GASOMETRY

From Big Medical Encyclopedia

GASOMETRY — qualitative and quantitative test of gas components in gas, vaporous, liquid and solid mixtures. And. it is applied to control of the course tekhnol. processes in the industry, for control for a dignity. state of environment (in particular, air of production and household rooms, tight cabins underwater and aircraft etc.), for control of structure of the exhaled and alveolar air in various conditions of life activity of a human body (see. Gas exchange ). G. is important and. various biol, environments (fabrics) of a live organism — blood, a lymph, muscular tissue.

M. V. Lomonosov and A. Lavoisier's works laid the foundation for development of methods and the equipment G. of ampere-second by a name of I. M. Sechenov the beginning of the doctrine about gas exchange is connected; in 1859 he designed the absorptiometer for the analysis of blood gases, creating over it the Torricellian emptiness. This principle is the cornerstone of the subsequent various constructive modifications of mercury pumps. E.g., the successful decision represents Van-Slayka's device, I. M. Sechenov and J. Haldane's principles — replacement of blood gases by a chemical way are united in designs to-rogo (see. Van-Slayka methods ).

The existing methods G. and. it is possible to classify by a way of determination of content of separate components in complex mixture; multi-component mixture in the course of the analysis or is divided into separate components with the subsequent determination of quantity of each of them, or such division is not made and the maintenance of a separate component is defined by measurement of any parameter of all mix. According to it distinguish chemical, physical. - chemical methods G. and.

Division of gas mixture into separate components by their consecutive absorption by a special chemical absorber is carried out in volume and manometrical gas analyzers (see).

By means of these devices measure or the volume of test of gas (when the partial pressure of formulation components is defined), or pressure (when volume concentration is defined). Determination of amount of the oxygen absorbed at breath is made or by measurement of amount of the oxygen coming to the closed system from an external source or on reduction of volume of system.

Gas analyzers of volume and manometrical type allow to determine at the choice of the corresponding chemical absorbers concentration of oxygen, carbon dioxide gas, hydrogen, ammonia and some other gases with a margin error by ±0,1 — 0,2%.

Broad application is found by gazokhromatografichesky and mass and spectrometer methods G. and. At a chromatography separate components of complex gas mixture are distributed between two phases, mobile and motionless (see the Chromatography). As mobile phase (carrier gas) most often serve inert gases, carbon dioxide gas and a pure air. Test of the analyzed mix is divided in a column into the components which are separately registered by the detector and the self-recording device. On the used motionless (stationary) phase distinguish gas adsorption and gas-liquid chromatography. Gazokhromatografichesky methods G. and. allow to define presence at mix practically of any substance in quantity 10^-12 asking and even less with relative error of ±2,5-10%.

At mass spectrometry (see) receive a range of gas mixture on mass numbers (the relation of mass of an ion of substance to its electric charge) of components. Advantage of mass and spectrometer methods G. and. high sensitivity, selectivity, speed of the analysis and a small consumption of the analyzed mix is. E.g., the mass spectrometer of MH-6202 which is specially developed for studying of physiology of breath at the same time registers change of concentration of nitrogen, oxygen and carbon dioxide gas in the course of each respiratory cycle. Limits of measurement (about. %) on nitrogen and oxygen — 0—10, 0—100 respectively, on carbon dioxide gas — 0 — 10. The combination of hromatografichesky and mass and spectrometer methods has big perspectives.

Along with methods G. and., based on pokomponentny unmixing, methods of definition of concentration of a component in gas mixture on any physical are used. or physical. - to chemical parameter of mix. E.g., heat conductivity of hydrogen exceeds heat conductivity of oxygen and nitrogen more than by 7 times. Therefore, measuring heat conductivity of mix of air with hydrogen, it is possible to judge with a big accuracy concentration of the last in air. There are many similar methods G. and.: termokonduktometrichesky, thermochemical, magnetoelectric, magnetomechanical, absorption of infrared radiation etc. (see the tab.).

The broadest application from this group of devices was found by gas analyzers of absorption of infrared radiation. With their help it is possible to control in the environment the content of carbon dioxide gas, carbon monoxide, methane and other gases with an accuracy of 2 — 5%. Molecules of these gases absorb infrared radiation only in the sites of a range inherent to them that allows to keep the selective analysis of complex gas mixtures.

Industrial gasometry — definition in air of the industrial enterprises of the gases and vapors having harmful effect on an organism. A polluter of the production air environment are tekhnol. the processes connected using or formation of harmful gases. For their definition use colorimetric, spectrophotometric, hromatografichesky, polyarografichesky, luminescent and other methods. From chemical the colorimetric methods based on highly sensitive staining reactions most were widely used (see. Colorimetry ). These methods are especially effective at division of mixes of the substances which are in microquantities. They are economic, do not demand the expensive equipment, allow to divide the gases close on the chemical properties. In view of the fact that the equipment for a chromatography has insignificant dimensions, these methods can be applied not only in stationary conditions, but also in forwarding researches.

It is possible to determine by methods of a thin-layer chromatography couples to - t (the C1 groups — C10) — from ant to pelargonic, vapors of aliphatic alcohol (the C1 groups — C10) — from methyl to decyl.

It is possible to determine by methods of gas chromatography in air vapors of such harmful substances as acetic aldehyde, acrolein, propionic, crotonic and oil aldehydes, acetone, methylethylketone, metilizopropilketon, propyl acetone, methylamylketone and other aldehydes and ketones, and also impurity of benzene, toluene, xylols and other aromatic hydrocarbons.

Use of a polyarografichesky method for definition of microconcentration of gases in air of the industrial enterprises is effective. The Polyarografichesky method allows to avoid unmixing of substances by the difficult chemical methods conducting to considerable mistakes (see. Polyarografiya ). It is possible to determine by this method impurity of hydrogen chloride, hydrogen cyanide, chlorine, ozone, benzene, toluene, a xylol, phenol, benzene chloride, paranitrotoluene, furfural, formaldehyde, acetaldehyde and other gases in the atmosphere of production rooms with an accuracy of 3 — 5%.

In air apply a luminescent method to definition of vapors of harmful inorganic matters (see. Fluorescence analysis ). For detection of vapors of polycyclic aromatic hydrocarbons in air it is possible to use spectral fluorescence analysis since many polycyclic aromatic hydrocarbons are capable to luminesce under the influence of exciting radiation. Fine structure of ranges of these gases is shown in the frozen paraffin solutions (Shpolsky's effect). At the same time instead of indistinct strips in absorption spectrums and a luminescence the large number of narrow lines — so-called quasilines is observed. The method has high sensitivity and allows to find presence of the analyzed gases at concentration 10 - 9 g/ml. For chemically unstable gases (ozone, nitric oxides, sulfur dioxide gas, etc.) the chemiluminescent method is perspective.

Methods of the express analysis are of great importance for industrial hygiene. The staining reaction proceeding in various environments — in solutions, on indicator paper or a firm sorbent is the cornerstone of each of them (usually on silica gel, impregnirovanny solution of reagent). The analytical receptions used in the express analysis of gases of air are various. In one cases apply the principle of linear colorimetry on paper or in an indicator tube, in others — colorimetry on a standard scale. Receptions when the analyzed air is passed through the absorption environment before receiving standard coloring are described. In this case apply only one standard corresponding to certain, obviously known amount of the studied substance.

Very original way of bystry definition of harmful gases in air — use of pencils indicators, to-rye is prepared by mixing of a reactant with a filler and a krepitel. The received mix is given the form of a pencil. Etc. put with a pencil on paper, a tree the line, edges changes coloring under the influence of the studied gas. Indicator pencils, as a rule, remain better, than indicator paper, because of the smaller surface of oxidation. However they cannot replace completely other methods of definition of harmful gases in air of the industrial enterprises of hl. obr. because the range of the concentration defined by express methods is limited.

For bystry definition of toxic gases in the atmosphere of industrial rooms gas analyzers and signaling devices of preferential stationary type are issued. Big distribution was gained by the devices based on photometric measurement of concentration of harmful gases of air in solution or on an indicator tape. These devices are universal and by selection of characteristic staining reactions can be used to definition of many gases. For definition of carbon monoxide it is possible to use thermochemical gas analyzers, action to-rykh it is based on the principle of measurement of heat effect of reaction of catalytic oxidation of carbon monoxide to dioxide. Devices, work apply to definition of vapors of mercury in air to-rykh it is based on absorption of the resonant line of mercury (wavelength of 253,7 nanometers). Are very perspective figurative — so-called tape automatic gas analyzers, action to-rykh it is based on the principle linearly - coloristic measurements.


TYPES of the PROCESSES which are THE CORNERSTONE of the MOST WIDESPREAD METHODS of GASOMETRY



Bibliogr. Litvinov L. D. and Rudenko B. A. Gas chromatography in biology and medicine, M., 1971, bibliogr.; E. A. rebuzzing and Ger - is not present E. V. Chemical analysis of air of the industrial enterprises, L., 1970; E. A. rebuzzing, B y x about in with to and I am M. S. and Gernet E. V. Bystrye methods of definition of harmful substances in air, M., 1970; Yavorovskaya S. F. Gas chromatography — a method of definition of harmful substances in air and biological environments, M., 1972; Air sampling instruments, Cincinnati, 1972. L. P. Iseev,

AA. H. Akanov; Yu. V. Novikov (gigabyte.).

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