Serum Calcium Using the Eel Flame Photometer

Flame photometry has many applications, and in the clinical field its use in the estimation of serum sodium and potassium is now well established. Difficulties have been encountered in the estimation of serum calcium by flame photometry, since the emission spectrum of calcium is relatively weak and is subject to interference by the presence of other ions, e.g., sodium. Although many methods have been published in America, using chiefly the Beckman DU spectrophotometer with flame attachment and an oxy-acetylene flame (Severinghaus and Ferrebee, 1950; Mosher, Itano, Boyle, Myers, and Iseri, 1951 ; Kingsley and Schaffert, 1953), only two procedures have been described using the Eel flame photometer (Powell, 1953; Llaurado, 1954) which is the most used British commercial instrument. Consequently in this country, at least, serum calcium is still widely estimated by the classical permanganate titration method. This method, which gives reproducible results in skilled hands, can lead to gross errors with faulty technique and is not suitable if much less than 2 ml. serum is available. Furthermore, the results obtained may not necessarily give the true amount of calcium present. Insufficient washing of the calcium oxalate precipitate leads to high results due to the presence of titratable ammonium oxalate, and too much washing produces low results on account of loss of calcium oxalate in the washing fluid. In flame-photometric methods similar problems are present. Excess oxalate depresses the emission of the calcium flame, sodium and potassium have a positive interference effect, and the possibility of loss of calcium in the washing fluid is still present. An attempt has been made to overcome these difficulties. Owing to the increasing demand for serum calcium estimations in infants, a micro-calcium method, simple to perform and sufficiently accurate and reliable for the routine estimation of serum calcium, is very desirable. The aim of the author has been to devise such a method using 0.2 ml. serum and the Eel flame photometer. Preliminary Experiments