Fourier transform infrared spectroscopy, or FTIR, is an analytical technology used in industry and academic laboratories to understand the structure of molecules and the composition of molecular mixtures. FTIR spectroscopy uses modulated mid-infrared energy to interrogate a sample. The infrared light is absorbed at specific frequencies directly related to the atom -to-atom vibrational bond energies in the molecule. When the bond energy of the vibration and the energy of the mid-infrared light are equivalent, the bond can absorb that energy. Different bonds in a molecule vibrate at different energies and therefore absorb different wavelengths of the IR radiation. The position or frequency and intensity of these individual absorption bands contribute to the overall spectrum, creating a characteristic fingerprint of the molecule. Since FTIR spectroscopy produces signals that are specific to the type of molecular bonds or functional groups, it is the ideal tool to measure the making and breaking of chemical bonds during a reaction. Coupling FTIR spectroscopy with attenuated total reflectance, or ATR, increases the utility of this technology by providing a means to monitor reactions in situ and in real time. Measurements via ATR-FTIR eliminate the need to manually sample the reaction for offline analysis, making it possible to determine in real time key reaction characteristics such as initiation, end point, reactive intermediates, kinetics, and mechanistic information. FTIR spectroscopy is fundamentally a qualitative or relative measurement technology. but can also produce quantitative measurements of important reaction components. FTIR follows the Beer Lambert Law, A equals ABC, where the molar absorptivity, A, and the path length, B, are essentially fixed and therefore constant. So the absorbance that a vibrational frequency for a specific bond is directly proportional to the number of this specific bond or concentration. Once calibrated, much like that for HPLC, each measurement by the FTIR instrument will be quantitative for the reaction components it was calibrated to measure. Now real-time quantitative information can be obtained throughout the duration of the reaction, which can be used as control variables for conditions such as add the next reagent, cool, or heat, and even end the reaction. For more information, go to mt.com slash FTIR.
Reaction Analysis Simplified
To understand chemical reactions, chemists must address the following:
- When does the reaction start? When does the reaction stop?
- What are the reaction kinetics and mechanisms?
- What is the effect of those transient intermediates?
- Did it react as expected? Did any by-products form and why?
- What happens if reaction temperature, dosing rates, and mixing rates change?
To get the best data and analyze reactions quickly, these are five key areas that ReactIR in-situ FTIR instruments leverage so that reaction understanding is available for every chemist — expert or not.
