HATR or Horizontal Attenuated Total Reflectance accessory offers a number of benefits over conventional sampling methods adopted for liquids and solids. Conventional sampling techniques are time consuming, often messy and are plagued with inconsistencies arising from in-homogeneities and mixture matrix ratio variations. Hygroscopicity of sampling salts further complicates the spectra. HATR provides solutions to problems arising under such situations.
Basic principle of HATR
HATR is based on measurement of changes that take place in a totally reflected IR beam passing through a crystal which is in intimate contact with the sample. The infrared beam is directed on the crystal surface at an angle greater than the critical angle so that instead of transmission it gets reflected multiple times internally before emerging. On each reflection the beam penetrates 0.5 to 5.0μ beyond the crystal surface into the sample and due to multiple reflections the emerging wave carries with it the absorption characteristics of the sample in contact with the crystal.
The accessory is easily adapted for analysis of liquids, films and fine powders. The crystal needs to be fully covered for achieving spectral reproducibility.
Several available options increase the versatility of the technique
- Choice of HATR plates with materials ranging from ZnSe, KRS – 5, Ge, Diamond, etc.
- Flat plate version for films and powders and trough plate version for liquids and slurries.
- Temperature controlled and flow-through crystal plates for real-time monitoring of reactions
- Software features for observing spectrum in real-time as applied force is increased on solid samples after clamping to arrive at optimum pressure needed to achieve the desired spectral quality..
All the available options discussed above extend the scope of applications to permit analysis of a wide range of samples with minimum sample preparation to include :
- Solid powders and films
- Liquid samples including highly viscous liquids and slurries
- Strongly absorbing samples and aqueous solutions. This is possible as the beam passes only a negligible path through the sample
Aqueous samples could not be analyzed using conventional techniques as water is a strong absorber in the IR region.