Stability Constant Measurements

Authors should provide sufficient information to enable the reader to establish quickly and unambiguously the exact conditions used, and also to evaluate properly the experimental results.

The following information should appear in any paper reporting stability constant measurements:

• The full name of the ligand(s) according to IUPAC nomenclature.
• The purity of reagents and solvents, and the procedures followed in solvent or reagent purification.
• The composition of the solution, especially the inert electrolyte and its ionic strength, and any other relevant factors including the range of metal and ligand concentrations investigated. For mixed solvent systems the solvent composition must be defined.
• Where appropriate, the pH range over which measurements were made, and the k_w value assumed.
• The instrument(s) (e.g. pH meter, electrodes, spectrophotometer, etc.) used in the experimental studies.
• The method used for electrode calibration, e.g. as an [H⁺] (concentration) probe or, as is often the case with a glass electrode calibrated using standard buffers, as an _H probe.
• The temperature and temperature range.
• The number of datum points recorded in a titration (or other experiment, as appropriate), and the number of replicate measurements.
• A clear definition of the ligand stoichiometry, H_nL, and of the equilibria defined by K_i, *K_i, _i or _p,q,r:
  
  

  

  
  
• The computer program, or other method of calculation, used to derive the final results from the experimental data, and a literature reference if the program is the work of others.
• The range of results, the standard deviation on the final result, the sources of error, and the methods used in establishing these parameters.
• Where appropriate, supplementary evidence to potentiometric data (e.g. spectroscopic, ESR or NMR data) to confirm stoichiometries and co-ordination mode inferred from the numerical analysis.         

Most stability constant measurements can be reported in brief tabular form if the points above are followed (see table) and any special comment placed in the text.

Finally, a discussion of the reasons which prompted the experiments, and of the chemical information subsequently derived from the measurements, would serve to make stability constant data part of chemistry as a whole, rather than a separate topic in itself. Similarly, comparisons with previous determinations on identical or similar metal ligand systems would help to place the work in a proper context. Stability constant measurements give useful quantitative chemical information, which can often be related to other structural and preparative work, and authors should show the relevance of their results.