Question

15. a. A scanning UV/Vis spectrometer and a diode array uv vis spectrometer ane two kinds of UV/Vis instruments. Please list one advantage of each design (2 points) b. Please describe the design of an ATR (attenuated total reflection) accessory for measurements of solid samples in the FTIR instruments, (use a drawing. 3 points

Answer 1

The advantage of an Ultraviolet - Visible Light Spectrophotometer (UV-Vis spectrophotometer) is its quick analysis ability and easy to use. In astronomy research, an UV / Vis spectrophotometer helps the scientists to analyze the galaxies, neutron stars, and other celestial objects. A UV spectrum can provide rich information of the velocity and the elements of an astronomical object. In other industries, UV / Vis spectrophotometer also brought the high-tech spectral analysis possibilities.

For example, in the food industry, the quality and safety of foods are two most important factor for consumers. Lose these two conditions, may lose the profit or even lose the reputation in the business and lead to bankrupt finally. Thus, in addition to the general sense of food quality factors, such as color, appearance, smell, taste, an UV / Vis spectrophotometer can further assist the food supplier an instrumentation ways of analysis by chemistry, biology and by the high standards of quality control and production processes to improve the shelf life of the foods as well as maintaining the safety.

Attenuated total reflectance is applied to samples where the composition of the surface needs to be measured. It is applied to soft samples such as paper, fur, polymers and textiles, which can achieve good contact with the crystal used. It is also used for aqueous samples and viscous or sticky samples such as pastes, soaps and detergents. The only consideration to be borne in mind is the need to obtain good optical contact between the surface of the sample and the crystal of the accessory, which can be made of diamond, ZnSe, Ge, Si, KRS-5, etc.

DESIN FOR ATR acessory:An ATR accessory operates by measuring the changes that occur in an internally reflected IR beam when the beam comes into contact with a sample. An IR beam is directed onto an optically dense crystal with a high refractive index at a certain angle. This internal reflectance creates an evanescent wave that extends beyond the surface of the crystal into the sample held in contact with the crystal.

In regions of the IR spectrum where the sample absorbs energy, the evanescent wave will be attenuated. The attenuated beam returns to the crystal, then exits the opposite end of the crystal and is directed to the detector in the IR spectrometer. The detector records the attenuated IR beam as an interferogram signal, which can then be used to generate an IR spectrum.