THE FUNDAMENTAL LAW OF LIGHT ABSORPTION

Physical-Chemical Methods of the Analysis. Photometry. Refractometry.

CLASSIFICATION OF PHYSICAL-CHEMICAL METHODS OF THE ANALYSIS: OPTICAL, ELECTROCHEMICAL, CHROMATOGRAPHIC, KINETIC.

PCMA are divided on:

§ Optical methods are based on measurement of optical properties of substances.

§ Chromatographic methods are based on usage of ability of different substances to selective sorption.

§ Electrochemical methods are based on measurement of electrochemical properties of substances.

§ Radiometric methods are based on measurement of radioactive properties of substances.

§ Thermal methods are based on measurement of heat effectsof substances.

§ Mass spectrometric methods are based on studying of the ionized fragments ("splinters") of substances.

§ Kinetic methods are based on measurement of dependence of speed of reaction from concentration of substance.

Advantage of PCMA

§ High sensitivity - a low limit of detection (10-9 mg) and definition;

§ High selectivity;

§ Rapid analysis methods;

§ Automation and computerization is possibility;

§ Analysis is possibility on distance;

§ Possibility of the analysis without destruction of the sample;

§ Possibility of the local analysis.

Lacks of PCMA

§ Definition error is near ± 5 % (on occasion to 20 %), whereas - 0,01-0,005 % for gravimetry and 0,1-0,05 % for titrimetry;

§ Reproducibility of results in separate methods is worse, than in classical methods of the analysis;

§ It is necessary of usage of standards and standard solutions, graduation of equipment and plotting of calibration charts;

§ Complexity of used equipment, its high cost, high cost of standard substances.

Photometry is the science of the measurement of light, in relation to its brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power.

The sensitivity of the eye is not equal to every wavelength of visible light. In modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Photopic vision is when there are light conditions, and, scotopic vision is when there are dark conditions. The eye has different reactions when it adjusts to these different conditions. Photometric measurements are based on the eye’s response. Therefore, the measurements do not specify the brightness of the source when there are dim light conditions. The luminance levels for photopic vision is based on the eye’s luminance levels over three candelas per square metre. Whereas, scotopic vision takes place below 2 × 10^-5 cd/m²

Measurement techniques for the effects of electromagnetic radiation changed based on the effects in the experiment and created different nomenclature. Thermometers are used to measure the heating effect of infrared radiation and this allowed for the development of radiometric units in relation to power and total energy. Research on the chemicals effects of ultraviolet radiation allowed for the classification by the total dose in photons per second.

Photopic (daytime-adapted, black curve) and scotopic (darkness-adapted, green curve) luminosity functions. The photopic includes the CIE 1931 standard (solid), the Judd-Vos 1978 modified data (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted). The horizontal axis is wavelength in nm.

Luminous Intensity

Luminous intensity is a measure of the amount of light that a point source radiates in a given direction. It is expressed by the luminous flux leaving the source in that direction per unit of solid angle. The SI unit of luminous intensity is the candela (cd). The human eye is only capable of viewing light in the visible spectrum and has a different sensitivity to light of different wavelengths. When there are photopic conditions, the eye is sensitive to light of wavelength 555 nm.

Luminous flux

Luminous flux is the measure of the observed power of light from the human eye. It’s changed so that is displays the various sensitivities of the human eye to different wavelengths of light. The SI unit of luminous flux is the lumen (lm). One lumen is the luminous flux of light that is made by a light source which produces one candela of luminous intensity over a solid angle.

Luminance

Luminance is a measure of the luminous intensity per unit area of light travelling in a given direction. It expresses the amount of light that passes through a specific area, and it appears within a certain solid angle. The SI unit for luminance is candela per square metre (cd/m²). A number of units have been used for luminance, apart from the candela per square metre. One candela per square metre is equal to, 10^-4 stilbs, π apostilbs, π×10^-4 lamberts, 0.292 foot-lamberts.

THE FUNDAMENTAL LAW OF LIGHT ABSORPTION