A Rapid Hydrogen Electrode Method for Determination of Hydrogen Ion Concentrations in Bacterial Cultures or in other Turbid or Colored Solutions

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Recently the determination of hydrogen ion concentrations has come into such general use in biologic work that the question often arises as to the choice of-a method for this purpose. The colorimetric method has proven suitable for most routine bacteriologic work, and has the advantage of yielding a large number of determinations in a given period of time. Its limitations however are noteworthy. In general, it does not permit of more than a fair degree of accuracy especially for colored or turbid solutions; for opaque solutions it cannot be used; when large percentages of or are in solution, its results are not dependable because of the so-called salt and protein errors of indicators; and the preparation of the standard solutions, in which one is required to assemble a great number of calibrated burets, pipets, bottles, etc., and to recrystalize, dry to constant weight and accurately weigh a number of reagents, many of which are difficult to obtain, makes it a cumbersome method. On the other hand, the extreme accuracy possible by the hydrogen electrode method, with potentiometer and constant temperature device, is seldom required in biologic investigation. Moreover, the cost of such equipment is prohibitive for many laboratories. More simplified outfits are described in texts on physical chemistry, but the obvious objection to them is the relatively enormous amount of time consumed in saturating the solution with hydrogen gas. This difficulty is obviated by observing the principle suggested by Hasselbach1 in which the solution and gas are brought into equilibrium in a few minutes by shaking in a closed vessel.