Résumé
A microfluidic system combined with substrate-integrated hollow waveguide (iHWG) vapor phase infrared spectroscopy has been developed for evaluating the chemical activity of volatile compounds dissolved in complex fluids. Chemical activity is an important yet rarely exploited parameter in process analysis and control. The instrumental approach developed herein uniquely enables controlled evaporation/permeation from a sample solution into a hollow waveguide structure, and analyzing the partial pressures of volatile constituents. It was shown that the chemical activity may be deduced from partial pressure measurements at thermodynamic equilibrium conditions. The combined microfluidic-iHWG mid-infrared sensor system allows realizing such studies in absence of any perturbations provoked by sampling operations. In this study, the first water activity measurement made by a microfluidic-iHWG device is presented. For proof-of-concept purpose water-NaCl mixtures are investigated.