title: Automatic determination of ligand purity and apparent dissociation constant (K(app)) in Ca(2+)/Mg(2+) buffer solutions and the K(app) for Ca(2+)/Mg(2+) anion binding in physiological solutions from Ca(2+)/Mg(2+)-macroelectrode measurements.
abstract: Calibration of Ca(2+)/Mg(2+) macroelectrodes and flurochromes in the nmolar and mumolar range, respectively, require the use of buffer solutions. In these buffers the apparent dissociation constant (K(app)) has to be measured since calculation based on tabulated constants gives variable results. The ligand concentration [Ligand](T) has also to be estimated. The most accurate and general method for measuring both is the ligand optimisation method based on macroelectrode potential measurements, but this iterative method is time consuming, thus limiting its application. This paper describes an automatic program based on the method, which on entering the measured macroelectrode data calculates K(app), [Ligand](T) and the ionised concentration [X(2+)] within minutes. This optimisation method cannot be used at K(app) values greater than 0.1mM, but can be extended into this region if the anion concentration is known. The program has been modified to cover this eventuality. Ca(2+)/Mg(2+) macroelectrodes in conjunction with these programs offer an accurate, routine method for determining K(app) and [Ligand](T) in buffer solutions at the appropriate ionic strength, temperature and pH and the K(app) for divalent cations binding to physiological anions under experimental conditions.
authors.affiliation: Department of Statistics, University of Glasgow, Glasgow G12 8QQ, UK. jim_w_kay@yahoo.co.uk
authors.forename: James W
authors.initials: JW
authors.lastname: Kay
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Steven
authors.forename: John A S
authors.initials: JA
authors.lastname: McGuigan
authors.forename: Hugh Y
authors.initials: HY
authors.lastname: Elder
mesh_terms: D000465:Algorithms; D000838:Anions / Q000737:chemistry; D002021:Buffers; D002118:Calcium / Q000032:analysis* / Q000737:chemistry; D002138:Calibration; D002614:Chelating Agents / Q000737:chemistry; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D017736:Ion-Selective Electrodes; D016018:Least-Squares Analysis; D008024:Ligands; D008274:Magnesium / Q000032:analysis* / Q000737:chemistry; D012984:Software; D014584:User-Computer Interface
chemical_list: D000838:Anions; D002021:Buffers; D002614:Chelating Agents; D005456:Fluorescent Dyes; D008024:Ligands; D008274:Magnesium; D002118:Calcium