Abstract
Since the work of Cullen 1 and others on the determination of the pH of serum with quinhydrone, some investigators have had difficulty with this method, because of the rapid drifts in potentials. Cullen, Wilson 2 and others have reported that satisfactory quinhydrone serum pH determinations can be made by reading potentials rapidly at noted times and extrapolating in order to obtain the potential at zero time.
In a recent study at this laboratory it was necessary to perform a large number of dog serum pH determinations, and it seemed desirable to check the colorimetric method by an electrometric method. When parallel pH determinations on dog serum were made with the colorimetric method, using the Hastings bicolorimeter 3 and with quinhydrone at room temperature (24° to 26°) it was found that the 2 methods agree to within 0.02 pH. The quinhydrone method is very rapid and convenient, and since it is free from the personal factor of matching colors, it has, in our hands, been more reliable than the colorimetric method. The procedure is briefly as follows:
The electrode vessel consists of 2 ordinary glass tubes which fit snugly one inside the other, a rubber connection which holds the tubes in any desired relative position, and a platinum wire sealed into the inner tube. The inner tube contains mercury through which metallic contact to the platinum wire can readily be made. The outside tube is 8 cm. in length, and 4 mm. in inside diameter, so that its total capacity is about 1 cc., although these dimensions can be varied at will. By moving the inner tube up or down through the outer tube, liquid can be conveniently drawn up or expelled.
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