Evaluation of automated isocratic and gradient nano-liquid chromatography and capillary electrochromatography

An automated liquid nano-separation system has been developed for nano-liqu id chromatography (nano-LC) and capillary electrochromatography (CEC) using both isocratic and gradient elution, One fused-silica nanocolumn, typicall y 75 mu m i.d. x 39 cm (25 cm effective packed length), packed with Spheris orb ODS 1, 3 mu m particle size, can be used with either technique without having to remove the column upon snitching from one mode to the other. The mobile phase is delivered by two reciprocating micro-LC pumps at a now rate of 30 mu L/min to a postinjection splitter that houses the nanocolumn inle t. The splitter is directly connected to a micro-injection valve with a 0.5 mu L injection volume. In the CEC mode, pressure is not applied (no restri ction on splitter) to the column inlet or outlet and the voltage is continu ously applied during sample injection and mobile phase delivery, In the nan o-LC mode, the restrictor is coupled to the splitter. Using the same nanoco lumn under isocratic conditions, the repeatabilities of retention time and peak area for nano-LC were better than 0.2% and 4%, respectively, and those for CEC were better than 0.6% and 6%, respectively. On average, column eff iciency was 57% higher in CEC compared to nano-LC. Gradient elution separat ions of parabens and polynuclear aromatic hydrocarbons (PAHs) were accompli shed by CEC.