Abstract
The choice of an appropriate background electrolyte (BGE) and its components for capillary electrophoresis analysis is the main step in capillary electrophoresis method development. The use of an inadequate co-ion component could lead to asymmetrical peaks and selecting an inappropriate counter-ion could affect the buffer capacity and the pH of the BGE, leading to unreliable analysis. In this paper, we describe a systematic procedure for the development of a capillary electrophoresis method, based on the effect of varying pH on the ion effective mobility, to optimize the BGE composition. The method was applied to the separation of L-ascorbic acid in different samples. The optimized background electrolyte composition was 40 mmol L-1 tris(hydroxymethyl)aminomethane and 20 mmol L-1 2-morpholinoethanesulfonic acid, at pH 8.1. Sorbic acid was used as the internal standard and separation was carried out in a fused-silica capillary (32 cm total length and 8.5 cm effective length, 50 µm inner diameter), with a short-end-injection configuration and direct ultraviolet (UV) detection at 266 nm. The separation was performed in 26 s. The method shows good linearity (R2 > 0.999), excellent values for inter-day and intra-day precision and good recovery (in the range of 94-107%). The values obtained for limit of detection (LOD) and limit of quantification (LOQ) were 0.14 and 41 mg L-1, respectively. The systematic procedure applied shows to be a very useful tool for the first step method development for capillary electrophoresis.
Highlights
Capillary zone electrophoresis (CZE) is the simplest and most widely used form of capillary electrophoresis (CE).[1]
This movement is governed by the electrophoretic mobility of the ion, this mobility being defined as the average velocity in which an ion moves under the influence of an applied potential field.[2]
Any substance presented in solution as different species, related each other by rapid acid-base equilibrium, migrates in the electric field as a single solute, exhibiting an effective mobility calculated by the following equation: J
Summary
Capillary zone electrophoresis (CZE) is the simplest and most widely used form of capillary electrophoresis (CE).[1] In this mode, a capillary is filled with an electrolyte (run buffer), the sample is introduced in the inlet and an electrical field is applied. Separations are accomplished through the movement of ions in the electric field This movement is governed by the electrophoretic mobility of the ion (μe), this mobility being defined as the average velocity in which an ion moves under the influence of an applied potential field (normalized to the electric field strength).[2] The difficulty, lies with determining the optimal conditions of the background electrolyte (BGE), which the charge-to-size ratio of the analytes is appreciably different from one another.[3]. Once the optimal wavelength for detection has been established, a buffer that
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