Triflic acid and sodium triflate as chaotropic mobile phase additives in RP-LC

Abstract

In reversed-phase liquid chromatography (RP-LC), the retention of cationic analytes such as basic drugs is known to be enhanced by the presence of chaotropic additives in the mobile phase. In this study, the chaotropic effect of triflate anion was evaluated. Four cationic drugs were chromatographed on a C18 column, comparing retention obtained between triflate, perchlorate, and trifluoroacetate mobile phase additives in the range from 5 to 30 mM. It was found that triflate exhibited very similar chaotropic effect to perchlorate. Retention factors afforded by triflate were typically within 5% of the corresponding perchlorate values throughout the entire concentration range studied. It was also found through dynamic vapor sorption studies that sodium triflate monohydrate salt was a more stable crystalline solid than the sodium perchlorate monohydrate salt with regard to hygroscopicity, showing good stability in the range of 10-70% relative humidity compared to sodium perchlorate monohydrate which was stable only within the range of approximately 20-40% relative humidity. The better physical stability and handling properties of the sodium triflate monohydrate salt suggests it may be an attractive alternative to sodium perchlorate monohydrate salt as a chaotropic additive in RP-LC analysis of pharmaceuticals.