Ionised concentrations in calcium and magnesium buffers: Standards and precise measurement are mandatory.

In Ca and Mg buffer solutions the ionised concentrations ([X]) are either calculated or measured. Calculated values vary by up to a factor of seven due to the following four problems: The calculated [X] in buffers are so inconsistent that calculation is not an option. Until standards are available, the [X] in the buffers must be measured. The Ligand Optimisation Method is an accurate and independently verified method of doing this (McGuigan & Stumpff, Anal. Biochem. 436, 29, 2013). Lack of standards means it is not possible to compare the published [Ca] in the nmolar range, and the apparent constant (K) values for Ca and Mg binding to intracellular ligands amongst different laboratories. Standardisation of Ca/Mg buffers is now essential. The parameters to achieve this are proposed.