Microfluidic Sample Injectors Absent Electrokinetic Injection
Microfluidic sample injection, which is based on a mechanical valve rather than electrokinetic injection into an integrated separation channel or a discrete separation column, can provide improved sample injections, enhanced capabilities, and can eliminate the need for changing the electric field in the separation channel to induce sample injection. An interface allowing the use of a discrete separation column easily allows for flexibility to utilize the microfluidic injector with existing analytical techniques. Multiple sample channels and/or sample sources can be utilized with the microfluidic sample injector.
1 . A microfluidic injector system comprising:
A flow layer comprising a first sample channel connected in a T-shaped arrangement to a loading channel at a first intersection, wherein the first sample channel has a source of pressure and is configured to maintain a sample pressure greater than that of the loading channel at the first intersection, and wherein the loading channel has a terminus comprising a port configured to interface with a separation column;
A control layer comprising a valving channel, wherein the valving channel in the control layer crosses over the first sample channel in the flow layer at or near the first intersection; and
A mechanical valve, not an electrokinetic-based injector, to control a sample injection from the first sample channel into the loading channel, the mechanical valve comprising a deformable membrane between the control layer and the flow layer and separating the valving channel and the first sample channel, wherein the membrane has a closed position to obstruct flow in the first sample channel, and an open position to permit flow in the first sample channel based on a first and second pressure, respectively, in the valving channel.
2 . The system of claim 1 , further comprising capillary electrophoresis (CE) electrodes arranged along the loading channel and configured to continuously apply an electric field for CE separation.
3 . The system of claim 1 , further comprising CE electrodes arranged along the separation column and configured to continuously apply an electric field for CE separation.
4 . The system of claim 3 , further comprising an electrospray ionization (ESI) emitter at the end of the separation column.
5 . The system of claim 1 , further comprising a plurality of sample sources connected to the first sample channel via a manifold.
6 . The system of claim 1 , further comprising at least one additional sample channel connected in a T-shaped arrangement to the loading channel at the first intersection or at an additional intersection, wherein the additional sample channel is configured to maintain a sample pressure greater than that of the loading channel at the first or additional intersection.
7 . The system of claim 6 , further comprising
an additional valving channel for each additional sample channel, wherein the additional valving channel in the control layer crosses over the additional sample channel in the flow layer at or near the first intersection or the additional intersection; and
an additional mechanical valve, not an electrokinetic-based injector, for each additional sample channel to control sample injection from the additional sample channel into the loading channel, the additional mechanical valve comprising a deformable membrane between the control layer and the flow layer and separating the additional valving channel and the additional sample channel, wherein the additional membrane has a closed position to obstruct flow in the additional sample channel, and an open position to permit flow in the additional sample channel based on a first and second pressure, respectively, in the additional valving channel.
8 . The system of claim 6 , further comprising a first sample source connected to the first sample channel and an additional sample source connected to the additional sample channel, wherein the first sample source contains an analyte or an analyte precursor, and wherein the additional sample source contains an analyte-derivatizing reactant or an analyte precursor.
9 . The system of claim 8 , wherein the analyte-derivatizing reactant comprises a radiolabel.
10 . The system of claim 8 , wherein the analyte-derivatizing reactant comprises a fluorescent label.
11 . The system of claim 8 , wherein the analyte-derivatizing reactant comprises an electrospray ionization efficiency enhancing label or a charge-state altering reactant.
12 . The system of claim 1 , wherein the sample injection has a volume less than 10 nL.
13 . The system of claim 1 , wherein the sample injection has a volume less than 1 nL.
14 . The system of claim 1 , wherein the sample injection has a volume less than 200 pL.
15 . The system of claim 1 , wherein the separation column comprises an open tubular capillary.
16 . The system of claim 1 , wherein the separation column contains a monolith.
17 . The system of claim 1 , wherein the separation column contains particles.
18 . The system of claim 1 , wherein the separation column contains a hydrogel or viscous polymer solution.
19 . The system of claim 1 , further comprising a liquid chromatography column connected to the first sample channel and providing liquid chromatography separation of the sample prior to injection into the loading channel.
20 . The System of claim 1 , wherein a ratio of cross-sectional area to length of the loading channel is at least 10 times greater than that of the separation column.