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There are a bewildering array of techniques available to
separate, detect and measure chemical compounds.
in order to measure the weight or volume of a final product. This is an
older process and can be quite painstaking, but is an essential first
step when dealing with certain mixtures of substances, like extracts
from organisms. Modern separation techniques such as HPLC often seek to
separate and determine amount or identity in a single automated
analysis by integrating a detector.
is a technique used to determine amounts present in solution or a
physical characteristic of a molecule such as an equilibrium constant.
- Analysis of substances with devices using spectroscopy.
By measuring the absorption or emmision of light by a substance we can
calculate the amounts of species or characterize the chemical species,
often without separation. Newer methods include atomic absorption spectroscopy
(AAS), nuclear magnetic resonance (NMR) and neutron activation analysis
spectrometry is used to determine the molecular mass, the
elemental composition, structure and sometimes amount of chemical
species in a sample by ionizing the analyte molecules and observing
their behavior in electric and magnetic fields.
- Many techniques combine two or more analytical
called "hyphenated" or "hybrid" methods). Examples of this include ICP-MS(Inductively-Coupled Plasma
- Mass Spectrometry), where volatilisation
of a sample occurs in the first step, and measuring of the
concentration occurs in the second. The first step may also involve a
separation technique, such as chromatography,
and the second a detection / measuring device.
- Techniques that involve volatilisation aim to produce
free atoms of
the elements making up the sample, which can then be measured in
concentration by the degree to which they absorb or emit at a
characteristic spectral frequency. These methods have the disadvantage
of completely destroying the sample, and any species contained within
it. These techniques include atomic
absorption spectroscopy and ICP-MS / ICP-AES.
These techniques can still be used to study speciation, however by the
incorporation of a separation stage before volatilisation.
From Wikipedia, the free
- Another example of a hybrid technique is Gas Chromatography-Mass
Spectrometry [GC/MS], which is primarily used for
volatilizable organic compounds. The compounds are separated on a
chromatographic column, and introduced directly, or via a specialized
interface, to an ionization chamber in a mass spectrometer. The
compounds are then ionized (typically by electron impact, or chemical
ionization) and accelerated through a carefully controlled
electromagnetic field. The time of flight, or the voltage applied at
the exact moment of impact is unique for compounds of the same mass. In
this manner, the retention time and mass are meaured for each compound.