Derivatization with boron trifluoride/methanol

Samar, A.M., Andrieu, J.L., Bacconin, A., Fugier, J.C., Herilier, H., and Faucon, G., Assay of lipids in dog myocardium using capillary gas chromatography and derivatization with boron trifluoride and methanols, J. Chromatogr., 339, 25, 1985. 

Epoxy fatty acids (as the methyl esters) give El mass spectra which are not easily interpreted in terms of the position of the oxygen atom (especially when double bonds are also present), although it is possible with some effort if suitable model compounds are available [116,473,481]. It is generally recommended that the epoxide be isomerised to a mixture of keto compounds [473], or that the ring should be opened with boron trifluoride-methanol reagent to a mixture of methoxy-hydroxy derivatives [481,833] or with lithium aluminium hydride to hydroxy derivatives followed by trimethylsilylation [940], for identification by GC-MS. MS was used to study the incorporation of into the oxirane ring of 9,10-epoxyoctadecanoic acid in wheat tissues [488]. If derivatization is undesirable, more useful spectra are obtained with chemical ionisation [474,717]. 

Synthesis of Derivatizing Reagent III. We placed 50 mL of methanol, which had been previously dried over 4-S molecular sieves, in a 100-mL round-bottom flask and added 6.0 g of 2-hydroxynicotinic acid and 3 mL of boron trifluoride etherate. The solution was heated to reflux for 24 h and the solvent was removed under reduced pressure. The residue was dissolved in 50 mL of 0.1-ff sodium hydroxide and extracted with 60 mL of chloroform. The chloroform extract was concentrated under reduced pressure and the residue crystallized from isopropyl alcohol. The yield of 3-carbomethoxy-2(lH)pyridone was 5.0 g mp 152.5-154°C NMR (CDCI3) 6 3.85 (s, 3, -CH3), 6.34 (t, 1,... 

The scope of biochemical GC would be quite limited without sample derivatization. Yet, a simple chemical conversion of the compounds of interest into suitable derivatives is frequently all that is required for successful chromatography. Benzoic acid, typical of many naturally occurring substances which, because of their polarity, are not well suited for gas-chromatographic analysis, is readily converted by treatment with methanol in the presence of an acidic catalyst (such as boron trifluoride) into the thermally stable methyl benzoate, which is more volatile than the parent acid and becomes easier to chromatograph. As another example, GC properties are favorably affected when the typical alcohol cholesterol is converted to the silyl ether by simple treatment with chlorotrimethylsilane in pyridine. 

The first article in IMS involving soils was the determination of 2,4-D residues in soils. In this method, samples were extracted, esterifled with methanol in the presence of a boron trifluoride catalyst, and then analyzed by capillary GC with an IMS as detector. The procedure depended on the use of an IMS analyzer, for which mobility selection of an ion was made using a dual-shutter design. Selective monitoring of the product ion formed with the methyl ester of 2,4-D permitted direct analysis of the derivatized extract without further preparation. Recovery was 93% of 2,4-D for 50 ppb in spiked soils. Later, supercritical fluid chromatography was substituted for the GC, ° allowing measurements without derivatization of the soil extract. The detection limit for 2,4-D was estimated as 500 ppb. 

As organic acids are polar, thermally unstable, and have low volatility, it is necessary for GC analysis to convert them into nonpolar, volatile, and thermally stable derivatives. Such derivatization is usually achieved by esterification. The most common method is trimethylsilylation with A,0-bis(trimethylsilyl)trifluoroacet-amide (BSTFA) containing 1% trimethylchlorosilane. However, methylation with diazomethane or methanolic hydrogen chloride/boron trifluoride in methanol is also possible [19,20]. The derivatization to other esters has also been reported, but is rather uncommon in routine analysis [21]. Oxoacids should be stabilized by formation of an oxime prior to the esterification described above. Otherwise, formation of multiple/nonstable derivatives would greatly impair the determination of this class of compounds. The oximes can then react with BSTFA to yield TMS-oxime TMS esters. 

Seed oils were characterized by fatty acid composition as well as bulk and compound-specific isotopic analyses. After fatty acid saponification and derivatization with methanolic sodium hydroxide and methanolic boron trifluoride, the fatty acid composition was assessed by GC-FID equipped with a 30 m Supelcowax-10 column. For the determination of bulk carbon, oxygen and hydrogen composition values in %o VPDB, and values in %o VSMOW), a continuous He-flow... 

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