Mixture‐designed electrolytes for the MEKC separation of natural and synthetic steroids

Abstract

In this work, the separation of 11 natural and synthetic steroids was studied using MEKC electrolytes modified by property-selected organic solvents: ethanol, ACN, and THF. The interplay between electrophoretic behavior and structural features was disclosed and the effects of organic modifiers to modulate retention and to alter selectivity were discussed in terms of system linear solvation energy relationships (LSER). The LSER indicated the total organic solvent percentage in the electrolyte as a major parameter to control retention and as a minor contribution, the hydrogen bond acidity. By evaluating the electropherograms obtained from mixture-designed electrolytes, a favorable separation condition for all solutes was achieved in ca. 25 min with an electrolyte composed of 20 mmol/L sodium tetraborate at pH 9.4, 20 mmol/L SDS and 20% EtOH (0.80% CV for migration time and 2.5% CV for peak area, n = five consecutive injections). The applicability of the proposed separation condition was demonstrated by the inspection of estrogens in urine sample (puberty stage).

Simultaneous determination of nine endogenous steroids in human urine by polymeric‐mixed micelle capillary electrophoresis

“…It is known that organic solvents modulate steroids separation and their addition helps to the resolution of complex mixtures since they enlarge the elution window, allowing better separation 1. We have investigated the electrolyte modification with: 5% methanol, 5% ACN, 5% THF, 5% ethanol, 2.5% THF/2.5% ACN and 2.5% THF/2.5% methanol.…”

“…Additionally, numerous synthetic steroids have been used as therapeutic agents in the hormonal replacement like in menopause and other hormonal diseases, as contraceptives, anti‐inflammatory or immunosuppressant agents 1–3.…”

“…For screening purposes, RIA and enzyme immunoassay are widely used in the analysis of steroids 13, 14. Although these immunological techniques are attractive because of simplicity, speed and high sensitivity they present many disadvantages such as high cross‐reactivity with a remarkable overestimation because antibodies are poly‐reactive and can recognize and interact with similar epitopes of what was originally intended to react, high‐grade lot‐to‐lot variation of antibodies, false positive and negative data and the additional disadvantage of the necessity to analyze hormones individually 1, 6.…”

“…Analytical methods for the analysis of certain estrogens using MEKC systems with SDS (MEKC‐SDS) or, cholic acid (CA), (MEKC‐CA) 1, 27–29 as surfactants with organic modifiers and/or cyclodextrins have been reported. Although these separations are fast and consume low sample and reagent volumes, analysis of steroids in biological fluids requires highly sensitive and selective methods because of the extremely low concentration of the analytes and presence of interferences in the samples 4.…”

“…Moreover, some steroids are difficult to resolve being necessary to change the detection system under the same operational condition 1.…”