Analysis of alkyl sulfates in protein solutions by isocratic and gradient ion chromatography

An ion-chromatographic analysis for separation and quantitation of long-chain alkyl sulfates in both commercial samples of sodium dodecyl sulfate (SDS) (lauryl sodium sulfate) and protein solutions was developed. The separation was performed on a hydrophobic resin-based column utilizing tetrabutylammonium hydroxide as an ion-pair reagent and acetonitrile as an organic modifier. Sensitive and selective detection of alkyl sulfates was achieved with an anion suppressor and a conductivity detector. Gradient elution with acetonitrile was developed for the detection of a broad range of alkyl chain lengths (C-10--C-20) at high sensitivity. Because of the wide linear range of this method (0.2-700 micrograms/ml), trace levels of C-10, C-14, C-16, C-18, and C-20 alkyl sulfates can be accurately measured in the presence of high concentrations of C-12 alkyl sulfate (SDS). Thus the alkyl sulfate purity of commercial SDS solutions can be accurately and precisely determined without any sample treatment. For analysis of alkyl sulfates from protein solutions, sample treatment consisted of a one-step ion-pair extraction prior to chromatographic resolution and quantitation. Alkyl sulfates from 2-150 micrograms/ml were recovered in high yield from wide variety of protein solutions.