A New Type of Centrifuge Tube for Preparation of Blood Serum for Accurate pH Work

Abstract

The conventional methods for the preparation of blood serum for pH determination involve the following steps: 1 the blood is drawn into centrifuge tubes under oil; the oil is displaced with wax or with a rubber stopper; after centrifuging, the wax or rubber stopper is again replaced with oil and the serum lying between the oil and the cells is withdrawn with a pipette which also contains some oil. Aside from being time-consuming this procedure has a primary difficulty in that the contact of the serum with the oil brings about changes in the CO₂ tension and thus in the pH of the serum. This difficulty has been overcome in part by using oil having the same CO₂ tension as the blood. Often, however, the CO₂ tension of the blood is not known beforehand and this remedy is at best time-consuming and approximate.

A centrifuge tube is here described which enables one to prepare serum from blood without contact with anything except glass and mercury. The accompanying sketch shows a tube with an S shaped capillary at the top and a U shaped capillary at the bottom. For filling the centrifuge tube with blood a T-tube with stopcock below the side-arm is attached to the upper capillary and the hypodermic needle is attached to the upper end of the T-tube, both through rubber connections. A rubber tube leading to a mercury leveling bulb is attached to the lower capillary through which the centrifuge tube is filled with mercury. Care must be taken to sweep all bubbles of air out of the S capillary. The mercury level is put a few millimeters above the side-arm of the T-tube and the stopcock below the side-arm is closed. The needle is now inserted into the blood vessel and about one cc. of blood is caused to flow through the side-arm of the T-tube above the stopcock, sweeping any air out ahead of it.