Ask the Editor: The Effect of Sample Diluent Ionic Strength

The following question and answer are taken from LCGC Europe's "CE Currents" column (1).

What is the effect of sample diluent ionic strength?

In capillary electrophoresis (CE) the typical length of an injection inside the capillary is a few millimeters. This is a significant length given that the total capillary length may be 30 cm and the detection window may be 0.1 mm. The peak width is directly related to the injection zone length. Ideally the injection zone length would be very small but this would result in sensitivity issues.

There are many different in-capillary concentration approaches in CE that can be used to improve method sensitivity and separation efficiency by reducing peak width after injection. These have been summarized and interested readers should read these more in-depth publications (2,3).

The most common approach to reducing the zone length of the sample injection is by using a process termed "stacking." Stacking reduces the width of the sample zone at the start of the separation when the voltage is initially applied and results in an improved sensitivity (because the sample becomes more concentrated inside the capillary) and increased peak efficiency.

(1) K. Altria, LCGC Europe, April 2008.

(2) Z.K. Shihabi, J. Chromatogr. A 902(1), 107-117 (2000).

(3) M.C. Breadmore, Electrophoresis 28(1-2), 254-281 (2007).

Questions?

LCGC technical editor Steve Brown will answer your technical questions. Each month, one question will be selected to appear in this space, so we welcome your submissions. Please send all questions to the attention of "Ask the Editor" at lcgcedit@lcgcmag.com We look forward to hearing from you.