What is nadph in biology. Dehydrogenases - enzymes of the oxidoreductase class (pyridine-dependent, flavin-dependent, aerobic and anaerobic types, physiology, biochemistry)
In the seventeenth century, denoting the totality of all the 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 spectrum of light is a collection of bands of optical radiation different frequency, 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 perception human eye, the spectrum of light is divided into the visible part and the invisible part. The latter, in turn, is exposed to infrared and ultraviolet light.
Types of spectra
There are also different types spectra. There are three of them, depending on the spectral density of the radiation intensity. Spectra can be continuous, line and 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
It also represents the types of spectra and comes from any substance that is in a gaseous atomic state. It is important to note here that it is in the atomic, not the molecular. Such a spectrum provides an extremely low interaction of atoms with each other. Since there is no interaction, the atoms emit waves of the same wavelength permanently. An example of such a spectrum is the glow of gases heated to a high temperature.
striped spectrum
The striped spectrum visually represents separate bands, clearly delimited by rather dark intervals. Moreover, each of these bands is not radiation of a strictly defined frequency, but consists of a large number closely spaced lines of light. An example of such spectra, as in the case of the line spectrum, 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 still do not end there. Additionally, another type is distinguished, such as an absorption spectrum. In spectral analysis, the absorption spectrum is dark lines against the background of a continuous spectrum and, in essence, the absorption spectrum is an expression of dependence on the absorption index of a substance, which can be more or less high.
Although there is wide range experimental approaches to measuring absorption spectra. The most common experiment is when the generated beam of radiation is passed through a cooled (for the absence of particle interaction and, consequently, luminescence) gas, after which the intensity of the radiation passing through it is determined. The transferred energy may well be used to calculate the absorption.
Spectral analysis, a method for the 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. Emissive spectral analysis carried out according to the emission spectra of atoms, ions or molecules excited different ways, absorption spectral analysis- by absorption spectra electromagnetic radiation analyzed objects (cf. Absorption spectroscopy). Depending on the purpose of the study, the properties of the analyte, the specifics of the spectra used, the wavelength range and other factors, the course of analysis, equipment, methods for measuring spectra, and metrological characteristics of the results vary greatly. According to this spectral analysis divided into a number independent methods(see, in particular, reflection spectroscopy, ultraviolet spectroscopy, ).
often under spectral analysis understand only atomic emission spectral analysis (AESA) - an elemental analysis method based on the study of the emission spectra of free atoms and ions in the gas phase in the wavelength range of 150-800 nm (see).
A sample of the test substance is introduced into the radiation source, where it evaporates, dissociates molecules, and excites the formed 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 analyte 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 (density of blackening or optical density of the analytical line on the photographic plate; light flux to the photoelectric receiver) of the desired element on its content in the sample. This dependence is determined in a complicated way by many difficult-to-control factors (gross composition of samples, their structure, fineness, parameters of the spectrum excitation source, instability of recording devices, properties of photographic plates, etc.). Therefore, as a rule, to establish it, a set of samples for calibration is used, which, in terms of gross composition and structure, are as close as possible to the analyzed substance and contain known amounts of the elements to be determined. Such samples can serve as specially prepared metallic. alloys, mixtures of substances, solutions, incl. and manufactured by industry. To eliminate the influence on the results of the analysis of the inevitable difference in the properties of the analyzed and standard samples, use different tricks; for example, they compare the spectral lines of the element being determined and the so-called comparison element, which is similar in chemical and physical properties to the one being defined. When analyzing materials of the same type, one and the same calibration dependences can be used, which are periodically corrected according to verification samples.
The sensitivity and accuracy of spectral analysis depend mainly on physical characteristics radiation sources (spectra excitation) - temperature, electron density, residence time of atoms in the spectrum excitation zone, source mode stability, etc. To solve a specific analytical problem, it is necessary to choose a suitable radiation source, achieve optimization of its characteristics using various techniques - the use of an inert atmosphere, the imposition 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. In view of the variety of mutually influencing factors, methods of mathematical planning of experiments are often used in this case.
When analyzing solids the most commonly used arc (direct and alternating current) and spark discharges, 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-conductive 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 analyte 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 fractionation of evaporation, additives to the analyzed substance of reagents are widely used that promote the formation of highly volatile compounds (fluorides, chlorides, sulfides, etc.) of the elements to be determined under high-temperature [(5-7) 10 3 K] carbon arc conditions. To analyze geological samples in the form of powders, the method of pouring or blowing samples into the zone of a carbon arc discharge is widely used.
In the analysis of metallurgical samples, along with spark discharges of various types, glow discharge light sources (Grim's 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 of evaporation and excitation of the elements being determined.
When analyzing liquid samples (solutions) best results are obtained by using high-frequency (HF) and microwave (microwave) plasmatrons operating in an inert atmosphere, as well as by flame photometric analysis (see). To stabilize the temperature of the discharge plasma at the optimum level, additives of easily ionizable substances, such as alkali metals, are introduced. An RF discharge with an inductive coupling of a toroidal configuration is especially successfully used (Fig. 1). It separates the RF energy absorption and spectrum excitation zones, which makes it possible to dramatically increase the excitation efficiency and the useful analytical signal-to-noise ratio and, thus, achieve very low detection limits for a wide range of elements. Samples are injected into the excitation zone using pneumatic or (rarely) ultrasonic atomizers. In the analysis using RF 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.
For the analysis of 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. RF plasma torch: 1-torch of exhaust gases; 2-zone of excitation of spectra; 3-zone of absorption of RF energy; 4-heating inductor; 5-inlet of cooling gas (nitrogen, argon); 6-inlet of plasma-forming gas (argon); 7-sprayed sample inlet (carrier gas - argon).
In the analysis of substances of high purity, when it is required to determine elements whose content is less than 10 -5%, as well as in the analysis of toxic and radioactive substances, the samples are pre-treated; for example, the elements to be determined are partially or completely separated from the base and transferred to a smaller volume of solution or introduced into a smaller mass of a substance more convenient for analysis. To separate the components of the sample, fractional distillation of the base (more rarely, impurities), adsorption, precipitation, extraction, chromatography, and ion exchange are used. Spectral analysis using the listed chemical methods sample concentration is generally referred to as chemical spectral analysis. Additional operations for separating and concentrating the elements to be determined significantly increase the complexity and duration of the analysis and worsen its accuracy (the relative standard deviation reaches 0.2-0.3), but reduces the limits of detection by 10-100 times.
A specific area of spectral analysis is microspectral (local) analysis. In this case, the microvolume of the substance (the depth of the crater is 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 the spectra, most often a pulsed spark discharge synchronized with a laser pulse is used. The method is used in the study of minerals, in metal science.
Spectra are recorded using spectrographs and spectrometers (quantometers). There are many types of these instruments, differing in luminosity, dispersion, resolution, and spectral working area. Large luminosity is necessary to detect weak radiation, large dispersion - to separate spectral lines with close wavelengths in the analysis of substances with multi-line spectra, as well as to increase the sensitivity of the analysis. As devices that disperse light, diffraction gratings (flat, concave, threaded, holographic, profiled) are used, having from several hundred to several thousand lines per millimeter, much less often - quartz or glass prisms.
Spectrographs (Fig. 2) that record spectra on special photographic plates or (rarely) 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 the relative cheapness, availability and ease of maintenance. The blackening 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 end results analysis.
Fig.2. Optical scheme of the spectrograph: 1-entrance slit; 2-turn mirror; 3-spherical mirror; 4-diffraction grating; 5-bulb illumination scale; 6-scale; 7-photographic plate.
Rice. 3. Scheme of a quantometer (out of 40 registration channels, only three are shown): 1-polychromator; 2-diffraction gratings; 3-exit slots; 4-photo-electron multiplier; 5-input slots; 6 tripods with light sources; 7 generators of spark and arc discharges; 8-electronic recording device; 9-control computer complex.
In spectrometers, photoelectric recording of analytical signals is carried out using photomultiplier tubes (PMT) with automatic data processing on a computer. Photoelectric multichannel (up to 40 channels and more) polychromators in quantometers (Fig. 3) allow you to simultaneously record the analytical lines of all determined elements provided for by the program. When using scanning monochromators, multi-element analysis is provided high speed scanning along the spectrum in accordance with the specified program.
To determine the 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 quantometers, 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 longest stages - dissolution, bringing solutions to a standard composition, oxidation of metals, grinding and mixing of powders, and sampling of a given mass. In many cases, multi-element spectral analysis is performed within minutes, for example: in the analysis of solutions using automated photoelectric spectrometers with RF plasmatrons or in the analysis of metals in the melting process with automatic sampling into the radiation source.
Have you ever wondered 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 emergence of spectral analysis has 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 the cosmos. Thanks to him, we have ceased to limit the Universe to the Milky Way. Spectral analysis revealed to us a great variety of stars, told 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 will forever remain a mystery to us. Indeed, in the view of those years, space objects will always remain inaccessible to us. Consequently, we will never get a test sample of any star or planet, and we will never know about their 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 the rainbow
Dark lines on the spectrum of the Sun were noticed back in 1802 by the inventor Wollaston. However, the discoverer himself did not particularly dwell on these lines. Their extensive study and classification was carried out in 1814 by Fraunhofer. In the course of his experiments, he noticed that the Sun, Sirius, Venus and artificial light sources have their own set of lines. This meant that these lines depend solely on the light source. They are not affected earth atmosphere or properties of an optical instrument.
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 vapor various substances. So they made a revolutionary discovery that each chemical element has its own set of spectral lines. Therefore, by the radiation of any object, one can learn about its composition. Thus, spectral analysis was born.
In the course of the following decades, thanks to spectral analysis, many chemical elements were discovered. These include helium, which was first discovered in the Sun, which is how it got its name. Therefore, initially it was considered exclusively solar gas, until three decades later it was discovered on Earth.
Three types of spectrum
What explains this behavior of the spectrum? The answer lies in the quantum nature of radiation. As you know, when an atom absorbs electromagnetic energy, its outer electron goes to a higher energy level. Similarly, with radiation - to a lower one. 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 it radiates and emits gas. At the same time, solid 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, solid and liquid bodies radiate a continuous spectrum, gases emit a line spectrum. The absorption spectrum is observed when the continuous radiation is absorbed by the gas. In other words, the colored 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. Interestingly, during the full solar eclipse The spectrum of the Sun becomes linear. Indeed, in this case, it comes from transparent outer layers her .
Principles of spectroscopy
Optical spectral analysis is relatively simple in technical execution. The basis of his work is 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, laying out the light in the same way, Wollaston noticed black lines on the spectrum. Spectrographs also work on this principle.
The decomposition of light can also take place with the help of diffraction gratings. Further analysis of light can be performed by a variety of methods. Initially, an observation tube was used for this, then a camera. Today, 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 areas 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 by 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 did was to use this method to study the composition of stars and other space objects. So each star has its own spectral class, reflecting the temperature and composition of their atmosphere. Also became known the parameters of the atmosphere of the planets 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, one can learn not only about qualitative composition objects.
Measure speed
Doppler effect in astronomy Doppler effect in astronomy
The Doppler effect was theoretically developed by the Austrian physicist in 1840, after whom it was named. This effect can be observed by listening to the horn of a passing train. The height of the horn of an approaching train will be noticeably different from the horn of a departing train. Approximately in this way the Doppler effect was proved theoretically. The effect is that for 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 towards the red side. Those. all wavelengths increase. In the same way, when the source approaches, they shift to the violet side. Thus, it became an excellent addition to spectral analysis. Now it was possible to learn from the lines in the spectrum what had previously seemed impossible. Measure the speed of a space object, calculate the orbital parameters of double stars, planetary rotation speeds and much more. special role effect of "redshift" produced 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 examining the brightness of Cepheids in various nebulae, he proved that many of them are located much further than the Milky Way. Comparing the obtained distances from the spectra of galaxies, Hubble discovered his famous law. According to him, the distance to galaxies is proportional to the speed of their removal from us. Although his law is somewhat different from modern ideas, Hubble's discovery expanded the scale of the universe.
Spectral analysis and modern astronomy
Today, almost no astronomical observation takes place without spectral analysis. With its help discover new exoplanets and expand the boundaries of the universe. Spectrometers carry rovers and interplanetary probes, space telescopes and research satellites. In fact, without spectral analysis, there would be no modern astronomy. We would continue to peer into the empty faceless light of the stars, about which we would not know anything.
Kirchhoff and Bunsen were the first to attempt spectral analysis in 1859. Two created a spectroscope that looks like a pipe irregular shape. On one side there was a hole (collimator) into which the studied light rays fell. A prism was located 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.
The scientists decided to conduct an experiment. Having darkened the room and hung the window with thick curtains, they lit a candle near the collimator slot, and then took pieces different substances and introduced them into the flame of a candle, observing whether the spectrum changes. 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.
Subsequently, Kirchhoff analyzed the spectrum of the Sun, finding that certain chemical elements were present in its chromosphere. This gave rise to astrophysics.
Features of spectral analysis
A very small amount of substance is needed for spectral analysis. This method is extremely sensitive and very fast, which allows not only to use it for a variety of needs, but also makes it sometimes simply irreplaceable. It is known for sure that each periodic table emits a special spectrum, only to him alone, therefore, with a correctly conducted spectral analysis, it is almost impossible to make a mistake.
Types of spectral analysis
Spectral analysis is atomic and molecular. By means of atomic analysis, one can reveal, respectively, the atomic composition of a substance, and by means of molecular analysis, the molecular composition.
There are two ways to measure the spectrum: emission and absorption. Emission spectrum analysis is carried out by examining which spectrum is emitted by selected atoms or molecules. To do this, they need to be given energy, that is, to excite them. Absorption analysis, in contrast, is carried out on the absorption spectrum of an electromagnetic study directed at objects.
Spectral analysis can be used to measure many 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 particular task, you need to choose the right equipment, the wavelength for the study of the spectrum, as well as the region of the spectrum itself.
Application of spectral analysis
Spectral analysis is a method that provides valuable and most diverse information about celestial bodies. It allows you to establish from the analysis of light the qualitative and quantitative chemical composition of the luminary, 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 put on the side face of a trihedral prism, then, refracting in the glass in different ways, the components White light the rays will give a rainbow strip on the screen, called the spectrum. In the spectrum, all colors are always arranged in a certain order.
As you know, light travels in the form of electromagnetic waves. Each color has a specific length. electromagnetic wave. The wavelength in the spectrum decreases from red to violet from about 0.7 to 0.4 microns. Beyond the violet rays of the spectrum lie ultra-violet rays, invisible to the eye, but acting on a photographic plate. Even shorter wavelengths are X-rays. The X-ray radiation of celestial bodies, important for understanding their nature, is delayed by the Earth's atmosphere.
Behind 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 are usually understood as observations in the range from infrared to ultraviolet rays.
To study the spectra, instruments called a spectroscope and a spectrograph are used. The spectrum is examined with a spectroscope and photographed with a spectrograph. A photo of a spectrum is called a spectrogram.
Exist the following types spectra:
A continuous or continuous spectrum in the form of a rainbow strip is given by solid and liquid incandescent bodies (coal, electric lamp filament) and rather dense masses of gas.
The line spectrum of radiation is produced by rarefied gases and vapors when strongly heated or under the action of an electromagnetic discharge. Each gas emits a strictly defined set of wavelengths and gives a line spectrum characteristic of a given chemical element. Strong changes in the state of a gas or the conditions of its glow, such as heating or ionization, cause certain changes in the spectrum of a given gas.
Tables have been compiled listing the 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 related to their structure and reflects certain changes that occur in them during the glow process.
A line absorption spectrum is given by gases and vapors when behind them is bright and more hot spring giving a continuous spectrum. The absorption spectrum is a continuous spectrum, intersected by dark lines, which are located in the very places where the bright lines inherent in this gas should be located.
The emission of spectra allows the analysis of the chemical composition of gases that emit light or absorb it, regardless of whether they are in the laboratory or in the heavenly 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 that arise when light passes through the stellar atmosphere. Therefore, the spectra of the Sun and stars are absorption spectra.
It must be remembered that spectral analysis makes it possible to determine the chemical composition of only self-luminous or radiation-absorbing gases. Chemical composition solid body cannot be determined by spectral analysis.
