Tn. Corso et al., REDUCTION OF FATTY-ACID METHYL-ESTERS TO FATTY ALCOHOLS TO IMPROVE VOLATILITY FOR ISOTOPIC ANALYSIS WITHOUT EXTRANEOUS CARBON, Analytical chemistry (Washington), 70(18), 1998, pp. 3752-3756
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.