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

TLDR

Fused‑silica capillaries have been connected to microfluidic devices for capillary electrophoresis by drilling into the device edge with 200‑µm tungsten carbide drills, but the standard pointed bits create a conical bottom that introduces a 0.7‑nL geometric dead volume and causes significant band broadening with 0.2‑nL sample plugs. The authors removed the conical area with a flat‑tipped drill bit, eliminating band broadening and achieving on average 98 % of the predicted plate numbers, while all measurements were taken with the device operating with an electrospray from the capillary end. The flat‑bottom connection yields plate numbers close to predictions (≈98 % of expected) and a minimal effective dead volume, enabling microfluidic devices to be connected to a wide variety of external detectors.

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.