complex without preliminary extraction Spec A = 506 nm (pH = 11.3)... 

Spectrophotometric analysis and complexometric titrations have long been used to determine calcium, with much effort devoted to developing reagents and indicators that permit the... 

Although changes in pM can readily be followed by physical means (e.g. potentiometrically), following colour changes associated with the formation and dissociation of metal coordination complexes visually or spectrophotometrically is a more versatile and convenient procedure. The serendipitous discovery of so-called metallochromic indicators made by G. Schwarzenbach (1945) led immediately to the introduction of murexide (50) as an indicator in calcium titrations and initiated the search for indicators for other metal-EDTA systems. It will be realized that the chosen metal indicator must be considerably less stable than the metal-EDTA complex, but not so weak as to dissociate appreciably in the vicinity of the end-point when the concentration of free metal... 

Where atomic absorption spectrophotometry is possible the ammonium acetate extract can be directly analysed for Ca and Mg. The spectrophotometric standards are prepared in the ammonium acetate solution and both the standard and extracts are read against ammonium acetate as blank. If AAS is not possible the calcium and magnesium are analysed by complexometric titrations using ethylene diamine tetra acetic acid (EDTA). 

H.V. Malmstadt, Rapid and accurate automatic titration of calcium and magnesium in dolomites and limestones. Use of EDTA titrant and automatic derivative spectrophotometric end-point termination, Anal. Chim. Acta 19 (1958) 563. 

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