Separation of homologous series of standard sodium N-acylated sarcosinates and fatty acid mono-isopropanol-amides with C12, C14, and C16 alkyl groups were studied by high speed liquid chromatography, employing octadecylsilica (TSK-Gel; LS-410, 5μm) as a column packing.
The recommended conditions for the separation were as follows : column size, 4mm i.d.×25cm; eluent, water-methanol (15 : 85, vol/vol) adjusted to pH 2.2 with phosphoric acid; column temp., 50°C; detector, UV (210nm).
The capacity factor (k') values of homologous series of sodium N-acylated sarcosinates were drastically affected with the eluent pH; the k' values increased with lowering the eluent pH. However, fatty acid monoisopropanolamides were not affected with the eluent pH. The logarithum values of the k' were directly proportional to the alkyl chain length of the standard surfactants.
By using the same eluent conditions, other commercial N-acylated amino acid salts (anionic sur-factants) such as mono sodium N-acylated glutamates, sodium N-acylated-N-methyl taurates, and fatty acid alkanolamides (nonionic surfactants) such as fatty acid mono- and diethanolamides could be easily separated to their corresponding homologous series. Typical separation of coconut and hydrogenated tallow fatty acid derivatives were described in this paper.
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