title: Use of the computer program EQUIL to estimate pH in model solutions and human urine.
abstract: The computer program EQUIL was designed to calculate relative supersaturations of solute components of common urinary stones. In an extended software version, quantitative consideration of charge balance for a priori or a posteriori pH estimation was added. The reliability of this computation was tested with hydrogen ion titration of buffer solutions containing HEPES [N-(2-hydroxyethyl)piperaizine-N'-ethanesulfonic acid] as well as samples of normal human urine. In the model solutions with HEPES, the difference between calculated pH values and the measured pH was smaller than 1.2% for any titration step within the buffer zone (pH 8.5-6.8). The pH values calculated for whole urine differed from the measured pH by 7% to 53%, and the calculated charge inbalance ranged from 2.6 to 9.6 mM. This net cation inbalance indicates that there is a need to account for other anionic components, including hippurate, amino acids, and isocitrate. In experimental solutions, charge balance calculations with EQUIL can be of great utility because they permit a priori estimation of pH or computation of the composition at a desired pH.
authors.affiliation: Department of Surgery, University of Florida, College of Medicine, Gainesville.
authors.forename: D
authors.initials: D
authors.lastname: Ackermann
authors.forename: C
authors.initials: C
authors.lastname: Brown
authors.forename: M
authors.initials: M
authors.lastname: Dunthorn
authors.forename: D L
authors.initials: DL
authors.lastname: Purich
authors.forename: B
authors.initials: B
authors.lastname: Finlayson
mesh_terms: D002021:Buffers; D006531:HEPES; D006801:Humans; D006863:Hydrogen-Ion Concentration; D012984:Software; D014545:Urinary Calculi / Q000652:urine; D014556:Urine / Q000032:analysis*
chemical_list: D002021:Buffers; D006531:HEPES