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    Home > Chemicals Industry > Chemical Technology > Polarimeter and Nicol prism

    Polarimeter and Nicol prism

    • Last Update: 2021-09-15
    • Source: Internet
    • Author: User
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    1.


    Polarimeter is an instrument for measuring the optical rotation of a substance


    1.


    The commonly used polarimeter is the domestic WXG-4 type circular polarimeter


    Figure 2-6 WXG-4 type circular polarimeter


    Figure 2-7 Schematic diagram of the internal structure of WXG-4 circulator

    The optical system of the polarimeter is installed on the base with an inclination of 20°


    When put into the test tube containing the test solution, due to the optical rotation of the solution, the plane-polarized light is rotated by an angle, and the zero-degree field of view changes, as shown in Figure 2-8 (1), (3) or (4) ) Shown


    Figure 2-8 Resolution diagram of zero-degree field of view

    (1) Greater or less than the zero-degree field of view (2) Zero-degree field of view (3) Less than or greater than the zero-degree field of view (4) Full-bright field of view

    2.


    (1) Turn on the power supply and turn on the power switch of the instrument.


    (2) Adjust the eyepiece of the polarimeter to make the light and dark areas and the dividing line in the field of view very clear; turn the dial to adjust the hand wheel, observe and be familiar with the law of light and dark changes in the field of view


    (3) Be familiar with the reading method of the vernier scale and record the maximum instrument error


    Reading method: The polarimeter adopts double cursor reading to eliminate the eccentricity of the dial



    (4) Check whether the zero position of the instrument is accurate, that is, when an empty polarimeter tube or a blank reagent is loaded into the tube, adjust the polarimeter to the state shown in Figure 2-8 (2), and see that the brightness of the two parts of the field of view is uniform and When it is dark, write down the corresponding readings on the left and right cursor windows on the dial as the zero reading


    (5) Put the test tubes filled with solutions of known concentration (four types in total) or unknown concentration (one type) into the instrument one by one, readjust the eyepieces to make the dividing line between bright and dark areas clear, and then rotate the analyzer to make the field of view uniformly bright And it is darker, as shown in Figure 2-8 (2), write down the corresponding angle from the left and right windows on the dial


    (6) The optical rotation (left-handed or right-handed) of the substance is determined by the direction in which the polarized light is rotated


    (7) Use known or measured data to plot to determine the optical rotation of the solution
    .

    (8) Find the concentration of the solution to be tested from the curve made
    .

    3.
    Matters needing attention

    (1) The solution should be filled with the vortex tube without bubbles; if there are bubbles in the vortex tube, the bubbles should be located at the bulge of the tube
    .

    (2) The outer side of the polarimeter and the transparent windows at both ends of the polarimeter should be cleaned before it can be installed in the polarimeter
    .

    (3) Pay attention to placing the polarimeter tube properly during operation to avoid breaking it
    .

    (4) Do not switch on and off the power of the instrument repeatedly.
    If the sodium light is off, stop it for a few minutes and then turn it on again
    .

    2.
    Introduction to Nicol Prism

    The Nicol prism is a polarizing prism made of calcite crystal after processing, the structure is shown in Figure 2-10
    .
    ABCD is the main plane of the Nicol prism
    .
    Cut the calcite vertically into two parts along sinθ in the main plane, and then glue them together with Canadian gum
    .

    Figure 2-10 Nicol prism diagram

    The working principle is: after natural light enters the AB end face of the prism, it is decomposed into o light and e light
    .
    The refractive index of calcite to o light and e light are n=1.
    658 and n=1.
    486, respectively, while the refractive index of Canadian gum is between the two (n=1.
    55)
    .
    When the incident light reaches the interface sinθ, yes
    .
    In terms of light, since the refractive index of the gum is smaller than that of the o light, the o light is totally reflected (the incident angle is 77° and the critical angle is 69° 15') and is absorbed by the black-painted BC side
    .
    The e-light can be emitted through the gum layer
    .
    In this way, natural light is converted into polarized light with light vibration in the principal plane
    .

    In addition to Nicol prisms, there are also Volast prisms and Rochon prisms with similar working principles, both of which are very good polarization beam splitting components
    .

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