Cephalexin-based drugs, produced in Russia, Belarus, Spain, China and India are registered in Russian Federation. Also a wide choice of products, the problem of drugs adulteration is not practically solved. This problem is compounded by the fact that for a number of antibiotics, including cephalexin are not developed control methods and standards. For the determination of cephalosporins in various objects immunological and microbiological express-tests, optical and chromatographic methods are using. Different variants of voltammetry (VA) may be used as alternative ones. VA method has the analysis and equipment low cost and combines a high information capacity with the simplicity of the signal measurement, because received voltammetric characteristic is used for identifying of substance as well as determination of its concentration. Namely, the position of the analytical signal (Ep) gives a qualitative characteristic, and its height quantitative. The aim of our work was to develop a voltammetric method for determination of cephalexin and analytical procedures for its control in pharmaceuticals used in veterinary medicine. During the study of model solutions the working conditions to obtain an analytical signal of the antibiotic at mercury-film electrode are determined: the potential electrolysis minus (0,35 ±0,05) V in supporting electrolyte 0.1 mol/dm 3 sodium citrate. Antibiotic concentration was determined by addition of certified mixtures and measuring of peak height in a potential range of minus (0,60±0,05)V. At the base on the fulfilled research for the first time developed voltammetric procedure for determination of cephalexin in aqueous solutions of drugs used in veterinary medicine in contents range from 0,1 to 2,0 g/dm 3 (Sr is not more than 15%) has been developed. The method is simple to perform, inexpensive and can be used for the detection of cephalexincontaining drugs counterfeit.

The voltammetry behavior of iodine and selenium has been studied on new organo-modified electrodes. The conditions have been proposed for the measurement of the analytical signals of iodide and selenium ions on a silver electrode modified by aryl diazonium tosylates containing an amino group in the presence of a 0.1 M solution of N 2 H 4 · H 2 SO 4 (pH 2–3) without oxygen removal. A new approach and a procedure have been developed for the simultaneous determination of iodine and selenium in tap, drinking, and mineral waters using the organo-modified electrode. The analytical range is from 0.003 to 1.5 mg/L for iodide ions and from 0.003 to 2.0 mg/L for selenite ions.

The aim of this research was to develop a new method of separation of selenium forms in natural sorbents and methods of quantitative chemical analysis of the total selenium content and its organic and inorganic forms in feed and feed additives by voltammetry. Researches on the choice of natural sorbent to the separation of organic and inorganic forms of selenium in model solutions carried out. As the absorption capacity sorbents are as follows: «Enterosorbent ECT-1» > «Polyphepan» > activated carbon. On the basis of experimental data for the separation of organic and inorganic selenium forms on the «Enterosorbent ECT-1,» operating conditions selected: exposure time 60 sec, pH 7, 0.3 g sorbent mass, and a method for preparing samples for determination of total selenium content and its organic and inorganic forms by voltammetry method. To determine the total selenium content the acid mineralization was used. For the separation of organic and inorganic selenium forms in analyzing solution the batch of the sorbent was injected, and the organic selenium forms quantitatively adsorbed on the «Enterosorbent eSt -1», and the inorganic forms remained in the solution. After filtering of the mixture, a concentration of inorganic selenium forms was determined in the filtrate by the VA, and the residue was subjected to ultrasonic treatment in 1 mol/dm 3 sulfuric acid solution, and after centrifugation a concentration of organic selenium forms in the supernatant was determined. On the basis of the proposed method of sample preparation, the voltammetric method for measuring mass concentrations of selenium and its inorganic and organic forms was developed. Validation of this method carried out by the «entered-found» method and by a comparison with the method proposed by the other methods. Error of this method for selenium and its inorganic form does not exceed 25 % in the range from 0.05 to 80 mg / kg and for the organic forms of selenium 22% in the range of 0.05 to 25 mg / kg.

The purpose of work consists in development of a technique of definition of iodine in forages and fodder additives method voltammetry (VA) on organo-modified electrodes (OME). It is investigated voltammetric behaviour of iodine ions on silver electrodes modified by salts aryl diazonium tosylate with various groups of substituents: carboxy (MAgE СООН), amino (MAgE NH2) and nitro (MAgE NO2) on a silver substrate. At comparison the calibration dependences of analytical signals of the iodine-ions received on modified electrodes, it is shown, that the electrode modified by aryl diazonium tosylate with an amino group as the assistant has the maximal sensitivity. This electrode has been used in the further work possesses. The main parameters of VA was selected definitions of iodine-ions on OME are chosen: the time of electrolysis, the accumulation potentials, the nature of the supporting electrolyte, etc. The studies found that the determination of iodide ions at this electrode in the selected conditions do not interfere with the following elements: Zn, Co, Ni, Pb, Cu, Hg, Fe, As and Cd, whose presence is possible in feed and feed additives. The proposed method of voltammetric determination of iodide ions on the OME allows to reduce the number of used reagents, eliminate mercury, as well as to perform measurements in the presence of dissolved oxygen. At the stage of sample preparation of analyzed objects, for elimination of preventing influence of organic substances of a matrix and translation of all forms of iodine in the electroactive form iodineions, alkaline fusion used. On the basis of the received results the algorithm of a technique of the quantitative chemical analysis of forages and fodder additives on the maintenance{contents} of iodine by method VA which is based on translation from test in a solution of all forms of iodine as iodine-ions, with the subsequent voltammetric definition on OME is offered. Thus accumulation of iodine-ions in a mixed solution carried out during 10-20 with electrolisys potential (0,0 ± 0,05) volt respect to the background electrodes silver chloride 0.1 mol/dm3 solution N2H4H2SO4 followed by registration of cathodic peaks in the differential pulsed voltammograms taken at scanning rate potential of 20 mV / sec. The concentration of iodide ions was determined using the highest peak in the range of potentials (0,4 ± 0,05) volt by the method of additives certified mixtures. A method for producing an analytical signal of iodide ions and the algorithm method of quantitative chemical analysis can determine the mass concentration of iodine by voltammetry in feed and feed additives within the 0,002 200 mg / kg with the relative standard deviation less than 20%. The correctness inspection of methodical data is carried out using the method put found, doubling weighed portion and comparing with State standard of the Russian Federation 52689-2006.