Page 366 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN0011A-541 July 25, 2001 17:27

Organic Chemistry, Compound Detection 469

4. Sugars and Related Compounds
The low volatility of sugars and related compounds such as
amino sugars, polyalcohols, and aldonic and uronic acids,
caused by the presence of several functional groups in one
molecule as well as their high molecular weight and ther-
mal lability are the reasons that they cannot be analyzed
by GC methods. Another complication occurs in the for-
mation of α- and β-anomers and pyranose and furanose
rings, either during the preparation of the derivative or
during the analysis itself.
The hydroxyl groups of saccharides and related sugars
are silylated relatively easily; TMS derivatives have been
widely applied to this group of substances.

5. Insecticides and Pesticides
FIGURE 7 α-Cyclodextrin.
This group of substances includes chemically very dif-
ferent compounds, such as ureas and carbamates, organic
phosphorus and sulfur compounds, chlorinated hydrocar-
surfaces attract water, and the β-CD, for example, be-
bons, and heterocyclic compounds. Depending on the type
comes distorted as a result of hydrogen bonding in the
of functional groups in the molecule, common derivatives
water molecules in the cyclodextrin cavity. Such hydrated
of these groups are applied. For the analysis of antibiotics
molecules represent a high energy state which readily ac-
TMS derivatives are generally prepared. Vitamins include
cepts a guest organic molecule in place of the water to
compounds that differ considerably in their chemistry and
form a complex. The reaction of cyclodextrins with bi- or
therefore the range of possible derivatives is fairly wide.
polyfunctional compounds yields copolymers. The abil-
ity of the cyclodextrin cavity in these polymers to form
complexes allows them to be used in chromatographic 6. Separation and Identification of Geometrical
separations such as liquid, gel inclusion, affinity, and su- and Optical Isomers
percritical fluid chromatography.
Lipids are readily separated by chromatographic tech-
niques into various components such as, for example, al-
a. Applications of cyclodextrins. cohols, sterols, fatty acids, and esters. However, these are
i. Chiral NMR shift reagents. α-CD and β-CD in not mostly single compounds but groups of compounds
D 2 O, 19 F NMR spectra of the A 3 B 3 type have been ob- differing in chain length, degree of unsaturation, position
served for C 6 H 5 C(CF 3 ) 2 OH, the induced nonequivalence of functional groups, and stereochemistry. The separation
between CF 3 groups arising from guest accommodation of some of these groups is accomplished by subjecting
in the optically active void of the host. them to chromatography on adsorbents that have been im-
ii. Resolving of enantiomers. It was observed that pregnated with compounds having the ability to complex
complex formation is slightly stereoselective, and this preferentially or interact with specific functional groups.
property is used to resolve some enantiomers. The res- Unsaturated compounds such as fatty acids (oleic,
olution of D,L-ethyl chloromandelate, sugars, penicillins, linoleic, etc.) form π complexes: AgNO 3 TLC is used ex-
estrogens, and drugs such as suprofen were resolved us- tensively to fractionate methyl esters of fatty acids accord-
ing β-CD bonded phase chromatographic columns. Cy- ingtotheirdegreeofunsaturation.Aromatichydrocarbons
clodextrins have been used as stationary phases in capil- as donors of π electrons are capable of forming donor–
lary gas chromatography (GC) to separate optical isomers. acceptor complexes with substances having electron-
iii. Analysis of elements in biological materials. Re- accepting properties, such as caffeine, tetracyanoethylene,
cently, it has been reported that gallium (Ga) can be and polynitro substances (e.g. 1,3,5-trinitrobenzene and
detected fluorometrically in biological materials, for 2,4,7-trinitrofluorenone).
example, liver, kidney, bone, and urine. Gallium forms an Chromatographic resolution of optically active isomers
inclusion complex with benzyl-2-pyridylketone 2-pyridyl requires the introduction of an asymmetric environment
hydrazone-β-CD at a pH of 5 to form an intense yellow either intramolecularly by conversion to diastereomers or
fluorescence. The detection and sensitivity limits of Ga intermolecularly by the use of chiral stationary or mobile
were as low as 0.25 and 0.17 ng/mL, respectively. phases. In GC excellent resolution of derivatized amino