Pre-concentration and separation of bacteria by volume coupling electrophoresis on supercritical water-etched fused silica capillary with two segments of different internal diameters and inner surface roughnesses.

The transient isotachophoretic stacking and sweeping was used for the on-line large-volume sample pre-concentration of bacteria, Escherichia coli and Staphylococcus aureus cells (methicillin-susceptible or methicillin-resistant), in the initial stage of micellar electrokinetic chromatography using a non-ionogenic surfactant or of capillary electrophoresis, respectively. These procedures were employed in single-piece fused silica capillary etched with supercritical water with two different internal diameter segments featuring different inner surface roughness. Large volumes (maximum 2.8 μL) of the high conductivity sample matrices, physiological saline solution, urine or blood (with purification step), spiked with examined cells were injected into the wider end of a capillary with an inlet inner diameter 195 μm. This novel on-line combination of preconcentration strategies for cells produced an up to 680-fold increase in sensitivity for E. coli or S. aureus cells. The average calculated resolutions, R, for five selected methicillin-susceptible or methicillin-resistant strains were found to be 6.3 for the agar-cultivated and 14.9 for the blood-incubated cells. A low number of bacteria similar to those in clinical samples were also tested. The modified surface roughness step helped to significantly narrow the cell zones and to increase resolution. The migration velocities of E. coli agar-cultivated and blood-incubated cells were approximately the same as those of S. aureus, probably due to the minimal differences in their surface properties. This procedure, on-line pre-concentration and separation of bacteria, is rapid and provides good reproducibility and repeatability.