What Is a Polarimeter?

Polarimeter is an instrument for measuring the rotation of a substance. By measuring the optical rotation of the sample, the concentration, content, and purity of the substance can be determined by analysis. Widely used in pharmaceutical, pharmaceutical inspection, sugar, food, spices, monosodium glutamate, and chemical, petroleum and other industrial production, scientific research, and teaching departments for laboratory analysis or process quality control.

Figure 1: 1. Light source 2. Frosted glass 3. Condenser 4. Color filter 5. Polarizer 6. Half-wave plate 7. Test tube 8. Polarizer 9. Object, eyepiece group 10. Focusing handwheel 11. Reading magnifier 12 .Dial and vernier 13.Dial turn handwheel

(1) Insert the power plug of the instrument into a 220V AC power source, and ground the ground pin reliably.

(2) Turn on the power switch. At this time, the sodium lamp should be turned on, and it needs to be warmed up by the sodium lamp for 5min to make it emit light and stable.

(3) Turn on the power switch (If the sodium light lamp goes out after the light source switch is turned on, turn the light source switch up and down repeatedly for 1 or 2 times to make the sodium light lamp light up under DC, which is normal).

(4) Turn on the measurement switch. At this time, the digital tube should have a digital display.

(5) Put the test tube containing distilled water or other blank solvents into the sample chamber, cover the lid, and press the zero button when the reading is stable. If there are air bubbles in the test tube, let the air bubbles float on the convex neck first. The misty water droplets on both ends of the clear surface should be dried with a soft cloth. The screw cap of the test tube should not be over-tightened, so as not to cause the action and affect the reading. Pay attention to the position and orientation of the mark when placing the test tube.

(6) Take out the test tube, inject the sample to be tested into the test tube, place it in the sample chamber in the same position and direction, and close the lid of the box. The instrument's digital display window will show the optical rotation of the sample.

(7) Press the repeat test button one by one, repeat reading several times, and take the average value as the measurement result of the sample.

(8) If the sample exceeds the measurement range, the instrument oscillates back and forth at ± 45. At this time, remove the test tube, open the lid of the box and press the zero return button in the box, and the instrument will automatically return to the zero position.

(9) After using the instrument, turn off the measurement, light source, and power switch in order.

(10) When the sodium lamp cannot be used when the DC power supply system fails, the instrument can also be tested with the sodium lamp AC power supply, but the performance of the instrument may be slightly reduced.

(11) When a small-angle sample (less than 0.5 °) is placed, the indication may change. At this time, as long as the retest button is pressed, a new number will appear.

(1) The polarimeter should be placed in a ventilated, dry and suitable place to prevent moisture and mold.

(2) The continuous use time of the polarimeter should not exceed 4 hours. If it is used for a long time, it should be turned off for 10 to 15 minutes in the middle. After the sodium light lamp is cooled down, continue to use it, or blow it with an electric fan to reduce the degree of heating of the lamp tube, so as not to reduce the brightness and life.

(3) After using the test tube, pour out the solution in time, wash it with distilled water, and dry it well. All lenses should not be rubbed directly by hand, and should be wiped with a soft flannel.

(4) When the polarimeter is disabled, put a plastic sleeve on it. When packing, put it in the box according to the fixed position and press it tightly.

(1) Solvent

The optical rotation of an optically active substance depends mainly on the structure of the substance itself. In addition, it is also related to the thickness of the light transmitting material, the wavelength and temperature of the light used in the measurement. If the test substance is a solution, the influencing factors also include the concentration of the substance, and the solvent also has a certain effect. Therefore, the optical rotation of optically active substances is usually different under different conditions.

(2) Temperature

Increasing the temperature will make the optical tube expand and lengthen, which will cause the density of the liquid to be measured to decrease. In addition, temperature changes will cause association or dissociation between the molecules of the substance to be measured, which will change the optical rotation. Different materials have different temperature coefficients, generally between-(0.01 ~ 0.04) ° C. For this reason, constant temperature must be used in the experimental measurement. The thermostat is equipped with a thermostatic jacket and connected to the super thermostatic bath.

(3) Concentration and length of optical tube

Under certain experimental conditions, the optical rotation and concentration of optically active substances are often considered to be directly proportional, because the ratio

MC024-WXG-4 Disc Polarimeter

Fundamental

As we all know, visible light is an electromagnetic wave with a wavelength of 380nm ~ 780nm. Due to the statistical properties of the luminous body, the direction of vibration of the electric vector of the electromagnetic wave can take any direction perpendicular to the direction of light propagation. With some devices (such as polarizers), the vibration direction can be fixed at a certain direction perpendicular to the direction of light wave propagation to form the so-called plane polarized light. When the plane polarized light passes through a certain substance, the vibration direction of the polarized light will be turned by Angle, this kind of material is called optical rotation material, the angle that polarized light is rotated is called optical rotation. If the plane-polarized light passes through some pure optically active substance, the degree of optical rotation is related to the following three factors:

a) The wavelength of the plane polarized light. The rotation is different for different wavelengths.

b) The temperature t of the optically active substance. The degree of optical rotation is different at different temperatures.

c) The types of optically active substances. Different optically active substances have different optical rotations.

A quantity called specific rotation [] t is used to represent the optical rotation ability of a certain substance.

[] t represents the optical rotation of a unit-length optically active substance at a temperature of t ° C for plane-polarized light with a wavelength of .

The optical rotation is related to the length L of the optically polarized material through which the plane polarized light passes, so that at a temperature of t ° C, the length is L, and the optical rotation of the optically polarized material having a specific rotation [] t to the plane-polarized light with a wavelength of The degree t is expressed by the following formula:

t = [] t · L (1)

If the optically active substance is dissolved in a non-optical solvent at a concentration of C, the following formula holds:

t = [] t · L · C (2)

Note: In the formulas (1) and (2), the length units of [] t and L must be the same.

If the wavelength must be at a standard temperature, such as 20 ° C, the specific rotation [] t of the test substance is known in advance, and the length of the test solution is constant. At this time, if the optical rotation t is measured by a polarimeter, then (2) The formula calculates the concentration C of the optically active substance in the solution

C = t / [] t · L (3)

If the solute contains a non-optical substance in addition to the optically active substance, the content or purity of the optically active substance can be calculated from the concentration when the solution is prepared and the concentration C of the optically active substance obtained from formula (3).

The disc polarimeter is used to determine the organic matter containing optical rotation, such as sugar solution, turpentine, camphor and so on. By measuring the rotation, the concentration, content, and purity of the test substance can be analyzed.

Specifically used for: testing sugar content and determining starch content in food condiments

Hospital clinical: determination of sugar content and protein in urine

Sugar industry: inspection of sugar solution concentration during production

Drug perfume: determine the optical rotation of drug perfume oil

Colleges and universities; teaching experiment

specification:

1. Measurement range of optical rotation: ± 180 & ordm;

2. Dial value: 1 & ordm;

3. Dial cursor reading value: 0.05 & ordm;

4. Magnification magnification: 4 times

5. Monochromatic light source: 5893A & ordm; (sodium light lamp)

6. Test tube length: 100mm200mm