Preparation for work . The device (Fig. 16) is connected to the network 30 minutes before the start of measurements by pressing the “network” button and the “start” key. Set the required wavelength, photocell and radiation source corresponding to the selected spectral measurement range. Before each new measurement, the slit width is set to 0.15 nm in order to avoid exposure of the photocells.
Determination of optical density . The light curtain switch knob must be closed. Install the cell holder in the cell compartment with cells filled as follows: the first one is filled with solvent or control solution; the second, third, fourth – with the studied solutions. Press the “Sh(0)” key and set the “zero” handle on the photometric display to a numerical value in the range from 0.05 to 0.1. The shutter of the light flux is opened and a cuvette with a solvent or control solution is placed in its path. Press the key “K (1)”, the display should be in the range from 0.5 to 5.0. If the reading is less than 0.5, the width of the slit should be increased; if the reading is greater than 5.0, the width of the slit should be reduced. Press the “D (5)” key, while the photometric display should show the reading 0.000 ± 0.001. The test solutions are installed alternately on the path of the light flux, moving the carriage with the handle. Press the “D (5)” key when a reading appears that differs from the previous one by no more than 0.1, take the reading from the photometric display.
The luminescent method is based on the transfer of molecules or atoms of a substance into an energetic excited state and measurement of the intensity of the glow that occurs when the molecules return to a state of equilibrium. The main method of quantitative chemical luminescent analysis is fluorimetry – a method for determining the amount of a luminescent substance from the intensity of the resulting luminescence. In this case, there is a certain relationship between the intensity of luminescence and the concentration of the substance.
For quantitative analysis, there are more complex devices – fluorimeters (Figure 17).
Table 1. Maximum permissible concentrations of certain harmful substances in the air of industrial premises and atmospheric air of populated areas
|Pollutant||Maximum allowable concentration, mg / m 3||Pollutant||Maximum allowable concentration, mg / m 3|
|working area||maximum single||average daily||working area||maximum single||average daily|
|Phenol||0.01||0.01||Fluorine compounds (in terms of fluorine)||0.5||0.02||0.005|
|Formaldehyde||0.5||0.035||0.012||Dust non-toxic (limestone)||0.5||0.05|
Sanitary microbiological study of air.
Microbial air pollution has a variable and local character, that is, the air microflora depends on the place and time of sampling. In summer, air contamination is several times higher than in winter. The atmospheric air is especially saturated with microorganisms over large cities. When considering the qualitative composition of the air microflora, one should distinguish between the microflora of atmospheric air and the air of residential premises. In the atmospheric air, staphylococci and streptococci are found only in 3.7% of samples taken in crowded places. Microorganisms are dominated by species living in the soil. Three groups of microorganisms are mainly found in the atmospheric air:
• Pigment-forming cocci on sunny days make up to 70-80% of the entire flora (the pigment protects bacteria from insolation).
• Soil spore and putrefactive microorganisms. Their content increases sharply in dry and windy weather.
• Molds and yeasts. Their content increases with increasing humidity.
In contrast to indoor air, self-purification processes are constantly taking place in the atmospheric air. This process occurs due to precipitation, insolation, temperature effects and other factors. In turn, atmospheric air in itself is a factor in purifying the air in residential premises.