Table 1. Preparation of Constant Ionic Strength McIlvaine Buffered Solutions Reference: P.J. Elving, J.M. Markowitz, I. Rosenthal, Analyt. Chem. 28(7): 1179-1180 (1956) pH Desired Composition, G/Liter of Solution Composition, Moles/Liter of Solution Buffer System G/Liter of KCl added per liter at 25 C H3C6H5O7.H2O Na2HPO4.12H2O H3C6H5O7.H2O Na2HPO4.12H2O Ionic Strength of Solution to produce IS of (MW 210.141) (MW 358.142) 210.141 358.142 (IS), M 1.0 M 0.5 M pH H3C6H5O7.H2O Na2HPO4.12H2O H3C6H5O7.H2O Na2HPO4.12H2O Ionic strength ( gm/L) (gm/L) (moles/L) (moles/L) (IS) 4.8 10.7 35.3 0.0509 0.0986 0.2320 5 10.2 36.9 0.0485 0.1030 0.2560 6.8 4.79 55.4 0.0228 0.1547 0.3920 The above table is taken from the reference cited by Elving et al. This table shows the concentrations (in grams/Liter) for Citric Acid monohydrate (MW 210.141) and Na2HPO4.12H2O (MW 358.142). I converted these to moles/Liter for the 3 pH values of interest (4.8, 5.0, and 6.8). The 3 ionic strength values are those provided by Elving et al. Unfortunately they do not show their calculations of IS in their publication and I have been unable to figure out how they arrived at these 3 values. I would greatly appreciate any help you can provide to show me how these values of IS were calculated. Thank you.