Nomenclature and
structure
Monoacylglycerols (MG) are widely used as emulsifiers mainly
in food and cosmetic industries. The presence of a fatty acid at one specific
position may also be used to detect a triglyceride and determine its amount.
Thus, the determination of 2-monopalmitin by HPLC in infant formula after
enzymatic lipase hydrolysis is used to appreciate the amount of triglycerides of
human milk origin or of triglycerides of similar structure (palmitic acid
in the sn-2 position is poorly hydrolyzed by pancreatic lipase in the
intestine and thus is well absorbed) (Lopez-Lopez A et al., J Chromatogr B
2001, 760, 97) . The estimation of the total quantity of MG in lipid
extracts can be made by the glycerol or fatty acid
quantification. The fatty acid analysis gives also information on the individual molecular
species present in the sample. If a previous separation by TLC
is made, the estimation of the relative amount of 1- and 2-MG can be made.
Other analytical methods based on HPLC have been reported for separation and
quantitative determination of mixtures of MG but a TLC followed by the analysis of fatty
acids after transmethylation appears the most simple and suitable procedure in routine
work.
A simple method based on solid phase extraction and gas chromatography has been
developed for the determination of MG at low levels in dairy products (Fagan
P et al., J Chromatogr A 2004, 1054, 251). The proposed method enabled
measurement of individual MG, including isomeric forms.
Gas chromatographic retention indices of TMS derivatives of 19 species of
saturated and 4 species of unsaturated monoglycerides on a non-polar stationary
phase has been reported (Isidorov VA et
al., J Chromatogr A 2007, 1166, 207).
An HPLC-based method for direct separation of the regioisomers and enantiomers
of MG has been reported (Deng L et
al., J Chromatogr A 2007, 1165, 93).
The method used a tandem column system (filled with silica gel) and an
evaporative light scattering detection system. The direct separation of isomers
by enantioselective HPLC was also reported (Deng
L et al., J Chromatogr A 2008, 1198-1199, 67).
