X-ray spectroscopy in the clinical laboratory. I. Calcium and potassium.

I N i earlier publication it was pointed out that x-ray spectroscopy was, potentially, a practical tool for the routine analysis of the elements in biologic systems (1), and was particularly applicable to the problems of the clinical laboratory (2). This is the first of a series of studies designed to evaluate this method of analysis for the routine laboratory of clinical chemistry. Specifically it deals with the application of this instrument to the analysis of total calcium and potassium levels in blood serum. For comparison, the sera were analyzed for potassium with the flame photometer, using the Baird instrument (3). These analyses were subsequently repeated to determine the precision of the method under routine laboratory conditions. This same procedure was used for calcium estimation, using the Clark-Collip method on 1 ml. of serum (4). The same sera were then assayed twice for potassium and twice for calcium using the x-ray spectrograph. Tables 1 and 2 compare the results obtained by the conventional methods as compared to the x-ray spectrograph. These tables also compare means and standard deviations. Figures 1 and 2 show the standard curves obtained with the x-ray spectrograph, using 25 l. of serum for calcium and potassium, respectively, at the different levels of concentration. Figures 3 and 4 are tracings obtained with the x-ray spectrograph, plotting counts per second obtained, against the angle (20) using different concentrations of the elements.