A Speciality Column for Surfactant Analysis

Dec 02, 2005

Surfactants are widely used in industrial, agricultural, pharmaceutical and consumer products (e.g., cleaning agents, pesticides, pharmaceutical formulations, laundry detergents, cosmetics, etc.). Their separation and identification can be challenging because of the diversity of surfactants and complexity of the sample matrix. High performance liquid chromatography (HPLC) is the preferred technique because it both characterizes surfactants according to their compositions and quantifies individual surfactants in a complex mixture. Surfactant analysis can be performed by reversed-phase, normal phase, ion exchange and size exclusion chromatography, depending on the surfactants of interest,1 but existing methods often suffer from problems such as poor peak shape for cationic surfactants, complex detection schemes, or the need for multiple methods to characterize all the surfactants in a sample. This application note describes the separation of cationic, nonionic and anionic surfactants with a single method, a single column and chromatographic run, and with no derivatization, using the new Acclaim Surfactant specialty column.

Experimental

Separations were performed on a modular Summit HPLC System (Dionex, Sunnyvale, California, USA) equipped with a P680 gradient pump, ASI-100 Autosampler, TCC-100 column oven and UVD 340 detector. Chromeleon 6.5 Chromatography Management Software (Dionex, Sunnyvale, California, USA) was used for system control and data processing. A Sedex 85 evaporative light-scattering detector (Sedere, Alfortville, France) was used as the universal detector. An Acclaim Surfactant column (5 μm, 4.6 × 150 mm) was used for all separations with an acetonitrile-ammonium acetate mobile phase system. Gradient elution was generated in situ with the proportioning valve in P680 gradient pump from solvent 'A' (acetonitrile) and solvent 'B' (0.1 M ammonium acetate, pH 5.4).

Results


Figure 1: Separation of cationic, nonionic and anionic surfactants and a hydrotrope in a single run.
Figure 1 shows the analysis of a mixture of one hydrotrope (sodium xylene sulphonate), two cationic surfactants (octylphenoxyethoxyethyl dimethylbenzyl ammonium chloride and lauryl benzyldimethyl ammonium chloride), one nonionic surfactant (Triton X-100), and three anionic surfactants (sodium salts of decyl sulphate, dodecyl sulphate and LAS). All compounds were separated with excellent resolution and peak shapes on an Acclaim Surfactant column using a linear gradient. This separation demonstrates the ideal selectivity of the Acclaim Surfactant column for simultaneous separation of different surfactant classes. Under the same conditions, a conventional C18 column provided a vastly inferior separation for the same mixture, with no retention for xylene sulphonate, poor resolution between anionic and nonionic surfactants, severe peak tailing, and excessively long retention times for cationic surfactants.

Conclusion

The Acclaim Surfactant column offers unprecedented capability for analysing different types of surfactants. The column is compatible with volatile mobile phases for separating anionic, cationic and nonionic surfactants within a single chromatographic run, and detecting them by ELSD. Its excellent peak shape for cationic surfactants, superior resolution of ethoxylated surfactant oligomers and compatibility with highly aqueous mobile phases, make the Acclaim Surfactant column ideal for quality assurance of individual surfactants, and suitable for the analysis of a variety of surfactant-containing formulations. These formulations include consumer products, pharmaceuticals, plating baths for semiconductor manufacturing and environmental samples.

References

1. T.M. Schimit, Analysis of Surfactants, 2nd ed., Surfactant Science Series 96, Marcel Dekker, Inc., New York, USA (2001).