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

In Ca²⁺ and Mg²⁺ buffer solutions the ionised concentrations ([X²⁺]) are either calculated or measured. Calculated values vary by up to a factor of seven due to the following four problems: The calculated [X²⁺] in buffers are so inconsistent that calculation is not an option. Until standards are available, the [X²⁺] 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 [Ca²⁺] in the nmolar range, and the apparent constant (K^/) values for Ca²⁺ and Mg²⁺ binding to intracellular ligands amongst different laboratories. Standardisation of Ca²⁺/Mg²⁺ buffers is now essential. The parameters to achieve this are proposed.