Coceth sulfate characterization by electrospray ionization tandem mass spectrometry.

Rationale: The anionic surfactants, among which are alkyl ether sulfates (AESs), are the most used class of surfactants in cleansing applications. The negatively charged head group of AESs is a sulfate moiety linked with a variable number of ethylene oxide units, i.e. a polyethylene glycol chain. The hydrophobic part of an AES is constituted by a linear alkyl chain of carbon atoms, generally obtained from natural fatty acids. Coconut oil fatty acids, including the sodium salts of coceth sulfate (CES) with chemical formula C H (OCH CH ) OSO Na, are widely used as feedstock for AESs synthesis. CES is added to many cleaning products and detergents defined as non-aggressive. Currently, no detailed structural information concerning the alkyl chain length x and, more importantly, the degree of ethoxylation n has been reported.

Methods: A commercial standard solution of CES was characterized by tandem mass spectrometry, employing direct injection into the electrospray ionization (ESI) source of a a linear quadrupole ion trap mass spectrometer.

Results: Two series of oligomeric species, characterized by a C12 and C14 alkyl chains, i.e. [C H (OCH CH )nOSO ] and [C H (OCH CH ) OSO ] with n ranging from 0 to 7, were successfully identified. The interpretation of these data was very useful for CES identification in three commercial dishwasher cleaning products.

Conclusions: Direct injection MS/MS analysis of CES revealed a well-defined molecular weight distribution and allowed the alkyl chain composition and the number of ethylene oxide units to be to identified.