CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in‐line concentration methods in capillaries and microchips, covering the period July 2016–June 2018. It includes developments in the field of stacking, covering all methods from field‐amplified sample stacking and large‐volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in‐line extraction methods that have been used for electrophoresis.

A stacking approach in capillary electrophoresis based on the reversal of the analytes' effective electrophoretic velocities at a dynamic stacking boundary formed between charged micelles (i.e., from long chain ionic surfactants) and neutral cyclodextrins (i.e., native α-, β-, or γ-cyclodextrin) is presented. The approach was demonstrated by the long injection of samples in a micellar solution followed by injection of a cyclodextrin solution zone, and then separation by co-electro-osmotic flow capillary zone electrophoresis. The reversal is caused by the formation of stable cyclodextrin-surfactant complexes at the boundary that significantly decreased the retention factor of the analytes in the presence of a micellar pseudostationary phase. The dynamic boundary was formed at the cyclodextrin zone as the micelles penetrated this zone. Under optimum conditions, the boundary disappears, and the stacking ends when all the micelles have electrophoretically migrated to the boundary. Cationic and anionic small molecules were enriched using oppositely charged micelles from sodium dodecyl sulfate and cetyltrimethylammonium bromide, respectively. There were 1-2 orders of concentration magnitude improvement in analyte detection, which is expected in stacking with hydrodynamic injection. The improvements in the peak signals (height/corrected area) were up to 236/445 and 101/76 for the cationic and anionic analytes tested, respectively. Linearity (r) and repeatability (%RSD of migration time, peak height, and corrected peak area) under the chosen stacking conditions (cations/anions) were ≥0.998/≥0.995 and ≤3.8%/≤5.7%, respectively. The stacking approach was also implemented in the direct analysis of peptides from trypsin digested bovine serum albumin.