Diffuse reflectance infrared Fourier transform spectroscopy or DRIFTS is a technology that allows collecting and analyzing scattered IR energy. This process spectroscopy is highly applied for the measurement of fine and powder particles, nevertheless, it can be used for rough surface measurement as well.
One of the advantages of diffuse reflectance spectroscopy is its simplicity because practically no sample preparation is needed. However, the following three procedures of sample preparation are recommended for the measurement by diffuse reflectance spectroscopy:
- It is necessary to fill the micro‐cup with the powder, then use diffuse reflectance accessory for the process spectroscopy, focus the beam on the sample surface by a focusing mirror, and finally, collect the necessary IR energy. Herewith, it should be noted that it is required to fill the micro-cup gradually to maintain the focus.
- It is possible to prepare the sample surface to the diffuse reflectance infrared Fourier transform spectroscopy by scratching its surface with an abrasive paper, then it is necessary to measure the number of particles holding to the piece of paper.
- The last method requires placing solution drops on a substrate, and then to evaporate the solvent. The remaining particles on the substrate need to be analyzed and measured.
The principle of the process spectroscopy operation is the following: the IR beam enters the sample, and the beam can be either transmitted through the particle or to be reflected off the sample surface. Usually, in the case of the surface reflection, the IR energy is lost, that is why it is necessary to save it during the diffuse reflectance spectroscopy.
For this purpose, it is necessary to make the IR beam reflecting off the next particle during its passing through a particle. Thus, at the time of the process spectroscopy, the transmission-reflectance action can occur several times in the sample that highly increases the pathlength. Therefore, we obtain the scattered IR energy collected with the help of a spherical mirror, which is focused onto the special detector and the detected light from the IR beam is absorbed by the sample particles, offering the necessary data about the sample.
Diffuse reflectance spectroscopy ideally suits for powdered or crystalline materials in the mid-IR and NIR spectral ranges., as well as intractable solid samples. The most important thing of such process spectroscopy for sampling measurement is considered to be in the possibility of its automation to increase sample throughput.
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