INDUSTRIAL AND ENGINEERING CHEMISTRY
30
However, the applicability of the erythrosin method is not limited to the conditions set forth in that procedure. One way of extending the scope of the method is based upon the use of standard solutions that have concentrations other than 0.1 M . A few determinations carried out with 0.05 M and 0.2 M lead nitrate showed that with these solutions accurate results can easily be obtained, provided the conditions (quantities of alcohol and indicator) are adjusted adequately. It will be worth while to study the titration with these standards more closely with the purpose of working out analytical procedures for the estimation of amounts of sulfate that are either larger or smaller than those of the above range. Such an extension of the method would also broaden the applicability of the successive determination of chloride and sulfate that has been suggested in this paper. Another
VOL. 11, NO. 1
fertile field for further investigation is the replacement of ethyl alcohol by diluents that can be obtained without legal restrictions. Preliminary experiments revealed that both acetone and isopropyl alcohol give satisfactory results, though a somewhat smaller volume is to be used for a given titration as compared to ethyl alcohol.
Literature Cited (1) Fajans, K., and Hassel, O., 2. Elektrochem., 29, 495-500 (1923). (2) Iyer, V., J . Indian Chem. Soc., 12, 164-7 (1935). (3) Kolthoff, I. M., Lauer, W. M., and Sunde, C. J., J . Am. Chem. SOC.,51, 3273-7(1929). (4) Ricci, J. E., IND. ENG.CHEM.,Anal. Ed., 8, 130-2(1936). (5) Roy, S. N., J . Indian Chem. SOC.,12,584-5 (1935). (6) Wellings, A. W., Trans. Faraday Soc., 28, 5 6 1 4 (1932). RECEIVED September 9, 1938.
Glass Electrode for Determining Blood pH at 38" C. >I. K. HORWITT Biochemical Research Laboratory, Elgin State Hospital, Elgin, Ill.
T
HE procedure for estimating the pH of blood under anaerobic conditions can be facilitated by building a glass electrode into the barrel of a hypodermic syringe. (This hypodermic electrode is now made by Rascher and Betzhold, Inc., Chicago, Ill.) The determination can then be made directly on blood drawn into the syringe within one minute after collection. Any size of barrel may be used, but the 1.5-cc. size has been found most convenient in this laboratory. The plungers on the market are made of a heat-resisting glass, which will not fuse to Corning 015; therefore, it is necessary to grind a 7.5-em. (3-inch) length of soft-glass tubing until i t fits the barrel to be used. This is easily accomplished with the aid of a turning lathe, using fine silicon carbide powder as an abrasive. One end of this tube is closed off with a thin layer of Corning 015; the maximum thickness of this layer will depend on the measuring instruments employed. One of the author's electrodes, which has a membrane about 0.25 mm. thick, used in conjunction with --.
+ c- RUBBER
a Beckman pH meter, has lasted for more than 5 months, during which time several hundred determinations have been made. The procedure for determining the p H of blood with this electrode is as follows: The plunger (after a preliminary soaking in 0.1 N hydrochloric acid for 24 hours) is half filled with a solution of 0.1 N hydrochloric acid cdntaining a slight excess of quinhydrone, and inserted into the barrel on which the metal clip for holding the plunger in place has been retained. Sufficient neutral sterile isotonic saline solution is then drawn into the syringe with needle attached to fill the air spaces in the needle and between the end of the plunger and the barrel. One drop of saline solution will fill all the air spaces in a well-constructed electrode. The syringe is then held in the hand for a few minutes to raise the temperature of the quinhydrone solution. About 1 cc. of blood is drawn into the syringe, all but about 0.2 cc. of which is immediately expelled, the needle is removed, and the syringe is half immersed in a saturated potassium chloride solution at 38" C. The potassium chloride solution serves as both the salt bridge and the constant-temperature bath as illustrated in Figure 1. A small calomel halfcell is kept in the potassium chloride bath during the procedure. A small thermometer (not shown in diagram) is also kept in the potassium chloride solution. Sufficient warm water at about 40" C. is siphoned to the 50-cc. beaker t o keep the contents at 38" C. Placing the 50-cc. beaker in a 100-cc. beaker helps t o insulate the contents. A steady e. m. f. should be obtained within 2 minutes after immersion of the electrode in the potassium chloride solution, the time being dependent on the difference in temperature between the glass electrode and the calomel halfcell. Readings taken more than 5 minutes after withdrawal of the blood from the vein are not to be trusted because of an acid shift which becomes appreciable at that time. No acid shift is observed in blood within the first 3 minutes if the temperature is carefully controlled. Clotting does not have a measurable effect on the observed pH (1). If one is careful to check each electrode with standardized buffers before and after each series of determinations, an accuracy of better than 0.02 pH unit may be obtained.
Literature Cited (1) Ferguson, J. H., and DuBois, D., J . Lab. Clin. M e d . , 21, 663-9 (1936).
FIGURE 1.
DIAGRAM OF APPARATUS
Corning 015 gl ss indicated by dotted line
RECEIVED July 6, 1938. Demonstrated at Baltimore meeting of hmerican Society of Biological Chemists, .4pril, 1938.
