High electric field strength two-dimensional peptide separations using a microfluidic device: Microfluidics and Miniaturization

New instrumentation has been developed to improve the resolution, efficiency, and speed of microfluidic two-dimensional separations using micellar electrokinetic chromatography (MEKC) coupled to high field strength capillary electrophoresis (CE). Previously published two-dimensional separation instrumentation [1] from our group was limited to a maximum potential difference of 8.4 kV, resulting in an electric field strength of only ~200 V/cm in the first dimension. The circuit described in this report has been designed to couple a higher voltage supply with a rapidly switching, lower voltage supply to utilize the best features of each. Voltages applied in excess of 20 kV lead to high electric field strength separations in both dimensions, increasing the separation resolution, efficiency, and peak capacity while reducing the required analysis time. Detection rates as high as 6 peptides per second (based on total analysis time) were observed for a model protein tryptic digest separation. Additionally, higher applied voltages used in conjunction with microfluidic chips with longer length channels maintained higher electric field strengths and produced peak capacities of over 4,000 for some separations. Total separation time in these longer channel devices was comparable to that obtained in short channels at low field strength; however, resolving power improved approximately 3 fold.