Gas chromartography is aplicable to volatile sample so its essential to derivatise to impart volatility to non-volatile samples

1. DERIVATIZATION IN GAS CHROMATOGRAPHY
Shinde Ganesh Shashikant
Assistant Professor
Pharmaceutical Analysis Dept.
Pravara College of Pharmacy ,Pravaranagar

4. General Reaction
 The most commonly used
derivatization procedures involve the
“substitution of active hydrogens”
on the compound to be derivatized
with a variety of functional groups.
 • These functional groups impart the
desired characteristics to the
compound, while eliminating the
adverse effects
 1. atom “A” = Oxygen, Sulfur,
Nitrogen or similar atoms
 2. atom “D” = Functional group on
the derivatization reagent
R1—AH + R2—D → R1 —AD + R2—
H

6. Derivatization Reagents
Produce more than 95% derivatives
No structural or molecular alterations
No sample loss
Non – interacting derivatives
Stable derivatives with time

8. Silylation
 •Introduction of a “silyl group” into a molecule, usually in
substitution for active hydrogen such as dimethylsilyl
[SiH(CH3)2], t-butyldimethylsilyl [Si(CH3)2C(CH3)3] and
chloro-methyl-dimethylsilyl [SiCH2Cl(CH3)2].
•Replacement of “active hydrogen” by a silyl group
reduces the polarity of the compound and reduces
hydrogen bonding.

11. Alkylation
Represents the replacement of active hydrogen by an
aliphatic or aliphatic-aromatic (e.g., benzyl) group in
process referred to as “ESTERIFICATION”.

 RCOOH + PhCH2X → RCOOCH2Ph + HX
 Where, X = Halogen group
 R’ = Alkyl substitution

12. NEED:
 Conversion “organic acids into esters”, especially methyl esters that
produce of better chromatograms than the free acids.
 To prepare ethers, thioethers and thioesters, Nalkylamines, amides
and sulphonamides.
 Alkyl esters formed offer “excellent stability” and can be isolated and
stored for extended periods if necessary.
 NOTE: Use of inorganic acids (HCl/SCl) for fats & oils

13. Alkylation Reagent

14. Alkylation Reagent

15.  Advantage
 1. Wide range of reagents avail.
 2. Reaction condition can vary
 from strongly acidic to strongly
 basic.
 3. Some reactions can be done in
 aqueous systems.
 4. Derivatives are generally
 stable.
 Disadvantage
 1. Limited to amines and acidic
 hydroxyls.
 2. Conditions frequently severe.
 3. Reagents often toxic.
 4. Optimization for particular
 compounds usually necessary