Surfactant compounds are often difficult to analyze by standard chromatographic methods; they typically take a long time to elute off of LC columns and can easily contaminate equipment. HPIMS provides an attractive alternative to chomatography for the analysis of surfactants because it is fast, and does not require columns or tubing. HPIMS has been shown to separate and identify a variety of surfactants based on their gas phase ion mobilities in a matter of seconds.
Surfactant compounds tend to build up on LC columns, capillary lines, and even needles; it is difficult to keep equipment clean while analyzing surfactants. Excellims’ Directspray ion source addresses this issue by eliminating places where contamination could occur. The sample does not travel through any capillary lines or tubes to get to the analyzer; it is ionized off the tip of a laboratory syringe as a built-in syringe pump pushes the sample directly into the analyzer. Disposable syringes can be used in order to completely eliminate cross contamination, although a glass gastight syringe is often sufficient.
In most cases, the polymeric structure of surfactants results in ion mobility spectra with multiple peaks corresponding to a chain length distribution. These “fingerprint” spectra are used to identify surfactants and to get a sense of their structure. Complex samples that contain multiple surfactants are characterized by running standards of individual compounds and correlating the standard peaks with those that appear in the mixture.