CN110531013A - Detection pool utilizing axial total reflection of capillary tube wall - Google Patents

Abstract

The invention discloses a detection cell utilizing axial total reflection of a capillary tube wall, and relates to a photodetector in a liquid chromatography system for testing or analyzing a material by separating the material into various components by using a chromatography. Comprises an optical absorption detector used for detecting a sample by a liquid chromatography system; the optical absorption detector comprises a flow path inlet, a detection cell and a flow path outlet; the flow path inlet and the flow path outlet are fixedly connected to the detection cell; the detection cell is a capillary tube, the capillary tube is made of transparent materials, and the refractive index of the capillary tube is larger than that of the sample; the periphery of the outer side of the outer tube wall of the capillary tube is provided with air or vacuum, and the refractive index of the sample is greater than that of the air or vacuum. The invention utilizes the phenomenon of total reflection of the outer wall of the capillary tube to reduce the light energy loss under the condition of increasing the optical path and reducing the inner diameter, thereby improving the detection sensitivity; and the critical angle of the incident light is larger.

Description

A Detection Cell Utilizing Axial Total Reflection of Capillary Tube Wall

technical field

The invention relates to a photodetector in a liquid chromatography system for testing or analyzing materials by using chromatography to separate materials into components, especially a detection pool using axial total reflection of capillary tube walls.

Background technique

Optical absorption detectors based on Lambert-Beer's law are the most commonly used type of detectors in liquid chromatography systems. The detection cell is the core component. When the sample flows through the detection cell, the light passes through the sample in the detection cell and is partially absorbed by the sample. The absorbance information of the sample can be obtained by recording the intensity of the incident light and the outgoing light. Theoretically, the longer the optical path of the detection cell, the greater the absorbance of the sample and the higher the sensitivity of the detector. However, when the inner diameter of the cell hole remains constant, the longer the optical path, the larger the cell volume, and the more obvious the diffusion of the sample in the detection cell, which will reduce the detection sensitivity. In the case of increasing the optical path, it is a solution to control the volume of the cell by reducing the inner diameter of the cell hole, but the reduction of the inner diameter of the cell hole will cause a decrease in the luminous flux, making the impact of noise more significant, and the same will cause a decrease in sensitivity. The detection cell of a conventional optical absorption detector is generally designed with an optical path of 8-10 mm, a cell hole of about 1 mm, and a cell volume of about 10 μL. When the liquid chromatography system used for separation is micro-column liquid chromatography or ultra-high performance liquid chromatography, a detection cell with higher sensitivity and lower cell volume is required.

In order to solve this problem, the current laboratory mostly adopts the method of on-column detection, that is, part of the coating of the capillary is removed, and this part is used as the detection window. This method can significantly reduce the volume of the detection cell, but since the detection optical path is only equivalent to the inner diameter of the capillary, the detection sensitivity is extremely low. Some commercial instruments use precision machining to reduce the diameter of the cell hole, and at the same time optimize the optical focusing system in an attempt to increase the luminous flux. However, this method requires high processing and focusing accuracy and is not easy to achieve. In addition, there is a design scheme that uses a material with a lower refractive index than the mobile phase as the detection cell wall to achieve total reflection on the inner wall of the detection cell. The wall material of this solution is relatively expensive, and the refractive index of the cell wall material is very different from that of the mobile phase. Close to, only slightly smaller than the refractive index of the mobile phase, so the incident angle range is small when total reflection occurs, and higher requirements are placed on the light focusing ability.

Publication number is CN205120679U Chinese utility model " a kind of liquid chromatography ultraviolet and visible light detector total reflection ultra-long optical path detection cell " provides a kind of liquid chromatography ultraviolet and visible light detector total reflection ultra-long optical path detection cell, including Detection cell wall, total reflection lining, liquid inlet pipe, liquid outlet pipe, inlet compression pad, outlet compression pad, inlet cell window, outlet cell window, inlet cell window gasket and outlet cell window gasket. A total reflection liner is attached to the inner side of the detection cell wall, so that there is basically no consumption reflection of the light between the cell walls, and the narrow spectral band is broadened, so that it is possible to increase the optical path length of the detection cell and achieve the purpose of improving the sensitivity of the detector. The total reflection lining used in this utility model is a kind of polymer material called TEFLONAF developed by DuPont Company. When the solvent and the sample flow through the detection cell, the light can undergo total reflection on the inner side of the detection cell wall, which improves the sensitivity of the detector. However, TEFLONAF polymer material is the only choice, and the refractive index of other materials is difficult to be lower than that of common solvents, and its price is very expensive, and it is not easy to obtain; and because the refractive index of TEFLONAF polymer material is not much different from that of solvents, total reflection can occur The critical angle range is relatively small.

Contents of the invention

The technical problem to be solved by the present invention is to provide a detection cell utilizing axial total reflection of the capillary wall with long optical path, small cell volume, high sensitivity, large range of critical angle for total reflection, easy-to-obtain materials and simple structure. .

In order to solve the above problems, the technical solution of the present invention is:

A detection cell utilizing axial total reflection of the capillary tube wall, comprising an optical absorption detector used for detecting samples in a liquid chromatography system, the optical absorption detector comprising a flow path inlet, a detection cell and the flow path outlet, the flow path inlet and the flow path outlet are fixedly connected to the detection pool, the detection pool is a capillary, the capillary is made of transparent material, and the refractive index of the capillary is greater than the refractive index of the sample, so The outside of the outer wall of the capillary is set as air or vacuum, and the refractive index of the sample is greater than the refractive index of the air or vacuum.

Further, a sleeve is also provided, and the sleeve is sleeved on the capillary.

Further, air or vacuum is set between the sleeve and the capillary.

Further, the length of the capillary is 10mm-200mm.

Further, the wall thickness of the capillary is 10 μm-360 μm.

Further, the inner diameter of the capillary is 5 μm-530 μm.

Further, the capillary is made of one of quartz glass, borosilicate glass, quartz glass doped graphite or borosilicate glass doped graphite.

Compared with the prior art, the present invention has the following beneficial effects:

1. The invention utilizes the phenomenon of total reflection on the outer wall of the capillary to reduce the loss of light energy and improve the sensitivity of detection when the optical path is increased and the inner diameter is reduced;

2. The present invention has a larger critical angle of incident light;

3. The present invention uses a commonly used quartz capillary as the light-absorbing region, the material is easy to obtain, and the coupling of light and flow path is easy to realize and easy to process;

4. The present invention can replace capillary tubes of different lengths according to needs, and adapts to the use requirements of different detection sensitivities.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram of a cross-sectional view of a capillary of the present invention;

Among them, 1 is the tube body; 2 is the sample; 3 is the light that does not hit the wall; 4 is the total reflection light; 5 is the outer wall; 6 is the emitted light.

Detailed ways

In order to easily understand the technical means, creative features, goals and effects of the present invention, the present invention will be further described below in conjunction with specific illustrations.

Example 1:

As shown in Figure 1, it is a detection cell that utilizes the axial total reflection of the capillary tube wall. Including an optical absorption detector, the optical absorption detector is used to detect the sample 2 in the liquid chromatography system, the optical absorption detector includes an ultraviolet absorption detector, etc., the optical absorption detector includes a flow path inlet, and detects A pool and a flow path outlet, the flow path inlet and the flow path outlet are fixedly connected to the detection pool. Sample 2 enters the detection cell from the inlet of the flow path, and then flows out from the outlet of the flow path. The detection cell is a capillary, and the capillary is made of transparent material. The refractive index of the capillary is greater than that of sample 2. The capillary is made of quartz glass, borosilicate glass, quartz glass doped graphite or borosilicate glass doped graphite. A material in which the mass fraction of graphite is 0.01% to 1%. The length of the capillary is 10mm-200mm, and the capillary of different lengths can be replaced according to the use requirements of different detection sensitivities. The thickness of the pipe wall is 10 μm-360 μm, and the inner diameter is 5 μm-530 μm. The outside of the tube wall of the capillary is set as air or vacuum, the refractive index of light in vacuum is approximately the same as that of air, and the refractive index of sample 2 is greater than that of air or vacuum.

When the incident light enters the capillary, it is partially absorbed by the sample 2 in the capillary. The parallel light rays entering the capillary or the light rays 3 that do not hit the wall at an angle of less than ±θ1 with the axis of the quartz capillary may directly pass through the sample 2 in the tube and exit the capillary without contacting the inner wall of the capillary. The total reflected light 4 with the included angle between +θ1 to +θ and between -θ1 to -θ with the quartz capillary will enter the capillary body 1 and be totally reflected at the outer wall 5 of the capillary. After passing through sample 2 in the tube, exit the capillary. The outgoing light 6 with an included angle greater than ±θ will directly exit the capillary body 1 and will not be detected.

The boundary values of the included angle θ1 and θ are related to parameters such as the focusing condition of the incident light, the inner diameter and length of the capillary, the refractive index of the sample 2, and the refractive index of the capillary wall. The included angle θ is the critical angle for total reflection, and its value is related to the ratio of the refractive index n1 of the sample 2 in the tube to the refractive index n0 of the air or vacuum outside the capillary, which is 90°-arcsin(n0/n1). For commonly used samples 2 water, methanol, and acetonitrile, the theoretical included angle θ is about 41.4°, 41.2° and 41.9° respectively, which is much higher than using a material with a refractive index lower than sample 2 as the detection cell wall to realize the detection on the inner wall of the cell. The critical angle of 16.2° for the total reflection scheme.

Example 2:

The difference between this embodiment and Embodiment 1 is that a sleeve is provided outside the capillary, and the sleeve is provided for improving the total reflection effect, protecting the capillary or for actual assembly. Air or vacuum is set between the sleeve and the capillary. The length of the sleeve is usually the same as that of the capillary. The material of the sleeve can be polytetrafluoroethylene or fluorinated ethylene propylene copolymer. The inner diameter of the sleeve is slightly larger than the outer diameter of the capillary by 30 μm.

Runtime:

When the liquid chromatography system is working, the effluent sample 2 separated by the chromatographic column enters the capillary through the fluid pipeline. For UV-Vis detectors, the monochromatic light split by the monochromator enters the capillary through an optical fiber or a focusing device, and is partially absorbed by the liquid flowing through the capillary. The absorbed monochromatic light exits the capillary and obtains light intensity information at the photocell. For the diode array detector, the composite light emitted by the light source is not split, and directly enters the capillary through the optical fiber or the focusing device, and is partially absorbed by the liquid flowing through the capillary. The absorbed recombined light passes through the slit and splits light at the grating, and then the light intensity at different wavelengths is obtained by the diode array detector. The transmittance or absorbance information of the liquid flowing through the liquid at different wavelengths can be obtained by performing a ratio or logarithmic operation on the light intensity of the incident light. Continuously collect absorbance information over a period of time to obtain chromatograms and even spectrograms.

Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments, and that the present invention also has various changes and improvements without departing from the spirit and scope of the present invention, and these changes and improvements all fall into the scope of the claims. within the scope of the present invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (7)

1. A detection pool utilizing capillary tube wall axial total reflection, comprising an optical absorption detector, the optical absorption detector is used for a liquid chromatography system to detect samples, and the optical absorption detector includes a flow path inlet, A detection pool and a flow path outlet, the flow path inlet and flow path outlet are fixedly connected to the detection pool, characterized in that: the detection pool is a capillary made of transparent material, and the capillary has a refractive index greater than the Refractive index of the sample, the outside of the outer wall of the capillary is set as air or vacuum, and the refractive index of the sample is greater than the refractive index of the air or vacuum. 2 . The detection cell according to claim 1 , which utilizes the axial total reflection of the capillary tube wall, characterized in that: a sleeve is also provided, and the sleeve is sleeved on the capillary. 3 . 3. A detection cell utilizing axial total reflection of capillary tube wall according to claim 2, characterized in that air or vacuum is set between the sleeve and the capillary tube. 4. A detection cell utilizing axial total reflection of a capillary wall according to claim 1, wherein the length of the capillary is 10mm-200mm. 5 . The detection cell utilizing axial total reflection of the capillary wall according to claim 1 , wherein the thickness of the capillary wall is 10 μm-360 μm. 6 . The detection cell utilizing the axial total reflection of the capillary wall according to claim 1 , wherein the inner diameter of the capillary is 5 μm-530 μm. 7. A detection cell utilizing capillary wall axial total reflection according to claim 1, characterized in that: said capillary is made of quartz glass, borosilicate glass, quartz glass doped with graphite or borosilicate Made of a material in glass doped with graphite.