Reduction of fatty acid methyl esters to fatty alcohols to improve volatility for isotopic analysis without extraneous carbon.

Abstract

Carbon in derivatization groups cannot be distinguished from analyte carbon by chromatography-based high-precision compound-specific or position-specific isotope analysis. We report the reduction of fatty acid methyl esters to fatty alcohols to facilitate high-quality chromatographic separation, without addition of extraneous carbon, with subsequent high-precision position-specific isotope analysis. Methyl palmitate is quantitatively reduced to 1-hexadecanol by LiAlH4 in a one-step reaction. Gas-phase pyrolysis of 1-hexadecanol results in a series of monounsaturated alcohols and alpha-olefins analogous to fragmentation found for methyl palmitate, as well as an additional peak corresponding to the pyrolytic dehydration product, 1-hexadecene. Carbon isotope analysis of the fragments yielded precision of SD (delta 13C) < 0.4/1000. Results of position-specific analysis of very low enrichment [1-13C]-1-hexadecanol (delta 13C = -4.00/1000) showed no evidence of scrambling of the C1 position, and isotope ratios in accord with expectations. The pyrolysis product 1-hexadecene was isotopically enriched relative to 1-hexadecanol, which may cause minor depletion of other pyrolysis products that can be taken into account by routine calibration. The procedure is general and can be extended to compound-specific and position-specific analysis of moderate molecular weight, low-volatility analytes containing acid groups that would otherwise be blocked with methyl, ethyl, acetyl, or trimethyl silyl groups containing extraneous carbon.

• Authors: T N Corso, B A Lewis, J T Brenna
• Journal: Analytical chemistry (Anal Chem) Vol. 70 Issue 18 Pg. 3752-6 (Sep 15 1998) ISSN: 0003-2700 [Print] United States
• PMID: 9751019 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Aluminum Compounds
• Carbon Isotopes
• Fatty Acids
• Fatty Alcohols
• Lithium Compounds
• Reducing Agents
• Carbon
• lithium aluminum hydride
• cetyl alcohol

Topics

• Aluminum Compounds
• Carbon (chemistry)
• Carbon Isotopes
• Fatty Acids (chemistry)
• Fatty Alcohols (analysis, chemistry)
• Gas Chromatography-Mass Spectrometry
• Lithium Compounds
• Oxidation-Reduction
• Reducing Agents
• Volatilization