A certain level of NO3- in water is necessary for the growth of algae. Most aquatic organisms can survive at relatively high nitrate levels, but concentrations higher than 0.2 mg/l cause fish diseases, eutrophication and algal bloom in aquariums. Thus, it is necessary to monitor the level of nitrates in aquarium water. When choosing the method of nitrate level analysis that will be used to develop an in-site saltwater monitor system, we should take into account several key factors, such as the threshold concentration and possible inferences, including high levels of Cl- in saltwater. Other desired criteria for the method are the need to get results in real time, low cost of production, and a way to perform the measurements in-site without the need for highly skilled personnel. The voltammetry was chosen as a method that satisfies our criteria. It is known that nitrate can be reduced quantitatively on a copper electrode. However, the copper electrode becomes poisoned after only a few minutes of use. Previous studies showed that a thin layer of copper deposited on the surface of various commonly used electrodes significantly improve the perfomance of the sensing system. This paper describes the fabrication process of voltammetric sensor and shows the advantage of using a glassy carbon electrode modified with electrodeposited copper layer to measure the concentration of nitrate in sea water. We have found that the modified sensor can be effectively used to catalyze nitrate reduction with a welldefined reduction wave with E= -1.1 V. We performed the cyclic voltammetric (CV) experiments and chose an optimal supporting electrolyte and the optimal conditions for the pretreatment. It was found that the peak current of nitrate increases with the increase of Cl- concentration and is stable in the range (2–3)⋅10-1 mol/l. The pH value from 3.5 to 6.0 does not influence the reaction on an electrode. The developed sensor was used to direct determine of nitrate in artificial seawater without of any sample preparation. Potentiometry with standard proсedure of Cl- precipitation was used to validate all the results. The values obtained by both methods were in good agreement with each other.

The azo coupling reaction with 2-aminonaphthalene-4,8-disulfonic acid (I) was used to develop a new cheap and rapid method of triclosan (II) determination in hygiene products. The calibration graph was linear in the range of 2.0−100 × 10−6 mol L−1. The detection limit was 2.0 μmol L−1.

Melamine may have toxic effects on humans and animals. It is well known that melamine accumulates in the body and causes reproductive damages, forms bladder or kidney stones, which can lead to bladder cancer. Trace amounts of melamine at ppm levels may occur in certain food commodities due to its migration from melamine-containing disposable tableware plastics. It was intentionally adulterated to milk products to show a false increase in protein concentration.Considering these facts there is a need for establishing sensitive and reliable methods of melamine determination. As uncostly, rapid and selective melamine detection methods are highly required, the hyphenated sorption-spectrophotometric and visual test methods seem to be perspective candidates.In the present work the optimal conditions of sorption concentration of melamine from aqueous solutions ontо the silica gel surface were studied. The calibration graph for the sorptionspectrophotometric method is linear in 0.02 -9.8 μmol . L -1 mg L -1 melamine concentration range.Proposed method allows naked-eye monitoring of biological samples.________________________________________________________________________________