DIETHYLBARBITURATE BUFFER

Abstract

In the series of buffers now used, there is no other buffer system to cover the range around pH = 8 with a sufficient reliability except for the borate buffer of Sorensen.This buffer has, however, certain disadvantages which are strongly felt in practical use.The borate buffer Eannot be used in compounds containing two or more hydroxyl groups, such as polyphenols, polyhydric alcohols, and especially carbohydrates of any kind.These substances combine with boric acid to form complex acids of an appreciable strength.Not only is the pH of the borate buffer perceptibly shifted in the presence of those substances but, what is worse, those substances themselves are no longer present in their original state in contact with the borate buffer.This disadvantage was encountered on the occasion of the investigation of the effect of pH on the activity of all carbohydrate-splitting enzymes and on the measurement of oxidation-reduction potentials of certain dyestuffs containing two hydroxyl groups, to be described in a subsequent paper.This gap in the buffer series is due to the fact that practically no acid was known with a dissociation constant around lo-*.Recently Kolthoff (1) found a dissociation constant of approximately lo+ for diethyl,barbituric acid (veronal).So it seemed likely to me that this acid might be useful as a buffer for the wanted range.This turned out to be true.The following data, calculated from the experimental calibration with the hydrogen electrode, will suffice for practical purposes.10.30 gm. of sodium diethylbarbiturate (Verona1 sodium) are dissolved in COz-free water to a volume of 500 cc.The quality of the commercial preparation was satisfactory without recrystalliza-33