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1632606 
Journal Article 
Quantitative Determination of Isostearic Acid Isomers in Skin Creams by GC-MS-SIM 
Vetter, W; Wegner, I 
2009 
Yes 
Chromatographia
ISSN: 0009-5893
EISSN: 1612-1112 
70 
1-2 
157-164 
WOS:000268055600021 
Isostearic acid is frequently listed as an ingredient of
skin creams and other cosmetics. In the four skin creams analyzed, ""isostearic acid"" was
esterified with isopropanol, as well as sorbitan or polyglycerols. ""Isopropyl isostearate"" was
isolated by HCl treatment and saponification whereas emulsifiers (sorbitan or polyglycerol
isostearates) were enriched by means of a C(18)-cartridge. Fatty acids in the resulting lipid
fraction were transferred into methyl esters. 25:0 and 19:0 methyl esters were used as internal
standards. GC-EI-MS was used to determine that ""isostearic acid"" was a mixture of many methyl-
branched isomers of stearic acid (18:0) in all four skin creams. Thus, it may be better termed
""isostearic acids"". The branched-chain nature of isostearates was verified by formation and
analysis of picolinyl esters of skin cream fatty acids by GC-EI-MS. Twenty-five 18:0 isomers were
detected and the main products had one methyl branch on carbons C(10)-C(14). Two late eluting
isostearic acid isomers were identified as 16-methyl heptadecanoic acid (i18:0) and 15-methyl
heptadecanoic acid (a18:0). GC-EI-MS in the selected ion monitoring (SIM) mode with m/z 87 as
quantification ion was used for the determination of i18:0 methyl ester. The quantities of i18:0
in the samples amounted to 10-20 mg g(-1) skin cream. The contribution of i18:0 to the sum of all
18:0 isomers in the four skin cream samples was 8.5 +/- A 1.1%. Instead of determining all
individual isostearates in a product, we suggest the quantitative determination of i18:0 followed
by multiplication with factor 11.75 (similar to reciprocal value of 8.5%, see above) as a simple
method for the quantification of isostearates in cosmetics. 
Gas chromatography-mass spectrometry; Lipid analysis; Methyl-branched fatty acids; Isostearates in cosmetics