LITERATURE REVIEW 8
2 EXPERIMENTAL 17
3 RESULT AND DISCUSSION 19
3.1 Absorption spectra 19
3.2 Kinetic curves 21
3.2.1 Development of neutral red absorbance 21
3.2.2 Development of neutral red absorbance in the presence of nitrite ion 22
3.2.3 Development of neutral red absorbance in the presence of hydroxylamine 23
3.2.4 Effect of the temperature 24
3.3 Choice of an oxidizing agent 26
3.3.1 Influence of different oxidizing agents 26
3.3.2 Influence of air oxygen 29
3.4 Influence of acidity 32
3.5 Effect of neutral red on the color development 34
3.6 Calibration curves 36
3.6.1 Calibration curves for hydroxylamine 36
3.6.2 Calibration curves for nitrite ion 37
3.7 Metrological characteristics 40
3.8 Analysis of a soil sample 42
4 CONCLUSION 46
REFERENCES 47
РЕФЕРАТ
Environmental pollution is causingserious health problems for humans, and their quantification is still a big challenge. Hydroxylamine (HA) and nitrite ion act as two important environmental pollutants [1].Hydroxylamine and its derivatives lead to the formation of methemoglobin in man and animals.It induces point mutation by reaction with cytosine, but in the presence of trace metal ions and oxygen it also produces radicals which rapidly inactivate DNA [2].On the other hand hydroxylamine and its derivatives such as hydroxamic acid and oxime are widely used as anticholinesterase and antitumor agents [3].Hydroxylamine is a short-lived and reactive intermediate in the natural nitrogen cycle. It is formed during microbial nitrification, where ammonium (NH4+) is oxidized via HA to nitrite (NO2-) and nitrate (NO3-) [4].
Nitrite ion is one of the most active intermediary species in the nitrogen cycle and a useful indicator about the equilibrium state of the oxidative and reductive ways of this cycle. It is ubiquitous within environmental, food and physiological systems. Nitrite ion is able to react with secondary amines oramides to form nitrosamines which can act as carcinogenic reagents [4].Nitrite is also a versatile chemical agent that has found numerous applications ranging from dye manufacture to food preservation.
Hydroxylamine and nitrite recycle through the hydrosphere as a result of microbial processes. These compounds are important intermediates in the biological nitrogen cycle and are present in soils and surface waters [5].
Methods of separate determination of these substances are numerous. Among other techniques the kinetic method was suggested, based on oxidation of a dye, for which hydroxylamine is an inhibitor [6].
In parallel to HA determination, sometimes nitrite ion was determined simultaneously, for example, spectrophotometrically [5], though to the best of our knowledge, no kinetic method of their simultaneously determination was suggested. There is a need in developing a simple, economical, reproducible, and accurate analytical method for the individual and simultaneous determination of the above mentioned compounds, which would be applicable in
environmental researches.The present work deals with kinetic determination of hydroxylamine, both individually and simultaneously with nitrite ion, in environmental analysis.
1. The optimal conditions for determination of hydroxylamine: concentration of neutral red is 6.92* 10-5 mol L-1; iodate is 0.024 mol L-1; sulfuric acid is 0.3 mol L-1. The calibration curve is linear in the (3.03* 10-6-3.00* 10-5)mol L-1range.
2. Nitrite ion can be determined simultaneously with hydroxylamine, if the described system absorbance is measured without iodate ion addition.The calibration curve is linear in (4.3x10-6-4.64x10-5)mol L-1range.
3. The metrological characteristics of hydroxylamine and nitrite ion determination are as follows:the reproducibility of the results of nitriteion determination is expressed by the relative error 2.7 %, while the relative error of accuracy proves to be 3.4%; the reproducibility of the results of hydroxylamine determination is expressed by the relative error 5.4 %, while the relative error of accuracy proves to be 1.3%.
4. The method was applied to soil analysis for the content of hydroxylamine and nitrite ion by the standard addition method.These substances were not found in the soil, but the determination of additions was carried out without a systematic error, namely: (1.48±0.03)x10-5mol L-1for added 1.45*10-5 mol L-1 of nitrite ion and (1.55 ± 0.05)x10-5mol L-1for added 1.51*10-5 mol L-1of hydroxylamine.
