Microfluidic Devices Connected to Fused-Silica Capillaries with Minimal Dead Volume

Abstract

Fused-silica capillaries have been connected to microfluidic devices for capillary electrophoresis by drilling into the edge of the device using 200-μm tungsten carbide drills. The standard pointed drill bits create a hole with a conical-shaped bottom that leads to a geometric dead volume of 0.7 nL at the junction, and significant band broadening when used with 0.2-nL sample plugs. The plate numbers obtained on the fused-silica capillary connected to the chip were about 16-25% of the predicted numbers. The conical area was removed with a flat-tipped drill bit and the band broadening was substantially eliminated (on average 98% of the predicted plate numbers were observed). All measurements were made while the device was operating with an electrospray from the end of the capillary. The effective dead volume of the flat-bottom connection is minimal and allows microfluidic devices to be connected to a wide variety of external detectors.

18 Coupling CE and microchip-based devices with mass spectrometry

“…Thus, Bings et al developed a method to obtain low deadvolume connectors, as small as 0.7 nL. 387 When the spray is generated from a transfer capillary, either a disposable nanospray emitter 388,389 or a fused-silica capillary transfer line can be inserted in the microchip. For the former, the ESI nozzle is usually made with a sharp, tapered capillary end from which the liquid sprays to produce small, well-defined droplets.…”

Utilization of the sol–gel technique for the development of novel stationary phases for capillary electrochromatography on a chip

“…The inlet and the outlet holes of the chips were subsequently enlarged by powder blasting [12]. Silica capillaries were inserted into these cavities using an in-house technique designed to minimize any dead volume, as suggested by Bings et al [13]. Epoxy glue (EPOTEK 353 NDT) was used to ®x the capillaries in their position.…”

Performance of HPLC/MS microchips in isocratic and gradient elution modes

“…One of the challenges of chip-MS is the development of a stable and effective interface. The existing chip-ESI-MS interfaces use one of the following approaches: (1) spraying directly from the edge of a chip, [10,11] (2) spraying from a chip-inserted fused-silica capillary [12,13] and (3) spraying from a chip-integrated (microfabricated) ESI-tip. [14 -16] For interfacing on-chip separation techniques like capillary electrophoresis or liquid chromatography (LC) to MS, the critical point of all interfacing methods is the associated dead volume.…”

“…Harrison's group has shown that even small dead volumes can significantly decrease the separation performance by post-column band broadening. [12,13] Most of the chip-MS systems described in the literature contain ESI-tips made from fused-silica capillaries that were attached after microchip fabrication. [8,9] There is, however, a growing number of MS chips with integrated ESI-tips.…”