The extra-thermodynamic tetraphenylphosphonium tetraphenylborate assumption has been tested for dimethylsulfoxide using ATR FTIR spectroscopy. Solute-affected DMSO spectra show that, contrary to the TPTB assumption, the charge density on BPh₄⁻ and Ph₄P⁺ ions is sufficiently high to influence the DMSO molecules orientation with respect to the cation and to the anion. Apparently, the Ph₄P⁺ cation does not affect the structure of DMSO whereas the BPh₄⁻ anion clearly breaks it up. Our results indicate that the TPTB extra-thermodynamic assumption is not a sound basis for splitting thermodynamic values obtained for DMSO solutions into ionic contributions.