Thermodynamical Aspects on the Determination of Bicarbonate in Urine

Abstract

Despite the fact that the composition of urine varies a lot during the day, this has essentially been neglected as a factor of importance in determinations of urine bicarbonate. The investigations reviewed in combination with an own study shows that qualitative and quantitative factors in urine composition impacts the solubility of carbon dioxide as well as the dissociation constant for the bicarbonate buffer system. These two “constants” are of outstanding importance in the determination of bicarbonate, using the total carbonic acid method as well as the carbon dioxide equilibration method. Nomograms are presented to quantify the influence of different urine compositions on the determinations of bicarbonate in final urine and tubular fluid.