GC—MS analysis of carboxylic acids in petroleum after esterification with fluoroalcohols

Abstract

SummaryThe GC-MS characteristics of carboxylic acid esters prepared from fluorine-containing alcohols were compared to those of methyl esters. The GC retention of 2,2,2-trifluoroethyl (TFE) esters was less than, and 2,2,3,3,4,4,4-heptafluoro-l-butyl (HFB) esters was approximately equivalent to that of methyl esters. Mass spectra of TFE and HFB aliphatic esters show significantly more intense molecular and key fragment ions than those of methyl esters. Also, owing to their significantly higher molecular weights, TFE or HFB ester molecular ions and most fragment ions of interest occur at significantly higher m/z values than most potential interfering ions.Data for about 70 individual TFE and HFB esters are reported. Application of the methodology to a petroleum-derived carboxylic acid concentrate resulted in identification of straight chain, isoprenoid, methyl-substituted straight chain (2-, 3-, 5-,lo-, 12-positions along chain), and dimethyl-substituted straight chain acids containing from 11 to 22 carbons. Benzoic acid and homologs with up to 3-carbons in alkyl substitutents were minor components in the sample.The procedure provided for forming TFE and HFB esters from free acids requires less time and effort than a previously reported method, while retaining its capability for achieving essentially quantitative conversion. Free hydroxyl groups in alcohols and phenols are converted to trifluoroacetate esters concurrently with formation of TFHHFB carboxylic acid esters. The reaction products, including compounds with two functional groups (diacids, salicylic acid, etc.), chromatograph well on conventional nonpolar GC stationary phases.

A derivatisation and liquid chromatography/electrospray ionisation multistage mass spectrometry method for the characterisation of naphthenic acids

“…Until recently NAs were routinely analysed by gas chromatography/mass spectrometry (GC/MS) following derivatisation to methyl esters commonly formed by reacting NAs with BF 3 in methanol or with diazomethane 15–19. However, BF 3 in methanol is known to be inefficient in derivatising certain aromatic acids20 and hindered alicyclic acids.…”

“…A wide variety of mass spectrometric techniques have also been applied to NAs, with those yielding little or no fragmentation preferred for their identification of molecular ions. Such methods have included electron impact,16, 17, 20, 24 chemical ionisation,13, 15 fast atom bombardment14 and electrospray ionisation12, 25, 26 (ESI). Rudzinski et al 27.…”

Perfluoroalkyl ketones: novel derivatization products for the sensitive determination of fatty acids by gas chromatography/mass spectrometry in electron impact and negative chemical ionization modes

“…Interesting results were obtained after esterification with fluoroalcohols 4. Mass spectra of fluoroesters show significantly more intense molecular ions and key fragment ions than those of methyl esters.…”

“…Mass spectra of fluoroesters show significantly more intense molecular ions and key fragment ions than those of methyl esters. Moreover, owing to their significantly higher molecular weight, fluoroester molecular ions and fragment ions of interest occur at higher m/z values than most potential interfering ions 4…”

Perfluoroalkyl ketones: novel derivatization products for the sensitive determination of fatty acids by gas chromatography/mass spectrometry in electron impact and negative chemical ionization modes

“…3 Interesting results were obtained after esterification with fluoroalcohols. 4 Mass spectra of fluoroesters show significantly more intense molecular ions and key fragment ions than those of methyl esters. Moreover, owing to their significantly higher molecular weight, fluoroester molecular ions and fragment ions of interest occur at higher m/z values than most potential interfering ions.…”