When measuring optical rotation with a polarimeter, what are the conditions of the solvent that is u

The use and precautions of polarimeter:

A before the determination of the instrument and the sample should be placed in a constant temperature chamber of 20 or a constant temperature chamber at a specified temperature, and a constant temperature water bath can also be used to keep the sample chamber or sample test tube above the constant temperature lh, especially some optical rotation substances that have a great impact on the temperature, which is particularly important.

b Before turning on the power supply, check whether there are foreign objects in the sample room, whether the sodium lamp source switch is in the specified position, whether the indicator switch is in the closed position, whether the instrument is placed in the appropriate position, and do not move the instrument after the sodium lamp is turned on.

c.After turning on the sodium lamp, the normal glow time is at least 20min, and the light can be stabilized. If there is a polarity switch, the polarity should be changed frequently after the shutdown to prolong the service life of the sodium lamp.

d Before the measurement, when the instrument is zeroed, the retest switch must be pressed repeatedly, so that the polarizer deviates from the optical zero position to the left or right respectively. By observing the stop points of the left and right retests, it is possible to check the repeatability and stability of the instrument. If the error exceeds the specification, the instrument should be repaired before use.

e Put the measuring tube filled with distilled water or blank solvent into the sample chamber, if there are bubbles mixed in the measuring tube, the bubbles should be floated on the convex neck, and the glass at both ends of the clear surface should be dried with a soft cloth. During the measurement, the position and direction of the measuring tube should be fixed as much as possible, and the marking should be done to reduce the error of the stress of the measuring tube and the coverslip.

f When the same optical rotation substance is measured with different solvents or different pH values, due to different associations, solvation and dissociation, the specific rotation changes, or even changes the direction of optical rotation, so the specified solvent must be used.

g The solution that is turbid or contains small particles cannot be determined, and the solution must be centrifuged or filtered first, and the initial filtrate must be discarded for determination. Some substances and solutions that change the optical rotation greatly after seeing light must be protected from light. Some places where the time of absence has a greater impact on the optical rotation must also be measured within the specified time.

h When measuring the blank zero point or the stop point of the test solution, the readings should be taken three times and the average value should be taken. For strict determination, the zero point should be corrected with a blank solvent before each measurement, and after the measurement, the zero point should be checked with a reagent for any change, and if the zero point is found to have changed greatly, it should be re-measured.

At the end of the assay, the assay tube should be washed and dried and put back in place. The instrument should avoid dust placed in a dry place, and a little desiccant can be placed in the sample chamber to prevent moisture.

1. Before the sample is measured, the zero point of the polarimeter should be checked in order to correct and ensure the accuracy of the test.

2. The solution used to do the zero point inspection liquid should usually be a liquid without optical rotation.

Determination of optical rotation:

Polarimetric method can be used for the quantitative determination or purity testing of various optically active substances, and the sample is prepared into a solution of a certain concentration in a specified solvent.

To study the reaction mechanism of optical molecules. Determination of the reaction rate constant of optical rotation substances, etc.

Some photorotational substances have different biological effects on left-handed or right-handed substances, such as the physiological role of glucose, chlorase, etc.

To calibrate and ensure the accuracy of the test, the solution used should usually be a liquid without optical rotation.

The optical rotation of molecules was first discovered by pasteur in the nineteenth century. He discovered that the crystallization of tartaric acid has two opposite crystal forms, and when it is formed into a solution, the light will rotate in opposite directions, so it is determined that the molecule has different structures of left-handed and right-handed. When ordinary light passes through a polarized lens or nicol prism, a portion of the light is blocked, and only light that vibrates in a direction parallel to the prism's crystal axis can pass through.

This kind of light, which vibrates in only one plane, is called planar polarized light, or polarized light for short. The vibrating surface of polarized light is chemically customarily called the polarization plane. When plane-polarized light passes through a solution of chiral compounds, the direction of the polarization plane is rotated by an angle.

This ability to rotate the polarization plane is called optical rotation. Among chiral molecules, racemates do not have optical rotation, and racemates have optical rotation after separating monomers.

The significance of measuring the optical rotation of optical rotation compounds is that the ratio to a specific compound can be determined.

The optical rotation of a substance is a constant, usually the ratio of optical rotation to a particular compound.

The object has optical rotation, and its structure cannot have the property of spatial inversion and invariance. For polycrystalline or solutions where the molecule can be randomly oriented, the molecule must be chiral. The optical rotation caused by the chirality of the organic molecule itself is called internal rotation, and the internal rotation is divided into left-handed and right-handed light, but if an object has both left and right rotational light inside or the structure of the object molecule itself has opposite chirality, then the object does not exhibit optical rotation.

Since the molecule inside the object that has both left and right optical rotation and does not exhibit optical rotation is called racemic, while the structure of the molecule itself has opposite chirality and does not exhibit optical rotation is called racemic.

Optical rotation can be described in terms of the dimensions of left-handed and right-handed light with different propagation velocities. Any polarized light can be seen as a superposition of left-handed and right-handed light. When superimposing left-right and left-handed light into polarized light, the direction of polarization is related to the phase difference between the two types of light.

If the two types of light travel at different speeds, an additional dimensional difference is created, causing the polarized light to rotate.

The purity and content of optical rotation can be checked by the measurement of optical rotation, and even the reaction rate constant of optical rotation can be determined, that is, the reaction mechanism of optical rotation substances can be studied.

There are several standard complex solutions.

Glare, proportional relationship bai

Make a comparison or use the drawing method to draw a diagonal line according to the zhi optical rotation of the standard solution, find the slope, and use the linear formula with the oblique line.

Determination of optical rotation: Polarimeter is an instrument used to determine the magnitude and direction of optical rotation capacity of optical active substances. In addition to the structure of the substance, the magnitude and direction of the optically active substance can rotate the polarized light plane, and the temperature at the time of measurement, the wavelength of the light used, the concentration and solvent of the solution, the length of the optical rotation tube, etc.

Generally, the monochromatic light source uses a sodium lamp with a wavelength of 589nm, which is represented by d. It is specified that the number of grams of solute contained in each milliliter of solution is used as the unit of mass concentration. After the angle of optical rotation is measured by the polarimeter, the optical rotation can be calculated as follows:

is the optical rotation measured with a polarimeter; c is the mass concentration of the solution (g ml); l is the length of the optical rotation tube dm; t is the temperature at the time of measurement ( ) is the wavelength of the light wave used in the measurement (sodium light is represented by d).When the photoactive substance is a liquid, the density (g ml) is used instead of c Significance: Measuring the optical rotation can determine whether the substance is left-handed or dextralative, and the concentration of the solution can also be determined.

The analytical method of using a polarimeter to measure the optical rotation of an optical rotation substance to determine its content is called () aHydrometer spring shed method.

b.Fold the light.

c.Optical rotation.

d.Capacity method.

Correct answer: c

In the experiment of measuring the concentration of the solution by the polarimeter, the role of the half-wave plate in the optical path of the optical instrument is ()aPolarized light is generated.

b.Rotating objects to polarized light.

c.Check for polarized light.

d.Produces monochromatic light.

Answer: B