Thermodynamics of the Second Dissociation of a Substituted Aminopropanesulfonic Acid (TAPSO) from 5 °C to 55 °C

Abstract

Electromotive force (emf) measurements of the cell without a liquid junction of the type Pt|H2|TAPSO (m1) + NaTAPSOate (m2) + NaCl (m3)|AgCl|Ag were made at intervals of 5 K from 5 °C to 55 °C, including 37 °C, with stoichiometric molalities m1 = m2 = m3 ranging from 0.01 to 0.1 mol·kg-1. At 25 °C, pK2 is 7.635, and consequently buffer solutions of TAPSO and its salt (NaTAPSOate) are useful for pH control in the region pH 6 to 8. The second dissociation constant (pK2) of TAPSO can be expressed by the equation 2254.0057/(T/K) − 4.9783 + 0.88672 ln(T/K), with a standard deviation of ±0.0008. The zwitterionic buffer TAPSO is represented as 3-[N-(tris(hydroxymethyl)methyl)amino]-2-hydroxypropanesulfonic acid, a derivative of the parent compound taurine.