Detectors for liquid chromatography

Abstract

A detector for a liquid chromatograph comprises: a light source (2); a flow cell (6) comprising a linear capillary (14) dividing a flow path for a sample liquid to flow, a holding member (18) holding one end of the capillary, an incident port (20) for causing light to enter the one end of the capillary, and an exit port (24) for causing light to exit from the other end of the capillary; a condenser (4) for directing light from the light source to the incident port of the flow cell; and a light receiver (12) for detecting light emitted from the exit port of the flow cell, wherein a lens (28) is provided between one end of the capillary of the flow cell and the condenser, and the lens is arranged in such a way that light in a central region near an optical axis of light directed from the condenser toward one end of the capillary is parallelized and a first reflection position of the light in the central region is away from one end.

Description

Technical Field

[0001] The invention relates to a detector for a liquid chromatograph. Background Art

[0002] In a liquid chromatograph, in order to analyze a small amount of sample with high sensitivity and high speed, it is important to seek small capacity and low diffusion of the system capacity. Therefore, in the detector, it is also preferred to reduce the inner diameter of the flow path for sample circulation as much as possible. The common flow cell used by detectors such as absorptiometry detectors is provided with a flow path for sample circulation in a block containing a material with chemical resistance such as SUS316. In this block-type flow cell, if the inner diameter of the flow path inside the cell is reduced, the cross-sectional area of ​​the flow path through which light passes becomes smaller, and then the frequency of light scattering on the wall surface of the cell also increases. As a result, S / N deteriorates.

[0003] Therefore, in order to achieve small capacity and low diffusion, a flow cell (also called a light guide cell) can be used, which uses a linear thin capillary to form a flow path for the sample to flow (see Patent Document 1). In the light guide cell disclosed in Patent Document 1, light incident on one end of the capillary is totally reflected at the interface between the outer peripheral wall surface of the capillary and the surrounding air layer and propagates to the other end of the capillary.

[0004] [Prior art literature]

[0005] [Patent Document]

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-041024

[0007] Patent document 2: U.S. Patent Specification No. 8086083 Summary of the invention

[0008] [Problems to be solved by the invention]

[0009] In the above-mentioned light guide cell, the two ends of the capillary are held by retaining members such as ferrules. The light incident on the light guide cell is also incident on the interface between the capillary and the retaining member. The reflectivity of the light guide including the capillary and the sample flowing inside it changes according to the difference in refractive index between the sample flowing in the capillary and the retaining member connected to the capillary. If the refractive index of the sample is constant, there is no problem, but in the gradient analysis in which the composition of the mobile phase changes with time, since the refractive index of the sample flowing through the capillary changes with time, the amount of light emitted from the capillary will change with time, and the baseline of the detector signal will change. This phenomenon is called the refractive index effect.

[0010] An object of the present invention is to suppress the change in baseline caused by the refractive index effect.

[0011] [Technical means to solve the problem]

[0012] The detector for liquid chromatograph of the present invention comprises: a light source; a circulation cell, comprising a linear capillary that divides a flow path for circulating a sample liquid, a holding member that holds one end of the capillary, an incident port for causing light to enter the one end of the capillary, and an exit port for causing light to exit from the other end of the capillary; a condenser for guiding light from the light source to the incident port of the circulation cell; and a light receiver for detecting light emitted from the exit port of the circulation cell, wherein a lens is provided between the one end of the capillary of the circulation cell and the condenser, and the lens is configured in such a manner that light in a central region near an optical axis of light directed from the condenser toward the one end of the capillary is parallelized and a first reflection position of the light in the central region is away from the one end.

[0013] Here, "parallelization" means refracting light to reduce the inclination angle relative to the optical axis. In addition, the "first reflection position of the light incident into the capillary" is the position where the light incident into the capillary first enters the interface between the outer peripheral surface of the capillary and the air layer and is reflected. In the present invention, the first reflection position of the light in the central area near the optical axis of the light from the condenser toward the one end of the capillary is moved away from the one end of the capillary, thereby reducing the amount of light incident on the interface between the outer peripheral surface of the capillary and the holding member.

[0014] [Effects of the Invention]

[0015] According to the detector for liquid chromatograph of the present invention, a lens is provided between one end of the capillary of the circulation pool and the condenser, and the lens is arranged in such a way that the first reflection position of light in the central area near the optical axis of the light directed from the condenser toward the one end of the capillary is away from the one end of the capillary, thereby reducing the amount of light incident on the interface between the outer peripheral surface of the capillary and the retaining member, thereby suppressing the change of the baseline of the detector signal during gradient analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic structural diagram showing an embodiment of a detector for liquid chromatograph.

[0017] Figure 2 This is a schematic cross-sectional view showing the structure of a flow cell according to the same embodiment.

[0018] Figure 3 This is a partially exploded cross-sectional view for explaining the structure of the lens mounting portion of the flow cell of the same embodiment.

[0019] Figure 4 This is a conceptual diagram for explaining the effect obtained by the lens using the flow cell of the same embodiment.

[0020] Figure 5 This is verification data of the effect of the lens of the same example on the light transmission efficiency.

[0021] Figure 6 This is the first verification data of the influence of the lens of the same embodiment on the refractive index effect.

[0022] Figure 7 This is the second verification data of the influence of the lens of the same embodiment on the refractive index effect.

[0023] [Explanation of Symbols]

[0024] 2: Light source

[0025] 4: Condenser

[0026] 6: Circulation pool

[0027] 8: Mirror

[0028] 9: Slit

[0029] 10: Raster

[0030] 12: Optical receiver

[0031] 14: Capillary

[0032] 16: Shell

[0033] 18: Keep components

[0034] 20: Entrance

[0035] 22: Import flow path

[0036] 24: Exit port

[0037] 26: Export flow path

[0038] 28: Lens

[0039] 30: Window panels

[0040] 32: Concave DETAILED DESCRIPTION

[0041] Hereinafter, one embodiment of a detector for liquid chromatograph will be described with reference to the drawings.

[0042] like Figure 1 As shown, the detector for liquid chromatograph of the embodiment includes a light source 2 , a condenser 4 , a flow cell 6 , a mirror 8 , a grating 10 and a light receiver 12 .

[0043] The light emitted from the light source 2 is reflected by the condenser 4 and focused on the incident port 20 of the flow cell 6 (see Figure 2 The flow cell 6 is formed by using a linear capillary 14 (see Figure 2 ) constitutes a light guide cell for the flow path through which the sample liquid flows. The positional relationship between the condenser 4 and the flow cell 6 is set so that the optical axis of the light reflected by the condenser 4 coincides with the central axis of the capillary 14 of the flow cell 6.

[0044] The light incident on the incident port of the flow cell 6 passes through the capillary 14 and exits from the emission port 24 (see Figure 2 ) is emitted. The light emitted from the flow cell 6 is reflected by the mirror 8, passes through the slit 9, and is guided to the grating 10 to be decomposed into each wavelength component. The light of each wavelength component decomposed by the grating 10 is incident on a light receiver 12 including, for example, a photodiode array, and the intensity of the light in each wavelength region is measured.

[0045] use Figure 2 The structure of the flow cell 6 will be described.

[0046] The flow cell 6 includes a capillary 14, a housing 16, a retaining member 18, a lens 28, and a window plate 30. The capillary 14 includes quartz glass, etc., and has an outer diameter of, for example, 0.5 mm. The two ends of the capillary 14 are retained by retaining members 18 such as ferrules and mounted on the housing 16. The outer peripheral surface of the capillary 14 is in contact with the air layer except for the two ends in contact with the retaining member 18. Light incident into the capillary 14 from one end (the left end in the figure) of the capillary 14 is repeatedly totally reflected at the interface between the outer peripheral surface of the capillary 14 and the surrounding air layer and travels to the other end (the right end in the figure) side in the capillary 14.

[0047] The housing 16 is provided with an inlet 20, an introduction flow path 22, an outlet 24, and an outlet flow path 26. The inlet 20 is an opening for allowing light to enter one end of the capillary 14, and the outlet 24 is an opening for extracting light emitted from the other end of the capillary 14. The introduction flow path 22 is a flow path for introducing sample water to one end of the capillary 14, and the outlet flow path 24 is a flow path for extracting the sample water flowing through the capillary 14 to the outside. The inlet 20 is sealed by a lens 28, and the outlet 24 is sealed by a flat window plate 30. In addition, an optical fiber may be inserted into the outlet 24 to emit light from the other end via the optical fiber.

[0048] like Figure 3 As shown, the lens 28 sealing the incident port 20 is embedded in a recess 32 provided at the edge of the incident port 20 of the housing 16. The recess 32 is provided so as to share a central axis with the capillary 14. The outer diameter of the lens 28 is substantially the same as the inner diameter of the recess 32, that is, the difference between the two is less than 1.13% of the outer diameter of the lens 28. Therefore, the center of the lens 28 embedded in the recess 32 is located on the central axis of the capillary 14.

[0049] In the embodiment, the lens 28 is a convex lens with a convex surface facing the condenser 4 side. An example of the size of the lens 28 is an outer diameter of 6 mm, a lens diameter of 4 mm, and a thickness of 2.3 mm. The surface of the lens 28 opposite to the convex surface is a flat surface, and includes a side surface perpendicular to the flat surface. By including such a side surface, the lens 28 can be stably held by the recess 32 when it is embedded in the recess 32.

[0050] The lens 28 is located between the condenser 4 and one end of the capillary 14, and is used to parallelize the light in the central region near the optical axis of the light from the condenser 4 toward one end of the capillary 14. Parallelization here means reducing the tilt angle relative to the optical axis. The central region is, for example, a 20% region on the central side of the light beam reflected at the condenser 4.

[0051] like Figure 4 As shown in FIG. 1 , if the lens 28 having a center is disposed on the optical axis of the light from the condenser 4, the light in the center region is refracted and parallelized at the lens 28, so that the position (first reflection position) at which the light is first reflected in the capillary 14 is shifted to a position away from one end of the capillary 14, compared with the case where the lens 28 does not exist. Therefore, the light in the center region of the light from the condenser 4 is less likely to be incident on the interface between the outer peripheral surface of the capillary 14 and the holding member 18, and the total reflection efficiency in the capillary 14 is improved.

[0052] On the other hand, it is also considered that the light in the outer region far from the center of the light from the condenser 4 is refracted at the lens 28, and the inclination angle relative to the optical axis becomes larger, and it is easy to be incident on the interface between the outer peripheral surface of the capillary 14 and the holding member 18, and the total reflection efficiency becomes poor. However, since the light from the light source 2 has a distribution with a large amount of light as in the central region, the influence caused by the deterioration of the total reflection efficiency of the light in the outer region of the light beam in the capillary 14 is smaller than the influence caused by the improvement of the total reflection efficiency of the light in the central region of the light beam in the capillary 14.

[0053] In the above embodiment, the lens 28 is mounted on the housing 16 and also functions as a window plate that seals the incident port 20, but the present invention is not limited thereto. The lens 28 can be provided separately from the flow cell 6 as long as it collimates the light from the central region of the light from the condenser 4 and makes the first reflection position away from one end of the capillary 14.

[0054] Figure 5 These are measurement data showing verification results regarding the influence of the lens 28 on the light transmission efficiency of the flow cell 6 .

[0055] In the above verification, the amount of light in each wavelength region detected by the light receiver 12 is measured while water is flowing through the capillary 14 of the flow cell 6. Figure 5In FIG. 1 , the embodiment (solid line) is measurement data obtained using the flow cell 6 described above, and the comparative example (dashed line) is measurement data obtained using a flow cell in which a flat window plate is installed at the incident port 20 instead of the lens 28 .

[0056] According to the above verification, the amount of light in each wavelength region detected by the light receiver 12 in the embodiment (solid line) is greater than that in the comparative example (dashed line). That is, by providing the lens 28 between the condenser 4 and the capillary 14, the light in the central region of the light incident on the capillary 14 is collimated, the total reflection efficiency in the capillary 14 is improved, and the amount of light transmitted through the flow cell 6 is increased.

[0057] Figure 6 and Figure 7 are measurement data showing verification results related to the influence of lens 28 on the refractive index effect. Figure 5 Likewise, the example is measurement data obtained using the flow cell 6 including the lens 28 , and the comparative example is measurement data obtained using a flow cell with a flat window plate installed at the incident port 20 instead of the lens 28 .

[0058] exist Figure 6 In the verification, the mobile phase was circulated in the capillary 14 (inner diameter 0.36 mm) of the circulation pool 6 at a flow rate of 0.8 mL / min, and the composition of the mobile phase was changed in sequence to A liquid (water): B liquid (acetonitrile) = 100:0, A liquid: B liquid = 95:5, A liquid: B liquid = 0:100, A liquid: B liquid = 100:0, and the absorbance of light with a wavelength of 250 nm was measured.

[0059] exist Figure 7 In the verification, the mobile phase was circulated in the capillary 14 (inner diameter 0.36 mm) of the circulation pool 6 at a flow rate of 0.8 mL / min, and the composition of the mobile phase was changed to liquid A (water: acetonitrile: trifluoroacetic acid (trifluoroacetic acid, TFA) = 95:5:0.05): liquid B (water: acetonitrile: TFA = 5:95:0.05) = 98:2, liquid A: liquid B = 0:100, 98:2, and the absorbance of light with a wavelength of 250 nm was measured.

[0060] It is known that Figure 6 and Figure 7 In all the verification results, the baseline of the measurement data in the embodiment is more stable than that in the comparative example, which indicates that the light incident on the capillary 14 is collimated in the central region by providing the lens 28 between the condenser 4 and the capillary 14, thereby suppressing the refractive index effect.

[0061] The above-described embodiment is merely an example of an embodiment of the detector for liquid chromatograph of the present invention. The embodiment of the detector for liquid chromatograph of the present invention is as follows.

[0062] An embodiment of the detector for liquid chromatograph of the present invention includes: a light source; a circulation cell, including a linear capillary that divides a flow path for a sample liquid to flow, a holding member that holds one end of the capillary, an inlet for causing light to enter the one end of the capillary, and an outlet for causing light to exit from the other end of the capillary; a condenser for guiding light from the light source to the inlet of the circulation cell; and a light receiver for detecting light emitted from the outlet of the circulation cell, wherein a lens is provided between the one end of the capillary of the circulation cell and the condenser, and the lens is configured in such a way that light in a central area near an optical axis of light directed from the condenser toward the one end of the capillary is parallelized so that a first reflection position of the light in the central area is away from the one end.

[0063] In the first form of the embodiment, the flow cell includes a shell, the incident port is provided in the shell, a circular recess sharing a central axis with the capillary is provided at the edge of the incident port of the shell, the outer diameter of the lens is substantially the same as the inner diameter of the recess, and the center of the lens is located on the central axis of the capillary by embedding the lens in the recess. In order to effectively suppress the refractive index effect of the lens, it is important to make the positional relationship between the condenser, the capillary and the lens close to the designed positional relationship. As in the first form, as long as the recess is provided in the shell having a substantially constant positional relationship with the flow cell, and the lens is embedded in the recess, the lens can be accurately and easily positioned relative to the capillary, thereby effectively suppressing the refractive index effect of the lens.

[0064] In the first aspect, the flow cell can be arranged so that the optical axis of the light reflected by the condenser coincides with the central axis of the capillary. By setting such a positional relationship, it is easy to design the size, shape, position, etc. of the lens for suppressing the refractive index effect.

[0065] In a second aspect of the embodiment, the lens is a convex lens having a convex surface facing the condenser mirror side.

Claims

1. A detector for liquid chromatograph, characterized in that: include: light source; A flow cell, comprising a linear capillary tube defining a flow path for a sample liquid to flow, a holding member for holding one end of the capillary tube, an incident port for causing light to enter the one end of the capillary tube, and an emission port for causing light to exit from the other end of the capillary tube, wherein the light incident into the capillary tube from the one end of the capillary tube is repeatedly reflected and travels toward the other end side in the capillary tube; a condenser lens for directing light from the light source to the incident port of the flow cell; as well as a light receiver, used to detect light emitted from the outlet of the flow cell, A lens is provided between the one end of the capillary of the circulation pool and the condenser, and the lens is configured in a manner to parallelize light in a central area near the optical axis of light directed from the condenser toward the one end of the capillary so that a first reflection position of the light in the central area initially reflected in the capillary is farther away from the one end from the portion held by the holding member, wherein the parallelization refers to reducing an inclination angle relative to the optical axis, and the central area is an area 20% of the center side of the light beam of light reflected at the condenser.

2. The detector for liquid chromatograph according to claim 1, characterized in that: The circulation pool includes a shell, the incident port is arranged in the shell, a circular recess sharing a central axis with the capillary is arranged at the edge of the incident port of the shell, the outer diameter of the lens is substantially the same as the inner diameter of the recess, and the center of the lens is located on the central axis of the capillary by embedding the lens in the recess.

3. The detector for liquid chromatograph according to claim 2, characterized in that: The flow cell is arranged so that the optical axis of the light reflected by the condenser mirror coincides with the central axis of the capillary.

4. The detector for liquid chromatograph according to claim 1, characterized in that: The lens is a convex lens with a convex surface facing the condenser lens side.

5. The detector for liquid chromatograph according to any one of claims 1 to 4, characterized in that: A mobile phase in which a plurality of liquids are combined and the combination of the liquids changes with time is caused to flow through the flow path.

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