Introduction
The chemical modification of an existing compound to produce a new compound having properties that are suitable for a specific analytical procedure. Derivatization is an integral part of chemical analysis in many areas of chemistry such as medical, forensic, food science, and environmental disciplines. Derivatization enables the analyst to analyze a wide variety of compounds by GC, GC-MS, HPLC and LC-MS that were otherwise less volatile and unstable for these techniques. In general, analytical derivatization is employed for two reasons:
1. To permit analysis of compounds with inadequate volatility or stability
2. To improve chromatographic behavior or detectability
The advantages of integrating derivatization with LC-MS analysis…show more content… Easily prepared
2. Large number of silylating reagents are available
3. Ability to silylate a variety of compounds
Disadvantages of Silylation
1. Silylation reagents are moisture sensitive
2. Must use aprotic (no proton available) organic solvents
Silylating Reagents
Hexamethyldisilzane(HMDS), Trimethylchlorosilane (TMCS), Trimethylsilylimidazole (TMSI), Bistrimethylsilylacetamide (BSA), Bistrimethylsilyltrifluoroacetamide (BSTFA), N-methyltrimethylsilyltrifluoroacetamide (MSTFA), Trimethylsilyldiethylamine (TMS-DEA), Nmethyl-N-t-butyldimethylsilyltrifluoroacetamide (MTBSTFA), and Halo-methylsilyl derivatization reagents.
Alkylation
The introduction of an alkyl moiety into a molecule via substitution of an active hydrogen. Alkylation involves the replacement of an active hydrogen by an aliphatic or aliphatic–aromatic (e.g. benzyl) group. Alkylating reagents react with compounds containing acidic hydrogens, for example, carboxylic acids and phenols, and can be used to prepare ethers from alcohols, thioethers from sulphur compounds, and N-alkylamines, amides, and sulphonamides from amines.(Kumirska et al. 2013)
General Reaction Mechanism
RCOOH + PhCH2X → RCOOCH2Ph + HX
Equation 2: General reaction for esterification process: X = halogen or alkyl group R, H = another alkyl group…show more content… Some reactions can be done in aqueous systems
5. Derivatives are generally stable
Disadvantages
1. Limited to amines and acidic hydroxyls
2. Conditions frequently severe
3. Reagents often toxic
4. Optimization for particular compounds usually necessary
Alkylating Reagents
Applications
Acylation
The introduction of an acyl moiety into a molecule via substitution of an active hydrogen. Acylating reagents target highly polar, multifunctional compounds, such as amino acids and carbohydrate.(Catalog and Reactions 1998) Acylated derivatives for -NH-, -OH and -SH groups are prepared using carboxylic acid, acid anhydride, acyl halide and activated acyl amide as derivatization reagents.(Wang et al. 2013) Acylations are normally carried out in pyridine, tetrahydrofuran or another solvent capable of accepting the acid by-product.(Catalog and Reactions 1998)
General Reaction Mechanism
Advantages and disadvantages
Advantages
1. Derivatives are hydrolytically stable
2. Perfluoro derivatives increase volatility
3. Increased sensitivity by added molecular weight
4. Increased detectability by ECD by added halogen atoms
5. Reacts with alcohols, thiols and amines
6. Can be used to activate carboxylic acids for