6
For more information, or to download product instructions,
Derivatization
The chemical literature contains an abundance of data on
derivatization, most of which is relevant to particular
compounds, classes of compounds and derivatization
reagents. Two books are recognized as standards in the
field of analytical derivatization. The first book,
Handbook
of Analytical Derivatization Reactions
by Daniel R. Knapp
1
,
provides a general collection of analytical derivatization
methods for chromatography and mass spectroscopy (MS)
that involves formation of covalent derivatives prior to
analysis. The second book,
Silylation of Organic
Compounds
by Alan F. Pierce,
2
“ was a significant factor in
the transfer of silylation reactions from the relatively
esoteric field of organosilicon chemistry to the status of
perhaps the most widely practiced of derivatization
methods.”
3
What is GC Derivatization?
Derivatization is the process of chemically modifying a
compound to produce a new compound which has
properties that are suitable for analysis using a GC.
Why Do we Derivatize?
Compounds or compound mixtures are derivatized before
analysis for the following reasons:
1. To make a compound that otherwise could not be
analyzed by a particular method suitable for analysis
4
2. To improve the analytical efficiency of the
compound
5,6
3. To improve the detectability of the compound
7
Suitability
Often compounds cannot be analyzed because they are
not in a form that is suitable for the particular analytical
technique. Examples include nonvolatile compounds for
GC analysis,
8,9,10
insoluble compounds for HPLC analysis
and materials that are not stable using the conditions of
the technique.
11
The derivatization procedure modifies the
chemical structure of the compounds, allowing analysis by
a desired technique.
12
Efficiency
Direct analysis can be difficult when compounds interact
with each other or with the column. These interactions can
lead to poor peak resolution and/or asymmetrical peaks that
make proper peak integration difficult or impractical. This
interference can be reduced with conversion to derivatized
products.
13,14
Compounds that exhibit co-elution can often be
separated by using the appropriate derivatization methods.
Detectability
As demand increases for the analysis of increasingly
smaller amounts of materials, it becomes important to
extend the detectability range of the materials in question.
This increased sensitivity can be accomplished by improved
detector design that is directed toward specific atoms or
functional groups.
Another popular approach to increase detectability is
the use of derivatization. Enhanced detectability can be
achieved by increasing the bulk of the compound, or by
introducing atoms or functional groups that strongly interact
with the detector.
16,17
This technique is performed in gas
chromatographic applications, with the addition of halogen
atoms for electron capture detectors,
18,19
and with the
formation of TMS derivatives to produce readily identifiable
fragmentation patterns and mass ions.
20
Types of Derivatization
Compounds containing functional groups with active
hydrogens (-COOH, -OH, -NH and -SH) are usually
derivatized prior to analysis by gas chromatography.
These functional groups have a tendency to form
intermolecular hydrogen bonds that affect the volatility,
their tendency to interact deleteriously with column
packing materials and their thermal stability.
The ideal derivatization procedure will:
1. Accomplish the desired modification.
2. Proceed quantitatively, or at least reproducibly.
3. Produce products that are readily distinguishable and
separable from the starting materials.
4. Proceed rapidly with simple and straight-forward
laboratory techniques that will be both selective and
applicable to a number of similar compounds.
5. Involve reagents and reactions that present no unusual
hazards.
Main Types of Derivatization
• Silylation
• Acylation
• Alkylation
Introduction to
Gas Chromatography Reagents