Abstract
A discussion of the bicolorimetric principle was first presented to this Society in November, 1921, 1 at which time we had the present work in mind. The method described below is essentially an adaptation of the colorimetric method of Cullen 2 for the determination of the PH of the blood plasma (or serum) to the bicolorimeter described by one of us. 3 As modified the final determination is carried out on 0.1 c.c. of plasma, and does not require more than 10 minutes after the blood has been obtained. The color comparison can be made with an accuracy of ± PH 0.02.
Blood is drawn without stasis in a narrow 5 c.c. Luer glass syringe containing sufficient mineral oil to fill any air spaces, and is at once delivered into a centrifuge tube of special design under oil. This tube is made of Pyrex glass and has at the bottom a bulb of 2 c.c. capacity (30 mm. in length with an internal diameter of 11 mm. and a neck of 4 mm.). Tubes with bulbs of 1 and 5 c.c. capacity have also been used, the latter being employed when a simultaneous estimation of the CO2 content of the plasma is to be made. One drop of neutral 20 per cent. potassium oxalate is dried in the tube, after which three drops of mineral oil are added. In transferring the blood from the syringe to the centrifuge tube, the point of the needle is placed under the oil and sufficient blood delivered to bring the oil into the neck of the bulb. With the slight pressure exerted the blood readily takes up the oxalate and does not clot. The tube is centrifuged at moderate speed for about two minutes to separate the plasma.
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