Stacking phenomena in electromigration: From basic principles to practical procedures

Abstract

The review describes principles of procedures and techniques used in capillary zone electrophoresis for enhancement of sensitivity that are based on increasing analyte mass in its zone during the electromigration process, for which the term stacking is generally used. Attention is paid to intrinsic stacking in samples with low conductivity, transient isotachophoretic stacking applied in samples with high conductivity, and sweeping in micellar electrokinetic chromatography. Principles of these stacking schemes are explained, new procedures and instrumental arrangements are discussed, and all contributions involving stacking principles that have been published since the year 2000 are surveyed.

Sensitive chiral analysis by capillary electrophoresis

“…When the voltage is applied to the end of the capillary, a potential gradient is generated along the capillary because the leading buffer contains ions with higher mobility than the analytes, and the terminating buffer contains ions of lower mobility being the analytes focused in zones. Although ITP may be performed in the same capillary where the electrophoretic separation is achieved, which is denominated transient ITP, two different capillaries may be coupled online, one for the ITP preconcentration and the other for the electrophoretic separation [91]. On-column preconcentration by sample stacking is based on the injection of a sample zone prepared in a matrix with a higher resistance, that is, with minor conductivity, than the separation buffer.…”

“…Nevertheless, when the sample is injected electrokinetically (applying a voltage for a certain time), the analytes are introduced into the capillary depending on the EOF of the sample, and of the charge and mobility of the analytes. If the preconcentration of the analytes is made during the electrokinetic injection, then the preconcentration is performed by field-amplified sample stacking (FASS), also called field-enhanced sample injection (FESI), or field-amplified sample injection (FASI) [91][92][93].…”

Electrokinetic supercharging for highly efficient peptide preconcentration in capillary zone electrophoresis

“…To accomplish both a suitable resolution and sensitivity, the analytes must experience at a given location a sudden decrease in their mobility in order to be concentrated in a zone sharper than the initial sample zone. Different mechanisms can be used to induce this concentration process [2][3][4][5][6][7].…”

Análise enantiosseletiva de fármacos: contribuições da cromatografia líquida de alta eficiência e eletroforese capilar

“…No caso específico da CE, na qual apenas pequenos volumes de amostra podem ser analisados, o que resulta em métodos com limites de detecção e quantificação superiores aos obtidos com HPLC, estão sendo desenvolvidos procedimentos específicos que permitem injetar um maior volume de amostra, sem que haja alargamento das bandas, com conseqüente perda de eficiência. Dentre esses procedimentos, o mais simples é chamado de empilhamento dos analitos ("stacking"), caracterizado pela dissolução da amostra em uma solução tampão em geral mais diluída que aquela usada na análise 108 . Outra preocupação dos usuários dessas técnicas em análises enantiosseletivas está nos procedimentos de preparação das amostras, que têm por finalidade eliminar interferentes, concentrar os analitos e torná-las compatíveis com o sistema usado.…”