Determining the Partial Pressure of Volatile Components via Substrate-Integrated Hollow Waveguide Infrared Spectroscopy with Integrated Microfluidics

Abstract

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. Access to chemical activity parameters enables systematic studies on phase diagrams of complex fluids, the detection of aggregation processes, etc. The instrumental approach developed herein uniquely enables controlled evaporation/permeation from a sample solution into a hollow waveguide structure and the analysis of the partial pressures of volatile constituents. For the example of a binary system, it was shown that the chemical activity may be deduced from partial pressure measurements at thermodynamic equilibrium conditions. The combined microfluidic-iHWG midinfrared sensor system (μFLUID-IR) allows the realization of such studies in the absence of any perturbations provoked by sampling operations, which is unavoidable using state-of-the-art analytical techniques such as headspace gas chromatography. For demonstration purposes, a water/ethanol mixture was investigated, and the derived data was cross-validated with established literature values at different mixture ratios. Next to perturbation-free measurements, a response time of the sensor <150 s ( t) at a recovery time <300 s ( t) has been achieved, which substantiates the utility of μFLUID-IR for future process analysis-and-control applications.

A microfluidic study of synergic liquid–liquid extraction of rare earth elements

“…Once fully integrated with computer controlled mixing capability and online characterization methods such as hollow waveguide FTIR, 24,99 XRF, 32 and ultimately small angle X-ray scattering, we anticipate that phase diagram exploration can be fully automatized, with very little down time. It would furthermore also give access to kinetics information and interfacial mass transfer rate constants, otherwise difficult to obtain.…”

“…In order to reduce time and volume, relying on microfluidic devices represents a very promising route. 15,[22][23][24][25][26][27][28][29][30][31] Indeed, since the pioneering work of Ismagilov and co-workers, 22 microfluidics has been developed as a popular method to save quantities of test materials needed to complete experimental plans in formulating efficient processes. The main difficulties in using microfluidics instead of the old ''batch'' method are related to the adsorption of electrolytes on all interfaces present and to the sensitivity required in elemental analysis.…”

Effects of porous media on extraction kinetics: Is the membrane really a limiting factor?

“…Finally, the feasibility to implement on-line analytical devices (FTIR) on milli-fluidic chip has been successfully demonstrated [21,60]…”

“…Microfluidics is an advantageous way of implementing assays for membrane-based extraction, whether for gas-liquid [21] or liquid-liquid interface [17,[22][23][24][25][26]. With regard to a pertraction device, a microfluidic chip offers the advantage of small sample consumption, faster equilibrium and better control over extraction kinetics [22].…”

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…iHWG-based cells provide excellent modularity and mechanical stability, with effective OPL of hundreds of millimeters and larger losses per unit length than Ag/AgI-HWG-based cells [32], which could achieve an effective OPL of several meters. The sensor could operate in the DAS, WMS, or intrapulse modulation regime as well [33,[133][134][135][136]. An integrated sensor consists of a compact MIR laser, a new gas cell, and a detector, as shown in Figure 1.…”