The nadfn formula is structural. biological functions

SPECTRAL ANALYSIS(with the help of emission spectra) is used in almost all sectors of the economy. It is widely used in the metal industry for the rapid analysis of iron, steel, cast iron, as well as various special steels and finished metal products, to establish the purity of light, non-ferrous and precious metals. Great Application has a spectral analysis in geochemistry in the study of the composition of minerals. AT chemical industry and related industries, spectral analysis serves to establish the purity of manufactured and used products, to analyze catalysts, various residues, sediments, turbidity and wash water; in medicine - for the discovery of metals in various organic tissues. A number of special problems, difficult to solve or not solvable in any other way, are solved quickly and accurately with the help of spectral analysis. This includes, for example, the distribution of metals in alloys, the study of sulfide and other inclusions in alloys and minerals; this kind of research is sometimes referred to as local analysis.

The choice of one or another type of spectral apparatus from the point of view of the sufficiency of its dispersion is made depending on the purpose and objectives of spectral analysis. Quartz spectrographs with greater dispersion, giving for wavelengths 4000-2200 Ӑ a strip of the spectrum with a length of at least 22 cm. For the remaining elements, m. Apparatuses are used that give spectra 7-15 cm long. Spectrographs with glass optics are generally of lesser importance. Of these, combined instruments are convenient (for example, by the firms of Gilger and Fuss), which, if desired, can be used as a spectroscope and spectrograph. The following energy sources are used to obtain spectra. one) The flame of the burning mixture- hydrogen and oxygen, mixtures of oxygen and lighting gas, mixtures of oxygen and acetylene, or finally air and acetylene. In the latter case, the temperature of the light source reaches 2500-3000°C. The flame is most suitable for obtaining spectra of alkali and alkaline earth metals, as well as for elements such as Cu, Hg and Tl. 2) Voltaic arc. a) Ordinary, ch. arr. direct current, with a power of 5-20 A. With great success, it is used for qualitative analysis hard-to-fuse minerals, which are introduced into the arc in the form of pieces or finely ground powders. For the quantitative analysis of metals, the use of a conventional voltaic arc has a very significant drawback, which consists in the fact that the surface of the analyzed metals is covered with an oxide film and the arc burning eventually becomes uneven. The temperature of the voltaic arc reaches 5000-6000°C. b) Intermittent arc (Abreissbogen) direct current with a power of 2-5 A at a voltage of about 80 V. Using special device arc burning is interrupted 4-10 times per second. This method of excitation reduces the oxidation of the surface of the analyzed metals. At a higher voltage - up to 220 V and a current strength of 1-2 A - an intermittent arc can also be used for the analysis of solutions. 3) spark discharges, obtained with the help of an induction coil or, more often, a DC or (preferably) AC transformer with a power of up to 1 kW, giving 10000-30000 V in the secondary circuit. Three types of discharges are used, a) Spark discharges without capacitance and inductance in the secondary circuit, called sometimes in an arc high voltage(Hochspannungsbogen). The analysis of liquids and molten salts using such discharges is highly sensitive. b) Spark discharges with capacitance and inductance in the secondary circuit, often also called condensed sparks, represent a more universal source of energy suitable for excitation of the spectra of almost all elements (except alkali metals), as well as gases. The switching circuit is given in Fig. one,

where R is a rheostat in the primary circuit, Tr is an AC transformer, C 1 is the capacitance in the secondary circuit I, S is a switch for changing the inductance L 1, U is a synchronous interrupter, LF is a spark arrester, F is a working spark gap. In resonance to the secondary circuit I, with the help of inductance and variable capacitance C 2, the secondary circuit II is tuned; a sign of resonance is greatest strength current, shown by a milliammeter A. The purpose of the secondary circuit II of the synchronous interrupter U and the spark arrester LF is to make electrical discharges possibly uniform both in nature and in number for a certain period of time; during normal work, such additional devices are not introduced.

When studying metals in the secondary circuit, a capacitance of 6000-15000 cm 3 and an inductance of up to 0.05-0.01 N are used. For the analysis of liquids, a water rheostat with a resistance of up to 40,000 Ohm is sometimes introduced into the secondary circuit. Gases are investigated without inductance with a small capacitance. c) Discharges of Tesla currents, which are carried out using the circuit shown in Fig. 2,

where V is a voltmeter, A is an ammeter, T is a transformer, C is a capacitance, T-T is a Tesla transformer, F is a spark gap where the analyzed substance is introduced. Tesla currents are used to study substances that have a low melting point: various herbal and organic preparations, sediments on filters, etc. In the spectral analysis of metals, in the case of a large number of them, they usually themselves are electrodes, and they are given some form, for example, from those indicated in Fig. 3,

where a is an electrode from the analyzed thick wire, b is from tin, c is a bent thin wire, d is a disk cut from a thick cylindrical rod, e is a shape cut from large pieces casting. In quantitative analysis, it is always necessary to have the same shape and dimensions of the electrode surface exposed to sparks. With a small amount of metal to be analyzed, it is possible to use a frame made of some pure metal, for example, gold and platinum, in which the metal to be analyzed is strengthened, as shown in Fig. four.

Quite a few methods have been proposed for introducing solutions into a light source. When working with a flame, a Lundegard atomizer is used, schematically shown in Fig. 5 together with a special burner.

The air blown through the atomizer BC captures the test liquid, poured in an amount of 3-10 cm 3 into recess C, and carries it in the form of fine dust to burner A, where it is mixed with gas. To introduce solutions into the arc, as well as into the spark, clean carbon or graphite electrodes are used, on one of which a recess is made. It must be noted, however, that it is very difficult to prepare the coals perfectly clean. The methods used for cleaning - alternate boiling in hydrochloric and hydrofluoric acids, as well as calcination in a hydrogen atmosphere up to 2500-3000 ° C - do not give coals free from impurities, Ca, Mg, V, Ti, Al, Fe, Si, V. Satisfactory purity is also obtained by calcining them in air with the help of an electric current: a current of about 400 A is passed through a carbon rod with a diameter of 5 mm, and the strong incandescence achieved in this way (up to 3,000 ° C) is sufficient for within a few seconds, most of the impurities polluting the coals have evaporated. There are also such ways of introducing solutions into a spark, where the solution itself is the lower electrode, and the spark jumps to its surface; any pure metal can serve as another electrode. An example of such a device is shown in Fig. 6 liquid Gerlyach electrode.

The recess where the test solution is poured is lined with platinum foil or covered with a thick layer of gilding. In FIG. 7 shows the Hitchen apparatus, which also serves to introduce solutions into the spark.

From vessel A, the test solution enters in a weak stream through tube B and quartz nozzle C into the sphere of action of spark discharges. The bottom electrode, soldered into a glass tube, is attached to the apparatus by means of a rubber tube E. Nozzle C, shown in FIG. 7 separately, has a cutout on one side for moaning mortar. D - a glass safety vessel in which a round hole is made to exit ultraviolet rays. It is more convenient to make this vessel quartz without a hole. The top electrode F, graphite, carbon or metal, is also fitted with a splash guard. For a "high-voltage arc", which strongly incandesces the analytes, Gerlely uses electrodes with cooling when working with solutions, as is schematically shown in Fig. eight.

On a thick wire (diameter 6 mm) a glass funnel G is fixed with a cork K, where pieces of ice are placed. At the upper end of the wire, a round iron electrode E 4 cm in diameter and 4 cm high is fixed, on which a platinum cup P is superimposed; the latter should be easy to remove for cleaning. The top electrode is also d. thick to avoid melting. In the analysis of small quantities of substances - sediments on filters, various powders, etc. - you can use the device shown in Fig. 9.

A lump is made of the test substance and filter paper, wetted for better conductivity with a solution, for example, NaCl, placed on the lower electrode, sometimes consisting of pure cadmium, enclosed in a quartz (worse glass) tube; the top electrode is also some kind of pure metal. For the same analyzes, when working with Tesla currents, a special design of the spark gap is used, shown in Fig. 10 a and b.

In the round hinge K, an aluminum plate E is fixed in the desired position, on which a glass plate G is superimposed, and on the latter - a preparation P on filter paper F. The preparation is wetted with some acid or salt solution. This whole system is a small capacitor. To study gases, closed glass or quartz vessels are used (Fig. 11).

For quantitative analysis of gases, it is convenient to use gold or platinum electrodes, the lines of which can be used for comparison. Almost all of the devices mentioned above for introducing substances into the spark and arc are fixed in special stands during operation. An example is the Gramont stand shown in Fig. 12:

using screw D, the electrodes are simultaneously moved apart and shifted; screw E is used to move the upper electrode parallel to the optical bench, and screw C - for lateral rotations of the lower electrode; screw B is used for lateral rotation of the entire upper part of the tripod; finally, with the help of screw A, you can raise or lower the entire upper part tripod; H - stand for burners, glasses, etc. The choice of energy source for a particular purpose of the study can be done, guided by the following approximate table.

Qualitative Analysis. In qualitative spectral analysis, the discovery of any element depends on many factors: on the nature of the element being determined, the energy source, the resolution of the spectral apparatus, and also on the sensitivity of photographic plates. Regarding the sensitivity of the assay, the following guidelines can be made. When working with spark discharges in solutions, you can open 10 -9 -10 -3%, and in metals 10 -2 -10 -4% of the element under study; when working with a voltaic arc, the opening limits lie about 10 -3%. The absolute amount that m. b. open when working with a flame, is 10 -4 -10 -7 g, and with spark discharges 10 -6 -10 -8 g of the element under study. The highest sensitivity of the discovery refers to metals and metalloids - B, P, C; lower sensitivity for metalloids As, Se and Te; halides, as well as S, O, N in their compounds, are not at all. open and m. b. discovered only in some cases in gas mixtures.

For qualitative analysis highest value have "last lines", and in the analysis the task is to most exact definition wavelengths of spectral lines. In visual studies, the wavelengths are measured on the drum of the spectrometer; these measurements can be considered only approximate, since the accuracy is usually ± (2-3) Ӑ and in the Kaiser tables this error interval can correspond to about 10 spectral lines belonging to various elements for λ 6000 and 5000 Ӑ and about 20 spectral lines for λ ≈ 4000 Ӑ. The wavelength is determined much more accurately by spectrographic analysis. In this case, on the spectrograms using a measuring microscope, the distance between the lines with known length wave and defined; according to the Hartmann formula, the wavelength of the latter is found. The accuracy of such measurements when working with a device that gives a spectral strip about 20 cm long is ± 0.5 Ӑ for λ ≈ 4000 Ӑ, ± 0.2 Ӑ for λ ≈ 3000 Ӑ and ± 0.1 Ӑ for λ ≈ 2500 Ӑ. By wavelength in the tables find the corresponding element. The distance between the lines during normal work is measured with an accuracy of 0.05-0.01 mm. It is sometimes convenient to combine this technique with recording spectra with so-called Hartmann shutters, two types of which are shown in Fig. 13a and b; with the help of their spectrograph slit it is possible to make different heights. Fig. 13c schematically depicts the case of a qualitative analysis of substance X - the establishment of elements A and B in it. The spectra of FIG. 13, d show that in the substance Y, in addition to element A, the lines of which are indicated by the letter G, there is an impurity, the lines of which are indicated by z. Using this technique, in simple cases, it is possible to perform a qualitative analysis without resorting to measuring the distances between the lines.

Quantitative Analysis. For quantitative spectral analysis, the most important are lines that have the highest possible concentration sensitivity dI/dK, where I is the line intensity, and K is the concentration of the element that gives it. The greater the concentration sensitivity, the more precisely analysis. Developed over time whole line methods of quantitative spectral analysis. These methods are as follows.

I. Spectroscopic methods(without photography) almost all are photometric methods. These include: 1) Barratt's method. At the same time, the spectra of two substances - the test and the standard - are excited, visible in the field of view of the spectroscope side by side, one above the other. The path of the rays is shown in Fig. fourteen,

where F 1 and F 2 are two spark gaps, the light from which passes through Nicol prisms N 1 and N 2, polarizing rays in mutually perpendicular planes. With the help of a prism D, the rays enter the slit S of the spectroscope. In his telescope is placed the third Nicol prism - the analyzer - by rotating which they achieve the same intensity of the two compared lines. Previously, when studying standards, i.e., substances with a known content of elements, a relationship is established between the angle of rotation of the analyzer and concentration, and a diagram is drawn from these data. When analyzing by the angle of rotation of the analyzer from this diagram, the required percentage. Method accuracy ±10%. 2). The principle of the method is that the light rays after the prism of the spectroscope pass through the Wollaston prism, where they diverge into two beams and are polarized in mutually perpendicular planes. The ray path is shown in Fig. fifteen,

where S is the slit, P is the spectroscope prism, W is the Wollaston prism. In the field of view, two spectra B 1 and B 2 are obtained, lying side by side, one above the other; L - magnifier, N - analyzer. If you rotate the Wollaston prism, then the spectra will move relative to each other, which allows you to combine any two of their lines. For example, if iron containing vanadium is analyzed, then the vanadium line is aligned with some nearby single-color iron line; then, turning the analyzer, achieve the same brightness of these lines. The angle of rotation of the analyzer, as in the previous method, is a measure of the concentration of the desired element. The method is especially suitable for the analysis of iron, the spectrum of which has many lines, which makes it possible to always find lines suitable for research. The accuracy of the method is ± (3-7)%. 3) Occhialini method. If the electrodes (for example, the analyzed metals) are placed horizontally and projected from the light source onto the vertical slit of the spectroscope, then both with spark and arc discharges, the impurity lines can be open depending on the concentration at a greater or lesser distance from the electrodes. The light source is projected onto the slit using special lens equipped with a micrometer screw. During analysis, this lens moves and the image of the light source moves with it until any impurity line in the spectrum disappears. A measure of impurity concentration is the reading on the lens scale. At present, this method has also been developed for work with the ultraviolet part of the spectrum. It should be noted that Lockyer used the same method of illuminating the slit of the spectral apparatus, and he developed the method of quantitative spectral analysis, the so-called. method of "long and short lines". four) Direct photometry of spectra. The methods described above are called visual. Instead of visual studies, Lundegard used a photocell to measure the intensity of spectral lines. The accuracy of determination of alkali metals when working with a flame reached ± 5%. With spark discharges, this method is not applicable, since they are less constant than a flame. There are also methods based on changing the inductance in the secondary circuit, as well as using artificial attenuation of the light entering the spectroscope until the spectral lines under study disappear from the field of view.

II. Spectrographic methods. With these methods, photographic images of spectra are studied, and the blackening they give on a photographic plate is a measure of the intensity of the spectral lines. The intensity is estimated either by the eye or photometrically.

BUT. Methods without the use of photometry. 1) Last lines method. When the concentration of any element in the spectrum changes, the number of its lines changes, which makes it possible, under unchanged operating conditions, to judge the concentration of the element being determined. A number of spectra of substances with a known content of the component of interest are photographed, the number of its lines is determined on the spectrograms, and tables are compiled that indicate which lines are visible at given concentrations. These tables serve further for analytical definitions. During the analysis on the spectrogram, the number of lines of the element of interest is determined and the percentage content is found from the tables, and the method does not give its unambiguous figure, but the concentration limits, i.e. "from-to". It is most reliably possible to distinguish concentrations that differ from each other by a factor of 10, for example, from 0.001 to 0.01%, from 0.01 to 0.1%, etc. Analytical tables are only relevant for well-defined operating conditions, which in different laboratories can vary greatly; in addition, careful observance of the constancy of working conditions is required. 2) Comparative spectra method. several spectra of the analyte A + x% B are photographed, in which the content x of element B is determined, and in the intervals between them on the same photographic plate - the spectra of standard substances A + a% B, A + b% B, A + c% B , where a, b, c - the known percentage of B. On the spectrograms, the intensity of the B lines determines between which concentrations the x value lies. The criterion for the constancy of working conditions is the equality of the intensity on all spectrograms of any nearby line A. When analyzing solutions, they add the same number any element that gives a line close to lines B, and then the constancy of working conditions is judged by the equality of the intensity of these lines. How less difference between the concentrations a, b, c, ... and the more precisely the equality of the intensity of the lines A is achieved, the more accurate the analysis. A. Rice, for example, used concentrations a, b, c, ... related to each other as 1: 1.5. The method of comparative spectra adjoins the method of "selection of concentrations" (Testverfahren) according to Güttig and Thurnwald, applicable only to the analysis of solutions. It consists in the fact that if in two solutions containing a% A and x% A (x is greater or less than a), which can now be determined from their spectra, then such an amount of element A is added to any of these solutions so that the intensity of its lines in both spectra becomes the same. This will determine the concentration x, which will be equal to (a ± n)%. You can also add some other element B to the analyzed solution until the intensity of certain lines A and B is equal and, by the amount of B, estimate the content of A. 3) homologous pair method. In the spectrum of a substance A + a% B, the lines of the elements A and B are not equally intense, and if there are a sufficient number of these lines, two such lines A and B can be found, the intensity of which will be the same. For a different composition A + b% B, the other lines A and B will be identical in intensity, etc. These two identical lines are called homologous pairs. The concentrations of B at which one or another homologous pair is carried out are called fixing points this couple. To work on this method, preliminary compilation of tables of homologous pairs using substances of known composition is required. How fuller table, i.e., the more they contain homologous pairs with fixing points that differ as much as possible less friend from each other, the more accurate the analysis. There are quite a few of these tables a large number of, and they can be used in any laboratory, since the conditions of the discharges are known exactly when they are compiled, and these conditions can be used. reproduced exactly. This is achieved using the following simple reception. In the spectrum of the substance A + a% B, two lines of the element A are selected, the intensity of which varies greatly depending on the magnitude of the self-induction in the secondary circuit, namely one arc line (belonging to a neutral atom) and one spark line (belonging to an ion). These two lines are called fixing pair. By selecting the value of the self-induction, the lines of this pair are made identical and the compilation is carried out precisely under these conditions, which are always indicated in the tables. Under the same conditions, the analysis is carried out, and the percentage is found according to the implementation of one or another homologous pair. There are several modifications of the homologous pair method. Of these, the most important is the method auxiliary spectrum, used when elements A and B do not have enough lines. In this case, the lines of the spectrum of element A are connected in a certain way with the lines of another, more suitable element G, and element G begins to play the role of A. The method of homologous pairs was developed by Gerlach and Schweitzer. It is applicable to both alloys and solutions. Its accuracy averages about ±10%.

AT. Methods using photometry. 1) Barratt method. Fig. 16 gives an idea of the method.

F 1 and F 2 are two spark gaps, with the help of which the spectra of the standard and the analyzed substance are simultaneously excited. Light passes through 2 rotating sectors S 1 and S 2 and with the help of a prism D forms spectra that are located one above the other. By selecting cuts of sectors, the lines of the element under study obtain the same intensity; the concentration of the element to be determined is calculated from the ratio of cutouts. 2) is similar, but with one spark gap (Fig. 17).

The light from F is divided into two beams and passes through the sectors S 1 and S 2, with the help of the Hufner rhombus R, two bands of the spectrum are obtained one above the other; Sp is the slit of the spectrograph. The slices of the sectors are changed until the intensity of the impurity line is equal to that of any nearby line of the main substance, and the percentage content of the element being determined is calculated from the ratio of the cutouts. 3) When used as a photometer rotating logarithmic sector the lines are wedge-shaped on the spectrograms. One of these sectors and its position relative to the spectrograph during operation are shown in Fig. 18, a and b.

The slice of the sector obeys the equation

- lg Ɵ = 0.3 + 0.2l

where Ɵ is the length of the arc in parts of a full circle, located at a distance I, measured in mm along the radius from its end. A measure of the intensity of the lines is their length, since with a change in the concentration of an element, the length of its wedge-shaped lines also changes. Previously, according to samples with a known content, a diagram of the dependence of the length of any line on the% content is constructed; in the analysis on the spectrogram, the length of the same line is measured and the percentage is found from the diagram. There are several different modifications of this method. It should be pointed out to the modification of Sheibe, who used the so-called. double logarithmic sector. The view of this sector is shown in Fig. 19.

The lines are then examined using a special apparatus. Accuracy achievable with logarithmic sectors, ±(10-15)%; the Scheibe modification gives an accuracy of ±(5-7)%. 4) Quite often, spectral line photometry is used with the help of light and thermoelectric spectrophotometers of various designs. Convenient are thermoelectric photometers, designed specifically for the purposes of quantitative analysis. For the example in FIG. 20 shows the scheme of the photometer according to Sheiba:

L is a constant light source with a condenser K, M is a photographic plate with the spectrum under study, Sp is a slit, O 1 and O 2 are lenses, V is a shutter, Th is a thermoelement that is attached to the galvanometer. The measure of the intensity of the lines is the deflection of the galvanometer needle. Less commonly used are self-registering galvanometers, which record the intensity of lines in the form of a curve. The accuracy of analysis using this type of photometry is ±(5-10)%. When combined with other methods of quantitative analysis, the accuracy can be. increased; for example, three line method Sheibe and Schnettler, which is a combination of the method of homologous pairs and photometric measurements, in favorable cases can give an accuracy of ±(1-2)%.

Ministry of Education and Science
Republic of Kazakhstan

Karaganda State University
named after E.A. Buketova

Faculty of Physics

Department of Optics and Spectroscopy

Course work

on the topic:

Spectra. FROM spectral analysis and its application.

Prepared by:

student of the FTRF-22 group

Akhtariev Dmitry.

Checked:

teacher

Kusenova Asiya Sabirgalievna

Karaganda - 2003 Plan

Introduction

1. Energy in the spectrum

2. Types of spectra

3. Spectral analysis and its application

4. Spectral devices

5. Spectrum of electromagnetic radiation

Conclusion

List of used literature

Introduction

The study of the line spectrum of a substance allows you to determine what chemical elements it consists of and how much each element is contained in this substance.

The quantitative content of the element in the sample under study is determined by comparing the intensity of individual lines of the spectrum of this element with the intensity of the lines of another chemical element, the quantitative content of which in the sample is known.

Method for determining the quality and quantitative composition substance on its spectrum is called spectral analysis. Spectral analysis is widely used in mineral exploration to determine the chemical composition of ore samples. In industry, spectral analysis makes it possible to control the compositions of alloys and impurities introduced into metals to obtain materials with desired properties.

The advantages of spectral analysis are high sensitivity and speed of results. With the help of spectral analysis, it is possible to detect the presence of gold in a sample weighing 6 * 10 -7 g, while its mass is only 10 -8 g. Determination of the steel grade by spectral analysis can be performed in several tens of seconds.

Spectral analysis allows you to determine chemical composition celestial bodies billions of light years away from Earth. The chemical composition of the atmospheres of planets and stars, cold gas in interstellar space is determined by absorption spectra.

By studying the spectra, scientists were able to determine not only the chemical composition of celestial bodies, but also their temperature. The shift of spectral lines can be used to determine the speed of a celestial body.

Energy in the spectrum.

The light source must consume energy. Light is electromagnetic waves with a wavelength of 4 * 10 -7 - 8 * 10 -7 m. Electromagnetic waves are emitted during the accelerated motion of charged particles. These charged particles are part of atoms. But, without knowing how the atom is arranged, nothing reliable can be said about the mechanism of radiation. It is only clear that there is no light inside an atom, just as there is no sound in a piano string. Like a string that begins to sound only after a hammer strike, atoms give birth to light only after they are excited.

In order for an atom to radiate, it needs to transfer energy. By radiating, an atom loses the energy it has received, and for the continuous glow of a substance, an influx of energy to its atoms from the outside is necessary.

Thermal radiation. The simplest and most common type of radiation is thermal radiation, in which the energy losses of atoms for the emission of light are compensated by the energy of the thermal motion of the atoms or (molecules) of the radiating body. The higher the body temperature, the faster the atoms move. When fast atoms (molecules) collide with each other, part of their kinetic energy is converted into excitation energy of atoms, which then emit light.

The heat source of radiation is the Sun, as well as an ordinary incandescent lamp. The lamp is a very convenient, but uneconomical source. Only about 12% of the total energy released in the lamp electric shock, is converted into light energy. The heat source of light is the flame. Grains of soot are heated by the energy released during the combustion of fuel, and emit light.

Electroluminescence. The energy needed by atoms to emit light can also be borrowed from non-thermal sources. When discharging in gases, the electric field imparts a large kinetic energy to the electrons. Fast electrons experience collisions with atoms. Part of the kinetic energy of electrons goes to the excitation of atoms. Excited atoms give off energy in the form of light waves. Due to this, the discharge in the gas is accompanied by a glow. This is electroluminescence.

cathodoluminescence. glow solids caused by bombardment with electrons is called cathodoluminescence. Cathodoluminescence makes the screens of cathode ray tubes on televisions glow.

Chemiluminescence. For some chemical reactions, going with the release of energy, part of this energy is directly spent on the emission of light. The light source remains cold (it has ambient temperature). This phenomenon is called chemioluminescence.

Photoluminescence. Light falling on a substance is partly reflected and partly absorbed. The energy of the absorbed light in most cases causes only heating of the bodies. However, some bodies themselves begin to glow directly under the action of the radiation incident on it. This is photoluminescence. Light excites the atoms of matter (increases their internal energy), after which they are highlighted by themselves. For example, luminous paints, which cover many Christmas decorations, emit light after they are irradiated.

The light emitted during photoluminescence has, as a rule, a longer wavelength than the light that excites the glow. This can be observed experimentally. If a light beam passed through a violet light filter is directed to a vessel with fluoresceite (an organic dye), then this liquid begins to glow green-yellow light, i.e., light of a longer wavelength than that of violet light.

The phenomenon of photoluminescence is widely used in fluorescent lamps. The Soviet physicist S. I. Vavilov proposed to cover inner surface discharge tube with substances capable of glowing brightly under the action of short-wave radiation of a gas discharge. Fluorescent lamps are about three to four times more economical than conventional incandescent lamps.

The main types of radiation and the sources that create them are listed. The most common sources of radiation are thermal.

Distribution of energy in the spectrum. None of the sources gives monochromatic light, that is, light of a strictly defined wavelength. We are convinced of this by experiments on the decomposition of light into a spectrum with the help of a prism, as well as experiments on interference and diffraction.

The energy that light from the source carries with it is distributed in a certain way over the waves of all wavelengths that make up the light beam. We can also say that the energy is distributed over frequencies, since there is a simple relationship between wavelength and frequency: ђv = c.

Flux density electromagnetic radiation, or intensity /, is determined by the energy &W attributable to all frequencies. To characterize the distribution of radiation over frequencies, it is necessary to introduce a new value: the intensity per unit frequency interval. This value is called the spectral density of the radiation intensity.

The spectral density of the radiation flux can be found experimentally. For this, it is necessary to use a prism to obtain the radiation spectrum, for example, of an electric arc, and to measure the radiation flux density falling on small spectral intervals of width Av.

You cannot rely on the eye when estimating the distribution of energy. The eye has a selective sensitivity to light: the maximum of its sensitivity lies in the yellow-green region of the spectrum. It is best to take advantage of the property of a black body to almost completely absorb light of all wavelengths. In this case, the energy of radiation (i.e., light) causes heating of the body. Therefore, it is sufficient to measure the body temperature and use it to judge the amount of energy absorbed per unit time.

An ordinary thermometer is too sensitive to be used successfully in such experiments. More sensitive temperature measuring instruments are needed. You can take an electric thermometer, in which the sensitive element is made in the form of a thin metal plate. This plate must be covered thin layer soot, which almost completely absorbs light of any wavelength.

The heat-sensitive plate of the instrument should be placed in one place or another in the spectrum. The entire visible spectrum of length l from red rays to violet corresponds to the frequency interval from v kr to y f. The width corresponds to a small interval Av. By heating the black plate of the device, one can judge the density of the radiation flux per frequency interval Av. Moving the plate along the spectrum, we find that most of the energy is in the red part of the spectrum, and not in the yellow-green, as it seems to the eye.

Based on the results of these experiments, it is possible to plot the dependence of the spectral density of the radiation intensity on frequency. The spectral density of the radiation intensity is determined by the temperature of the plate, and the frequency is not difficult to find if the device used to decompose the light is calibrated, i.e., if it is known what frequency the given section of the spectrum corresponds to.

Plotting along the abscissa axis the values of the frequencies corresponding to the midpoints of the Av intervals, and along the ordinate axis the spectral density of the radiation intensity, we obtain a series of points through which a smooth curve can be drawn. This curve gives a visual representation of the distribution of energy and the visible part of the spectrum of an electric arc.

Since the discovery of “spectral analysis”, there has been a lot of controversy around this term. First physical principle spectral analysis implied identification method elemental composition samples according to the observed spectrum, which was excited in some high-temperature source of flame, spark or arc.

Later, spectral analysis began to be understood as other methods of analytical study and excitation of spectra:

Raman scattering methods,
absorption and luminescence methods.

Eventually, X-ray and gamma spectra were discovered. Therefore, when speaking about spectral analysis, it is correct to mean the totality of all existing methods. However, more often the phenomenon of identification by spectra is used in understanding emission methods.

Classification methods

Another classification option is the division into molecular (determination of the molecular composition of the sample) and elementary (determination of the atomic composition) spectra studies.

The molecular method is based on the study of absorption spectra, Raman scattering and luminescence; the atomic composition is determined from the excitation spectra in hot springs (molecules are mainly destroyed) or from the data of X-ray spectral studies. But such a classification cannot be rigorous, because sometimes both of these methods coincide.

Classification of spectral analysis methods

Based on the tasks that are solved by the methods described above, the study of spectra is divided into methods used to study alloys, gases, ores and minerals, finished products, pure metals etc. Each object under study has its own characteristic features and standards. Two main areas of spectrum analysis:

Qualitative
Quantitative

What is studied during their implementation, we will consider further.

Diagram of spectral analysis methods

Qualitative spectral analysis

Qualitative analysis is used to determine what elements the analyzed sample consists of. It is necessary to obtain the spectrum of the sample, excited in some source, and to determine which elements they belong to by the detected spectral lines. This will make it clear what the sample consists of. The complexity of qualitative analysis is a large number of spectral lines on the analytical spectrogram, the interpretation and identification of which is too laborious and inaccurate.

Quantitative spectral analysis

The method of quantitative spectral analysis is based on the fact that the intensity of the analytical line increases with an increase in the content of the element being determined in the sample. This dependence is built on the basis of many factors that are difficult to calculate numerically. Therefore, it is practically impossible to theoretically establish a relationship between the line intensity and the element concentration.

Therefore, relative measurements intensities of the same spectral line with a change in the concentration of the element being determined. Thus, under the same conditions of excitation and registration of the spectra, the measured radiation energy is proportional to the intensity. The measurement of this energy (or a quantity dependent on it) gives the empirical relationship we need between the measured quantity and the concentration of the element in the sample.

Spectral analysis

Spectral analysis- a set of methods for qualitative and quantitative determination of the composition of an object, based on the study of the spectra of the interaction of matter with radiation, including the spectra of electromagnetic radiation, acoustic waves, mass and energy distributions of elementary particles, etc.

Depending on the purpose of the analysis and the types of spectra, there are several methods of spectral analysis. Atomic and molecular spectral analyzes make it possible to determine the elemental and molecular composition of a substance, respectively. In the emission and absorption methods, the composition is determined from the emission and absorption spectra.

Mass spectrometric analysis is carried out using the mass spectra of atomic or molecular ions and makes it possible to determine the isotopic composition of an object.

Story

Dark lines on the spectral stripes have been noticed for a long time, but the first serious research of these lines was only undertaken in 1814 by Josef Fraunhofer. The effect was named Fraunhofer Lines in his honor. Fraunhofer established the stability of the position of the lines, compiled their table (he counted 574 lines in total), assigned an alphanumeric code to each. No less important was his conclusion that the lines are not associated with either optical material or the Earth's atmosphere, but are natural characteristic sunlight. He found similar lines in artificial light sources, as well as in the spectra of Venus and Sirius.

It soon became clear that one of the clearest lines always appears in the presence of sodium. In 1859, G. Kirchhoff and R. Bunsen, after a series of experiments, concluded that each chemical element has its own unique line spectrum, and the spectrum of celestial bodies can be used to draw conclusions about the composition of their matter. From that moment on, spectral analysis appeared in science, a powerful method for remote determination of chemical composition.

To test the method in 1868, the Paris Academy of Sciences organized an expedition to India, where a full solar eclipse. There, scientists found that all the dark lines at the time of the eclipse, when the emission spectrum changed the absorption spectrum of the solar corona, became, as predicted, bright against a dark background.

The nature of each of the lines, their connection with the chemical elements were gradually elucidated. In 1860, Kirchhoff and Bunsen, using spectral analysis, discovered cesium, and in 1861, rubidium. And helium was discovered on the Sun 27 years earlier than on Earth (1868 and 1895, respectively).

Principle of operation

The atoms of each chemical element have strictly defined resonant frequencies, as a result of which it is at these frequencies that they emit or absorb light. This leads to the fact that in the spectroscope, lines (dark or light) are visible on the spectra in certain places characteristic of each substance. The intensity of the lines depends on the amount of matter and its state. In quantitative spectral analysis, the content of the test substance is determined by the relative or absolute intensities of lines or bands in the spectra.

Optical spectral analysis is characterized by relative ease of implementation, the absence of complex preparation of samples for analysis, and a small amount of a substance (10–30 mg) required for analysis on big number elements.

Atomic spectra (absorption or emission) are obtained by transferring a substance to a vapor state by heating the sample to 1000-10000 °C. As sources of excitation of atoms in the emission analysis of conductive materials, a spark, an alternating current arc are used; while the sample is placed in the crater of one of the carbon electrodes. Flames or plasmas of various gases are widely used to analyze solutions.

Application

AT recent times, most widespread received emission and mass spectrometric methods of spectral analysis based on the excitation of atoms and their ionization in the argon plasma of inductive discharges, as well as in a laser spark.

Spectral analysis is a sensitive method and is widely used in analytical chemistry, astrophysics, metallurgy, mechanical engineering, geological exploration and other branches of science.

In signal processing theory, spectral analysis also means the analysis of the distribution of the energy of a signal (for example, sound) over frequencies, wave numbers, etc.