The estimation of calcium in urine by flame photometry, with a note on the estimation of sodium and potassium.

Many methods for calcium estimation by flame spectrophotometry have been described. Investigations of biological material have dealt chiefly with plasma (Baker, 1955; Chen and Toribara, 1953; Denson, 1954; Kingsley and Schaffert, 1953; Llaurado, 1954; Maclntyre, 1954; Mosher et al., 1951; Rothe and Sapirstein, 1955; Winer and Kuhns, 1953; Zak et al., 1953), with application to urine in some cases (Chen and Toribara, 1953; Kingsley and Schaffert, 1953; Rothe and Sapirstein, 1955; Severinghaus and Ferebee, 1950; Winer and Kuhns, 1953). The removal of interfering substances has been accomplished by precipitating calcium by oxalate (Chen and Toribara, 1953; Kingsley and Schaffert, 1953; Llaurado, 1954) or diammonium hydrogen phosphate (Mosher et al., 1951) and by cation exchange columns (Brabson and Wilhide, 1954; Denson, 1954). Direct readings have been employed, using synthetic standards to compensate for interfering elements (Baker, 1955; Kingsley and Schaffert, 1953; Maclntyre, 1954; Winer and Kuhns, 1953) or determining sodium and potassium before calcium (Chen and Toribara, 1953; Severinghaus and Ferrebee, 1950). Radiation buffers (West et al., 1950) and selfstandardization methods (Rothe and Sapirstein, 1955) have also been used. Most of these methods are either very time consuming or may be used only for specimens such as plasma and tissue which have a narrow range of variation. It is difficult to adapt one method to urine which will compensate for the widely varying composition found in both normal and pathological specimens. Rothe and Sapirstein (1955) survey the difficulties and demerits of the various published