POLYAROGRAFIYA

From Big Medical Encyclopedia

POLYAROGRAFIYA — the method of the qualitative and quantitative physicochemical analysis, to-rogo is the cornerstone registration of the volt-ampere curves (polyarogramm) representing graphic expression of dependence of size of current (I) on tension (V) in the chain consisting of the studied solution in which electrodes are shipped working (polarized) and auxiliary (not polarized). It is possible to determine the content of various gases, organic and inorganic matters in air by P., in water of reservoirs, in biol, liquids. In particular, use a polyarografichesky method at measurement of the oxygen content in fabrics of the functioning organism, during the studying of kinetics of oxygen consumption, regulation of speed of its transfer hemoglobin (see) and myoglobin (see) and receipts in fabric, and also passings of oxygen through biol, membranes, during the studying fiziol, and molecular mechanisms of adaptation of an organism to extreme conditions, defiant hypoxia (see) and hyperoxia (see), hypo - and a hyperthermia, etc.

P. as a method was offered by the Czech scientist Ya. Geyrovsky in 1922.

Fig. 1. Polyarogramma: on ordinate axis — current, on abscissa axis — tension attached to electrodes; and — the potential of decomposition, bc — «plateau», H — height of a wave, h — height of a half wave, Vh — the potential of a half wave.

Measurement of size of the current passed through an electrolytic cell with the studied solution during the giving on it the changing tension (fig. 1) is the cornerstone of a method P. At low sizes of the given tension current is almost equal to zero. At increase in tension the so-called potential of decomposition is reached, later to-rogo current begins to increase. At achievement of a certain size of the given tension current to the bolynena increases, a nevzirayana increase in tension (on the subprogramme the so-called plateau appears). The site of a curve which is abruptly rising up on a polyarogramma is called a wave. For interpretation of results of measurements measure height of a wave (N) on a polyarogramma, calculate height of a half wave (h) and find the size of the potential corresponding to a half wave (so-called potential of a half wave of Vh). Potential of a half wave is the indicator characteristic of each substance, i.e. it is a quality indicator. Height of a wave is a quantitative index: it is possible to determine concentration of the analyzed substance by height of a wave of H. The item allows to carry out the analysis of several substances which are contained in one test of the examinee of solution.

In P. apply electrodes (see) with constantly renewed surface, usually liquid mercury and drop. However for nek-ry objects, napr, animal fabrics, it is necessary to use firm metal electrodes, most often platinum, together with I do not polarize - shchimisya comparison. The technique of definition of oxygen based also on use of firm (platinum) electrodes was widely adopted. Firm electrodes need periodic calibration by means of standard solutions. Electrodes of open type are arranged so that their working surface directly contacts to the studied environment. These electrodes have small inertance, however sometimes they undergo the uncontrollable changes caused aggressive biol, Wednesday that distorts results of measurements. Apply electrodes of the closed type to elimination of influence of the disturbing factors, the solution of so-called background electrolyte washing a working surface of an electrode is provided in a design to-rykh. This solution is separated from the analyzed environment by a kislorodopronitsayemy polymer film. Nevertheless electrodes of the closed type are insufficiently reliable because of bystry aging of polymer films and have noticeable inertance.

Polarograph

Fig. 2. Scheme of the polarograph: 1 — the measuring instrument of current, 2 — the measuring instrument of tension, 3 — a potentiometer, 4 — a source of constant tension, 5 — a reference electrode, 6 — the studied solution or the biological environment, 7 — the polarized electrode, 8 — a polyarografichesky cell.

For registration polyarogramm use the devices called by polarographs and allowing to carry out graphic creation of volt-ampere curves (otherwise they are called by curves current potential). Polarographs consist of the polyarografichesky cell including the working (polarized) electrode and an auxiliary electrode — a reference electrode (not polarized electrode), besides, the power supply and the metering device are a part of the polarograph. The scheme of the elementary polarograph is submitted in fig. 2.

The most important metrological characteristics of polarographs are sensitivity and the dividing and allowing abilities. Understand the minimum concentration of the examinee of solution determined by height of a wave with the set exceeding of rather devirage quadratic deviation for an interprocedural interval or a polyarografichesky cycle as sensitivity. Under the dividing ability — extremely possible attitude of concentration of the accompanying (disturbing) component towards the minimum concentration of the analyzed component. Understand a difference of values of potentials of half waves of two substances as resolving power, at a cut these waves still can be distinguished on the subprogramme with the same height of a wave.

During the work on the elementary polarograph the polyarogramma is built on visually noted points. The polarographs released by the industry, napr, the PPT-I (PU-1) polarograph produced in the USSR in lots, are supplied with the device for automatic recording of the subprogramme. The potentiometer works from the synchronous motor, with the help to-rogo impose the changing potential on the polarized electrode and register the proceeding current.

If values of potentials of two next polyarografichesky half waves differ less than on 150 mV, then on usual postoyannotokovy polyarogramma these waves merge. In the presence of the device differentiating current, the postoyannotokovy polarograph is called the differential polarograph, resolving power at the same time reaches 50 mV.

Resolving power is equal in polarographs of alternating current to 40 mV. the dividing ability fluctuates from 100 to 1000, sensitivity reaches to 10 - 7 mol/l. The dividing ability of the oscillographic polarograph reaches several thousand, and sensitivity 5*10 - 7 mol/l.



Bibliography: Brook B. S. Polyarograficheskiye methods, M., 1972, bibliogr.; Kovalenko E. A., Berezovsky V. A. and Epstein I. M. Polarographic reduction of oxygen in an organism, M., 1975, bibliogr.; M. V fists. Technological measurements and devices for chemical productions, M., 1974.

G. V. Sumarokov; M. Ya. Kaabak (tekhn.).

Яндекс.Метрика