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Index >> Microbes and Atmosphere >> Impingement

Microbes and Atmosphere
Part-1
Relationship between Microbes and Atmosphere
Atmosphere as a Habitat
Transport of Spores
Sampling of Air
Launching
Transport of Microorgannisms in Air
Deposition and Adhesion
Types of Deposition
Gravitational Settling
Surface Impaction
Rain and Electrostatic Deposition
Methods of Air Sampling
Impingement
Impaction
Centrifugation
Filtration and Deposition
Sampling Methods and their characteristics

Impingement

	Impingement An impinger (Fig. 10.4) operates by drawing air through an inlet that is similar in shape to the human nasal passage. The air is transmitted through a liquid medium where the air particles become associated with the fluid and are subsequently trapped. The AGI-30 impinger (All Glass Impinger) is a liquid-filled cylinder which collects particles by their impingement into a fluid. The capillary tip of the inlet tube inside the cylinder is located 30 mm from the impinger bottom, thus the nomenclature. AGI - 30 is easy to use, inexpensive, portable, reliable, easily sterilised and has high biological sampling efficiency in comparison to many other sampling devices but there may be loss in viability of the collected biological sample due to sheer force used to collect the air.
The usual volume of collection medium is 20 m1 and the typical sampling duration is approximately 20 minutes which prevents evaporation during the sampling of warm climates or freezing of the liquid medium when sampling at lower temperatures. The liquid and suspended microorganisms can be concentrated or diluted by using this method of impingement.
A simple medium is 0.85% sodium chloride which is an osmotically balanced, sampling medium used to prevent osmotic shock of recovered organisms. Another medium in use is peptone (1%) which is used as a medium for stressed organisms. Finally, enrichment medium can be used to sample selectively for certain types of organisms. A major drawback when using an impinger is that there is no particle size discrimination which prevents accurate characterisation of the sizes of the airborne particles that are collected.

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