Determination of Blood pH Without Transferring the Sample.

Abstract

The simple procedure described here has been devised to obviate the necessity of transferring the blood and of using mineral oil, both of which tend to complicate the technique for determining the pH colorimetrically. The only special apparatus∗ required for this consists of a sampling tube identical in shape and size (10 × 1.5 cm.) with the tubes used to contain the standard solutions. It is provided with a double-holed, hollow, glass stopper, which is ground-in and which has sealed to it a small, two-way stop-cock with two holes. (Fig. 1.) The apparatus is made of clear Pyrex or Nonsol glass and connections are made with special rubber tubing, which will not cause excessive film formation on the mercury. Before use all apparatus, including the mercury, is cleaned and tested for neutrality in a manner similar to that outlined by Austin, Cullen, et al. 1

The general method followed is essentially that of Cullen 2 as modified by Hastings and Sendroy. 3 Whole blood is used instead of plasma in accordance with the method of Hawkins. 4 The necessary correction factor for converting the colorimetric readings to the true pH value is found by the method proposed by Austin, Stadie and Robinson. 5

When a determination is to be made, the apparatus is assembled as shown in the accompanying figure. Mercury is run from the bulb B into the sampling tube and connecting tubes until these are completely filled to the three-way inlet stop-cock C, thereby excluding all air. The sampling tube held by a clamp attached to the stop-cock S is then inverted. With the stop-cocks S and C open to make direct communication between T and E, the latter is immersed in a small flask of indicator-saline solution, which has been adjusted previously to a pH of approximately 7.40, and the air in E is displaced with mercury by elevating B.