Evaluation of Automated Isocratic and Gradient Nano-Liquid Chromatography and Capillary Electrochromatography

Abstract

An automated liquid nano-separation system has been developed for nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) using both isocratic and gradient elution. One fused-silica nanocolumn, typically 75 μm i.d. × 39 cm (25 cm effective packed length), packed with Spherisorb ODS 1, 3 μm particle size, can be used with either technique without having to remove the column upon switching from one mode to the other. The mobile phase is delivered by two reciprocating micro-LC pumps at a flow rate of 30 μL/min to a postinjection splitter that houses the nanocolumn inlet. The splitter is directly connected to a micro-injection valve with a 0.5 μL injection volume. In the CEC mode, pressure is not applied (no restriction on splitter) to the column inlet or outlet and the voltage is continuously applied during sample injection and mobile phase delivery. In the nano-LC mode, the restrictor is coupled to the splitter. Using the same nanocolumn 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 efficiency was 57% higher in CEC compared to nano-LC. Gradient elution separations of parabens and polynuclear aromatic hydrocarbons (PAHs) were accomplished by CEC.

Electro-osmotic and pressure-driven flow properties of frits for packed column capillary electrochromatography prepared from functionalised and bare silica packings

“…13 In the latter case the chromatographic support is immobilised by chemical bonding to the capillary walls, but with all other packing methods a retainer is necessary to keep the particles inside the column. This can be accomplished either by modification of the capillary design using tapered capillaries as described recently 14 or through the use of frits, which can be inserted into the column mechanically, 15 or generated inside the capillary by various chemical or physical means. In the literature published so far, the latter method is still the most widely used and a number of techniques for the preparation of frits have been described.…”

Liquid flow in capillary (electro)chromatography: Generation and control of micro‐ and nanoliter volumes

“…The pre-split injection design was first presented 1994 by Behnke and Bayer [85], then by Eimer et al [86], and was further developed by Huber et al [87], Kitagawa et al [88], and Zhang et al [89]. Later, optimized setups, e.g., with autosampler, minimized dead volume, in-line filters to prevent clogging, and outlet restrictor capillary to prevent bubble-formation were presented by Taylor et al [90,91] (similar to the Unimicro [92] starter kit configuration shown in Figure 10.b), Behnke and Metzger [93], Strickmann et al [94], and Alexander et al [95]. Nearly all publications demonstrated the importance of an optimized design of the capillary column inlet device which is schematically shown in Figure 7.a.…”

Comparison of the chromatographic behavior of monolithic capillary columns in capillary electrochromatography and nano-high-performance liquid chromatography

“…Alexander et al [6] have assembled a modular system that could be operated in the CEC or nano-pLC mode. With this instrument, gradient elution was possible in both modes.…”