Reduction of fatty acid methyl esters to fatty alcohols to improve volatility for isotopic analysis without extraneous carbon.
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.
Corso
T N
TN
Division of Nutritional Sciences, Savage Hall, Cornell University, Ithaca, New York 14853, USA.
Lewis
B A
BA
Brenna
J T
JT
D017607:Aluminum Compounds; D002244:Carbon / Q000737:chemistry; D002247:Carbon Isotopes; D005227:Fatty Acids / Q000737:chemistry*; D005233:Fatty Alcohols / Q000032:analysis / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D018020:Lithium Compounds; D010084:Oxidation-Reduction; D019163:Reducing Agents; D014835:Volatilization
D017607:Aluminum Compounds; D002247:Carbon Isotopes; D005227:Fatty Acids; D005233:Fatty Alcohols; D018020:Lithium Compounds; D019163:Reducing Agents; D002244:Carbon; C042073:lithium aluminum hydride; C005031:cetyl alcohol