PHOTOMETRY

From Big Medical Encyclopedia

FOTOMETRYYa — the section of physical optics and the measuring equipment devoted to the theory and methods of measurement of power characteristics of optical radiation in the course of its emission, distribution in various environments and interactions with bodies. On the practician F. carry out in the ranges of ultraviolet radiation (see), visible radiation (see Light) and infrared radiation (see). The photometry is widely used in medicobiological researches (see Gemoglobinometriya, Colorimetry, the Luminescence, Nefelometriya, Spektrofotometriya, Flyuori-metr iya).

Measurements in F. make in power and photometric units. Power units characterize radiation (see) regardless of its action on any receiver of radiation. Photometric units estimate radiation on its action on any receiver, napr, an eye of the person (in this case they are called light photometric units), but to his influence on life activity of microorganisms (bactericidal photometric units), processes of photosynthesis (fotosin-tetichesky photometric units), etc.

Basic power concept F. the flow of radiation, i.e. the average power transferred by electromagnetic radiation is. For the accounting of spacing of a flow of radiation use units which are derivative of a flow of radiation — area density of a radiant flow (W/sq.m), power luminous intensity (the W / erased), power brightness (the W/sq.m • erased) ', etc. As the main units of light sizes of optical radiation serve the candela (unit of luminous intensity) and lumen (unit of a light flow).

Use devices (photometers) and different standards of luminous intensity and a light flow (photometric lamps) to measurement of photometric sizes. Measurements of absolute and relative flows of radiation by means of various receivers of radiation are the cornerstone of photometric .metod. One of the most important photometric methods in the practical relation is the spektrofotometriya, including an absorbing spektrofotometriya in the passing and reflected light, and an issue spektrofotometriya.

Often carry to photometric methods of the analysis issue flame F. and absorbing flame F., used during the carrying out an atomic spectral analysis (see. Spectral analysis). At issue flame F., gained the greatest distribution in medical practice, subject to the analysis solutions of elements or their connections, to-rye by means of the sprayer enter into a flame of gas mixture (air or oxygen with hydrogen, propane, butane or acetylene). Determination of quantitative content of an element in test is usually carried out, comparing intensity of the spectrum line received for the analyzed solution to the similar line received on a series of the standard solutions containing the defined element in the known concentration. The method is applied generally to definition alkaline and earth metals, and also lead, copper, manganese, phosphorus, etc.; test-sensitivity makes for alkali metals 0,1 — 0,01 mkg/ml, for the others — 5 — 0,1 mkg/ml.

Absorbing flame F. it is based on ability of free atoms of metal in a flame to absorb resonant light energy with lengths of waves, characteristic of each element. During the use of this method the analyzed solution is entered into a flame in the form of an aerosol that causes decrease in intensity of the light flow passing through a flame. As concentration of an element in solution in the known limits is proportional to the optical density of a flame, for determination of content of an element in test compare values of optical density for the analyzed solution to the values received for a series of standard solutions. Absorbing flame F. allows to define the maintenance of a number of the elements which are not defined at issue flame F in test. (zinc, mercury, gold, etc.).

Photometric methods of the analysis widely use in biology and medicine during the definition of concentration of enzymes (amylases, a glucocraw phosphate — dehydrogenases, etc.), vitamins, hormones, carbohydrates and many other connections in biol. fabrics and liquids.

In medical practice, biological and hygienic researches apply photometers. Depending on purpose distinguish light meters — for measurement of illumination (see Lighting), lyuminomet-ra — for measurement of a luminescence of the chemical and biological nature (e.g., luminescences at free radical oxidation of lipids, activation of phagocytes, reactions of a bioluminescence proceeding in the presence of nek-ry oxidation-reduction enzymes), the integrating photometers — for measurement of a light flow and light energy, colorimeters — for measurement

of chromaticity (see Colorimetry), etc.

Colorimeters apply to definition of concentration of the substances directly or indirectly changing coloring depending on their quantitative contents in the studied test. Colorimeters use during the definition of various substances in blood, urine (sugar, protein, bilirubin, etc.), in other biol. substrates, at pharmacological researches, etc.

The device of all photometers, though has constructive distinctions, is essentially executed according to the uniform scheme. The optical block of a photometer consists of lenses, light-scattering plates, attenuators of light, light filters, diaphragms, receivers of radiation, in to-rykh a flow of radiation will be transformed to the electric signal registered by devices like the microampermeter, the voltmeter, etc. In pulse photometers as registrars use various electrometers which are memorable oscillographs, peak voltameters.

Big systematic errors of measurements (St. 5%) therefore photometric measurements demand careful observance of conditions of measurement, disturbance to-rykh sharply are characteristic of the photometers intended for measurement of absolute values of intensity of a light flow increases an error of measurement.

The photometers intended for p z me turnips and I about tn about with an ita of l n y x in e l and a rank of intensity of a light flow (coefficient svetopropus a kaniye, reflections, etc.), have higher precision. Consistently measure intensity of a flow of radiation at installation in the photometers constructed according to the single-channel scheme control and a test piece on the way of a bunch of light rays. In two-channel photometers and z I died an eniye of wasps at shches t in l I am UTS p to an uta of m of direct comparison of intensity of the flows of radiation nro-going through control and pilot samples.

At the same time usually make equalizing of flows of radiation by means of adjustable diaphragms, photometric wedges and other devices.

In visual colorimeters equality of two fields of comparison (equalizing of light flows) is carried out visually. Among such devices equipped with light filters for allocation of certain sites of a range there are also specialized, napr, gemoglobinometra intended for definition of concentration of hemoglobin in the blood, nephelometers intended for definition of a turbidity of fluid mediums on coefficient of light scattering, etc.

Along with visual colorimeters use physical colorimeters, in to-rykh assessment of photometric size it is carried out by means of the physical receiver. The greatest distribution was gained by photocolorimeters (photoelectrocolorimeters) with the receiver of light in the form of photo cells of various design. Pulfrikh's photometer and photoelectrocolorimeters Federal Energy Regulatory Commission-60 and BIAN-120 belong to their number. Photoelectrocolorimeters are intended for definition of concentration of substances in the transparent painted solutions. In particular, BIAN-120 provides measurement of coefficient of a svetonropuskaniye from 100% to 5% and optical density from 0 to 1,3. Accuracy of measurement of coefficient of a svetonropuskaniye of ±2,5% on a scale of a svetopropuskaniye. The device is completed with a set of scales with a millimetric grid for drawing sizes of concentration on them the measured substances according to the calibration which is carried out in the course of the research and also set of 7 light filters for fixing of ranges of measurement (the maximum of their svetopropuskaniye is in ranges of lengths of waves of 420—440, 450—465, 500— 515, 520—540, 585—595, 635—645 and 715 — 725 nanometers) and a set a ditch with thickness of the studied nappe of 10 mm. As the converter of a light flow serves the vacuum photo cell, and a source of a light flow — a filament lamp of STs-76.

The colorimeter nephelometer the photo-electric Federal Energy Regulatory Commission-N-57 and the photocolorimeter Federal Energy Regulatory Commission-60 are intended for definition of concentration of the painted solutions, suspensions, emulsions, colloid solutions by comparison of the light flows passing through control and pilot test (samples). Previously make graduation on a set of standard solutions of various concentration.

Due to the development of quantitative researches by means of diagnostic strips and multilayer films for the emergency clinicodiagnostic works reflective photometers (reflectometers) gained distribution, to-rye are constructed according to the scheme of physical photometers. Microcolorimeters, tests, allowing to investigate minimum by quantity, napr, the microcolorimeter the medical photo-electric MKMF-1 providing determination of coefficients of a svetopropuskaniye (optical density) the painted solutions in tests of 0,07 — 0,5 ml and 2,0 ml on lengths of waves of the maximum svetopropuskaniye of 425, 465, 520, 540, 570 and 615 nanometers at an error no more than ± 2,5% are developed.

Big distribution was gained by automatic photometers (colorimeters), in to-rykh filling measuring ditches, control and research measurements, emptying and washing ditches, and also delivery of results of measurement are carried out automatically. Also automatic flame photometers are created, in to-rykh ranges of the defined substances automatically are registered. The greatest distribution from them was gained by flame photometers of the IAN-140 type B. The atomnoabsorbtsionny spectrophotometers surpassing flame photometry in the accuracy and width of analytical opportunities enter practice.

Bibliography: Asatiani V. S. New methods of biochemical photometry, M., 1965, bibliogr.; With and both about N and to about in R. A. Theoretical photometry, M., 1977; With M. V au stakes. Applied biophotometry, M., 1982, bibliogr.

R. R. Lidemang; V. I. Belkevich (tekhn.).

Яндекс.Метрика