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In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample ...
The electrode geometry is chosen so that, under the given physical parameters (pressure, ignition voltage, gas constant, see Paschen's law), flexibility regarding the plasma medium is ensured. This allows the generation of stable cold plasma even in ambient air. In the simplest application, ambient air can be directly analyzed.
In the late 1970s an APCI mass spectrometer system (the TAGA, for Trace Atmospheric Gas Analyzer), mounted in a van for mobile operation, was introduced by SCIEX, [19] [20] providing high sensitivity for monitoring polar organics in ambient air in real time. In 1981 a triple quadrupole mass spectrometer version was produced, allowing real-time ...
Atmospheric pressure photoionization (APPI) is a soft ionization method used in mass spectrometry (MS) usually coupled to liquid chromatography (LC). Molecules are ionized using a vacuum ultraviolet (VUV) light source operating at atmospheric pressure (105 Pa), either by direct absorption followed by electron ejection or through ionization of a ...
Reaction is only possible if energetically allowed, i.e. if the proton affinity of R is higher than the proton affinity of H 2 O (691 kJ/mol [3]).As most components of ambient air possess a lower proton affinity than H 2 O (e.g. N 2, O 2, Ar, CO 2, etc.) the H 3 O + ions only react with VOC trace components and the air itself acts as a buffer gas.
The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases. [2] The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. [3]
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The gas which comprises an atmosphere is usually assumed to be an ideal gas, which is to say: = Where ρ is mass density, M is average molecular weight, P is pressure, T is temperature, and R is the ideal gas constant. The gas is held in place by so-called "hydrostatic" forces. That is to say, for a particular layer of gas at some altitude: the ...