Solid phase extraction with capillary electrophoresis
Methods, systems and devices that provide fluid devices with at least one SPE bed adjacent (upstream of) a separation channel which may be in communication with an inlet of a Mass Spectrometer. The fluid device can be configured to operate using independently applied pressures to a BGE reservoir and a sample reservoir for pressure-driven injection that can inject a discrete sample plug into a separation channel that does not require voltage applied to the sample reservoir and can allow for in-channel focusing methods to be used. The methods, systems and devices are particularly suitable for use with a mass spectrometer but optical or other electronic detectors may also be used with the fluidic devices.
1. A microfluidic analysis system, comprising:
a microfluidic device comprising at least one separation channel in fluid communication with a background electrolyte (BGE) reservoir, a sample channel in fluid communication with a sample reservoir and the separation channel and comprising at least one solid phase extraction (SPE) bed, and a waste reservoir in fluid communication with the separation channel;
a first gas supply tube that connects a first pressurized gas supply to a sealed headspace of the BGE reservoir through a first valve;
a second gas supply tube that connects a second pressurized gas supply to a sealed headspace of the sample reservoir through a second valve;
a third gas supply tube that connects a third pressurized gas supply or a pressure-reducing device to a sealed headspace of the waste reservoir through a third valve, wherein the waste reservoir is in fluid communication with a waste channel that fluidly connects the waste reservoir to the separation channel;
an electrode configured to be coupled to a voltage source and extending into the BGE reservoir so that when fluid is present in the BGE reservoir, the electrode contacts the fluid; and
a controller configured to couple to the voltage source and to communicate with the first, second and third valves, and further configured so that during operation of the system, the controller directs the first, second and third valves to open and close to flow a sample through the sample channel, across the at least one SPE bed and into the separation channel, and electrophoretically separate an analyte component from the sample in the separation channel, without applying an electrokinetic voltage and/or a voltage gradient across the sample channel and/or SPE bed.
2. The system of claim 1 , wherein the sample channel comprises at least one blocking member positioned adjacent to an end of the at least one SPE bed that is closest to the separation channel to retain SPE material within the SPE bed.
3. The system of claim 1 , wherein the SPE bed comprises a length, measured along a flow direction defined by the sample channel, of between 100 μm and 1000 μm, and a volume of between about 50 pL to about 10 nL.
4. The system of claim 1 , wherein the sample channel is valveless so that the SPE bed is in uninterrupted fluid communication with the separation channel.
5. The system of claim 1 , wherein a leading end of the at least one SPE bed is positioned at a distance of between 50 μm and 500 μm from the separation channel.
6. The system of claim 1 , wherein the sample channel has a branched segment of first and second branches that merge into a single channel segment that holds the SPE bed.
7. The system of claim 6 , wherein the first branch is in fluid communication with a first reservoir and the second branch is in fluid communication with the sample reservoir.