Exploring the elution mechanism of selenium species on liquid chromatography.

ABSTRACT

In the present work, the chromatographic behavior of eight selenium species, namely selenites (Se(IV)), selenates (Se(VI)), seleno-DL-methionine (Se-Met), selenocystine (Se-Cyst), selenocystamine (Se-CM), selenourea (Se-U), dimethylselenide ((CH(3))(2) Se) and dimethyldiselenide ((CH(3))(2) Se(2)), was investigated under different stationary and mobile phase conditions, in an effort to unravel secondary interferences in their underlying elution mechanism. For this purpose, two end-capped and a polar-embedded reversed-phase stationary phases were employed using different mobile phase conditions. Retention factors (log k(w)) were compared with octanol-water distribution coefficients (log D) as well as with log k(w) values on two immobilized artificial membrane (IAM) columns and two immobilized artificial plasma proteins stationary phases, obtained in our previous work. The role of electrostatic interactions was confirmed by introducing the net charge of the investigated Se species as an additional term in the log k(w)/log D interrelation, which in most cases proved to be statistically significant. Principal component analysis of retention factors on all stationary phases and octanol-water log D values, however, showed that the elution of the investigated selenium species is mainly governed by partitioning mechanism under all different chromatographic conditions, while the pH of the mobile phase and the special column characteristics have only a minor effect.