Patent Application
20120127469
The present invention relates to a flow cell, a detector, and a liquid chromatograph, specifically, a liquid chromatograph measuring an absorbance of a liquid sample flowing inside a flow cell.
In a liquid chromatograph, an ultraviolet absorbance detector is most widely used to measure a sample fluid processed by a separation column (see non-patent document 1). The Lambert-Beer's law tells that an absorbance is expressed in the following formula,
A=εcl=log(Io/I)
wherein: A is the absorbance; E is a mol absorbance coefficient; c is a mol concentration; l is a length of an optical path; Io is an intensity of an incident light; and I is an intensity of a passing light. The formula indicates that the absorbance A is proportional to the length of the optical path 1. Generally, a signal generated by a photo detector measuring the intensity of the passing light I in a measurement of the absorbance A is proportional to an intensity of a received light, while a noise that is simultaneously detected is proportional to the square root of the intensity of the received light. Therefore, a signal-to-noise ratio is proportional to a square root of the intensity of the received light. Meanwhile, the intensity of the received light by the photo detector is proportional to a light incident area. Therefore, the signal-to-noise ratio of the photo detector is proportional to the square root of the light incident area. Therefore, in order to ensure a signal-to-noise ratio large enough for detecting a subject substance with an absorbance measurement, an optical path and a light incident area having more than a certain level of length and area are needed.
Normally, an inner diameter of tubing used for a liquid chromatograph is as small as around 0.1 mm, and this inner diameter is so small that the absorbance measurement can not acquire an adequate level of the optical path length and the light incident area. Therefore, in order to acquire an optical path length and a light incident area large enough for the detection, a channel called flow cell having an adequate channel length and channel width is employed.
The conventional technology provides a flow cell having the structure disclosed in patent document 1.
The channel of the flow cell comprises:
The detecting portion has a capacity of 3 to 15 μl, a length of 3 to 10 mm, and a inner diameter of 0.5 to 1.5 mm. An emitting direction of a detecting light and a flow direction of a sample fluid are parallel to each other. The flow direction of the sample fluid changes greatly at the moment the sample fluid is flowing from an inflow channel into the detecting portion as well as at the moment of flowing out of the detecting portion into an outflow channel.
Patent document 2 discloses a flow cell, which makes the concentration of a sample fluid even across a cross section of a channel by generating a vortex inside a detecting portion with the sample fluid passing through a vortex-generating channel to flow into the detecting portion. Like other conventional flow cells, in the flow cell of patent document 2, an emitting direction of a detecting light and a flow direction of a sample fluid are parallel to each other and the flow direction of the sample fluid changes greatly at the moment the sample fluid is flowing from an inflow channel into the detecting portion as well as at the moment of flowing out of the detecting portion into an outflow channel.
Each of patent documents 3, 4, and 5 discloses a flow cell provided with a plurality of inflow channels in order to evenly lead a sample fluid into a detecting portion. In these flow cells, an emitting direction of a detecting light and a flow direction of the sample fluid are different from each other, and the flow direction of the sample fluid is almost constant through the inflow channel, the detecting portion, and an outflow channel.
An objective for the present invention to attain is to suppress a peak broadening of a chromatogram caused by a flow cell, in which an emitting direction of a detecting light and a flow direction of a sample fluid are parallel to each other, and in which the flow direction of the sample fluid changes at the moment the sample fluid is flowing from an inflow channel into the detecting portion as well as at the moment of flowing out of the detecting portion into an outflow channel.
In the conventional flow cell of patent document 1, the flow of the sample fluid is stagnated at a flow inlet connecting an inflow channel and a detecting portion, and at a flow outlet connecting the detecting portion and an outflow channel. A sample molecule trapped in the stagnation stays longer in the detecting portion than a sample molecule free from the stagnation, leading to a peak broadening of a chromatogram.
The stagnation around the flow outlet is caused by a change in the flow direction of the sample fluid. When the emitting direction of the detecting light and the flow direction of the sample fluid are parallel to each other, an end face of the detecting portion provides a cross section of the detecting portion for the detecting light to pass through. Inevitably, the flow outlet is disposed on a side face of the detecting portion forcing the sample fluid to change its flow direction at the moment the sample fluid is flowing out of the detecting portion into the outflow channel. This change in the flow direction is accompanied by a reduction of the flow rate around a corner defined by the bending flow of the sample fluid (Hereinafter, the corner is referred to as “the flow bend”.). Then, the stagnation is generated around the flow bend. Therefore, the farther away from the flow outlet is positioned the flow bend, the longer the sample molecule takes to come out of the detecting portion.
On the other hand, around the flow inlet, the channel width is abruptly widened, causing the flow of the sample fluid to be detached from a channel wall. As a result, a vortex is generated and the vortex causes the stagnation. Once a sample molecule is trapped in the vortex, only a molecular diffusion allows the trapped molecule to come out of the vortex. A rate of motion of a molecule driven by the molecular diffusion is determined by a diffusion coefficient, which is a property attributed to the interaction between the sample molecule and a solvent, and is independent of the flow rate of the sample fluid. Therefore, the larger is the scale of the vortex trapping the sample molecule, the longer the trapped molecule takes to come out of the vortex. As a result, the sample molecule accordingly takes longer time to come out of the detecting portion.
In the flow cell disclosed in patent document 2, a generated vortex around a flow inlet is such a type that rather diminishes the stagnation into a smaller scale than the vortex in a conventional flow cell. The flow outlet, however, has a same configuration as a flow outlet in a conventional flow cell. Therefore, the flow cell of patent document 2 suffers from a flow stagnation around the flow outlet to the same extent as a conventional flow cell.
In the flow cells disclosed patent documents 3, 4, and 5, an emitting direction of a detecting light and a flow direction of a sample flow in a detecting portion are different from each other, and the flow directions of the sample fluid in an inflow channel and in the detecting portion are same as each other. The detecting portion is provided with a plurality of inflow channels connected to the detecting portion and having a smaller width than the width of the detecting portion. Therefore, the flow inlets generate vortices, which cause flow stagnations.
An objective for the present invention to attain is to suppress a peak broadening of a chromatogram caused by a flow cell.
A flow cell of the present invention comprises:
the outflow portion is provided with one or more channels leading the sample fluid out of the detecting portion in a plurality of directions.
A flow cell of the present invention suppresses a peak broadening of a chromatogram, improving an accuracy of analysis with a liquid chromatograph.
By means described in the following paragraphs, the present invention can suppress a peak broadening of a liquid chromatogram produced by a flow cell. In the flow cell an emitting direction of a detecting light and a flow direction of a sample fluid are parallel to each other inside a detecting portion. Also, in the flow cell, the flow direction of the sample fluid changes at the moment when the sample fluid is flowing from an inflow channel into the detecting portion as well as the moment of flowing out of the detecting portion into an outflow channel.
The first means is a disposition of a plurality of outflow channels to shorten a distance between the flow outlet and a flow bend, where the stagnation occurs, in order to diminish a flow stagnation around a flow outlet inside the detecting portion. In this manner, a sample molecule trapped in the stagnation can come out of the detecting portion in a shorter time.
The second means is a disposition of a plurality of inflow channels symmetrical with respect to the central axis of the detecting portion to collide jets of the incoming sample fluid from the inflow channel into the detecting portion in order to diminish a flow stagnation around a flow inlet inside the detecting portion. In this manner, directions of the generated jets are symmetrical with respect to a central plane including the central axis of the detecting portion scaling down a vortex as well as enabling a sample molecule to come out of the vortex in a shorter time.
The third means is a disposition of a plurality of inflow channels leading the sample fluid into a detecting portion in directions offset from a direction to the central axis of the detecting portion to generate a circular flow of an incoming jet from the inflow channel into the detecting portion in order to diminish a flow stagnation around a flow inlet inside the detecting portion. In this manner, one vortex generated by a circling flow is offset by another vortex generated by another circling flow scaling down the entire vortex as well as enabling a sample molecule to come out of the vortex in a shorter time.
The first means may be combined with either the second or the third means to further suppress a peak broadening of a chromatogram.
In following paragraphs, a configuration of a liquid chromatograph device of the present invention is described with reference to
In following paragraphs, the first working example of the present invention is described with reference to
In this configuration, the presence of the two flow outlets 401, 402 shortens a distance between the flow outlets and the flow bend. As a result, it takes a shorter time for a molecule to move from the flow bend to a branched outflow channel, which is the reason for a suppression of a peak broadening of a liquid chromatogram. The outflow channels 41, 42 are preferably disposed to be symmetrical with respect to a central plane of detecting portion 22 including the central axis of detecting portion 21 in order to minimize the distance between the flow bend and the branched flow outlet.
The larger is the number of the outflow channels, the shorter becomes the distance between the flow outlets inside the detecting portion 2 and the flow bend. Therefore, accordingly, it takes a shorter time for a molecule to move from the flow bend to a branched outflow channel. More than three of the outflow channels are also preferably disposed to be symmetrical with respect to the central axis of detecting portion 21.
The present invention shortens the distance between the flow outlets and the flow bend, accordingly making it take a shorter time for a molecule to move from the flow bend to a branched outflow channel than in a conventional flow cell, which is the reason for a suppression of a peak broadening of a liquid chromatogram. As a result, the accuracy of analysis of a liquid chromatograph can be improved.
In following paragraphs, the second working example of the present invention is described with reference to
In the mechanism of a generation of a stagnation around the flow inlet inside the detecting portion 2, an abrupt enlargement of the channel width at the flow inlet causes the flow of the sample fluid to be detached from the channel wall, subsequently making the detached flow a jet accompanied by a generation of a vortex, which is the cause of the stagnation. The longer is the distance, in which the jet is sustained, the larger the vortex grows. In a conventional flow cell provided with a single inflow channel, the incoming jet does not dissipate until the jet hits a surface of a wall of a detecting portion. On the other hand, in the flow cell 1 of the present invention, the branched inflow channels 31, 32 are disposed to be symmetrical with respect to the central plane of detecting portion 22 including the central axis of detecting potion 21, leading incoming jets from the branched inflow channels 31, 32 to collide with each other on the central plane of detecting portion 22. The collision dissipates the jets on the central plane of detecting portion 22. Therefore, the flow cell 1 of the present invention has a shorter distance, in which the jet is sustained, than a conventional flow cell. Accordingly, the vortex generated by the jet is scaled down. As a result, a sample molecule can come out of the vortex in a shorter time, leading to a suppression of a peak broadening of a liquid chromatogram.
As shown in
The present invention scales down a vortex generated around a flow inlet inside a detecting portion, leading to a suppression of a peak broadening of a liquid chromatogram. As a result, the accuracy of analysis of a liquid chromatograph can be improved.
In following paragraphs, the third working example of the present invention is described with reference to
The inertia of the flow of the sample fluid led from the circling inflow channels 33, 34 into the detecting portion makes the flow a jet.
Each of the circling inflow channels 33, 34 leads the sample fluid in a direction not intersecting the central axis of detecting portion 21. Therefore, the incoming jet from each of the circling inflow channels makes a circular flow along a surface of an inner wall of the detecting portion 2. The inertia of the jet is lost in a short distance due to a generated friction between the jet and the surface of the inner wall of the detecting portion 2, leading to a dissipation of the jet. Accordingly, the generated vortex accompanying the jet is scaled down. When the detecting portion is provided with two of the inflow channels, an incoming jet from one of the inflow channels suppress a generation of a vortex by an incoming jet from the other inflow channel. Therefore, the generated vortex is further scaled down than the vortex generated in a conventional flow cell. As a result, a sample molecule can come out of the vortex in a shorter time leading to a suppression of a peak broadening of a chromatogram.
In following paragraphs, the fourth working example of the present invention is described with reference to
The smaller size of the vortex generated around the flow inlet inside the detecting portion of a flow cell of the present invention than a vortex produced by a conventional flow cell can suppress a peak broadening of chromatogram. As a result, the accuracy of analysis of a liquid chromatograph can be improved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-225879 | Sep 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/004072 | 6/18/2010 | WO | 00 | 2/3/2012 |
