What is Attenuated Total Refraction (ATR)?

Infrared spectroscopy is an important method to analyze the structure of compounds. The conventional transmission method USES press sheet or coating film for measurement, and it is difficult to test some special samples (such as insoluble, insoluble, incomable, etc. Attenuated Total reflection Infrared spectrometer (ATR) was designed to overcome these shortcomings.

The application of ATR greatly simplifies the testing of some special samples, and makes the analysis of micro-area components convenient and fast. The detection sensitivity can be up to 10-9 g order of magnitude, and the diameter of micro-area can be measured up to several microns.

Medium infrared spectrum:

The mid - infrared spectrum is the absorption spectrum of a substance in the mid - infrared region.

Generally, the infrared band of 2.5-25 m is classified as the mid-infrared region.

At the same time, because of the most mature, simple, long history of use, widely used, the data accumulation is the largest.

Because the fundamental frequency vibration is the most absorbed vibration in the infrared active vibration, the region is most suitable for the qualitative and quantitative analysis of infrared spectrum.

In environmental monitoring, mid - infrared spectroscopy is mainly used for organic pollution monitoring.

The infrared absorption spectrum that says commonly, point to namely in infrared spectrum, this infrared area is measured instrument has infrared spectrophotometer, not dispersive infrared photometer and Fourier transform infrared spectrometer.

The advantages of ATR and conventional infrared analysis:

Compared with the conventional infrared technology, there is no need to make sample and destroy sample, it can directly identify monofilament, cloth and garment, which greatly improves the inspection speed and easy to operate. The experimental results show that the method is easy to operate, sensitive to measurement and can obtain high quality infrared spectra.

The distinction of ATR and conventional infrared analysis:

The difference between attenuated total reflection technique (ATR) and conventional infrared analysis is weak in the infrared spectrum intensity of ATR in the area of 4000~2000 cm-1. However, the absorption peak in the fingerprint region is the same as the conventional infrared spectrum, so it does not affect the judgment of the spectrum, and the quality of the spectrum is relatively high.

ATR theory:

ATR accessories are designed based on the principle of internal reflection of light.

The infrared light from the light source passes through the crystal with a large refractive index and then projects to the surface of the sample with a small refractive index. When the incident Angle is larger than the critical Angle, the incident ray will produce total reflection.

In fact, the infrared light is not reflected back completely, but penetrates to a certain depth inside the sample surface and then returns to the surface. In this process, the sample has selective absorption in the incident light frequency region, and the reflected light intensity weakens, generating a similar figure to transmission and absorption, so as to obtain the structural information of the surface chemical composition of the sample.