Comprehensive isotachophoresis-capillary zone electrophoresis using directly inserted columns having different diameters with a periodic counterflow and dual ultraviolet detectors

Isotachophoresis (ITP) coupled to capillary zone electrophoresis (CE) in a comprehensive manner was used to separate mixture components in both insuff icient and sufficient quantities without heart-cutting or splitting. Exampl es of comprehensive ITP-CE involving multiple CE injections of preconcentra ted ITP zones are demonstrated. In the comprehensive arrangement, all of th e sample in the first dimension (ITP) is subjected to analysis in the secon d dimension (CE), without significant sample loss or decrease in sample det ectability resulting from removal of a portion of the sample. This is espec ially important for analytes at low concentrations which may form a single mixed zone instead of individual ITP zones. Direct on-line coupling of ITP to CE in this comprehensive arrangement involved the use of columns having different diameters with one directly inserted inside of the other. A compu ter-controlled counterflow was applied when the isotachophoretic sample sta ck reached the bifurcation point. Large volume (10 muL) injections were mad e using an electrically insulated commercial polymeric rotary valve injecto r for increased reproducibility compared to previous comprehensive ITP-CE s tudies, with ITP and CE retention time RSD's ranging from 2 to 5%. An ultra violet (UV) detector positioned at the bifurcation point was used to determ ine the beginning of CE injection. Application of a splitting voltage at th e bifurcation point showed no affect on analyte transfer into the CE column . In using multiple injections of the ITP band(s), CE column overloading wa s not observed. (C) 2001 John Wiley & Sons, Inc.