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absorption

absorption in chemistry in chemical engineering means the absorption of particles of gas or liquid in liquid or solid material. An other term is for a more general process is sorption, which do not distinguish between absorption and adsorption, but integrates the two.

The process of absorption can be described with the absorption coefficient, which gives the amount of gas or vapour beeing able to absorb in 1cm3 liquid or solid. Absorption coefficient is higher on low temperature and high pressure, than on high temperature and low pressure.

Environmental technologies use absorption 1. for contaminated soil gas treatment, 2. for the absorption of the gaseous phase desorbed from contaminated soil surface during the application of a thermal desoption technology, 3. for the treatment of off-gases from incineration or pirolysis of contaminated solid waste or soil.

Biology and biotechnology uses the term absorption too: menas the process of taking in. For a person or an animal, absorption is the process of a substance getting into the body through the eyes, skin, stomach, intestines, or lungs. Absorption by skin is a route by which substances/toxic chemical substances can enter the body through the skin. Toxicologists and pharmacologists investigate absorption of drugs in body. Absorption of nutrients by the small intestine is part of the human digestion process.

Absorption of electromagnetic radiation, light, sound, solar energy and ionisation radiation is possible by materials or devices, which are named absorbers.

atomic absorption spectrometry
abbreviated as AAS, the most common technique for detecting elements. It is a high through-put method: it takes not more than 5-6 min to measure the concentration of an element. Atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths. The decrease in the light intensity is in direct connection with the concentration of the atoms absorbing the light at the given wavelength. Atomization can be induced by flame (flame atomic absorption spectroscopy) or with graphite furnace (graphite furnace atomic absorption spectroscopy). The method is widely applied for determination of elements in environmental samples (soil, ground water, sludge, sediment) and in wastes. Atomic absorption spectrometry is a fairly universal analytical method for determination of metallic elements when present in both trace and major concentrations. The EPA employs this technique for determining the metal concentration (dissolved, suspended and total) in samples from a variety of matrices. About 70 elements can be measured except B, C, N, O, S, halogens, noble gases and transuranic elements with short life time. A disadvantage of the AAS technique is the non linearity of the calibration curves when absorbance becomes higher than 0.5 to 1. Detection limits (LOD) for flame AAS vary enormously: from 1 - 5 ppb (e.g. Ca, Cd, Cr, Cu) to more than 1000 ppb (e.g. P).
atomic absorption spectroscopy being founded analysis
flame atomic absorption spectrometry
a method for elemental analysis, abbreviated as FAAS. The sample is atomised in the flame, through which radiation of a chosen wavelength (using a hollow cathode lamp) is sent. The amount of absorbed radiation is a quantitative measure for the concentration of the element to be analysed. The gas mixtures used are hydrocarbons, e.g. methane, propane, propane-butane, air/acetylene and nitrous-oxide/acetylene. The latter resulting in higher atomisation efficiencies and thus better detection limits for elements like Si, Al, Sc, Ti, V and Zr. The air/acetylene flame can be used for easy atomisable elements (e.g. As and Se). The temperature of the flame is 2300 oC, high enough for atomization of the most frequently measured 30 elements. The liquid samples are introduced by nebulization, most frequently by pneumatic nebulization, PN, for the solid samples laser ablation and electrothermal vaporization. (Source: Posta József: Atomabszorpciós spektrometria. Debreceni Egyetem, 2008, Kempelen Farkas Digitális Tankönyvtár. www.tankonyvtar.hu/kemia/atomabszorpcios-080904-63). The method is useful for elemental analysis of environmental (soil, groundwater, sludge, deposit) and waste samples.
graphite furnace atomic absorption spectroscopy
a technique for elementary analysis using electrothermal atomization, abbreviated as GAAS. Samples in solution or in solid form are deposited on the surface of a graphite tube, which is then heated to high temperature to vaporize and thermally dissociate the sample. Graphite can be heated reproducibly; it will be sublimated at 3700 oC. The experimental error in measurement of solid samples can be decreased by measuring suspensions. The method is used for environmental samples (soil, ground water), solid and liquid wastes.
sound absorption