Systems and methods for electrospray using chromatographic columns with conducting or semiconducting stationary phases
Systems, methods, and cartridges taught herein improve chromatographic performance in electrospray systems that feature chromatographic columns having a conductive or semiconductive stationary phase by electrically connecting a fluid junction located upstream of the chromatographic column to a fluid union located downstream of the chromatographic column using an electrical conductor. The electrical conductor creates a voltage equipotential between a first end of the chromatographic column and a second end of the chromatographic column that neutralizes current flow through the chromatographic column. Accurate electrospray current measurements are enabled while post-column peak dispersion and repeatable retention time are achieved.
1 . An electrospray system, comprising:
a first pre-column fluid junction to receive a fluid sample;
a chromatographic column for separating analytes within the fluid sample, the chromatographic column including a conductive or semi-conductive stationary phase disposed between a first end and a second end of the chromatographic column, the first end fluidically connected to the first pre-column fluid junction;
a post-column fluid union having a first fluid port and a second fluid port, the first fluid port receiving separated analytes in the fluid sample from the second end of the chromatographic column;
an electrospray emitter fluidically connected to the second fluid port; and
an electrical conductor connected to the post-column fluid union and the first pre-column fluid junction to equalize electrical potential between the post-column fluid union and the first pre-column fluid junction.
2 . The electrospray system of claim 1 , further comprising a current sensing circuit having a high side and a low side, the low side of the current sensing circuit being electrically connected to the electrical conductor.
3 . The electrospray system of claim 2 , further comprising a power supply electrically connected to the high side of the current sensing circuit.
4 . The electrospray system of claim 3 , further comprising a second pre-column fluid junction to deliver the fluid sample to the first pre-column fluid junction, wherein the power supply is electrically connected to supply high voltage to the second pre-column fluid junction.
5 . The electrospray system of claim 1 , wherein the post-column fluid union and the first pre-column fluid junction are electrically connected in parallel with one another and in series with a current sensing circuit.
6 . The electrospray system of claim 1 , wherein a fluidic path connecting the second end of the chromatographic column and the post-column fluid union has an inner diameter of 30 micrometers or less to reduce peak broadening.
7 . The electrospray system of claim 1 , wherein the chromatographic column, the post-column fluid union, the electrospray emitter, the electrical conductor, and the first pre-column fluid junction are housed in a replaceable cartridge.
8 . The electrospray system of claim 7 , wherein the cartridge includes a high-voltage electrical connector that is electrically connected to the electrical conductor or to a current sensing circuit in series with the electrical conductor.
9 . The electrospray system of claim 8 , wherein the current sensing circuit is housed in the replaceable cartridge.
10 . The electrospray system of claim 7 , wherein the replaceable cartridge includes a housing that electrically shields the first pre-column fluid junction and the post-column fluid union.
11 . The electrospray system of claim 1 , wherein a length of a fluidic path between the first pre-column fluid junction and the chromatographic column and a length of a fluidic path between the chromatographic column and the post-column fluid union are each less than 100 mm.
12 . The electrospray system of claim 1 , further comprising a third pre-column fluid junction electrically connected to ground, the second pre-column fluid junction and the third pre-column fluid junction forming a pre-column voltage spacer.
13 . A method for reducing electro-chromatographic effects in an electrospray system, comprising:
flowing a fluid sample from a first pre-column fluid junction to a first end of a chromatographic column, the chromatographic column including a conductive or semi-conductive stationary phase disposed between the first end and a second end of the chromatographic column;
separating analytes within the fluid sample using the chromatographic column;
outputting the separated fluid sample from the second end of the chromatographic column to a first fluid port of a post-column fluid union, the post-column fluid union having a second fluid port connected to an electrospray emitter; and
applying an equipotential voltage in a range of +1 to +10 kilovolts or in a range of −1 to −10 kilovolts at both the first pre-column fluid junction and at the post-column fluid union using an electrical conductor in electrical contact with the first pre-column fluid junction and the post-column fluid union.
14 . The method of claim 13 , further comprising:
applying a first voltage to a high side of a current sensing circuit using a power supply; and
transmitting the equipotential voltage from a low side of the current sensing circuit to the electrical conductor.
15 . The method of claim 14 , wherein the post-column fluid union and the first pre-column fluid junction are electrically connected in parallel with one another and in series with the current sensing circuit.
16 . The method of claim 13 , wherein outputting the separated fluid sample from the second end of the chromatographic column to a first port of the post-column fluid union includes flowing the separated fluid sample through a fluidic path having an inner diameter of 30 micrometers or less to reduce peak broadening.
17 . The method of claim 13 , wherein flowing the fluid sample from the first pre-column fluid junction to the first end of the chromatographic column includes flowing the fluid sample through a fluidic path having a length of less than 100 mm.
18 . The method of claim 13 , wherein the chromatographic column, the post-column fluid union, the electrospray emitter, the electrical conductor, and the first pre-column fluid junction are housed in a replaceable cartridge, the method further comprising:
connecting a second pre-column fluid junction of the cartridge to a source of the fluid sample; and
flowing the fluid sample from the second pre-column fluid junction to the first pre-column fluid junction.
19 . The method of claim 18 , wherein the cartridge includes a high-voltage electrical connector in electrical connection with the electrical conductor, the method further comprising:
electrically connecting a power supply to the high-voltage electrical connector.
20 . The method of claim 14 , wherein the first voltage is greater than the equipotential voltage.