The use of the bicolorimeter for the estimation of the hydrogen-ion concentration of urine

In connection with a study of the acid-base balance of the blood in alkalosis it seemed necessary to secure information regarding the hydrogen ion concentration of the urine. The use of the bicolorimeter for this purpose was suggested in an earlier communication, 1 but details of the technique remained to be worked out. The method as now employed is outlined below. We believe that it increases the simplicity, delicacy and accuracy of the determination.

Three indicators have been employed—phenol red, brom cresol purple and brom cresol green (or methyl red). Wedges are calibrated for each of these indicators, the range employed for phenol red being pH 6.6 to 8.6; for brom cresol purple pH 5.2 to 7.0; and for brom cresol green (or methyl red) pH 4.6 to 5.4. Phenol red is employed in an 0.02 per cent concentration, while an 0.04 per cent solution is used for the other two indicators. The alkaline wedges employed with the phenol red and brom cresol purple indicators are filled with m/15 secondary phosphate diluted with 10 per cent of the indicator solution (1 cc. for 10 cc. of phosphate solution); while the acid wedges are filled with m/15 primary phosphate similarly diluted with indicator. The wedges for the brom cresol green indicator are made up with Clark's phthalate-NaOH mixture, the alkaline wedge having a pH of 5.8, and the acid wedge of 4.0. In the calibration of the wedges Clark's phthalate-NaOH mixture is used for the range pH 4.6 to 5.2, and Sorenson's buffer phosphates for the range pH 5.2 to 8.6. Since brom cresol purple covers the range pH 5.2 to 7.0 it will take care of the great majority of urines, although for very strongly acid urines, or for alkaline urines, the other two indicators are necessary.