Calcium determination by flame photometry; methods for serum, urine, and other fluids.

The convenience and accuracy of flame photometric determinations of sodium and potassium in biological fluids (1, 2) have suggested the desirability of extending these advantages to determinations of calcium. Since calcium emission lines are much less intense than those of sodium and potassium (3), the samples of diluted serum (1: 50) customarily used for sodium and potassium determinat.ions are not adequate for the measurement of calcium concentrations. Serum dilutions of the order of 1: 10 are adequate provided their viscosity is reduced by precipitation of the proteins with trichloroacetic acid. At the wave-length used for calcium measurements, a correction is necessary for the effect of sodium and potassium upon calcium emission and upon flame background. The correction may be easily derived. The resulting determinations of calcium agree well with those obtained by the Van Slyke-Sendroy technique and in our hands are somewhat more rapid and accurate.