What is a refractometer?
Refractometer - optical instrument, which measures the refractive index of light in a medium. Refractometry, performed using refractometers, is one of the most common methods for identifying chemical compounds, quantitative and structural analysis, determination of physical and chemical parameters of substances.
The operation of a refractometer is based on measuring the refractive indices of light in various media. If the density of a substance increases, its refractive index increases proportionally (for example, when sugar is dissolved in water). A refractometer reads the relative "weight" of a sample compared to distilled water.
Point the refractometer towards natural daylight and look through the eyepiece. You will see a circular area (box) centered at the bottom. (Figure 1 shows the scale without calibration fluid or any other fluid.) |
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Tighten the calibration screw until the boundary between the upper blue area and the lower white area meet exactly at the zero mark. |
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Picture 1 This drawing illustrates what you can see in the eyepiece without any reference. Notice that the entire scale is colored blue. When viewing, make sure you use natural daylight. You should not take readings in the presence of fluorescent light. |
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Figure 2 This is what you see after the refractometer has been calibrated. Please note that for proper calibration, the border of the blue and white scale should be exactly at the zero mark when using distilled water as a sample. |
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Figure 3 This example shows a scale for measuring grape juice. You can see that the meter shows 23% Brix, the most the right time for making wine! After finishing the measurement, make sure you clean and dry the refractometer. |
Refractometer maintenance
Accurate measurement depends on careful and correct calibration. As a reminder, differences between ambient temperature and sample temperature will reduce the accuracy of the reading. Be sure to wait approximately 30 seconds before taking a reading.
Do not immerse the instrument in water or allow water to get inside.
Do not measure harsh or corrosive chemicals with this instrument because they may damage the prism coating.
Clean the instrument between each measurement using a soft cloth.
A refractometer is an optical instrument. It requires careful handling and storage. When used carefully and proper storage This tool will provide reliable performance for many years.
The air temperature during calibration should be 20° C. However, many modern models come with ATC (automatic temperature compensation), so you don't have to worry about calibration air temperature or sample temperature.
Sources: www.grapestompers.com, www.patech.ru
Refractometry(from lat. refractus- refracted and Greek. metreo- measure) - a method of analysis based on the phenomenon of refraction of light when passing from one medium to another. The refraction of light, that is, the change in its original direction, is due to at different speeds distribution of light in various environments.
In this case, the ratio of the sine of the angle of incidence of the beam ( ε ) to the sine of the angle of refraction
(ε 1) for two contacting media there is a constant value called the refractive index (n).
Rice. 1. Ray path at the interface between two media
n = -------
Refractive index ( n) depends
From the nature of substances;
On temperature (the refractive index is determined at a temperature of 20 0 C);
From the concentration of the solution;
From the wavelength (measurements are made at a wavelength of 589.3 nm).
Note: When the substance concentration is less than 3- 4% it is not recommended to use the refractometry method.
Refractometer is a device used to determine the refractive index of light rays in transparent liquids. The principle of operation of the device is based on the phenomenon of total internal reflection, which occurs at the interface between two media, when a beam passes from an optically denser one to
optically less dense medium.
As a result, a sharp boundary between light and dark areas is formed in refracted rays.
The main part The refractometer is a system of two rectangular prisms (Fig. 2), made of glass with a high refractive index (n = 1.7). The limits for measuring refractive indices are 1.3-1.7.
The refractive index measured at 20°C and a light wavelength of 589.3 nm is designated by the index n 0. Refractive index n 0 for water measured under these conditions is equal to a constant value of 1.3333.
The dependence of the refractive index on the concentration of a substance in percent is expressed by the formula:
C % =-------
In g/ml with the following formula:
C g/ml =-------
where n and n 0 are the refractive indices of the solution and solvent; C is the concentration of the substance in solution; F is the refractive index factor.
The values of refractive indices and factors for various concentrations of solutions of substances are given in the refractometric tables, which are available in Appendix 4.
Refractometer device
Fig 3. Appearance refractometer IRF-454
The IRF-454 refractometer consists of the following main parts: body 2, telescope with eyepiece 1 and refractometric unit 3, the lower part is a measuring prism, and the upper part is a lighting prism.
The refractometric unit is rigidly connected to the scale of the reading device located inside the device body. To find the border
section and align it with the crosshairs of the reticle, it is necessary, by rotating screw 8, to tilt the refractometric unit to the desired position. For
A compensator serves to eliminate the coloration of the observed interface. Screw 10 can be used to rotate the compensator prisms simultaneously in different sides, while eliminating the colored border border
section. The liquid under study is illuminated by mirror 6 (in Fig. 3 it
shown in closed position), and the refractive index scale is
mirror 5.
Operating procedure
1. Before starting measurements, check the cleanliness of the contacting surfaces of the prisms.
2. Checking the zero point. Apply 2-3 drops of distilled water to the surface of the measuring prism and carefully cover with the lighting prism. Open the lighting window 3 and set it in the direction of the highest intensity of the light source using mirror 6. By rotating screw 8, obtain a sharp, clear, colorless distinction between the light and dark fields in the field of view of the eyepiece. Rotating screw 8, draw a line of light and shadow exactly until it coincides with the point of intersection of the line in the upper window of the eyepiece. The vertical line in the lower window of the eyepiece indicates the measurement result - the refractive index of water at 20°C is 1.333. In case of other readings of the refractive index of water, the measurement should be repeated, pre-treat the refractometric unit 3 with alcohol and wipe thoroughly with filter paper.
3. After installing the device to the zero point, lift the chamber of the lighting prism and wipe off the water with filter paper. Then 1-2 drops of the test solution are applied to the plane of the measuring prism, and the chamber is closed. Rotate the screws until the border of light and shadow coincides with the point of intersection of the lines. The refractive index of the solution is measured using a scale in the lower window of the eyepiece.
is an optical instrument designed to measure the concentration of solutions using the phenomenon of light refraction. The term " refraction"(from Latin refractus - refracted and Greek metreo - measure) was introduced into science by Newton at the beginning of the 18th century.
Modern refractometers include industrial, laboratory and portable ones.
Industrial and laboratory refractometers are intended for the study of substances in scientific laboratories and control of technological processes in production. They have high accuracy measurements and relatively large sizes.
Portable refractometers designed for operational control of substances in the laboratory, production or field conditions. In turn, portable refractometers are divided into digital and manual.
Digital portable refractometers have a liquid crystal screen on which the measurement result is displayed. They usually also have additional functions, such as simultaneous measurement of the density and refractive index of a solution, converting results into various units of measurement, maintaining the temperature of the sample, etc.
They are compact in size and do not contain any electronic circuits or batteries, which makes them easy to use for measurements both in production and at home. Today, such refractometers are very popular due to their accuracy, ease of use, portability and reasonable price.
Operating principle of hand-held refractometers
Operating principle of a refractometer is based on the use of the phenomenon of light refraction. When passing from one substance to another, a ray of light deviates from the rectilinear direction by a certain angle. The ratio of the angle of entry of a light ray into a substance and its angle of refraction at the interface between two media is called the refractive index.
The structure of a refractometer is shown schematically in the figure below. The main optical element of a refractometer is the main prism onto which the test substance is applied. The main prism consists of a material with a high refractive index.
Due to this, the incident light, passing through the substance and the prism, is refracted at a sufficiently large angle. Next, through a system of optical lenses, the light falls on the refractometer scale (graduated circle). Depending on the angle of refraction, the light beam appears higher or lower on the scale of the device. The illuminated part of the scale will be light; the part that the light ray does not hit will be dark. The angle of refraction of light depends on the composition of the solution and its concentration. Thus, by the position of the interface between light and shadow, the refractive index or optical density of the solution under study can be unambiguously determined.
However, it must be borne in mind that the refractive index of a substance also depends on temperature. Some models of hand-held refractometers take into account the influence of temperature using the ATC (Automatic Temperature Compensation System) function. Inside their body there is a bimetallic plate. It contracts or expands depending on temperature changes. The bimetallic plate is connected to the optical system of the refractometer, moving it smoothly as the temperature changes. The magnitude of the shifts is calculated so that the effect of temperature on the refractive index of the substance is completely compensated. When purchasing a refractometer, be sure to pay attention to the presence of an ATC function. If it is absent, it is necessary to use special tables to recalculate the obtained values depending on the ambient temperature.
Taking measurements
Before taking measurements manual refractometer needs to be calibrated. Most refractometers use distilled water to calibrate. A few drops of water are applied to the main prism using a pipette, then the protective glass is closed. In this case, you need to ensure that the water under the protective glass evenly covers the surface of the prism, without leaving air bubbles. Next, using the calibration screw, the value of 0.0 is set on the instrument scale. After calibration, the prism should be carefully wiped with a soft cloth. The refractometer is now ready for measurements.
To carry out measurements, the same steps are performed as during calibration, but instead of distilled water, the test solution is applied to the prism of the device. The calibration screw remains in its original position. After applying the solution, you must wait 30 seconds for the temperature of the solution to equal the temperature of the device. Then refractometer point at a light source (daylight or incandescent lamp) and take readings.
After taking measurements, the prism must be wiped again with a soft cloth. The hand-held refractometer must not be immersed in water; This may cause water to enter the instrument and cloud the scale. Do not use the refractometer on hard or corrosive substances as they may damage the prism coating.
Application of refractometers
Widely used in various areas human activity. Some of the applications of refractometers are listed below:
In the following articles about refractometers, we will consider their use in various industries to solve specific problems.
The principle of operation of a refractometer is based on the fact that only the refraction angle of the liquid under study is determined, and the refractive index of the measuring prism is known.
1 - lighting mirror; 2 - auxiliary folding prism; 3 - main measuring prism; 4 - matte edge of the folding prism; 5 - test liquid; 6 - Amici prisms of the compensator; 7 - telescope lens; 8 - rotary prism; 9 - telescope eyepiece
Figure 2 - Optical diagram of the IRF-22 refractometer.
How to use a refractometer:
1. Before starting work, you need to check the setting of the refractometer zero point. The zero point setting and measurements on the refractometer must be carried out at the same temperature. Checking and setting the zero point is carried out using distilled water. When studying distilled water, the limit of light and shade should be at 1.33299 on the solids scale and 0% on the dry matter scale. Checking and setting the zero point for distilled water is carried out as follows:
Open the upper chamber and rinse the surfaces of the measuring and lighting prisms with distilled water or alcohol and wipe dry with a clean linen napkin;
Using the melted end of the stick, apply one or two drops of distilled water to the plane of the measuring prism and close the upper chamber;
By shifting the illuminator, direct the light beam into the window of the upper chamber;
By moving the handle with the eyepiece up and down along the scale, find the border of light and shade in the field of view;
By moving the handle, the chiaroscuro boundary is aligned with the hairline (if, when aligned with the center of the reticle crosshair, it passes through the scale division 3 = 1.33299 and 0% of the dry matter scale, the zero point is set correctly).
Measuring the refractive index of transparent liquids and the percentage of dry substances for sucrose is carried out similarly to the measurement of distilled water when setting the zero point: after aligning the chiaroscuro boundary with the crosshairs of the grid, make a reading on the scale of refractive indices and the percentage of dry substances for sucrose. Measure three times. The arithmetic mean of three measurements is the final measurement result.
Product Measurement sugar production can be performed at a temperature of 10-30°C, taking into account the correction for temperature according to the table (take the table from the teacher).
For example, if measurements are made at a temperature of 17°C, the scale reading is equal to 37.8% of dry matter. From the table we find the correction equal to 0.22. The refractometer reading will be:
37.80 - 0.22 = 37.58% dry matter.
After taking measurements, it is necessary to open the upper chamber, rinse, wipe dry the surfaces of the upper and lower chambers and smoothly lower the upper chamber of the device.
Calculation of the concentration of a substance based on the refractive indices of the solution is carried out using the following methods: using a calibration graph, using tables, using the refractometric factor, and the method of additives.
According to the calibration graph: the calibration graph is plotted using solutions of the substance known concentration(concentration - refractive index), the refractive index of the analyzed solution is measured, and the concentration is determined on the graph based on the refractive index.
According to tables: for many substances, tables have been compiled that show the refractive indices of solutions with known concentrations.
By refractometric factor: if the refractometric factor is known, the formula is used to calculate concentrations:
where s 1 is the refractive index of the solution;
z0 is the refractive index of the solvent;
F is a refractometric factor showing an increase in the refractive index with an increase in the concentration of a substance by 1%.
The refractometric factor is determined experimentally or using refractive index tables.
For example, for NaCl, factor F is equal to the difference between the refractive indices of a 4% solution z1 = 1.3397 and a 2% solution z2 = 1.3364, divided by the difference in concentration (equal to 2%):
Automatic refractometers for continuous recording of n in liquid flows are used in production for monitoring and automatic control of technological processes, as well as in laboratories for monitoring rectification and as universal detectors of liquid chromatographs.
All currently produced refractometers, regardless of their purpose, are built on the principle of Abbe-type or Pulfrich-type refractometers, but in both of them, measurements are based on determining the value of the limiting refraction angle.
1) The principle of construction of refractometers of the Abbe and Pulfrich type.
The main typical unit of Abbe type refractometers is a complex of measuring and lighting prisms. A thin layer of the liquid under study is located between the tightly pressed edges of both prisms.
The surface of the lighting prism in contact with the liquid being tested is matte, rough, and scatters light entering the liquid layer through it, as a result of which light rays penetrate the liquid in different directions.
The beam, the angle of incidence of which is closest to the direct one (the limiting beam), divides the field visible through the telescope into dark and light halves. Using a special handwheel, the block of prisms can be installed in a position in which the limiting beam will be aligned with the optical axis of the telescope, and the boundary of the light and dark fields with the intersection of two straight lines visible through the tube, through which this imaginary axis passes. Based on the position of the reference line observed in the sighting tube on the scale, the value of the refractive index is determined. The boundary between the dark and light fields would be blurred and colored in all the colors of the rainbow due to the decomposition of white light as it passes through the measuring prism. To prevent this phenomenon, Abbe-type refractometers use special devices - dispersion compensators.
The refractive index of liquids changes significantly under the influence of temperature. Therefore, in refractometers, temperature control is used to increase accuracy. Thermostatic control in Abbe-type refractometers is carried out by circulating water at a certain temperature through the lower and upper chambers of the prism block. The temperature must be maintained with an accuracy of ±0.1-0.5°C.
In Pulfrich-type refractometers there is only one prism, to which a cup is attached, into which the liquid being tested is poured. A light beam directed along the liquid-prism interface is not distorted, so the angle of incidence of this beam is exactly 90°, which determines the greater accuracy of devices of this type.
Submersible refractometers are devices whose measuring prism is immersed in a glass with the liquid being tested. In such refractometers there is no lighting prism and the cut of the measuring prism is in direct contact with the liquid being tested. Modern refractometers are accurate to, and when used special methods Refractometry accuracy can be increased by 10-1000 times.
The domestic industry produces various refractometers, including a universal laboratory refractometer (RLU), a laboratory refractometer, a precision laboratory refractometer, IRF-22 and IRF-23 refractometers.
2) The IRF-23 refractometer is intended for determining the refractive indices of liquid and solids in the range of 1.33-1.78, with an accuracy of 1H The IRF-23 refractometer is the most complex, so its description is given below.
The optical part of the device consists of a measuring prism, a reference system, a telescope and a system for illuminating the object under study. The reading system includes a dial with protective glass, illuminated through a condenser, a light filter with an incandescent lamp, and a reading microscope consisting of a lens, reflective prisms and an eyepiece. A red spiral scale with an index is placed in the focal plane of the eyepiece. The reading device is designed to accurately measure the angle of rotation of the telescope along the dial. The dial is covered with a casing. The scale division value is 1°. Coarse rotation of the telescope is done by hand, fine rotation is done with a micrometer screw. The eyepiece of the tube has compensatory aiming for visual acuity.
The telescope consists of a lens, a reflective prism, a crosshair, an illuminating prism and an eyepiece. A spotting scope can operate on the principle of an autocollimator, in which lamp light reflected by two reflective prisms and a collecting lens is used to illuminate the crosshairs.
The object can be illuminated with light from discharge tubes or a sodium lamp.
For accurate measurements, the temperature of the measuring prism and the liquid being tested must be maintained constant within ±0.5°. For this purpose, there are two fittings on the prismatic chamber onto which rubber hoses are put on and connected to the ultra-thermostat. The Carl Zeiss company (GDR) produces numerous models of refractometers, including Abbe refractometers, submersible ones, and for work in the field (manual). One of the latest models (model P) of the Abbe refractometer is not fundamentally different from the domestic RLU refractometer.
The Zeiss submersible refractometer is equipped with thermal prisms, allowing research to be carried out at relatively high temperatures(up to 50°C). An important advantage of thermoprisms is also the ability to use small quantities of substances (on average 0.04 ml) and study volatile substances. In addition to the specified thermal prism, a flow prism is attached to the device, which allows the study of continuously flowing liquids, as well as substances that decompose in air.
The flow prism consists of an immersion prism and a corresponding flow housing mounted on the refractometer. If thermal regulation is necessary, the body of the flow prism can be connected to a thermostat, for which there are fittings on it.
The field (manual) refractometer from this company is of particular interest.
The device is designed to work directly in fields, orchards and vineyards and is used to determine the content of sugary substances in root crops (sugar beets), berries, and grapes.
In addition to the refractometer, the kit contains: a device for taking a sample, a press tongs for squeezing small amount juice The determination of sugar content is based on a natural relationship between the content of sugary substance in juice and its light refraction. One or two drops of juice are applied to the prism of the refractometer, cover with a lid and look against the light into the eyepiece, where the scale is visible, top part which is darker than the bottom one. The dividing line, which coincides with a certain indicator on the scale, corresponds to the content of sugary substances in the juice. The device allows for determination with an accuracy of 0.2%.
3) Refractometer IRF-454 B2M
The IRF-454B2M refractometer is designed to measure the refractive index and average dispersion of non-aggressive liquids and solids.
The IRF-454 B2M refractometer has a number of advantages:
Speed of measurement;
Ease of maintenance;
Minimum consumption of the test substance, which is especially important when working with expensive materials.
Refractometer IRF-454 B2M is used:
1. In medical institutions: to determine protein in urine, blood serum, urine density, analysis of brain and joint fluid, density of subretinal and other eye fluids. The use of a refractometer can significantly reduce time spent during mass examinations of patients.
2. In the pharmaceutical industry: the IRF-454b2m refractometer can be used to study aqueous solutions of various drugs: calcium chloride (0% and 20%); novocaine (0.5%, 1%, 2%, 10%, 20%, 40%); ephedrine (5%); glucose (5%, 25%, 40%); magnesium sulfate (25%); sodium chloride (10%); cordiamine, etc.
3. In the food industry:
at sugar and bakery factories, confectionery factories for the analysis of products and raw materials, semi-finished products, culinary and flour products, the IRF-454 b2m refractometer determines the moisture content of honey (up to 20%)
to determine the proportion of dry substances in various worts (GOST 5900-73), “wetting”, sugar-agrarian syrup, syrup for marmalade, marshmallows, creams and gingerbreads, “circulation” for gingerbread;
to determine the mass fraction of soluble solids by sucrose (BRIX) in processed products of fruits and vegetables, to determine the percentage of fat in solid food products (gingerbreads, waffles or baked goods) and salt concentrations.
4. When servicing equipment, the IRF-454 B2M refractometer is used to determine with greater accuracy the volumetric concentration of the anti-crystallization liquid "IM", which is added to aviation fuel in an amount of 0.1 to 0.3%. Further processing of the results is carried out according to " Methodological recommendations on analysis of the quality of fuels and lubricants in civil aviation" Part II p. 159. Experience in the use of refractometers has shown that these devices significantly reduce the time and increase the reliability of obtaining analyzes on the percentage of liquid "IM" in aviation fuel.
4) Refractometer ALR-3
Auto laboratory refractometer ALR-3 with microprocessor control is designed to study the concentration of a wide range of liquid media of both low and high viscosity, regardless of transparency and color.
The device automatically measures the refractive index of a solution sample, calculates its concentration and displays the result on a digital LCD indicator. The refractometer has a standard calibration for the concentration of sugar in water (Brix scale), but can be calibrated for the concentration of any solutions at the request of the customer with the corresponding scales being stored in the memory.
The ALR-3 refractometer measures the temperature of the test solution and automatically compensates for its influence on the measurement result.
Refractometric detectors, unlike photometric detectors that react only to substances that absorb light in the ultraviolet, visible and infrared regions of the spectrum, refractometric detectors are universal. They are especially useful when substances do not have strong absorption in UV light, do not fluoresce, and do not have electrochemical activity. Their principle of operation is based on the differential measurement of the refractive index of a pure solvent and a solution of the analyte in this solvent. The contribution of the solute to the change in the refractive index of the solvent is proportional to the volume concentration of this substance, and the solvent is also a detectable substance, since it has a certain refractive index.
These detectors have average sensitivity, their readings are highly dependent on fluctuations in parameters affecting the composition of the mobile phase, such as pressure, temperature and concentration of the analyte. Therefore, a refractometric detector is of little use for gradient chromatography. A painstaking selection of solvent systems with similar refractive indices is required. Only then does it become possible to carry out gradient elution within certain concentration limits of the solvent mixture. The sensitivity of the detector to temperature changes ranges from 5×10-4 to 5×10-5 refractive index units per 1°C for different solvents. As for pressure sensitivity, it is 1×10-4 - 5×10-4 refractive index units per 1 MPa.
The sensitivity of the detector to temperature requires special measures to stabilize the temperature of the detector itself and the mobile phase at the entrance to the detector. In this case, the use of longer connecting tubes at the detector inlet, acting as heat exchangers, leads to high extra-column peak broadening and reduces the separation efficiency achieved in the column. In a chromatograph equipped with a refractometric detector, in order to stabilize the eluent flow and the retention parameters of sorbates in the column, it is advisable to use thermostatting of the column and detector. To realize the maximum sensitivity of the detector at the level of 10-8 units of the refractive index, the temperature control accuracy should be no more than ±0.01°C. With good temperature control, the detector is little sensitive to changes in the flow rate of the mobile phase. It is simple in design, easy to use, non-destructive and provides high reproducibility of readings. The disadvantage of the detector is its insensitivity to substances that have the same refractive index as the solvent.
Most modern refractometric detectors operate based on three different signal measurement principles: deflection, reflection and interference.
A method based on the law of light reflection (Fresnel's law), according to which the intensity of reflected light incident on the interface between liquid and glass is proportional to the angle of incidence and the difference in the refractive indices of the two media. The advantage of detectors operating on this principle is a smaller cell volume (< 3 мкл), в связи с чем они могут работать при небольших расходах элюента и с высокоэффективными колонками. Однако чувствительность таких детекторов в 50-100 раз ниже чувствительности других типов рефрактометрических детекторов, что, кстати, делает их более пригодными для градиентного элюирования. Так как детектирование происходит на границе раздела жидкости и стекла, для получения стабильной работы детектора необходимо следить за чистотой стекла.
A Fresnel type detector includes a light source, a condenser, a differential cell, glass rods, a lens and a photodetector. It also includes heat exchangers and a diaphragm to regulate the intensity of the light flux. The light source, equipped with an infrared blocking filter, is designed to create a luminous flux in the visible part of the spectrum. The condenser is designed to form a flat beam of light incident on the cell. The refractometer cell is made of of stainless steel, sealed protective glass, prism and Teflon gaskets. Glass rods and a lens focus the light fluxes passing through the cells onto the photosensitive elements of the photodetector. Focusing eliminates light overlap that can cause chromatographic peaks to differentiate.
The operation of the third type of refractometric detector is based on the interferometric shear principle. Light rays from a visible light source are divided into two parts by a divider, focused by a lens, and passed through a 5-μL working and reference cell. The light rays are then combined using another lens and a splitter and hit the sensing element. The difference in refractive indices between the working and reference eluent flows results in a difference in optical path length, which is measured by the interferometric detector as a change in the wavelengths of light. The readings of this type of detector have sufficient wide range linearity, and the sensitivity is 10 times higher than for other refractometric detectors. Under optimal operating conditions, detection of approximately 3 µg/ml of solute is possible. The detector detects any type of analyte, regardless of structure, molecular weight and others physical and chemical properties. The detection limit for the best refractometric detectors reaches 108 refractive index units. However, the noise level in these detectors is 2 orders of magnitude higher than the noise of a UV detector. They are optimal for applications where high sensitivity is not required, such as preparative LC.
Figure 3 - 1. Sucrose 2. Glucose 3. Fructose 4. Sorbitol Chromatogram apple juice. Column: Rezex RCM-Monosaccharide 300x7.8 mm 8 µm, protective column: SecurityGuard Carbo-Ca2+ 4x3 mm, separation mode: isocratic, mobile phase: water, flow rate: 0.6 ml/min, column temperature: 85°C, volume samples: 20 µl, detector: refractometric.
A refractometer is a portable optical-mechanical device, without power sources, with a minimum amount of sample, in a few seconds, measuring the concentration of substances dissolved in a liquid using a light beam.
The name of the device is a composite of “refracto” and “meter”, which to a first approximation explains the principle of operation of a refractometer, if we remember about refraction or bending of light.
And if you can’t remember, let’s take a closer look at the pictures, and you will understand that despite the strict and sonorous name, a refractometer is an optical instrument that even a schoolchild can work with.
But first, a few words about where a manual refractometer is in demand, who keeps a stylish, reliable and portable one in their arsenal? measuring device, which does not need batteries or power at all, but all it needs is light.
Optics with wide range applications, useful and in demand throughout all 4 seasons of the year - a hand-held refractometer, in the laboratory, apiary, garden, garage, warehouse, involved at all stages, from production to sale of finished products.
Let's explain with an example.
Suppose you want to measure the sugar content in fruit juice. Everyone wants to enjoy sweet apples, plums and pears!
Depending on the degree of ripeness of the fruit, the concentration of sucrose will increase, and the harvest time, conservation costs, and, of course, the taste preferences of buyers - and therefore demand, price and the final financial result - depend on this.
A gardener, of course, can periodically eat one fruit for analysis, but relying on the subjectivity of taste buds is at least frivolous.
Nobody canceled laboratory tests.
Prepare special glassware, reagents, invite qualified personnel, purchase furniture, equipment, supply electricity and, most importantly, reserve time.
Chemical research is clearly not the fastest method of analysis.
In addition, let us pay attention to 3 more factors.
Eat Alternative option much faster and cheaper - the price of which is several times less than the average monthly salary.
A refractometer is a lightweight, compact and high-speed measuring device that allows you to avoid mistakes, identify dangerous trends in a timely manner, save financial resources in the budget of a company or family, make money on sales, and preserve the integrity of industrial equipment and support on high level business reputation in business.
* The Brix scale is a globally recognized measure of measuring the concentration of substances dissolved in a liquid (as a percentage)
The first thing you need to know is that a refractometer is a portable optical measuring instrument.
The operating principle of the refractometer is based on original method using the phenomenon of light refraction to measure the concentration of a solution.
Figuratively speaking, the operating principle of an optical measuring device is based on the synergy of two sciences, the quintessence of 4 words: “physics of light + chemistry of solution.”
The analyzed solutions consist of at least two components - a solvent and a solute. As the liquid becomes saturated, the density and optical permeability to light rays change. This is the first "trick".
Sunlight or stream artificial lighting pierce both the air around us and optically transparent objects, including glass and water.
The beam sequentially passes from one medium to another and at the boundary a practically important physical effect of refraction is observed - the curvature of the direction of movement of light. This is the second “trick”, thanks to which the refractometer readings become a reality.
The picture shows a lens - solid, but a similar phenomenon is observed in liquids and even in the atmosphere. It is not the state of aggregation that is important, but the optical density.
To understand the principle of operation of a refractometer, it is enough to remember that in the layer of the analyzed solution, absolutely the same refractive processes occur (hence the name - manual refractometer). There really is no other way to describe it. Well, for example, “a refracting ray of light” is too pretentious...
A carefully processed lens - in the picture, dark blue, like a boundless sea, is optically homogeneous, and its refractive index is unchanged. This is guaranteed by the manufacturing quality of the manufacturer.
If the density of the protective glass and the prism remains unchanged throughout its entire service life, then the only medium that can change the readings is the thinnest film of solution between the glass and the prism.
As the density of a solution droplet increases, evenly placed between the measuring instrument lens and the protective glass, the line of light moves up or down on the Brix scale - a kind of display - and is visually observed through a monocular lens.
In other words, a refractometer is a measuring device that deflects a beam as the concentration of the liquid being studied increases (decreases). The principle of operation of a refractometer is based on this.
Note important function individual adjustment. Optics is limited not only to the phenomenon of refraction. A manual refractometer “takes into account” the visual acuity of the beholder - it only costs in a circular motion adjust the sharpness of the eyepiece and the readings will again become bright and clear.
Before mass production begins, marketers agree on the range of refractometers based on market expectations and customer needs. Engineers design a line of measuring instruments depending on the scope of application - first of all, they develop models for each niche depending on the expected concentration of the chemical compounds being analyzed.
The principle of operation of the refractometer remains unchanged, but the upper limit changes:
Based on them technological process, it is necessary to determine in advance the maximum upper limit and buy a refractometer for which the degree of saturation of the solution and the optical density of the medium under study will never reach the values when the beam deviates beyond the scale and the readings go off scale.
A refractometer is a unique direct-action measuring instrument. And there is no pathos here. There are only 3 theses:
The principle of operation of a refractometer is very simple - you can measure the content of a dissolved substance in a solution almost instantly - at the speed of light!
Remembering your school physics course and understanding how a refractometer works is important, but in order to profitably use all the possibilities and measure the concentration of a solution with a minimum error, you should remember!
