Derivatization in Mass Spectrometry—2. Acylation

Abstract

The present review is devoted to acylation as a widely employed derivatization procedure for protection of OH (alcohols, polyols, phenols, enols), SH (thiols) and NH (amines, amides) groups in order to increase volatility, improve chromatographic properties and, if possible, improve mass spectral properties of derivatives. Chemical aspects of derivatization and various acylating agents are characterized. Mass spectral [electron ionization (EI), chemical ionization (CI) and negative-ion (NI) CI] properties of derivatives that are helpful in identification, structure elucidation and quantitative determination of the analyzed compounds are discussed. Some recent analytical applications of the procedure in synthetic organic chemistry, clinical chemistry, environmental chemistry etc. are summarized.

Derivatization Reactions and Reagents for Gas Chromatography Analysis

“…Compounds that contain active hydrogens (e.g., -OH, -SH and -NH) can be converted into esters, thioesters and amides, respectively, through acylation (Zenkevich, 2009). Acylation is also a popular reaction for the production of volatile derivatives of highly polar and in volatile organic materials (Zaikin and Halket, 2003). Acylation also improves the stability of those compounds that are thermally labile by inserting protecting groups into the molecule.…”

“…Understanding the chemistry of the analytes, derivatizing reagents used in sample preparation, and the detailed functionality of Gas Chromatography are important to get reliable results. For GC analysis, compounds containing functional groups with active hydrogens such as -SH, -OH, -NH and -COOH are of primary concern because of the tendency of these functional groups to form intermolecular hydrogen bonds (Zaikin and Halket, 2003). These intermolecular hydrogen bonds affect the inherent volatility of compounds containing them, their tendency to interact with column packing materials and their thermal stability (Sobolevsky et al, 2003).…”

Derivatization in Mass Spectrometry– 3. Alkylation (Arylation)

“…In principle, alkylation (esterification) of acids is the same reaction as acylation of alcohols discussed in a foregoing review. 2 The only formal, although not so strong, difference may be that in acylation reactions, higher molecular weight alcohols are modified by low molecular weight acids and, in the case of alkylation, the opposite occurs.…”

“…At present, the most common and rapid procedure for the esterification of carboxylic acids is the reaction with diazomethane (CH 2 N 2 ) and homologous diazoalkanes: R -COOH + CH 2 N 2 ® R -COOCH 3 + N 2 …”

“…10,11 The reaction is usually performed under heating. 2 O, polyphosphoric acid, acidic cation-exchange resins etc. After the reaction, excess catalyst is removed (BF 3 , for example, is evaporated under nitrogen gas) and the solution is introduced into a gas chromatograph via a syringe.…”