A novel capillary forces-founded accessory for reliable measurements of ATR-FTIR spectra of volatile liquids

Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) is one of the most commonly used IR sampling techniques. This is due to the simplicity and fastness of operation, and no need to pre-prepare samples. Furthermore, ATR is a non-destructive technique that allows the analysis of very small amounts of sample. Nevertheless, while it is easy to measure good-quality spectra of solids and non-volatile liquids, reliable ATR-FTIR analysis of volatile samples stays quite challenging so far. This is because of the changes that occur over the measurement time in the sample composition associated with its evaporation. Herein, we proposed a novel, simple accessory which makes feasible the long-time measurements of ATR-FTIR spectra of such samples. The concept is based on the capillary rise effect. Trapping the sample in the capillary minimizes its contact with the atmosphere, and therefore prevents its evaporation and possible interactions with oxygen. The tests carried out for two highly volatile mixtures (i.e. polystyrene dissolved in dichloromethane and automotive gasoline) revealed that using the developed accessory enables stabilization of the sample at an acquisition time extended for up to 40 min. This in turn allows for improving the quality of the spectra, which feature a 2.7-2.9 times higher signal-to-noise level than for the conventional measurements.

Automated summary

Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) is a commonly used IR sampling technique due to its simplicity and quick operation, as well as its ability to analyze small sample amounts. However, reliable ATR-FTIR analysis of volatile samples has been challenging because of changes in sample composition during measurement. The proposed capillary rise effect accessory allows for long-time measurements of volatile samples, improving spectrum quality with higher signal-to-noise levels.