Specific rotation. Determination of specific rotation constant and concentration of sugar solution Specific rotation formula

Polarimetry is an optical research method based on the ability of optically active compounds to rotate the plane of vibration of linearly polarized light (see Isomerism).

Atoms and molecules of luminous bodies emit electromagnetic waves. When there is complete disorder in the arrangement of these particles, bodies emit so-called natural light, in which the oscillation of the electric (or magnetic) field strength vectors occurs in all planes passing through the direction of propagation of the light wave. Order in the direction of field oscillations is called polarization of light. Such light, in which fluctuations in the strength of electric (magnetic) fields occur in one plane, is called plane polarized light, and the plane in which the strength of the magnetic field of light rays fluctuates is called a plane of polarization. Polarized light can be produced by passing natural light through polarizing prisms made from special crystals. Such crystals include Iceland spar crystals, from which polarizing prisms (Nicol prisms) are usually prepared. When polarized light passes through a solution of an optically active substance, the plane of polarization rotates, but it can only be detected using a second similar polarizing prism (analyzer). The study of rotation of the plane of polarization is used to study the structure of optically active compounds, as well as for their quantitative determination. Optical activity is characterized by the value of specific rotation [α], i.e., the angle of rotation of the polarization plane of a solution containing 1 g of an optically active compound in 1 ml with a liquid layer thickness of 1 dm.

Specific rotation is calculated from the amount of rotation of a solution of a given compound with a known percentage concentration:

[α] = α100/l·C
where α is the angle of rotation in degrees, C is the concentration in %, l is the thickness of the solution layer in dm. The specific rotation changes with temperature and wavelength of light. Therefore, the determination is carried out in monochromatic light at a certain temperature. Wavelength and temperature are marked at [a]. Knowing the specific rotation of a given compound from reference tables and determining the angle of rotation of the solution of this compound, it is easy to calculate the concentration:

C = α100/[α]l
The solution must not contain other optically active compounds.

To determine the rotation of the plane of polarization, optical instruments-polarimeters are used. The polarimeter (Fig. 1) consists of two polarizing prisms: a fixed one - a polarizer and a rotating one - an analyzer and a tube with the test solution. The rotation angle can be determined by setting the analyzer to equal illumination of the entire field of view, first without a solution, and then with a solution of an optically active compound. In this case, the analyzer must be rotated at an angle equal to the angle of rotation of the plane of polarization of the solution being studied. The angle of rotation is measured in a circle with divisions (limbo). If, after installing the tube with the solution, the analyzer is rotated clockwise, then we speak of right (+), if counterclockwise, we speak of left (-) rotation. To improve accuracy, polarimeters are equipped with additional quartz parts. In some polarimeters, leveling the illumination after installing the solution and measuring the concentration of the optically active substance is carried out by linear movement of a quartz wedge. The accuracy of conventional polarimeters is 0.05°. To obtain monochromatic light, filters are usually used. The polarimetry method is widely used in laboratories; In clinical laboratories and food industry laboratories, polarimetry is used to determine the sugar content. Polarimeters used to determine the content of cane sugar are called saccharimeters (Fig. 2).

Rice. 1. Schemes of polarimeters of various types: a - system with two biquartz plates; b - penumbral with nicol; c - penumbra with two nicols. 1 - polarizer; 1" and 1" - nicoli; 2 - biquartz plate; 3 - tube with solution; 4 - analyzer (on the right - diagrams of illumination of polarimeter fields).

Rice. 2. Wedge polarimeter-saccharimeter SOK (diagram): 1 - illuminator; 2 - light filter; 3 - diaphragm; 4 - lens; 5 - nicole; 6-tube for the test solution; 7 - fixed quartz wedge; 8 - movable quartz wedge; 9 - analyzer; 10-eyepiece; 11 - cover; 12 - screw; 13 - magnifying glass.

2. Before connecting the device to the network, set the minimum sensitivity of the device by rotating the “Setup 100” knob counterclockwise until it stops.

3. Check the correspondence of the zero position of the microammeter needle; if necessary, adjust it with screw 7 of the corrector (Fig. 3).

4. Insert the green absorber "3" with the "Absorbers" handle.

5. Connect the device to the network.

6. Open the cover 1 of the photoelectrocolorimeter and remove the cell holder.

7. Remove the “Solvent” cuvette, fill it 2/3 of the volume with water and place it in place. Install the cuvette holder into the photocolorimeter. Do not close the cuvette chamber lid.

8. Use handle 3 “Cuvettes” to position the cuvette with the solvent in the path of the light flux.

9. Set zero on the microammeter scale using handle 5 “Setting 0”.

10. Close the lid 1 of the cuvette compartment and use handle 4 “Setting 100” to set the microammeter needle to the hundredth division.

11. Open the lid 1 of the cuvette chamber and remove the cuvette holder. Remove the empty cuvette, fill it 2/3 of the volume with the test solution of the lowest concentration and replace it.

N to table 1.

14. Open the lid 1 of the cuvette chamber and remove the cuvette holder. Remove the cuvette with the test solution and pour it into a jar with a solution of the same concentration. Wipe the cuvette, fill it 2/3 full with the following solution and replace it.

15. Place the cuvette holder in the photocolorimeter. Using handle 3 “Cuvettes”, place the cuvette with the test solution in the path of the light flux. Close the cuvette chamber lid.

16. Take a reading on the microammeter scale 6 and write down N to table 1.

17. Repeat steps 14 – 16 with the remaining solutions.

18. Carry out two more series of experiments according to points 14 – 16 with all solutions, starting with the solution of the lowest concentration. Don't forget to drain the last solution.

19.Disconnect the device from the network.

Processing of measurement results

	1. By values				Determine N for all experiments					Using
formula (9). Record your results in Table 1.
	2. Using Table 2, determine D for all (see note) and its mean
its value, enter the results in table 1.
										table 2
	Note. The first column of the table gives the values ​​of optical
skaya density			D through 0.1, and its hundredths are placed in the top line

shares. At the intersection of a row and a column, the corresponding transmittance values ​​are given. When looking for absorbance values ​​corresponding to transmittance values ​​less than 0.081, first increase the given transmittance by 10 times, then find the absorbance value corresponding to the obtained transmittance and add one to this value.

3. Calculate its absolute error for all values ​​of D using the formula D | D av D meas | , find the average value of D,

record the results in table 1.

Note. If the result of calculating the absolute error in optical density is zero, then accept D 0.01.

4. Based on the average values ​​of optical density D avg for all

known concentrations, taking into account its absolute error, construct a calibration graph D f (C).

5. Mark on the graph the point corresponding to the average optical density of a solution of unknown concentration.

6. Mark on the graph the interval of the average absolute error in the optical density of a solution of unknown concentration.

7. Determine the concentration of the solution from the graph C x,

lowering the perpendicular to the corresponding coordinate axis.

8. Determine the absolute error of the solution concentration from the graph (see example on page 15).

9. Determine the relative error in determining the concentration of an unknown solution using the formula:

Control questions

1. What is the phenomenon of absorption of light by matter?

2. What is light intensity? In what units is it measured?

3. What law describes the phenomenon of light absorption by matter? Formulate it and write it down mathematically.

4. What is the physical meaning of the absorption coefficient? In what units is it measured and how is it designated?

5. What is transmittance? In what units is it measured and how is it designated?

6. What is optical density? In what units is it measured and how is it designated?

7. Formulate and write Beer's law.

8. Formulate and write down the law Bouguer-Lambert.

9. Draw the optical diagram of a photoelectrocolorimeter and describe the purpose of its main parts.

10. What is the method for determining the concentration of a substance in a solution using a photoelectrocolorimeter.

Laboratory work No. 5

DETERMINATION OF SUGAR CONCENTRATION IN SOLUTION WITH A SUCHARIMETER

Purpose of the work: to study the general patterns of light polarization; become familiar with the structure and operating principle of a saccharimeter; determine the concentration of sugar in the solution and the specific rotation constant of sugar.

Equipment: saccharimeter, cuvettes with sugar solutions.

Basic theoretical information

Light radiation is part of a wide spectrum of electromagnetic waves. Electromagnetic wave is called alternating magnetic and electric fields that mutually generate each other and propagate in space. From the electromagnetic theory of light it follows that light waves are transverse. At each point on the line of propagation of such a wave, perpendicular to its direction

spread (across)	oscillate two vector cha-
characteristics: tension		electric field				induction
					E and
magnetic field B. Vectors E		and B are mutually perpendicular between
yourself (Fig. 1).
The electric field strength vector is called light
			vector, since fi-
			physiological,
			mystical,		photovoltaic
			logical and other actions
				are caused by col-
				person
Rice. 1. Electromagnetic wave diagram			perceives
			electrical

emitting electromagnetic light wave.

Light is the total electromagnetic radiation of many atoms of a light source. Atoms emit light waves independently of each other, therefore a light wave emitted by the body as a whole is characterized by all possible equally probable co-

Rice. 2. Oscillations of the light vector in natural (a) and polarized (b) light

fluctuations of the light vector. Light with all possible directions of oscillations of the light vector is called natural (Fig. 2 a).

The sun, incandescent lamps, mercury lamps, and fluorescent lamps are sources of natural light. Light in which the directions of oscillations of the light vector are ordered in some way is called

polarized (Figure 2 b). If co-

fluctuations of the light vector occur only in one plane,

light is called plane-polarized

bathroom The plane in which the light vector oscillates is called the plane

polarization (Fig. 3).

Polarization of light occurs when light is reflected from the surface of dielectrics, during refraction in them, as well as when light passes through some crystals (quartz, tourmaline, Iceland spar). These substances, called polarizers (polaroids), transmit vibrations parallel to only one plane (the plane of polarization), and completely block vibrations perpendicular to this plane.

When natural light hits the dielectric boundary (Fig. 4), the refracted and reflected light waves turn out to be partially polarized.

The degree of polarization of the reflected beam changes with changing angle of

Denia. There is an angle

Rice. 3. Polarized wave and plane of polarization

Rice. 4. Polarization of light during reflection and refraction

incidence, at which the reflected beam is completely polarized, and the refracted beam is as much as possible. This angle of incidence is called full polarization angle or Brewster angle α Br.

Brewster's angle can be determined by Brewster's law of the same name: if the angle of incidence is equal to the Brewster angle, then

the reflected and refracted rays are mutually perpendicular, while the tangent of the angle of total polarization is equal to the ratio of the absolute refractive index of the second medium to the absolute refractive index of the first:

Br n 1

where n 2 and n 1 are the absolute refractive indices of the second and first media, respectively.

The eye does not distinguish natural light from polarized light, therefore polarized light is detected by phenomena unique to it. Polarized light can be detected using a conventional polarizer. Polarizers designed to study polarized light are called analyzers, i.e. the same Polaroid can be used both as a polarizer and as an analyzer.

The polarization of light in polaroids obeys Malus's law: if natural light passes through two polarizing devices, the polarization planes of which are located at an angle to each other, then the intensity of the light transmitted by such a system (Fig. 5) will be proportional to cos2, while in the first polarizer the light is lost half its intensity:

			I eat cos 2	I 0 cos2,

where I is the intensity of polarized light passing through the polarizer and analyzer;

I eat – intensity of natural light;

I 0 – intensity of polarized light passing through the polarizer; α is the angle between the polarization planes of the analyzer and the polarizer.

Figure 5. Passage of light through the polarizer-analyzer system

If the polarization planes of the analyzer and polarizer are parallel (=0, 2), then it follows from Malus’ law that light of the maximum possible intensity passes through the analyzer. If the polarization planes of the analyzer and the polarizer are perpendicular (= /2, 3 /2), then no light will pass through the analyzer at all.

Light intensity has no precise definition. This term is used instead of the terms luminous flux, brightness, illumination, etc. in cases where their specific content is unimportant, and it is only necessary to emphasize their greater or lesser absolute value. Most often in optics light intensity is called the radiation power through the surface of a unit area, i.e. the radiation energy passing per unit time through the surface of a unit area. In this case, the unit of intensity in SI: =1 W/m2 ( watt per square meter).

When polarized light passes through some crystals (quartz, cinnabar and others), as well as through solutions of sugar, urea, and proteins, the plane of vibration rotates through a certain angle. This phenomenon is called rotation of the plane of field oscillations -

represented light. Substances that rotate the plane of polarization

are called optically active.

For the majority of optically active crystals, the existence of two modifications has been discovered, rotating the plane of polarization clockwise (right-handed) and counter-clockwise (left-handed) for an observer looking towards the beam.

In solutions, the angle of rotation of the plane of polarization is proportional to the thickness of the solution and the concentration of the optically active substance:

0 l C,

where o is the specific rotation constant; l is the thickness of the solution;

C is the concentration of the optically active substance.

Physical meaning The specific rotation constant is that it shows by what angle the plane of polarization rotates an optically active substance of unit concentration when passing light of a unit length. In general, it depends on the temperature of the solution and on the wavelength of light passing through the solution.

Unit of measurement of specific rotation constant in SI: [φ 0 ]=1

rad/m∙% (radians per meter-percent).

The International Sugar Scale is widely used in production, in which 100 S = 34.62 angular degrees. Taking this into account, the unit of measurement of the specific rotation constant can be presented as: [φ 0 ]=1 S /m∙% ( degree of sugar scale on meter-percent).

Rationale for the method

The phenomenon of rotation of the plane of vibration of polarized light is used to determine the concentration of an optically active substance in solutions using instruments called polarimeters. Polarimeters whose scale is graduated in units of the International Sugar Scale are called saccharimeters.

Determination of the concentration of sugar solutions using polarimeters and saccharimeters is used in research in agriculture, in laboratories of the chemical, food, and oil industries.

The simplest polarimeter (Fig. 6) consists of two polarizers, a light source and a device for measuring angular values.

Rice. 6. Diagram of a simple polarimeter

Before starting measurements, polarizers are installed so that their planes of polarization are mutually perpendicular. In this case, light does not pass through the polarizer-analyzer system, and the observer sees darkness. If an optically active substance is placed between two polarizers, the field of view is brightened. This occurs because the active substance rotates the plane of polarization of the light emerging from the first polarizer by an angle φ. As a result, some of the light passes through the analyzer, and the observer can notice it. To get darkness again, you need to rotate the analyzer against the direction of rotation of the plane of polarization at an angle equal to the rotation angle φ. The angle of rotation of the analyzer is easy to measure. Knowing the specific rotation constant of the substance and the thickness of the solution of the optically active substance, we can use formula 3 to determine the concentration of the solution.

Often, when measuring the concentration of optically active substances in solutions, the specific rotation constant is unknown. In this case, taking a solution of known concentration C from the same substance, determine the angle of rotation of the plane of polarization with this solution from the same substance using a polarimeter, and the specific rotation constant o is calculated from formula (3):

	With information

To find the concentration of an unknown solution Cx, use a polarimeter to determine the angle of rotation of the plane of polarization of light by this solution x. Using formulas (3) and (4), provided that the thickness of the solutions l is equal, C x is determined by the formula:

C x C inv.

With this determination of the concentration of an unknown solution, as can be seen from formula (5), knowledge of the numerical value of the specific rotation constant and the thickness of the layer rotating the plane of polarization of the substance is not necessary.

Description of installation

In this work, a universal saccharimeter SU-4 is used to determine the specific rotation constant of sugar and its concentration in solution. The schematic diagram of the saccharimeter is shown in Figure 7.

Rice. 7. Schematic diagram of a penumbral saccharimeter

The substance under study 5 is placed between a penumbral polarizer, consisting of two halves 3 and 4, and the analyzer 6. The transmittance of the analyzer changes in accordance with Malus's law when the angle between the polarization plane of the analyzer 6 and the polarization plane of the light incident on it changes.

The use of penumbral polarizers 3 and 4 is due to the fact that setting a conventional polarizer to darkness cannot be carried out accurately enough. In penumbral polarizers the production

Rice. 8. View of the field of view in Sakha the setting is not for darkness, but rimeter with penumbral field - on the equality of the illumination of the two halves of the visual fields I and II by the two lenses (Fig. 8a). The human eye is very sensitive to violations of equality

illumination of two adjacent fields (Fig. 8 b, c), therefore, using a penumbral device, the position of the polarization plane can be established with much greater accuracy than by installing

polarizer for darkness.

MINISTRY OF HEALTH OF THE RUSSIAN FEDERATION

GENERAL PHARMACOPOEIAN ARTICLE

PolarimetryOFS.1.2.1.0018.15
In return for the Global FundXII, part 1, OFS 42-0041-07

Optical rotation is the property of a substance to rotate the plane of polarization when polarized light passes through it.

Depending on the nature of the optically active substance, the rotation of the plane of polarization can have a different direction and magnitude. If from the observer to whom the light passing through an optically active substance is directed, the plane of polarization rotates clockwise, then the substance is called dextrorotatory and a sign (+) is placed in front of its name; if the plane of polarization rotates counterclockwise, then the substance is called left-handed and a (–) sign is placed in front of its name.

The amount of deviation of the plane of polarization from the initial position, expressed in angular degrees, is called the angle of rotation and is denoted by the Greek letter α. The magnitude of the rotation angle depends on the nature of the optically active substance, the path length of polarized light in the optically active medium (pure substance or solution) and the wavelength of the light. For solutions, the rotation angle depends on the nature of the solvent and the concentration of the optically active substance. The magnitude of the rotation angle is directly proportional to the length of the light path, i.e., the thickness of the layer of an optically active substance or its solution. The effect of temperature is in most cases negligible.

For a comparative assessment of the ability of various substances to rotate the plane of polarization of light, the value of specific rotation [α] is calculated.

Specific optical rotation is the rotation angle α of the plane of polarization of monochromatic light at the line wavelength D spectrum of sodium (589.3 nm), expressed in degrees, measured at a temperature of 20 ºС, calculated for a layer thickness of the test substance of 1 dm and reduced to a substance concentration of 1 g/ml. Expressed in degrees-milliliters per decimeter-gram [(º) ∙ ml ∙ dm -1 ∙ g -1 ].

Sometimes the green line of the mercury spectrum with a wavelength of 546.1 nm is used for measurement.

When determining [α] in solutions of an optically active substance, it must be borne in mind that the value found may depend on the nature of the solvent and the concentration of the optically active substance.

Replacing the solvent can lead to a change in [α] not only in magnitude, but also in sign. Therefore, when giving the specific rotation value, it is necessary to indicate the solvent and the solution concentration chosen for measurement.

Specific rotation is determined in terms of dry substance or from a dried sample, which must be indicated in the pharmacopoeial monograph.

The rotation angle is measured using a polarimeter, which makes it possible to determine the rotation angle with an accuracy of ± 0.02 ºС at a temperature of (20 ± 0.5) ºС. Optical rotation measurements can be carried out at other temperatures, but in such cases the method of taking temperature into account must be specified in the pharmacopoeial monograph. The scale is usually checked using certified quartz plates. The linearity of the scale can be checked using sucrose solutions.

The optical rotation of solutions must be measured within 30 minutes from the moment of their preparation; solutions or liquid substances must be transparent. When making measurements, first of all, you should set the zero point of the device or determine the correction value with a tube filled with a pure solvent (when working with solutions) or with an empty tube (when working with liquid substances). After setting the device to the zero point or determining the correction value, carry out the main measurement, which is repeated at least 3 times.

To obtain the rotation angle α, the instrument readings obtained during measurements are algebraically summed with the previously found correction value.

The value of specific rotation [α] is calculated using one of the following formulas.

For substances in solution:

l– layer thickness, dm;

c– concentration of the solution, g of substance per 100 ml of solution.

For liquid substances:

where α is the measured angle of rotation, degrees;

l– layer thickness, dm;

ρ – density of liquid substance, g/ml.

Measuring the rotation angle is carried out to assess the purity of an optically active substance or to determine its concentration in a solution. To assess the purity of a substance, the value of its specific rotation [α] is calculated using equation (1) or (2). The concentration of an optically active substance in a solution is found by the formula:

Since the value of [α] is constant only in a certain concentration range, the possibility of using formula (3) is limited to this range.

Polarimetry theory

The optical activity of substances is very sensitive to changes in the spatial structure of molecules and to intermolecular interactions.

Study of optical activity of substances

Using optical polarimeters, the amount of rotation of the plane of polarization of light is determined when it passes through optically active media (solids or solutions).

Polarimetry is widely used in analytical chemistry for quickly measuring the concentration of optically active substances (see Saccharimetry), for the identification of essential oils, and in other studies.

• The magnitude of optical rotation in solutions depends on their concentration and the specific properties of optically active substances.
• Measuring the rotational dispersion of light (spectropolarimetry, determining the angle of rotation when changing the wavelength of light allows one to study the structure of substances.

see also

Literature

• Volkenshtein M.V., Molecular optics, M.-L., 1951
• Djerassi K., Optical Rotation Dispersion, trans. from English, M., 1962
• Terentyev A.P., Organic analysis, M., 1966

Wikimedia Foundation. 2010.

• Specific heat
• Electrical conductivity

See what “Specific rotation” is in other dictionaries:

Specific rotation- see Rotational capacity of chemical compounds...

specific rotation of matter- The angle through which the plane of polarization of optical radiation of a certain wavelength rotates when it passes a path of unit length in a substance. [GOST 23778 79] Topics: optics, optical instruments and measurements EN specific rotation of... ...

specific rotation of solution- The ratio of the angle through which the plane of polarization of optical radiation of a certain wavelength rotates when it passes a path of unit length in a solution of a substance to the concentration of this substance. [GOST 23778 79] Topics: optics, optical ... Technical Translator's Guide

Specific rotation of some organic substances- Substance Solvent Specific rotation* Sucrose Water +66.462 Glucose Water +52.70 … Chemical reference book

relative specific rotation of matter- The ratio of the specific rotation of a substance to the density of this substance. [GOST 23778 79] Topics: optics, optical instruments and measurements EN relative specific rotation of substance DE relative spezifische Materialdrehung FR rotation relative spécifique… … Technical Translator's Guide

Rotation of the plane of polarization- transverse wave is a physical phenomenon consisting in the rotation of the polarization vector of a linearly polarized transverse wave around its wave vector when the wave passes through an anisotropic medium. The wave can be electromagnetic,... ... Wikipedia

ROTATION OF THE PLANE OF POLARIZATION- ROTATION OF THE POLARIZATION PLANE, changing the direction (plane) of oscillations of rays of polarized light (see Optical polarization). This property is possessed by: 1. All transparent bodies, if they are placed in a magnetic field (magnetic V.p.p.). For… … Great Medical Encyclopedia

SPECIFIC MAGNETIC ROTATION- the same as (see VERDE CONSTANT). Physical encyclopedic dictionary. M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1983 ... Physical encyclopedia

Rotational capacity of chemical compounds- The rotational ability of chemical compounds refers to the ability, inherent in some of them, to deflect the plane of polarization of a light beam from its original direction. Let us assume that in a beam of such polarized light... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

Sucrose- (chemical) name derived from the word sucrose, a synonym for cane sugar; systematically used to designate carbohydrates of the general formula C12H22O11 only in the present Enc. sl. and in volume 1 op. Tollensa Handb. der Kohlenhydrate (Bresl... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

The specific rotation of the plane of polarization by an optically active substance is defined as the angle of rotation per unit thickness of the transilluminated material:

If the rotation angle is measured in angular degrees and the layer thickness l- in mm, then the specific rotation dimension will be [deg/mm].

Accordingly, the specific rotation of an optically active liquid (not a solution) with a density c [g/cm 3 ] is determined by the expression

Since the optical activity of liquids is much less than the optical activity of solids, and the thickness of the liquid layer is measured in decimeters, the specific rotation of liquids has the dimension [deg cm-3 / (dm g)].

Specific rotation of a solution of an optically active substance in an optically inactive solvent with concentration WITH(g/100 ml) of solution is determined by the formula

In organic chemistry, the value of molar rotation is also used as a type of specific rotation.

Determination of the concentration of dissolved optically active substances based on the results of measuring the rotation angle b [deg] at a given layer thickness l[dm] for a certain wavelength [nm] is produced by Biot's equation (1831):

Biot's law is almost always satisfied in the region of low concentrations, while at high concentrations significant deviations occur

Interfering factors in polarimetric measurements

With each refraction and reflection from a surface not perpendicular to the direction of light, a change in the polarization state of the incident light occurs. It follows that any kind of turbidity and bubbles in the test substance due to the multitude of surfaces greatly reduces the polarization, and the sensitivity of the measurement may decrease below an acceptable level. The same applies to dirt and scratches on the cuvette windows and the protective glass of the light source.

Thermal and mechanical stresses in the protective glasses and cuvette windows lead to double refraction and, consequently, to elliptical polarization, which is superimposed on the measurement result in the form of apparent rotation. Since these phenomena are in most cases uncontrollable and not constant over time, care should be taken to ensure that mechanical stress does not appear in the optical elements.

The strong dependence of optical activity on wavelength (rotational dispersion), which, for example, for sucrose is 0.3%/nm in the visible light region, forces the use of extremely narrow spectral bands in polarimetry, which is usually required only in interferometry. Polarimetry is one of the most sensitive optical measurement methods (the ratio of the sensitivity threshold to the measurement range is 1/10000), therefore, for full-fledged polarimetric measurements, only strictly monochromatic light, i.e., isolated lines of the spectrum, can be used. High-pressure burners, which provide high light intensity, are unsuitable for polarimetry due to the broadening of spectral lines with changes in pressure and the increased proportion of continuous radiation background for this case. The use of wider spectral bands is possible only for instruments that provide compensation for rotational dispersion, such as, for example, in instruments with compensation using a quartz wedge (saccharimeter with a quartz wedge) and instruments with compensation by the Faraday effect. Instruments with a quartz wedge have limited compensation options when measuring sucrose. By compensating for the Faraday effect by appropriate selection of material, rotational dispersion can be subjected to various requirements; however, it is not possible to achieve universality of the methods used.

When measuring with a finite spectral band width near the absorption bands, under the influence of absorption, a shift in the effective center of gravity of the wavelength distribution occurs, distorting the measurement results, from which it follows that when studying absorbing substances it is necessary to work with strictly monochromatic radiation.

When monitoring fast-flowing continuous flows of solutions, the elliptical polarization resulting from the double refraction of light by the flow can degrade the sensitivity of polarimetric measurement methods and lead to gross errors. These difficulties can only be eliminated by careful flow shaping, for example, by ensuring laminar parallel flow in the cuvettes and reducing its speed. polarization light rotation optical