A contribution to the development of the flame-photometric determination of sodium and potassium in blood serum

Abstract

1. 1. An apparatus is described for the flame-photometric determination of alkali elements. With the exception of the burner, it is constructed from already existing standard accessories. The burner is of the type used by Heierman and Vendrik, the atomizing spray is of the type designed by Boon. The optics consist of one lens and several combinations of glass filters to select the spectral lines. For detection a CsCs 2O vacuum phototube is used. The photocurrent is measured with an a.c. galvanometer after a.c. amplification, according to Milatz et al. 2. 2. With this apparatus sodium and potassium can be determined in 0.5 ml of blood serum. The accidental error of a determination is 2%. 50 samples can be analyzed in 3 hours, including all operations for calibration and calculation. It has also been used to determine lithium an calcium. 3. 3. The serum to be investigated is deproteinized by tenfold dilution with a 5% solution of trichloroacetic acid and the filtrate is examined in the apparatus. 4. 4. Mean values found from 40 determinations in sera of normal human subjects over a period of six months were: Na, 333 mg/100 ml; K, 20.7 mg/100 ml. Recoveries of added alkalis were 96% and 97% respectively for Na and K. 5. 5. The excess of chlorine in the flame, due to the trichloroacetic acid, prevents irregularities which might otherwise be caused by a shifting of the dissociation equilibria for KCl and NaCl. The situation is somewhat complicated owing to the presence of hydrogen in the flame. 6. 6. Several organic solvents enhance the atomization, giving at most an eightfold increase of the galvanometer deflections for 2 mg K per 100 ml solution. 7. 7. The form of the standard curves is discussed. Self-absorption accounts for the curvature of the Na graph; the form of the K graph is determined by the ionization of the K under the prevailing circumstances. 8. 8. The presence of an excess of Na has a marked influence on the determination of K. This is theoretically and experimentally shown to be mainly caused by the repression of the ionization of K by electrons originating from the Na. In practice a simple graphical correction removes this difficulty. 9. 9. The error of 2% in the determination is quantitatively accounted for by a critical evaluation of the separate accidental errors involved in the procedure.