Conductivity detection of aliphatic alcohols in micellar electrokinetic chromatography using an oscillometric detector

Abstract

Although conductivity is usually applied to detect ionic species in capillary electrophoresis (CE), nonionic species can also be detected by their indirect effects on the conductivity of the running electrolyte. This approach was used for detection of aliphatic alcohols in micellar electrokinetic chromatography (MEKC) with an oscillometric detector. Although the detector operates at 600 kHz, for the range of electrolyte concentration used in CE, the response is mainly due to variations of conductivity. A 50 mM phosphate and 50 mM SDS solution was used as running electrolyte and as the solvent for mixtures of some isomers of propanol, butanol, and pentanol. A set of negative peaks was obtained and assigned to the components by spiking the samples. The limits of detection (LOD) ranged from 2.1 mM for 2-methyl-2-propanol to 5.3 mM for 1-pentanol. Due to the high affinity for the interior of the micelles, 1-hexanol could not be easily-detected, but by the addition of 10% methanol to the running electrolyte it was possible. For this electrolyte, the LOD was improved, ranging from 0.8 mM for 2-methyl-2-propanol to 1.5 mM for 1-pentanol. Calibration plots were linear up to 40 mM at least. These results indicate that conductivity may be useful for detection of nonionic species in CE, especially when optical methods can not be conveniently applied.