Investigation of the factors that induce analyte peak splitting in capillary electrophoresis

Sample plug induced peak splitting in capillary electrophoresis studied using dual backscattered interferometry and fluorescence detection

The appearance of unexpected peaks in capillary electrophoresis (CE) is common and can lengthen the time of method development as assay conditions and experimental parameters are varied to understand and mitigate the effects of the additional peaks. Additional peaks can arise when a single-analyte zone is split into multiple zones. Understanding the underlying mechanism of these phenomena, recognizing conditions that favor its presence, and knowing how to confirm and eliminate the effect are important for efficient method optimization. In this study, we examine how the overlap of analyte zones with the sample plug can lead to peak splitting. This is explored experimentally using dual detection CE, which enables both the sample plug and analyte zones to be independently and simultaneously measured from the same detection volume. Simulations performed via COMSOL Multiphysics confirm the origin of the splitting and help guide experiments to reduce and eliminate the effect. Our findings show that this peak splitting mechanism can arise in separations of both small and large molecules but is, especially, prevalent in separations of slowly migrating macromolecules. This effect is also more prevalent when using a short length-to-detector, as is commonly found in microfluidic applications. A simple diffusion-less model is introduced to develop strategies for reducing peak splitting that avoids modifying the apparatus, such as by lengthening the separation length, which can be difficult. Decreasing the sample plug length and slowing the electroosmotic flow can both reduce this effect, which is confirmed experimentally.

Assay of levodopa in brain by CE

This article reports a CE (capillary electrophoresis) method for the determination of Levodopa (L-DP) in rabbit brain tissue. L-DP was separated and determined on a fused quartz capillary (75 microm ID, 75 cm length, 50 cm effective length, Beckman Co.) with a mobile phase of phosphate buffer (pH = 2.5, 20 mmol/L THAM, 3% carboxymethyl-beta-cyclodextrin), sample pressure 0.6 kPa x 6 s, separation voltage 20 KV, detected at 280 nm and temperature 25 degrees C. The calibration curve was linear (r = 0.9999, n = 6) within the range of 0.5-16 microg/ml for L-DP. The recovery ratio was 87.87%. The mean relative standard deviation (RSD) was 2.73% (n = 5). This method is convenient, rapid, accurate, and brings about good recovery; it can be used for content determination of levodopa in rabbit brain tissue.

Separation of doxorubicin and doxorubicinol by cyclodextrin-modified micellar electrokinetic capillary chromatography

Doxorubicinol (DOXol) is a human metabolite of the chemotherapy agent doxorubicin (DOX), and is associated with dose-dependent cardiotoxicity and decreased drug efficacy. Due to the structural similarities and equal molecular charges of DOXol and DOX, their electrophoretic separation is commonly ineffective. A method for separating and detecting DOX and DOXol, as well as two DOXol enantiomers, was established using cyclodextrin-modified micellar electrokinetic capillary chromatography with laser-induced fluorescence detection. Differential DOXol production was detected in a DOX-sensitive and resistant pair of cell lines, with a 0.08 +/- 0.01 fmol limit of detection.