Gratin - Gas-recycling atom-economic infrared spectroscopy
Being based on the jet-FTIR principle of the filet-jet, the new gratin-jet setup includes some new experimental features. Although the nozzle (700 × 0.2 mm2) is even longer, an improved alignment of nozzle and buffer volume allows for the downsizing of the buffer to 4 m3. However, the main differences are the recycling of expanded gases and the possibility to heat the nozzle as well as the vacuum chambers and tubings.
After the expansion through the nozzle, the gas mixture is recompressed and routed back to the 200 L reservoir, before it is expanded again. A total air leakage rate in the order of 10-4 hPa⋅L/s facilitates several hours of jet-FTIR measurements of one single gas filling until contaminates aggregate to problematic concentrations and the gas mixture needs to be dumped. Consumption of carrier gas and analytes is therefore reduced by up to two orders of magnitude compared to the filet-jet, rendering the utilization of expensive analytes or carrier gases, such as neon, possible. Heating the vacuum chambers, tubing, and nozzle to 80°C and evacuating with a Pfeiffer HiPace 2300 C turbomolecular pump between measurements removes contaminations of air and previous analytes. Furthermore, the custom-made Horst heating enables measurements of samples having insufficient vapor pressure at room temperature.
Liquid or solid analytes can be cleaned and subsequently introduced into the vacuum via two home-built gates. Gaseous samples and carrier gases can be routed directly into the vacuum chambers. For the jet-FTIR measurements of the thus created mixtures, the gas pulses with a length of 70-150 ms are synchronized to the Bruker Vertex 70V spectrometer. By waiting 20-30 s between pulses, the desired stagnation pressure in the reservoir is restored before a new pulse and the background pressure in the buffer is kept sufficiently low during the pulse. CaF2 or KBr optics combined with a 50 or 150 W tungsten lamp or Globar rod as lightsource and an InSb/HgCdTe sandwich or InGaAs detector are available to record spectra in the near (8000 cm-1) to mid (800 cm-1) infrared range.
- Optimization of the setup
- Study of hydrogen bonding competitions between different acceptor sites (e.g. carbonyls)
Below you find a few impressions of the newest member in our family of jet-spectrometers.