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 c arbon by chromatography-based high-precision compound-specific or posi tion-specific isotope analysis. We report the reduction of fatty acid methyl esters to fatty alcohols to facilitate high-quality chromatogra phic separation, without addition of extraneous carbon, with subsequen t high-precision position-specific isotope analysis. Methyl palmitate is quantitatively reduced to 1-hexadecanol by LiAlH4 in a one-step rea ction. Gas-phase pyrolysis of 1-hexadecanol results in a series of mon ounsaturated alcohols and alpha-olefins analogous to fragmentation fou nd for methyl palmitate, as well. as an additional peak corresponding to the pyrolytic dehydration product, 1-hexadecene, Carbon isotope ana lysis of the fragments yielded precision of SD(delta(13)C) < 0.4%. Res ults of position-specific analysis of very low enrichment [1-C-13]-1- hexadecanol (delta(13)C = -4.00%) showed no evidence of scrambling of the C-1 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 produ cts that can be taken into account by routine calibration. The procedu re is general and can be extended to compound-specific and position-sp ecific analysis of moderate molecular weight, low-volatility analytes containing acid groups that would otherwise be blocked with methyl, et hyl, acetyl, or trimethyl silyl groups containing extraneous carbon.