Well-known cause of frequent failures of closed oxygen sensors is the appearance of gas bubbles in the electrolyte. The problem is traditionally associated with insufficient sealing of the sensor that is not always true. Study of a typical temperature regime of measurement system based on Clark sensor showed that spontaneous release of the gas phase is a natural effect caused by periodic warming of the sensor to a temperature of the test liquid. The warming of the sensor together with the incubation medium causes oversaturation of electrolyte by dissolved gases and the allocation of gas bubbles. The lower rate of sensor heating in comparison with the medium reduces but does not eliminate the manifestation of this effect. It is experimentally established, that with each cycle of heating of measuring system up to 37°C followed by cooling the volume of gas phase in the electrolyte (KCl; 60 g/L; 400 μL) increased by 0.6 μL approximately. Thus, during just several cycles it can dramatically degrade the characteristics of the sensor. A method was developed in which the oxygen sensor is heated in contact with the liquid, (depleted of dissolved gases), allowing complete exclusion of the above-mentioned effect.
Pineal hormone melatonin is widely used in the treatment of disorders of circadian rhythms. The presence of melatonin receptors in various animal tissues motivates the use of this hormone in some other diseases. For this reason, in recent years investigators continued the search for synthetic analogues of melatonin which are metabolically stable and selective to receptors. This review includes recent information about the most famous melatonin analogues, their structure, properties, and physiological features of the interaction with melatonin receptors.
In this work we studied the effect of intraperitoneal ad min istration of melatonin in a dose of 1 mg per kg on lip ids and microstructure of rats' skin. A single inject ion of melatonin induced a change in lipid profile most notably in phospholipids and triacylglycerol fractions which contents varied oscillatory in opposite each other with a maximu m divergence at 3 hours. By 24 hours there was a significant increase in triglycerides, and after 48 hours the lipid profile approached the init ial values. After regular daily ad ministration of melatonin for 6 days, the contents of almost all lipid fractions were significantly reduced (most in triacylg lycerols and phospholipids) with growing level of free fatty acids. By 21st day the contents of lip ids in the skin increased again, but did not reach the initial values. Reduction of lip id level was accompanied by pro minent degenerative changes in the microstructure of the skin by the 6th day of experiment. In general, the administration of melatonin in any way caused the changes in skin's lipid profile but after a single introduction parameters of lip id spectrum in two days were restored to their in itial values, and a regular ad min istration for 6 days led to sustained changes in lip id profile and structure of the skin.
False oxygen consumption effect characterized by a decrease of the polarographic sensor readings by the introduction of neutral microadditives into the incubation medium was modeled and tested. These neutral microadditives neither consume oxygen nor cause its consumption by other components of the medium. It is shown that microadditives less than 3% of the volume of incubation medium can cause statistically significant effect of false oxygen consumption more than 4% of the initial oxygen content. The effect can reach more than 15% at higher volumes of additives. The most important properties of additives enhancing the effect are low oxygen content, low temperature, and low concentration of oxygen salting out components.
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