Diazomethane, derivatizing reagent

The many derivatizing reagents commercially available include methanolic HC1 and diazomethane for methylation, and iV,(9-bis(trimethylsilyl)trifluoroacetamide (BSTFA), with or without 1% trimethylchlorosilane (TMCS), for silylation. Using BSTFA, hydroxyl moieties also can be silylated, giving the corresponding trimethylsilyl ethers. 

Derivatization is also useful to detect volatile metabolites. Liu et al. [282] described a specific, rapid, and sensitive in situ derivatization solid-phase microextraction (SPME) method for determination of volatile trichloroethylene (TCE) metabolites, trichloroacetic acid (TCA), dichloroacetic acid (DCA), and trichloroethanol (TCOH), in rat blood. The metabolites were derivatized to their ethyl esters with acidic ethanol, extracted by SPME and then analyzed by gas chromatography/negative chemical ionization mass spectrometry (GC-NCI-MS). After validation, the method was successfully applied to investigate the toxicokinetic behavior of TCE metabolites following an oral dose of TCE. Some of the common derivatization reagents include acetyl chloride and TV-methyl-iV- ft-b u (y Idi methyl si I y I) tro (1 uoroacctam i nc (MTBSTFA) for phenols and aliphatic alcohols and amines, dansyl chloride and diazomethane for phenols, dansyl chloride for amines, acidic ethanol and diazomethane for carboxylic acids, and hydrazine for aldehydes. 

In the case where liquid chromatography is not available, acidic herbicides need to be derivatized because they can dissociate in water and are not usually volatile to be analyzed by gas chromatography. The basic methods used for chlorophenoxy acid herbicides are esterification, silylation, and alkylation, as described in a recent exhaustive review.The derivatization step is performed after preconcentration and cleanup. The step consists of the formation of esters and ethers from the carboxyl and phenol groups of the acidic herbicides. A lot of reagents and chemical mechanisms can be used to perform derivatization reactions. The most employed derivatization reagents are diazomethane, methyliodide, trimethylsulfonium (or anilinium) hydroxide, bis (trimethylsilyl) trifluoroacetamide (BSTFA), pentafluorobenzyl bromide, and anhydride acetate. It should be noted that explosive and hazardous diazomethane was replaced by safer agents. Authors also underline that surface water generally contains humic substances, which can interfere with the derivatization reaction. ... 

Derivatization reagents, such as TMS and other silylation compounds (8), are used frequently to make materials volatile enough for GC-MS analysis. For example, diazomethane and other methylation reagents are often used for phenols and acids. These derivatives also make MS analysis by the direct probe technique possible in many cases. 

Examples of applications of derivatization reagents include diazomethane for acids and phenols acetic anhydride for phenols heptafluorobutyric acid for anilines and phenols. 

The mixture of methylphosphonic dichloride, appropriate alcohol and 30 ml of benzene was refluxed during a period of 6 hours. After the reaction was completed, the mixture was shaken with alkalyzed water and water layer after acidification was reextracted with chloroform. No further purification was performed. Methylphosphonic dichloride was synthesized in Military Institute of Chemistry and Radiometry, Warsaw, Poland and its purity was 98% as determined by GC/MS method. All alcohols were analytical grade products of POCH, Gliwice, Poland, used without further purification. M-series standards (n-alkyl-bis(trifluoromethyl)phosphine sulfides) were obtained from HNU-Nordion (Helsinki, Finland). Derivatization reagents were ether solution of diazomethane obtained by... 

A method involving SPE was developed for the determination of ten A-nitroso amino acids in cured meat products. These compounds were derivatized with diazomethane followed by O-acylation of hydroxyl groups with acetic anhydride-pyridine reagent. The methyl esters and their acylated derivatives were separated by GC on a DB-5 fused silica capillary column and quantified with a TEA-CLD specific for the nitric oxide derived from the thermal denitrosation of nitrosamines recovery exceeded 75% at the 10 ppb level579. 

Methylation by diazomethane is a simple method for derivatization of relatively acidic compounds [e.g., phenols (pA = 9-10) or carboxylic acids (pi = 4.4 0.2)]. The application of this reagent for methylation of aliphatic alcohols requires additional acid catalysis. Methyl iodide is the most convenient reagent for synthesis of permethylated derivatives of polyols (including carbohydrates) and phenols. Dimethyl sulfate [(01130)2802] can be used in basic aqueous media for methylation of phenols, but the yields of methyl ethers, in this case, are not enough for quantitative determinations of initial compounds by GC. 

Gas chromatographic methods are considered to be specific for determination of hippuric acid and methylhippuric acid, although they require a derivatization procedure with various reagents for example, several investigators have used diazomethane others have used trimethyl-silyl derivatives. 

Bupivacaine (49a) and its phenolic metabolites (49b-c) were detected in urine after the samples underwent hydrolysis, LLE with ether, concentration by evaporation and derivatization with diazomethane, to obtain the methyl ethers (49d). End analysis was by GC-MS in the SIM mode". Another methylation reaction with this reagent was mentioned in Section III.A.2 . On-site methylation with tetramethylammonium hydroxide was proposed for the analysis of phenolic additives in polymeric materials, by the pyrolysis-GC method" . Pressurized LLE using phenytrimethylammonium hydroxide (50) or trimethylsulfonium hydroxide (51) for simultaneous methylation was applied to the... 

Methylation with diazomethane is rarely apphed as the only derivatization step to short-chain organic acids.It is, however, used in combination with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBHA) for ketoacids (see below). Once diazomethane has been generated, it is added to the extract which can then be injected in the GC, thus making this reagent rather convenient. Heating of the sample mixture is not required since the reaction takes place at low temperatures. The major disadvantages of diazomethane are its hazardous and explosive nature, and the necessity to generate it before it can be applied. ... 

Most FRs can be analyzed with GC without derivatization. Eor some of the analytes, however, derivatization can improve its GC analysis. Eor brominated and chlorinated derivatives of bisphenol A, for example, a silylation step using A,G-bis(trimethylsilyl)trifluoroacetamide as reagent can be carried out after clean up. Phenolic compounds, such as TCBPA, TBBPA, and brominated phenols, can also be methylated with, e.g., diazomethane. ... 

Einarsson et al. [106] introduced (-t-)-l-(9-fluorenyl)-ethyl chloroformate (41) as a versatile reagent for the simple chiral derivatization of primary and secondary amino acids to give stable, highly fluorescent products, which are readily separated by reversed phase liquid chromatography, or by GC after methylation with diazomethane. The authors also illustrated a selective method using this reagent for the determination of imino acids in the presence of primary amino acids. 

Such agents function less instantaneously than diazomethane. They react faster at quite high temperatures. One way to achieve those has been to mix them with the injection solution. Upon flash vaporization in the hot injection port or the start of the column, the derivatization reaction is nearly instantaneous and complete. This procedure is known as on-column derivatization. Such a mode of introduction of this reagent also achieves the purpose of reacting with and deactivating the free -Si-OH, active site groups in the column, as described at the very end of Section 11.5. This treatment is called silanization. 

Similarly, detection of phenoxy acid herbicides by GC is complicated by the fact that these compoimds exhibit low volatilities due to the H bonding of their carboxylic acid and phenol fimctionalities. To convert phenoxy acid to esters, derivatization with diazomethane [96,103], dimethyl sulfate [23], and benzyl bromide before extraction [95] was adopted by some authors. Rodriguez et al. [94] developed a method to derivatize phenoxy acid herbicides and dicamba on an SPME fiber phenoxy acid herbicides and dicamba, using N-methyl-N-(ferf-butyldimethylsilyl)-trifluoroacetamide as reagent for silylation. 

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