What is nadphn in biology. Dehydrogenases are enzymes of the oxidoreductase class (pyridine-dependent, flavin-dependent, aerobic and anaerobic types, physiology, biochemistry)
In the seventeenth century, denoting the totality of all meanings of any physical quantity. Energy, mass, optical radiation. It is the latter that is often meant when we talk about the spectrum of light. Specifically, the light spectrum is a set of bands of optical radiation different frequencies, some of which we can see every day in the world around us, while some of them are inaccessible to the naked eye. Depending on the possibility of perception by the human eye, the light spectrum is divided into visible and invisible parts. The latter, in turn, is exposed to infrared and ultraviolet light.
Types of spectra
There are also different types spectra. There are three of these, depending on the spectral density of the radiation intensity. Spectra can be continuous, line or striped. The types of spectra are determined using
Continuous spectrum
A continuous spectrum is formed by solids or gases heated to a high temperature. high density. The well-known rainbow of seven colors is a direct example of a continuous spectrum.
Line spectrum
Also represents types of spectra and comes from any substance in a gaseous atomic state. It is important to note here that it is in the atomic, not the molecular. This spectrum ensures extremely low interaction of atoms with each other. Since there is no interaction, the atoms emit waves of permanently the same length. An example of such a spectrum is the glow of gases heated to a high temperature.
Band spectrum
The striped spectrum visually represents individual bands, clearly delimited by fairly dark intervals. Moreover, each of these bands is not radiation of a strictly defined frequency, but consists of large quantity light lines located close to each other. An example of such spectra, as in the case of line spectra, is the glow of vapors at high temperature. However, they are no longer created by atoms, but by molecules that have an extremely close common bond, which causes such a glow.
Absorption spectrum
However, the types of spectra do not end there. Additionally, there is another type known as the absorption spectrum. In spectral analysis, the absorption spectrum is dark lines against the background of a continuous spectrum and, essentially, the absorption spectrum is an expression of the dependence on the absorption rate of the substance, which can be more or less high.
Although there is wide range experimental approaches to measuring absorption spectra. The most common is an experiment in which the generated beam of radiation is passed through a cooled (so that there is no interaction of particles and, therefore, glow) gas, after which the intensity of the radiation passing through it is determined. The transferred energy may well be used to calculate absorption.
Spectral analysis, a method for qualitative and quantitative determination of the composition of substances, based on the study of their emission, absorption, reflection and luminescence spectra. Distinguish between atomic and molecular spectral analysis, whose tasks are to determine, respectively, the elemental and molecular composition of a substance. Emission spectral analysis carried out using the emission spectra of atoms, ions or molecules excited different ways, absorption spectral analysis- by absorption spectra electromagnetic radiation analyzed objects (see Absorption spectroscopy). Depending on the purpose of the study, the properties of the analyzed substance, the specifics of the spectra used, the wavelength region and other factors, the course of analysis, equipment, methods of measuring spectra and metrological characteristics of the results vary greatly. According to this spectral analysis divided into a number independent methods(see in particular reflectance spectroscopy, ultraviolet spectroscopy, ).
Often under spectral analysis understand only atomic emission spectral analysis (AESA) - a method of elemental analysis based on the study of the emission spectra of free atoms and ions in the gas phase in the wavelength range 150-800 nm (see).
A sample of the test substance is introduced into a radiation source, where it evaporates, dissociates molecules and excites the resulting atoms (ions). The latter emit characteristic radiation, which enters the recording device of the spectral instrument.
In qualitative spectral analysis, the spectra of samples are compared with the spectra of known elements given in the corresponding atlases and tables of spectral lines, and thus the elemental composition of the analyzed substance is established. In quantitative analysis, the amount (concentration) of the desired element in the analyzed substance is determined by the dependence of the magnitude of the analytical signal (blackening density or optical density of the analytical line on a photographic plate; luminous flux to the photoelectric receiver) of the desired element on its content in the sample. This dependence is determined in a complex manner by many difficult-to-control factors (the bulk composition of samples, their structure, dispersion, parameters of the source of excitation of the spectra, instability of recording devices, properties of photographic plates, etc.). Therefore, as a rule, to establish it, a set of samples is used for calibration, which in terms of gross composition and structure are as close as possible to the substance being analyzed and contain known quantities of the elements being determined. Such samples can serve as specially prepared metallic materials. alloys, mixtures of substances, solutions, incl. and produced by industry. To eliminate the influence on the analysis results of the inevitable differences in the properties of the analyzed and standard samples, use different techniques; for example, they compare the spectral lines of the element being determined and the so-called reference element, which is similar in chemical and physical properties to the defined. When analyzing materials of the same type, you can use the same calibration dependencies, which are periodically adjusted using verification samples.
The sensitivity and accuracy of spectral analysis depend mainly on physical characteristics sources of radiation (excitation of spectra) - temperature, electron concentration, residence time of atoms in the zone of excitation of spectra, stability of the source mode, etc. To solve a specific analytical problem, it is necessary to select a suitable radiation source, optimize its characteristics using various techniques - the use of an inert atmosphere, the application magnetic field, the introduction of special substances that stabilize the discharge temperature, the degree of ionization of atoms, diffusion processes at an optimal level, etc. Due to the variety of mutually influencing factors, methods of mathematical planning of experiments are often used.
When analyzing solids Most often, arc (direct and alternating current) and spark discharges are used, powered by specially designed stabilizing generators (often electronically controlled). Universal generators have also been created, with the help of which discharges are obtained different types with variable parameters affecting the efficiency of the excitation processes of the samples under study. A solid electrically conductive sample can directly serve as an arc or spark electrode; Non-conducting solid samples and powders are placed in the recesses of carbon electrodes of one configuration or another. In this case, both complete evaporation (spraying) of the analyzed substance and fractional evaporation of the latter and excitation of the sample components are carried out in accordance with their physical and chemical properties, which improves the sensitivity and accuracy of the analysis. To enhance the effect of evaporation fractionation, additives to the analyzed substance of reagents are widely used, promoting the formation of highly volatile compounds (fluorides, chlorides, sulfides, etc.) of the determined elements under high-temperature [(5-7)·10 3 K] coal arc conditions. For the analysis of geological samples in the form of powders, the method of sprinkling or blowing samples into the carbon arc discharge zone is widely used.
When analyzing metallurgical samples, along with spark discharges of various types, glow discharge light sources (Grim lamps, discharge in a hollow cathode) are also used. Combined automated sources have been developed in which glow discharge lamps or electrothermal analyzers are used for evaporation or sputtering, and, for example, high-frequency plasmatrons are used to obtain spectra. In this case, it is possible to optimize the conditions for evaporation and excitation of the elements being determined.
When analyzing liquid samples (solutions) best results are obtained by using high-frequency (HF) and ultra-high-frequency (microwave) plasmatrons operating in an inert atmosphere, as well as by flame photometric analysis (see). To stabilize the temperature of the discharge plasma at an optimal level, additives of easily ionizable substances, such as alkali metals, are introduced. An HF discharge with an inductive coupling of a toroidal configuration is especially successfully used (Fig. 1). It separates the RF energy absorption and spectral excitation zones, which allows for dramatic increases in excitation efficiency and the useful analytical signal-to-noise ratio and, thus, achieving very low detection limits for a wide range of elements. Samples are introduced into the excitation zone using pneumatic or (less commonly) ultrasonic sprayers. When analyzed using HF and microwave plasmatrons and flame photometry, the relative standard deviation is 0.01-0.03, which in some cases allows the use of spectral analysis instead of accurate, but more labor-intensive and time-consuming chemical methods analysis.
To analyze gas mixtures, special vacuum installations are required; the spectra are excited using RF and microwave discharges. Due to the development of gas chromatography, these methods are rarely used.
Rice. 1. HF plasmatron: 1-exhaust gas torch; 2-spectrum excitation zone; 3-zone of HF energy absorption; 4-heating inductor; 5-cooling gas inlet (nitrogen, argon); 6-input of plasma-forming gas (argon); 7-input of atomized sample (carrier gas - argon).
When analyzing substances of high purity, when it is necessary to determine elements whose content is less than 10 -5%, as well as when analyzing toxic and radioactive substances, samples are pre-treated; for example, the elements being determined are partially or completely separated from the base and transferred to a smaller volume of solution or added to a smaller mass of a substance more convenient for analysis. To separate sample components, fractional distillation of the base (less often impurities), adsorption, precipitation, extraction, chromatography, and ion exchange are used. Spectral analysis using the listed chemical methods Sample concentration is usually called chemical spectral analysis. Additional operations of separation and concentration of the elements being determined significantly increase the complexity and duration of the analysis and worsen its accuracy (the relative standard deviation reaches values of 0.2-0.3), but reduces the detection limits by 10-100 times.
A specific area of spectral analysis is microspectral (local) analysis. In this case, a microvolume of the substance (crater depth from tens of microns to several microns) is usually evaporated by a laser pulse acting on a section of the sample surface with a diameter of several tens of microns. To excite spectra, a pulsed spark discharge synchronized with a laser pulse is most often used. The method is used in the study of minerals and metallurgy.
Spectra are recorded using spectrographs and spectrometers (quantometers). There are many types of these devices, differing in aperture, dispersion, resolution, and working spectral range. Large aperture is necessary for recording weak radiations, large dispersion is necessary for separating spectral lines with similar wavelengths when analyzing substances with multiline spectra, as well as for increasing the sensitivity of the analysis. Diffraction gratings (flat, concave, threaded, holographic, profiled) with from several hundred to several thousand lines per millimeter are used as light-dispersing devices; much less often, quartz or glass prisms are used.
Spectrographs (Fig. 2), which record spectra on special photographic plates or (less often) on photographic films, are preferable for qualitative spectral analysis, because allow you to study the entire spectrum of the sample at once (in the working area of the device); however, they are also used for quantitative analysis due to comparative cheapness, availability and ease of maintenance. The darkening of spectral lines on photographic plates is measured using microphotometers (microdensitometers). The use of computers or microprocessors provides auto mode measurements, processing their results and issuing final results analysis.
Fig.2. Optical design of the spectrograph: 1-entrance slit; 2-turn mirror; 3-spherical mirror; 4-diffraction grating; 5-light scale lighting; 6-scale; 7-photo plate.
Rice. 3. Quantometer diagram (out of 40 recording channels, only three are shown): 1-polychromator; 2-diffraction gratings; 3-exit slots; 4-photo-electron multiplier; 5-entry slots; 6-tripods with light sources; 7 spark and arc discharge generators; 8-electronic recording device; 9-control computer complex.
Spectrometers carry out photoelectric recording of analytical signals using photomultiplier tubes (PMTs) with automatic data processing on a computer. Photoelectric multichannel (up to 40 channels or more) polychromators in quantometers (Fig. 3) allow simultaneous recording of analytical lines of all determined elements provided by the program. When using scanning monochromators, multi-element analysis is provided high speed scanning across the spectrum in accordance with a given program.
To determine elements (C, S, P, As, etc.), the most intense analytical lines of which are located in the UV region of the spectrum at wavelengths less than 180-200 nm, vacuum spectrometers are used.
When using quantum meters, the duration of the analysis is determined to a large extent by the procedures for preparing the starting material for analysis. A significant reduction in sample preparation time is achieved by automating the most time-consuming stages - dissolution, bringing solutions to a standard composition, oxidation of metals, grinding and mixing powders, taking samples of a given mass. In many cases, multi-element spectral analysis is performed within a few minutes, for example: when analyzing solutions using automated photoelectric spectrometers with RF plasmatrons or when analyzing metals during the melting process with automatic supply of samples to the radiation source.
Have you ever thought about how we know about the properties of distant celestial bodies?
Surely you know that we owe such knowledge to spectral analysis. However, we often underestimate the contribution of this method to understanding itself. The advent of spectral analysis overturned many established paradigms about the structure and properties of our world.
Thanks to spectral analysis, we have an idea of the scale and grandeur of space. Thanks to him, we no longer limit the Universe to the Milky Way. Spectral analysis revealed to us a great diversity of stars, telling us about their birth, evolution and death. This method underlies almost all modern and even future astronomical discoveries.
Learn about the unattainable
Two centuries ago, it was generally accepted that the chemical composition of planets and stars would forever remain a mystery to us. Indeed, in the minds of those years, space objects will always remain inaccessible to us. Consequently, we will never get a sample of any star or planet and will never know its composition. The discovery of spectral analysis completely refuted this misconception.
Spectral analysis allows you to remotely learn about many properties of distant objects. Naturally, without such a method, modern practical astronomy is simply meaningless.
Lines on a rainbow
Dark lines on the spectrum of the Sun were noticed back in 1802 by the inventor Wollaston. However, the discoverer himself was not particularly fixated on these lines. Their extensive research and classification was carried out in 1814 by Fraunhofer. During his experiments, he noticed that the Sun, Sirius, Venus and artificial light sources have their own set of lines. This meant that these lines depended solely on the light source. Doesn't affect them earth's atmosphere or properties of an optical device.
The nature of these lines was discovered in 1859 by the German physicist Kirchhoff together with the chemist Robert Bunsen. They established a connection between the lines in the spectrum of the Sun and the emission lines of vapors various substances. So they made the revolutionary discovery that each chemical element has its own set of spectral lines. Consequently, by the radiation of any object one can learn about its composition. This is how spectral analysis was born.
Over the next decades, many chemical elements were discovered through spectral analysis. These include helium, which was first discovered in the Sun, which is how it got its name. Therefore, it was initially thought to be exclusively a solar gas until it was discovered on Earth three decades later.
Three types of spectrum
What explains this behavior of the spectrum? The answer lies in the quantum nature of radiation. As is known, when an atom absorbs electromagnetic energy, its outer electron moves to a higher energy level. Similarly with radiation - to a lower level. Each atom has its own difference in energy levels. Hence the unique frequency of absorption and emission for each chemical element.
It is at these frequencies that the gas emits and emits. At the same time, hard and liquid bodies when heated, they emit a full spectrum, independent of their chemical composition. Therefore, the resulting spectrum is divided into three types: continuous, line spectrum and absorption spectrum. Accordingly, a continuous spectrum is emitted by solids and liquids, and a line spectrum is emitted by gases. The absorption spectrum is observed when continuous radiation is absorbed by a gas. In other words, the colorful lines on dark background line spectrum will correspond to dark lines on a multi-colored background of the absorption spectrum.
It is the absorption spectrum that is observed in the Sun, while heated gases emit radiation with a line spectrum. This is explained by the fact that the photosphere of the Sun, although it is a gas, is not transparent to the optical spectrum. A similar picture is observed in other stars. What's interesting is that during full solar eclipse the spectrum of the Sun becomes lined. Indeed, in this case it comes from transparent outer layers her .
Principles of spectroscopy
Optical spectral analysis is relatively simple in technical implementation. Its work is based on the decomposition of the radiation of the object under study and further analysis of the resulting spectrum. Using a glass prism, in 1671 Isaac Newton carried out the first "official" decomposition of light. He also introduced the word “spectrum” into scientific use. Actually, while arranging the light in the same way, Wollaston noticed black lines on the spectrum. Spectrographs also operate on this principle.
Light decomposition can also occur using diffraction gratings. Further analysis of light can be done using a variety of methods. Initially, an observation tube was used for this, then a camera. Nowadays, the resulting spectrum is analyzed by high-precision electronic instruments.
So far we have been talking about optical spectroscopy. However, modern spectral analysis is not limited to this range. In many fields of science and technology, spectral analysis of almost all types of electromagnetic waves is used - from radio to x-rays. Naturally, such studies are carried out using a variety of methods. Without various methods of spectral analysis, we would not know modern physics, chemistry, medicine and, of course, astronomy.
Spectral analysis in astronomy
As noted earlier, it was from the Sun that the study of spectral lines began. Therefore, it is not surprising that the study of spectra immediately found its application in astronomy.
Of course, the first thing astronomers began to do was use this method to study the composition of stars and other cosmic objects. Thus, each star acquired its own spectral class, reflecting the temperature and composition of their atmosphere. The parameters of the planets' atmospheres also became known. solar system. Astronomers have come closer to understanding the nature of gas nebulae, as well as many other celestial objects and phenomena.
However, with the help of spectral analysis you can learn not only about quality composition objects.
Measure speed
Doppler effect in astronomyDoppler effect in astronomy
The Doppler effect was theoretically developed by an Austrian physicist in 1840, after whom it was named. This effect can be observed by listening to the whistle of a passing train. The pitch of the whistle of an approaching train will be noticeably different from that of a moving train. This is roughly how the Doppler Effect was proven theoretically. The effect is that, to the observer, the wavelength of the moving source is distorted. It increases as the source moves away and decreases as it approaches. Electromagnetic waves have a similar property.
As the source moves away, all the dark bands in its emission spectrum shift to the red side. Those. all wavelengths increase. In the same way, when the source approaches, they shift to the violet side. Thus it has become an excellent addition to spectral analysis. Now, from the lines in the spectrum, it was possible to recognize what had previously seemed impossible. Measure the speed of space objects, calculate the orbital parameters of double stars, the rotation speed of planets and much more. Special role produced a “red shift” effect in cosmology.
The discovery of the American scientist Edwin Hubble is comparable to the development of the heliocentric system of the world by Copernicus. By studying the brightness of Cepheids in various nebulae, he proved that many of them are located much further than the Milky Way. By comparing the obtained distances with the spectra of galaxies, Hubble discovered his famous law. According to it, the distance to galaxies is proportional to the speed of their removal from us. Although his law differs somewhat from modern ideas, Hubble's discovery expanded the scope of the Universe.
Spectral analysis and modern astronomy
Today, almost no astronomical observation occurs without spectral analysis. With its help, new exoplanets are discovered and the boundaries of the Universe are expanded. Spectrometers are carried on Mars rovers and interplanetary probes, space telescopes and research satellites. In fact, without spectral analysis there would be no modern astronomy. We would continue to gaze at the empty, faceless light of the stars, about which we would know nothing.
Kirchhoff and Bunsen first attempted spectral analysis back in 1859. Two created a spectroscope that looks like a pipe irregular shape. On one side there was a hole (collimator) into which the light rays under study fell. There was a prism inside the pipe; it deflected the rays and directed them towards another hole in the pipe. At the output, physicists could see light decomposed into a spectrum.
Scientists decided to conduct an experiment. Having darkened the room and covered the window with thick curtains, they lit a candle near the collimator slit, and then took pieces different substances and introduced them into a candle flame, observing whether the spectrum changed. And it turned out that the hot vapors of each substance gave different spectra! Since the prism strictly separated the rays and did not allow them to overlap each other, it was possible to accurately identify the substance from the resulting spectrum.
Kirchhoff subsequently analyzed the spectrum of the Sun, discovering that certain chemical elements were present in its chromosphere. This gave rise to astrophysics.
Features of spectral analysis
To carry out spectral analysis, a very small amount of substance is required. This method is extremely sensitive and very fast, which allows not only to use it for a wide variety of needs, but also sometimes makes it simply irreplaceable. It is known for sure that each periodic table emits a special spectrum, only for him alone, therefore, with a correctly carried out spectral analysis, it is almost impossible to make a mistake.
Types of Spectral Analysis
Spectral analysis can be atomic or molecular. Using atomic analysis, one can reveal, respectively, the atomic composition of a substance, and through molecular analysis, the molecular composition.
There are two ways to measure the spectrum: emission and absorption. Emission spectral analysis is carried out by studying what spectrum selected atoms or molecules emit. To do this, they need to be given energy, that is, to excite them. Absorption analysis, on the contrary, is carried out using the absorption spectrum of electromagnetic study aimed at objects.
Through spectral analysis it is possible to measure a variety of various characteristics substances, particles or even large physical bodies(for example, space objects). That is why spectral analysis is further divided into various methods. To obtain the result required for a specific task, you need to correctly select the equipment, wavelength for studying the spectrum, as well as the spectral region itself.
Application of spectral analysis
The method that provides valuable and most diverse information about celestial bodies is spectral analysis. It allows you to determine from the analysis of light the qualitative and quantitative chemical composition of the star, its temperature, the presence and strength of the magnetic field, the speed of movement along the line of sight, and much more.
Spectral analysis is based on the decomposition of white light into its component parts. If a beam of light is directed onto the side face of a trihedral prism, then, refracting in the glass in different ways, the components White light the rays will produce a rainbow stripe on the screen called a spectrum. In the spectrum, all colors are always located in a certain order.
As you know, light travels in the form of electromagnetic waves. Each color corresponds to a specific length electromagnetic wave. The wavelength in the spectrum decreases from red rays to violet rays from approximately 0.7 to 0.4 μm. Beyond the violet rays of the spectrum lie ultra-violet rays, invisible to the eye, but acting on the photographic plate. They have even shorter wavelengths X-rays. X-ray radiation from celestial bodies, important for understanding their nature, is blocked by the Earth's atmosphere.
Beyond the red rays of the spectrum is the region of infrared rays. They are invisible, but they also act on special photographic plates. Spectral observations usually mean observations in the range from infrared to ultraviolet rays.
To study spectra, instruments called spectroscope and spectrograph are used. The spectrum is examined with a spectroscope, and photographed with a spectrograph. A photograph of a spectrum is called a spectrogram.
Exist the following types spectra:
A solid or continuous spectrum in the form of a rainbow stripe is produced by solid and liquid hot bodies (coal, electric lamp filament) and fairly dense masses of gas.
A line spectrum of radiation is produced by rarefied gases and vapors when strongly heated or under the influence of an electromagnetic discharge. Each gas emits a strictly defined set of wavelengths and produces a line spectrum characteristic of a given chemical element. Strong changes in the state of a gas or its glow conditions, such as heating or ionization, cause certain changes in the spectrum of a given gas.
Tables have been compiled with a list of lines of each gas and indicating the brightness of each line. For example, in the spectrum of sodium, two yellow lines are especially bright.
It has been established that the spectrum of an atom or molecule is associated with their structure and reflects certain changes that occur in them during the glow process.
A line absorption spectrum is produced by gases and vapors when there is a bright or brighter light behind them. hot spring giving a continuous spectrum. The absorption spectrum is a continuous spectrum, cut by dark lines, which are located in the very places where the bright lines inherent in a given gas should be located.
Emission spectra make it possible to analyze the chemical composition of gases that emit or absorb light, regardless of whether they are in a laboratory or on a celestial body. The number of atoms or molecules lying on our line of sight, emitting or absorbing, is determined by the intensity of the lines. The more atoms, the brighter the line or the darker it is in the absorption spectrum. The Sun and stars are surrounded by gaseous atmospheric absorption lines created when light passes through the atmosphere of stars. Therefore, the spectra of the Sun and stars are absorption spectra.
It must be remembered that spectral analysis allows one to determine the chemical composition of only self-luminous or radiation-absorbing gases. Chemical composition solid cannot be determined using spectral analysis.
