Abstract
Scientific questions in fields such as catalysis, monitoring of biological processes, or environmental chemistry demand analytical technologies combining orthogonal spectroscopies. Combined spectroscopic concepts facilitate in situ online monitoring of dynamic processes providing a better understanding of the involved reaction pathways. In the present study, a low-liquid-volume multispectroscopic platform was developed based on infrared attenuated total reflection (IR-ATR) spectroscopy combined with Raman spectroscopy and luminescence sensing. To demonstrate the measurement capabilities, exemplary analyte systems including water/heavy water and aqueous solutions of ammonium sulfate were analyzed as proof-of-principle studies. It was successfully demonstrated that three optical techniques may be integrated into a single analytical platform without interference providing synchronized and complementary data sets by probing the same minute sample volume. In addition, the developed assembly provides a gastight lid sealing the headspace above the probed liquid for monitoring the concentration of molecular oxygen also in the gas phase via luminescence quenching. Hence, the entire assembly may be operated at inert conditions, as required, for example, during the analysis of photocatalytic processes.
Highlights
For many state-of-the-art analytical questions including reaction pathway monitoring during photocatalysis or biological processes, rapid and time-resolved tracking of molecular structures, composition, and quantities is a prerequisite
We have developed an analytical assembly combining the benefits of infrared attenuated total reflection (IR-ATR) spectroscopy with its complementary vibrational spectroscopic counterpart, Raman spectroscopy
To evaluate the performance of the developed measurement platform with regard to water and deuterium oxide mixtures, the intensity ratios were determined by calculating the ratio of the mean value of the peak intensity for 100% H2O and D2O for IR and Raman
Summary
For many state-of-the-art analytical questions including reaction pathway monitoring during photocatalysis or biological processes, rapid and time-resolved tracking of molecular structures, composition, and quantities is a prerequisite. Midinfrared (MIR) spectroscopy has matured into one of the most prevalent analytical techniques for monitoring molecular processes owing to its inherent selectivity, nondestructiveness, and rapid data acquisition capabilities. IR-ATR is frequently used as an analytical tool for the detection, identification, and quantification of molecules in the gas, liquid, and solid phase.[1,2] Owing to the excitation of specific vibrational, rovibrational, and rotational modes, characteristic spectral patterns are obtained enabling qualitative and quantitative analysis, and providing access to chemical and structural characteristics, that is, “fingerprinting” any molecular species. The use of Fourier transform infrared (FTIR) spectrometers facilitates time-resolved studies for in situ and online monitoring, for example, in process control, during reaction pathway elucidation, and in environmental analysis.[1,3−5]
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