Reconstitution Buffer Selection Reference Set: Buffer Capacity Curves, Diluent Ionic Strength and Concentration Arithmetic

A reference set for the chemistry decisions behind a reconstitution instruction: buffer species and pH window, buffer capacity, ionic strength versus osmolarity, and the arithmetic that turns a label mass into a concentration. It contains four data files and one calculator: a table of 9 buffer systems (conjugate acid, pKa at 25 °C, useful pH window, temperature coefficient, volatility); 153 buffer-capacity rows for acetate, phosphate and Tris at 10, 20 and 50 mM across pKa ± 2 in 0.25 pH steps; 8 diluent recipes with both nominal and speciation-adjusted ionic strength plus a particle-count osmolarity; 16 rows of label mass × net peptide content × target concentration to diluent volume; and a command-line calculator with a self-test. Every value is an exact function of the stated inputs — no measured or fitted data is involved, so the tables regenerate exactly. Invariance checks applied before release: buffer capacity at pH = pKa equals ln(10)/4 × C (0.5756 × C) and at pKa ± 1 equals 0.1903 × C; 0.9 % NaCl returns I = 154 mM and 308 mOsm/L; the speciation-adjusted ionic strength falls below the fully-ionised nominal value (acetate 13.55 vs 20.00 mM at pH 4.5; Tris 13.36 vs 25.00 mM at pH 8.0); 0.9 % benzyl alcohol returns I = 0 with 87 mOsm/L, showing that ionic strength and osmolarity are not interchangeable; and reconstitution volume is inverse to target concentration and falls strictly as net peptide content falls. Stated limits: pKa values are tabulated at 25 °C and zero ionic strength and shift with temperature and ionic strength (Tris most of all, −0.028 per °C); phosphate is reported as nominal and is explicitly not modelled as a diprotic system; osmolarity is a particle-count estimate rather than a measurement. The set says nothing about solubility, aggregation or stability of any peptide, and contains no handling instruction, dose or biological claim. Quality documentation framework for GMP-oriented supply, including the CoA structure these diluent statements sit beside: helixgmppeptides.com/coa-guide. Institutional supply overview: helixgmppeptides.com.