A multicomponent fluid composition monitoring and compositional control system, in which a component analysis is effected by titration or other analytical procedure, for one or more components of interest, and a computational means then is employed to determine and responsively adjust the relative amount or proportion of the one or more components in the multicomponent fluid composition, to maintain a predetermined compositional character of the multicomponent fluid composition. The system is usefully employed in semiconductor manufacturing photoresist and post-etch residue removal, in which the cleaning medium is a semi-aqueous solvent composition, and water is the monitored and responsively adjusted component.