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Modern particulate samplers use a volumetric flow control system that pulls air through the particle separator at the velocity required to achieve the desired cutpoint. For air pollution applications, the definition of "particulate" does not include uncombined water , and water from a particulate sample must be removed before it is weighed.
An impactor is a device that classifies particles present in a sample of air or gas into known size ranges. It does this by drawing the air sample through a cascade of progressively finer nozzles. The air jets from these nozzles impact on plane sampling surfaces and each stage collects finer particles than its predecessor.
An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen: . 2 H 2 O 2 → 2 H 2 O + O 2. This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available.
Andersen's schematic for the six-stage Andersen sampler, detailing movement of air and hole sizes for the top two stages [1]. An Andersen sampler, Andersen impactor, or sieve impactor [2] is a cascade impactor used to determine the amount of viable pathogens in a given area, in particular bacteria and fungi.
Physical methods measure an air sample without changing it, for example, by seeing how much of a certain wavelength of light it absorbs. Chemical methods change the sample in some way, through a chemical reaction, and measure that. Most automated air-quality sensors are examples of active measurement. [5]
Techniques for ionization have been key to determining what types of samples can be analyzed by mass spectrometry. Electron ionization and chemical ionization are used for gases and vapors. In chemical ionization sources, the analyte is ionized by chemical ion-molecule reactions during collisions in the source.
Physicists have found that observation of quantum phenomena by a detector or an instrument can change the measured results of this experiment. Despite the "observer effect" in the double-slit experiment being caused by the presence of an electronic detector, the experiment's results have been interpreted by some to suggest that a conscious mind ...
An autosampler for liquid or gaseous samples based on a microsyringe. Autosamplers for liquids work along many kinds of machines that perform different kinds of chemical measurements, like titrators, gas chromatographers, liquid chromatographers, water analyzers (like total carbon analyzers, dissolved inorganic carbon analyzers, nutrient analyzers) and many others.