<abstract xmlns="http://www.w3.org/1999/xhtml">Prior to the start of experimental oil production in the Kashagan field (northern part of the Caspian Sea), n-alkanes and carboxylic acids contained in samples obtained from bottom sediments in the area of artificial island “D” were investigated by gas chromatography–mass spectrometry. Concentrations of 10 n-alkanes (composed of C10-C13, C15-C20) and 11 carboxylic acids (composed of C6-C12, C14-C16) were identified and measured. Concentrations of individual alkanes and carboxylic acids in bottom sediments of the various samples varied between 0.001 ÷ 0.88 μg/g and 0.001 ÷ 1.94 μg/g, respectively. Mass spectra, in particular the M+ molecular ion peak and the most intense peaks of fragment ions, are given. The present study illustrates the stability of molecular ions to electronic ionisation and the main fragment ions to the total ion current and shows that the initial fragmentation of alkanes implies radical cleavage of C2H5 rather than CH3. All aliphatic monocarboxylic acids studied were characterised by McLafferty rearrangement leading to the formation of F4 cation-radical with m/z 60 and F3 cation-radical with m/z 88 in the case of ethylhexanoic acid. The formation of oxonium ions presents another important aspect of acid fragmentation. Using mass numbers of oxonium ions and rearrangement ions allows determination of the substitution character in α- and β- C atoms. The essence of our approach is to estimate the infiltration of hydrocarbon fluids from the enclosing formation into sea water, comprising an analysis of derivatives of organic compounds in bottom sediments. Thus, concentrations of derived organic molecules can serve as a basis for estimates of the depth at which hydrocarbon fluids leak, i.e., to serve as an auxiliary technique in the search for hydrocarbon deposits and to repair well leaks.</abstract>

Prior to the start of experimental oil production in the Kashagan field (northern part of the Caspian Sea), n-alkanes and carboxylic acids contained in samples obtained from bottom sediments in the area of artificial island “D” were investigated by gas chromatography–mass spectrometry. Concentrations of 10 n-alkanes (composed of C10-C13, C15-C20) and 11 carboxylic acids (composed of C6-C12, C14-C16) were identified and measured. Concentrations of individual alkanes and carboxylic acids in bottom sediments of the various samples varied between 0.001 ÷ 0.88 μg/g and 0.001 ÷ 1.94 μg/g, respectively. Mass spectra, in particular the M+ molecular ion peak and the most intense peaks of fragment ions, are given. The present study illustrates the stability of molecular ions to electronic ionisation and the main fragment ions to the total ion current and shows that the initial fragmentation of alkanes implies radical cleavage of C2H5 rather than CH3. All aliphatic monocarboxylic acids studied were characterised by McLafferty rearrangement leading to the formation of F4 cation-radical with m/z 60 and F3 cation-radical with m/z 88 in the case of ethylhexanoic acid. The formation of oxonium ions presents another important aspect of acid fragmentation. Using mass numbers of oxonium ions and rearrangement ions allows determination of the substitution character in α- and β- C atoms. The essence of our approach is to estimate the infiltration of hydrocarbon fluids from the enclosing formation into sea water, comprising an analysis of derivatives of organic compounds in bottom sediments. Thus, concentrations of derived organic molecules can serve as a basis for estimates of the depth at which hydrocarbon fluids leak, i.e., to serve as an auxiliary technique in the search for hydrocarbon deposits and to repair well leaks.

Gas chromatographic-mass spectrometric investigation of n-alkanes and carboxylic acids in bottom sediments of the northern Caspian Sea

JSC A.B. Bekturov Institute of Chemical Sciences

L.N. Gumilyov Eurasian National University

Geologos

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Prior to the start of experimental oil production in the Kashagan field (northern part of the Caspian Sea), n-alkanes and carboxylic acids contained in samples...

Gas chromatographic-mass spectrometric investigation of n-alkanes and carboxylic acids in bottom sediments of the northern Caspian Sea

Published Online: May 17, 2018

Page range: 69 - 78

Received: Nov 07, 2016

Accepted: Feb 02, 2018

DOI: https://doi.org/10.2478/logos-2018-0005

Keywords
Gas chromatography–mass spectrometry, carbocations, oxonium ions

© 2018 Akimgali Kenzhegaliev et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Gas chromatographic-mass spectrometric investigation of n-alkanes and carboxylic acids in bottom sediments of the northern Caspian Sea

Published Online: May 17, 2018

Page range: 69 - 78

Received: Nov 07, 2016

Accepted: Feb 02, 2018

DOI: https://doi.org/10.2478/logos-2018-0005

KeywordsGas chromatography–mass spectrometry, carbocations, oxonium ions

© 2018 Akimgali Kenzhegaliev et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Gas chromatography–mass spectrometry, carbocations, oxonium ions