Page 357 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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460 Organic Chemistry, Compound Detection

Droplet countercurrent chromatography (DCCC) in which both of the frequency axes corresponds to
Separation technique based on liquid–liquid partition homonuclear shifts in a single spectrum. Also known
chromatography. as COSY.
Flash chromatography Also known as rapid column Infrared spectroscopy Technique in which many func-
chromatography. tional groups and atoms are characterized by their vi-
Fourier transform Technique in which a short power- brationsanddeformationsinthe4000–200cm −1 range.
ful radio-frequency pulse (microseconds) excites either Ion-exchange chromatography (IEC) Technique in
1
all the H nuclei or 13 C nuclei simultaneously. Each which the stationary phase consists of a rigid matrix
nucleus shows a free induction decay (FID) which is (polymer), the surface of which carries a net positive
an exponentially decaying sine wave with a frequency (cationic) or negative (anionic) charge to give an ion
−
+
equal to the difference between the applied frequency exchange site R or Y , respectively, which will attract
and the resonance frequency for that nucleus. and hold the counterions. Ion exchangers are divided
Gas–liquid chromatography (GLC) Technique in into anion and cation exchangers.
which the organic sample is carried through a column Lab on-a-chip This technique uses a planar device on
by a carrier gas (mobile phase) and the separation of which a number of chemical processes are being per-
the organic compounds occurs in the stationary phase formed in order to go from reactants to products or
(the column packing). The compounds are estimated from a sample to analysis.
by means of a detector. Liquid–solid (absorption) chromatography (LSC)
Gas–solid chromatography Technique in which the Separation of compounds (from a mixture) by a liq-
moving phase is a mixture of gases and the station- uid mobile phase and a solid stationary phase which
ary phase is a solid phase. The carrier gas such as ni- reversibly absorbs the solute molecules.
trogen or helium replaces the solvent in column chro- Mass spectrometry Technique in which a vaporized
matography. The solid may be finely powdered Celite sample of a substance is bombarded with a beam of
or kieselguhr. The technique is suitable for organic sub- electrons, and the relative abundance of the resulting
stances that are volatile without decomposition up to positively charged molecular fragments is determined.
about 300 C. Therelativeabundanceversusmass-to-chargeratiothat
◦
Gel permeation chromatography (GPC) Technique is produced from the substance by the mass spectrom-
that separates substances according to their molecu- eter is called the mass spectrum of the substance.
lar size and shape. Three classes of stationary phases Matrix-assisted laser desorption-ionization mass spec-
are used: aerogels (porous glass), xerogels (crosslinked trometry (MALDI–MS) MALDI–MS technique en-
dextran), and xerogel-aerogels (polystyrene). ables ionization a broad range of materials, with high
1
H NMR “polarimetry” Technique using chiral shift sensitivity, broad mass range of materials, fast sample
reagents in NMR spectroscopy for the determination preparation, and the absence of fragmentation.
of enantiomeric purity of natural semiochemicals. Matrix isolation (MI) Technique used with Fourier
Heteronuclear shift correlation (HETCOR) 2D-NMR transform infrared spectrometer (FT-IR) to detect spec-
technique where a two-dimensional map is generated in troscopically transient chemical species at ambient
13
which one frequency axis corresponds to C chemical temperatures.
shift or other nonproton nuclei, and the other frequency Nuclear magnetic resonance spectroscopy Measures
1
axis corresponds to the H chemical shift. the absorption of light energy in the radio-frequency
1
High-performance thin-layer chromatography portion of the electromagnetic spectrum. H NMR
(HPTLC) Technique enabling the separation of very spectroscopy furnishes indirect information about
complex mixtures of organic compounds. The plates the carbon skeleton of organic molecules. In 13 C
are prepared from optimized thin adsorbent layers. NMR peaks corresponding to all carbon atoms are
HPTLC offers greater separation efficiency through recorded.
smaller plate heights than the conventional TLC Paper chromatography (PC) Technique in which the
plates, shorter analysis time, and detection limits in fixed phase is a sheet of filter paper. The sample is
the nanogram and picogram range. placed near the edge of the paper as a small spot. The
High-pressure liquid chromatography (HPLC) Tech- edge is then dipped in the developing solvent (mobile
nique consisting of a stationary phase (a solid surface, phase). The solvent rises up the paper by capillary ac-
a liquid, an ion-exchange resin, or a porous polymer), tion taking the substance along. The positions of the
held in a glass or metal column with the liquid mobile spots are observed by visible or UV light or by spray-
phase being forced through under pressure. ing with a chromogen.
Homonuclear shift correlation (HOMCOR) 2D-NMR Raman spectroscopy (RS) Technique which involves
technique where a two-dimensional map is generated the analysis of the intensity of Raman scattering of