Answer to Question #105133 in Chemistry for Riya

Question

Write the principle involved in chemiluminescence and spectrophotometry for air pollutant determination. Also state the pollutants which can be analysed using these methods

Answer 1

Luminescence-radiation that is an excess over the thermal radiation of the body and continues for a time significantly exceeding the period of light vibrations. The first part of the definition separates luminescence from thermal equilibrium radiation and shows that the concept of "luminescence" applies only to a set of atoms and molecules in a state close to equilibrium.

The second part of the definition was introduced to separate luminescence from various types of light scattering and reflection, parametric light conversion.

Luminescence — one of the most sensitive methods of analysis - is used to determine trace amounts of elements. In contrast to spectrophotometry, where the difference between two signals (I_0 and I) is measured, in luminescence, the signal itself is measured and the detection limit depends on the intensity of the source and the sensitivity of the detector.

Chemiluminescence — luminescence that accompanies chemical reactions. Radiation is emitted by reaction products or other components that are excited as a result of energy transfer to them from the reaction products. A special case of chemiluminescence is bioluminescence (the glow of rotting wood, some insects and marine animals). The bioluminescence efficiency of some fireflies is close to 100%. More than 160 kJ/mol of energy is required to excite chemiluminescence in the visible region of the spectrum. The brightness of chemiluminescence is proportional to the reaction rate and chemiluminescence efficiency (the number of quanta of chemiluminescence per reaction act).

The low intensity of chemiluminescence itself proved to be the main obstacle to its widespread use for analytical purposes. The measurement of chemiluminescence in the presence of certain compounds, which are called activators in the Russian literature, and abroad — chemiluminescence enhancers, is widely used. According to the mechanism of action, activators are divided into two groups — physical and chemical.

In the chemiluminescent method of analysis, there is no need to use excitation sources, so the equipment of the method is simpler than that used in luminescent analysis.

The advantage of the chemiluminescent method of analysis is the low detection limits of 10-10-10-4 g / ml with a cuvette volume of 2-5 ml, sufficient detection accuracy, expressiveness, and simplicity of the equipment. The disadvantage is the low selectivity of reactions, but varying the determination conditions and the use of masking agents often allow to eliminate this disadvantage.

Chemiluminescence is used to determine the content of hydrogen peroxide, alcohols, aniline derivatives, some toxic substances, glucose, some metals, as well as nitrogen and sulfur oxides in the air.