Etched electrochemical detection for electrophoresis in nanometer inner diameter capillaries

Capillary electrophoresis in nanometer inner diameter capillaries allows for the analysis of extremely small volume samples, such as the contents of single cells. However, the utilization of these ultrasmall capillaries requires a very sensitive and low volume detector. An improved method for end-column amperometric detection for capillary electrophoresis in nanometer inner diameter (i.d.) capillaries is presented. This new method involves etching both the electrode and the detection end of the capillary. These design improvements allow for better alignment between the capillary bore and the electrode. As a result, dead volume in the detector is minimized. The etched method for electrochemical detection in ultrasmall capillaries provides average coulometric efficiencies of 70 ± 10% for dopamine and 40 ± 20% for catechol in 770 nm i.d. capillaries. Furthermore, this technique provides peak efficiencies as high as 100 000 theoretical plates and detection limits as low as 340 zmol for both dopamine and catechol.