IONOMETRIC DETERMINATION OF ZINC IN MILK

The possibility of ionometric determination of zinc in the rhodanide complex form in milk is represented. The indicator electrode was ion-selective electrode (ISE) with solution of tetradecylammonium bromide in nitrobenzene as a membrane. As a complexing agent the potassium thiocyanate with 1.0 mol/l optimal concentration in investigated solutions was selected. The calibration dependence E = f(pCZn(II)) were typical anionic functions. The steepness of the electrode function (29±2 mV/pC), close to the theoretical value for the doubly−charged ions, suggests that the electrochemically active anions are [Zn(NCS)4]2-. The interval of linearity of calibration curves is 1.0 to 5.7 pC, the detection limit is equal to 1∙10-6 mol/l. The selectivity of determination of zinc in the rhodanide complex form was investigated with “The mixed solutions” method in the presence of potassium, calcium, aluminum, iron (III), manganese (II), copper (II) chlorides potassium iodide and nitric acid solutions. The background concentration of extraneous (j) substances in investigated solutions was calculated with usage of published data and corresponds to their maximum content in milk. It was founded that the ionometric determination of zinc is possible in range from 1.0 to 5.0 pC for all investigated j-ions. The technique for different types of milk was developed including preliminary sample preparation, used in special certified laboratories and based on dry mineralization of sample and dissolving in nitric acid solution. The concentrations of zinc-ions in analyzed samples were determined with “limiting solutions” method. The correctness of obtained data was confirmed with “entered-found” scheme. The relative standard deviation was not higher then 0.08.

CONTROL OF FLUORINE IN METALLURGICAL FUEL

Metallurgical fuel, including various types of mineral fuels: coke, hard coal, brown coal, peat, combustible shales and products of their technological conversion – needs environmental control of their use safety. When burning metallurgical fuel, harmful substances fall into the environment such as chlorine, fluorine, sulfur, arsenic, which worsen the environmental situation. Technical regulations on the safety of coal products contain requirements to limit the content of harmful impurities and their maximum permissible concentrations. Due to the wide spread of fluorine in natural and technological objects and the high toxicity of its compounds, the control of fluorine content is an urgent problem in the industrial use of metallurgical fuel. Physical methods for the determination of fluorine in solid fuel based on excitation of different spectra of the studies allow to identify it without decomposition directly in the source solid material, however, they have several limitations (sensitivity, accuracy of definition, complexity of hardware design). In other methods, mainly in ionchromatography and ionometry, samples are decomposed and fluorine is transferred into the solution. High temperature processes: pyrohydrolysis and combustion melting are usually used for decomposition. The aim of this work was to create a selective method for ionometric determination of fluorine with a fluoride-selective electrode. The study objects were samples of coal: brown, gas, semicoke, coke nut. Effective decomposition of the samples by two-stage high-temperature melting with KNaCO3 is proposed. Hydrolysis coprecipitation of accompanying interfering cations with chloride iron (II) was carried out for fluorine discharge in the solution in the form of free fluoride. The procedure of decomposition and ionometric determination of fluorine is described. The estimation of trueness and reproducibility of the developed technique by the method of sample variation was carried out. Fluorine content in the studied samples did not exceed the limit- tolerance values for commercial samples of coal products, which indicates the environmental safety of the samples in their subsequent energy application. The developed method is promising for the control of fluorine impurity in metallurgical fuel and is characterized by selectivity and simple carrying out.

IONOMETRICAL DETERMINATION OF IRON (III) IN VEGETABLES AND FRUITS

The ability of iron (III) ionometric determination in a form of its thiosulfate complex was shown. Conditions of analysis were optimized. The obtained anionic electrode function E=f(pCFe(III) obeys to the Nernst equation in the range of 2.0 to 5.0 unit of MS and has a slope equals to 56±2 mV/pC. The determination selectivity in the presence of a number of cations and anions was studied by the “mixed” solutions method. The method was applied for the analysis of iron (III) content in some fruit and vegetables.