Calcium chelatometric determination

Chelatometric determination of calcium itself is carried out with chela-tone at pH 12-13 using murexide as the indicator (from red to violet), or a mixture of murexide and fluoroexone and thymolphthalexone (from green to violet-pink). By this method it is possible to determine calcium at concentrations of 10-200 mg 1 [13, 14). 

Major and minor elements in coal, having concentrations easily detectable by most modem analytical techniques, can be determined by a number of acceptable procedures. Various approaches, combining a. number of specific procedures, are frequently referenced in the literature. For example, the presently accepted procedure (ASTM D-2795) determines silicon, aluminum, iron, titanium, and phosphorus colorimetrically, calcium and magnesium chelatometrically, and sodium and potassium by flame photometry. This standard test method was withdrawn in 2001 but is still used in some laboratories. 

There are also test methods (ASTM, 2011k,w) for the analysis of coal (and coke) ash which cover the determination of nine major constituents of ash silicon dioxide, aluminum oxide, ferric oxide, titanium dioxide, phosphorous pentoxide, calcium oxide, magnesium oxide, sodium oxide, and potassium oxide (ASTM, 2011k) by a combination of spectrophotometric techniques, chelatometric techniques, and flame photometry. Determination of these same constituents, including manganese dioxide, can be achieved by atomic absorption (ASTM, 2011w). 

Calcium and magnesium ions are determined side by side in a solution by chelatometric titration, with for example voltammetric end-point indica-... 

Calcium ions are determined together with magnesium ions in a solution by chelatometric titration, with for example voltammetric indication. For this purpose, first the sum (Ca2+ + Mg " ) is titrated with Na2EDTA, and then Ca " is titrated alone with Na2EGTA under working conditions in which IVlg is not determined. The Mg2+ content is given by the difference. 

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