Polarimetry

Polarimetry is an optical method of study is based on the ability of optically active compounds rotate the plane oscillations of a linearly polarized light (see Isomerism).
Atoms and molecules luminous bodies emit electromagnetic waves. When complete disorder in the arrangement of these particles body emit so-called natural light, in which the oscillation of the vectors of the electric (or magnetic) field occurs in all planes passing through the direction of propagation of light wave. Orderliness in the direction of oscillation fields is called the polarization of light. This light, in which the fluctuations of the electric (magnetic) fields occur in the same plane, called the plane of polarised light, and the plane in which varies the intensity of a magnetic field of light rays - plane of polarization. Polarized light can be obtained by letting natural light through polarizing prisms made of special crystals. These crystals are crystals of Iceland spar, which usually serves polarizing prisms (prism Nicolas). With the passage of polarized light through an optically active substance is the rotation of the polarization plane, but find it only by using the same polarizing prisms (analyzer). Investigation of the rotation of the polarization plane is used for studying the structure of optically active compounds, and also for a quantitative their definitions. Optical activity is characterized by the value of the specific speed [α], i.e., the rotation angle of the polarization plane of a solution containing 1 ml 1 g optically active compounds in a thickness of a layer of liquid in 1 inch
Specific rotation calculated according to the rotation rate of the solution of the connection with known percent concentration:
[α] = α100/l·C
& alpha is the angle of rotation in degrees, C - concentration in %, l is the thickness of a layer of a solution in inch Specific rotation varies with the change of temperature and wavelength of light. Therefore, the definition is carried out in monochromatic light прb a certain temperature. Wavelength and temperature are marked with values [and]. Knowing from reference tables specific rotation of this connection, and having determined the rotation angle of the solution of this connection, it is easy to calculate the concentration:
C = α100/[α]l
The solution should contain no other optically active compounds.
To determine the rotation of the plane of polarization of optical devices-polarimeters. Polarimeter (Fig. 1) consists of two polarizing prisms: fixed - rotating polarizer and analyzer and tubes with the test solution. The swing angle can be defined by setting the analyzer on an equal illumination of the entire field of view first, without mortar, and then optically active compounds. In this case the analyzer must be turned at an angle equal to the angle of rotation of the polarization plane of the investigated solution. The angle of rotation counts in a circle with divisions (limbu). If after installation of a tube with a solution and the parser will rotate clockwise, this is called the right (+)if counterclockwise, on the left (-) rotation. To improve accuracy polarimeters equipped with additional details from quartz. In some polarimeters alignment light after installation of the solution and the reference concentration of optically active substances produced by linear movement quartz wedge. The accuracy of conventional polarimeters of 0.05 degrees. For obtaining monochromatic light usually use filters. Method polarimetry is widely used in laboratories; clinical laboratories and laboratories of the food industry method polarimetry used to determine the sugar content. Polarimeters, used for determining the content of sugar cane, are called sheremetye (Fig. 2).

Fig. 1. Scheme of polarimeters of different types: a system with two plates of bechvarzh, b - semi-transparent with Nicholl; - semi-transparent with two Nikolai. 1 - polarizer; 1' and 1" - Nicoli; 2 - record of bicarsa; 3 - tube with a solution; 4 - analyzer (right - schema light fields polarimeters).
Fig. 2. The V-polarimeter-Sheremet JUICE (scheme): 1 - illuminator; 2 - filter; 3 - aperture; 4 - lens; 5 - Nicole; 6-tube researched solution; 7 - stationary quartz wedge; 8 - mobile quartz wedge; 9 - analyzer; 10-eyepiece; 11 - cover; 12 - screw; 13 - magnifier.