CN101000299A - Sandwich liquid core waveguide structure investigating pond - Google Patents

Abstract

A detection cell with a sandwich-type liquid core waveguide structure, mainly composed of a liquid core optical fiber, a flow cell body, a three-way joint, and an ordinary optical fiber, wherein: a liquid core optical fiber runs through the center of the flow cell body, and a pass through is provided on both sides of the flow cell body A liquid outlet and a liquid inlet, a light source hole is axially opened on the body wall of the flow cell; a three-way joint is connected to each end of the flow cell body, one of the three-way joints has an inlet of the flow cell, and the other has an outlet of the flow cell , used to connect to an external separation or analysis system; the refractive index of the liquid injected through the water inlet of the flow cell body should be greater than the refractive index of the liquid core waveguide material used, which is 1.31, so as to form a dense refraction index inside the flow cell body. Sparse-dense sandwich structure, that is, another layer of liquid wall structure with total internal reflection capability is formed outside the liquid core fiber. This outer total internal reflection layer can prevent side-fired light from entering the inside of the liquid core fiber, thereby reducing The intensity of scattered light improves the signal-to-noise ratio of detection.

Description

A detection cell with a sandwich liquid core waveguide structure

technical field

The invention belongs to the design and development category of analytical instruments, and in particular relates to a liquid core waveguide (LCW)-based detection cell with a sandwich-type liquid core waveguide structure.

Background technique

Liquid Core Waveguide (LCW), also known as liquid core fiber. It refers to the phenomenon that when the refractive index of the peripheral material is lower than that of the liquid core, the light wave input from one end of the liquid core will produce total internal reflection at the interface between the liquid core and the tube wall, and can be transmitted from the other end with almost no loss. .

The research on LCW first began in the middle of the 19th century. Colladon, Babinet, Tyndall and others studied the phenomenon of light propagating in stream water through total internal reflection. By the end of the 19th century, the phenomenon was widely known for its application in illuminated fountains. Around 1970, researchers began to pay attention to the possibility of LCW as a communication medium, and manufactured LCW composed of thin glass tubes filled with high refractive index liquid. However, due to the obvious advantages of solid optical fibers, LCW has not been applied in communications. However, it shows attractive application prospects in analytical chemistry.

In order to achieve total internal reflection, the refractive index of the liquid core must be higher than that of the tube wall. Generally, the refractive index of glass is greater than or equal to 1.46, while the refractive index of common solvents, such as water (1.333), methanol (1.329), acetonitrile (1.34), etc., are all lower than glass. In order to apply LCW to analytical chemistry, the devices with light guiding ability developed in the early stage mainly include: metal-coated glass and fused silica tubes, clean glass and fused silica tubes, and plastic tubes.

Waveguides based on highly reflective metals have been used in visible absorption spectroscopy [11, Dasgupta P K. Anal. Chem., 1984, 56: 1401-1403]. The advantage is that light can be transmitted through any transparent liquid or gas, regardless of the refractive index, and light can be received over a wide range of solid angles. However, most devices have a large light loss and cannot reach the level of total internal reflection [14, Matsuura K, Matsuura Y, Harrington J A. Opt. Eng., 1996, 35: 3418-3421].

LCWs made directly from glass capillaries also suffer from several serious deficiencies. First of all, internal reflection occurs on the outer surface of the glass tube, and the light not only travels in the liquid core, but also in the glass, which will inevitably lead to the appearance of the Raman band of silica, which will become the source of background noise. In addition, light travels through the glass making it less likely to travel through the liquid. Furthermore, the rough outer surface of the glass tube will also cause an increase in light loss. The brittleness of glass capillaries is also a problem. Therefore, its application is greatly limited.

Plastic capillaries with low refractive index are elastic and not easy to break, making them ideal for LCW. These materials are perfluorinated polymers, such as polytetrafluoroethylene (PTFE), tetrafluoroethylene and hexafluoropropylene copolymer (FEP) and tetrafluoroethylene and perfluoropropyl vinyl ether copolymer (PFA), etc. , and their refractive indices are 1.34-1.35, respectively. However, the refractive index of these fluorinated polymers is higher than that of water, and it is difficult to use them in aqueous solution systems.

In the 1990s, DuPont introduced the only commercial plastic that can be made into liquid-core optical waveguides, Teflon AF[25, Dupont Fluoroproducts, Teflon AF Amorphous Fluoropolymers.H-16577-1, Wilmington, DE 19880-0711, December 1989 ], the research and application of LCW got a fundamental breakthrough. Teflon AF is an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole and polytetrafluoroethylene, and its refractive index varies with the content of dioxole increase and decrease. There are currently two varieties, Teflon AF1600 with a refractive index of 1.31 and Teflon AF2400 with a refractive index of 1.29. Teflon AF also has the following unique properties [29, http://www.dupont.corn/teflon/af/unique.html ]: it is resistant to all solvents and chemicals except a limited number of perfluorinated solvents; The adsorption of the substrate is very small; it has excellent light transmittance from the far ultraviolet to most of the infrared region; it has a very low dielectric constant and dissipation factor; the thermal expansion is small; Very good mechanical properties and physical properties;

Marquardt et al [Marquardt B J, Vahey P G, Synovec R E, Burgess L W. Anal. Chem., 1999, 71: 4808-4814] designed an LCW Raman spectroscopic detector coupled with HPLC to detect alcohols The limit is 1000 times lower than conventional Raman measurements. DijKstra [Dijkstra R J, Bader A N, Hoornweg G Ph, Brinkman U A Th. Gooijer C. Anal. Chem., 1999, 71: 4575] and others designed the LCW detection cell used in conjunction with conventional reversed-phase HPLC, p-aniline The detection limit of the concentration is 10 μg/mL.

Gooijer et al [Gooijer C, Hoomweg G Ph, Beer T de, Bader A, van Iperen DJ, Brinkman U A Th.J.Chromaogr.A, 1998, 824:1-5] used Teflon AF2400-based LCW for HPLC- UV/Vis absorption detector. For the detection of atrazine, diuron, rituron and other pesticides, the minimum detection concentration is 0.3-0.5μg/L, and the sensitivity is 30-50 times higher than that of conventional detection pools.

Dasgupta [Dasgupta P K, Zhang G, Li J, Boring C B, Jambunathan S, Al-Hor R. Anal. Chem., 1999, 71: 1400-1407] designed a fluorescence detector based on Teflon AF2400, which can Excited with a variety of light sources and inexpensive. Combined with FIA for LED array excitation, the concentration detection limits of methylene blue and rhodamine 560 are 50nmol/L and 1nmol/L, respectively. Hanning et al. [Hanning A, Lindberg P, Westberg J, Roeraade J. Anal. Chem., 2000, 72: 3423-3430] designed a CE laser-induced fluorescence detection cell based on LCW, which was detected in continuous flow mode. Fluorescein The concentration detection limit is 2.7pmol/L. However, expensive lasers and CCD detectors are used.

Contents of the invention

The object of the present invention is to provide a detection cell with a sandwich type liquid core waveguide structure.

The sandwich-type liquid core waveguide structure detection cell provided by the present invention can be used in various optical detectors, such as fluorescence detectors, ultraviolet/visible absorption detectors, Raman spectrum detectors, etc., can greatly reduce the intensity of scattered light, improve Signal-to-noise ratio for optical signal detection.

In order to achieve the above purpose, the sandwich-type liquid core waveguide structure detection cell provided by the present invention is mainly composed of a liquid core optical fiber, a flow cell body, and a tee joint, wherein:

A liquid core optical fiber runs through the center of the flow cell body, and a liquid outlet and a liquid inlet are arranged on both sides of the flow cell body, and a light source hole is opened on the wall of the flow cell body in the axial direction, and the light emitted by the light source hole directly shines on the side of the liquid core fiber On the wall; each end of the flow cell body is connected to a three-way joint, one of the three-way joints has a flow cell inlet, and the other has a flow cell outlet, which is used to connect to an external separation or analysis system;

Among them, the refractive index of the liquid injected through the water inlet of the flow cell body should be greater than the refractive index of the used liquid core waveguide material 1.31, so as to form a dense-dense-dense sandwich structure with a refractive index inside the flow cell body, that is, in Another liquid wall structure with total internal reflection capability is formed on the outside of the liquid core fiber. This outer total internal reflection layer can prevent side light from entering the liquid core fiber, thereby reducing the intensity of scattered light and improving the signal-to-noise detection Compare.

In the detection cell with a sandwich-type liquid core waveguide structure, the liquid core optical fiber is a Teflon AF capillary.

In the detection cell with a sandwich-type liquid core waveguide structure, the end of the flow cell body is connected to a tee with a cell body joint with a plastic taper sleeve, and the tee is made of stainless steel or PEEK engineering plastic.

In the detection cell with a sandwich-type liquid core waveguide structure, the body of the flow cell is made of metal or non-metallic engineering plastics, preferably made of stainless steel.

In the detection cell with a sandwich-type liquid core waveguide structure, an optical fiber or a light emitting diode is installed in the light source hole on the body of the flow cell.

The sandwich-type liquid core waveguide structure detection cell, wherein the light source used when installing the optical fiber is: unsplit white light, broadband light filtered by an optical filter, monochromatic light split by a spectrometer or laser, hollow Monochromatic light from cathode lamps.

In the detection cell with a sandwich-type liquid core waveguide structure, the two ends of the liquid core fiber are coupled to the ordinary optical fiber through a three-way joint, and the ordinary optical fiber is used to introduce light or export light signals to the liquid core fiber. The common optical fiber is silica optical fiber or plastic optical fiber.

Description of drawings

Fig. 1 is the schematic diagram of the detection pool of the sandwich type liquid core waveguide structure of the present invention;

Fig. 2 is the chromatogram of embodiment 2.

Detailed ways

Please refer to FIG. 1 , which is a schematic diagram of a detection cell with a sandwich-type liquid core waveguide structure according to the present invention.

The LCW-based sandwich liquid core waveguide structure detection cell provided by the present invention is mainly composed of a liquid core optical fiber, a flow cell body, a tee joint, an ordinary optical fiber and the like.

The liquid-core optical fiber 1 is supported by Teflon AF capillary in the center of the flow cell body 2, and connected to the tee joints 4 and 4' by the cell body joint 8 with a plastic cone sleeve and sealed and light-shielded. The flow cell body needs to support the entire sandwich-type liquid core waveguide structure detection cell and should have the necessary mechanical strength. It can be made of metal or non-metal engineering plastics, preferably stainless steel. A row of holes 3 are axially drilled on the body wall of the flow cell, the diameter of which is consistent with the outer diameter of the light-emitting diode casing, and used to install the light-emitting diodes; optical fibers or other devices can also be used to introduce the required light source as required, and the holes from the light source The emitted light should be directed at the side wall of the liquid core fiber. A water inlet 6 and a water outlet 7 through which liquid can be fed are installed at both ends of the flow cell body. The entire flow cell assembly is sealed with a chemically stable and light-tight sealing material. Liquid core fiber can be selected according to needs. Available liquid core fibers include Teflon AF1600 or Teflon AF2400 materials with different inner diameters and different lengths.

The inlet and outlet of the flow cell connected to the three-way joint can be used to connect the detection cell with other separation and analysis systems such as HPLC.

The type and quantity of the light-emitting diodes installed in the axial direction of the flow cell body can be selected according to needs. When photodiodes with different emission wavelengths are installed at the same time, it can have the ability of multi-wavelength excitation. Other light sources can also be used if necessary, including unsplit white light, broadband light filtered by an optical filter, monochromatic light split by a spectrometer, or monochromatic light such as lasers and hollow cathode lamps.

Both ends of the liquid core optical fiber 1 can be coupled with common optical fibers 5 through a tee joint 4 . Ordinary optical fiber 5 can be used to introduce light or export optical signals to the liquid core optical fiber. Ordinary optical fiber can be silica optical fiber or plastic optical fiber. If necessary, light or light signals can also be directly transmitted through the transparent light window. Optical signals can be detected with any weak light measuring device. In typical designs, detection can be performed using a chemiluminescence or spectrofluorometer.

The sandwich-type liquid core waveguide structure detection cell of the present invention can inject pure water or other suitable liquids into the body of the flow cell through the water outlet and the water inlet during operation. The refractive index of this liquid should be greater than the refractive index of the liquid core waveguide material used to form a dense-dense-dense sandwich structure with a refractive index inside the flow cell body, that is, another layer with Liquid wall structure with total internal reflection capability. The total internal reflection layer on the outside can prevent most of the side light from entering the liquid core fiber, thereby greatly reducing the intensity of scattered light and improving the signal-to-noise ratio of detection.

The present invention is described in detail below in conjunction with embodiment.

Example 1

The sandwich-type liquid core waveguide structure detection cell shown in Figure 1 is mainly composed of liquid core optical fiber, flow cell body, tee joint, ordinary optical fiber and other parts.

The liquid-core optical fiber 1 is a Teflon AF2400 capillary tube with an outer diameter of 792 μm, an inner diameter of 193 μm, and a length of 18 cm, and is installed in the center of the flow cell body 2; the flow cell body 2 is a stainless steel tube with an outer diameter of 30 mm, an inner diameter of 27 mm, and a length of 160 mm. There are five rows of light source holes in the axial direction, 20 in each row, 100 in total, and each light source hole is equipped with a light-emitting diode 3 with a center wavelength of 470nm; the light-emitting diodes in each row are connected in parallel and powered by a DC stabilized power supply. The voltage is 3.2V, and the working current is 20mA-30mA; the five columns of light-emitting diodes can be controlled separately. When installing the light-emitting diode, it needs to be sealed with epoxy resin, polyacrylate or other suitable adhesives to avoid liquid leakage in the cavity. The rear end of the liquid core optical fiber 1 is connected to a three-way joint 4 made of engineering plastics such as stainless steel or PEEK, but the axial direction is not coupled to the optical fiber and closed with a nut. A stainless steel or PEEK tube with a length of several centimeters to tens of centimeters is connected to the vertical direction of the tee joint 4 to discharge the liquid in the liquid core optical fiber 1 . At the front end of the liquid core optical fiber 1, it is axially and concentrically coupled with a 50cm multimode quartz optical fiber 5 through a stainless steel or plastic tee joint 4'; the other end of the quartz optical fiber 5 is coupled to the photomultiplier tube window of the chemiluminescence detector On (for known technology, not shown in the figure). The optical signal is received and amplified by the photomultiplier tube and displayed as a voltage value on the digital voltmeter, and at the same time input to the chromatographic workstation for processing as a time-light intensity curve. A stainless steel tube or PEEK tube with a length of several centimeters to more than ten centimeters is connected with a high-performance liquid chromatograph. The chromatographic column is a Kromasil C18 reversed-phase column with an internal diameter of 4.6mm and a length of 250mm (for known technology, not shown in the figure). Show).

Using methanol as the mobile phase, the flow rate is 1.0ml/min, the liquid flows through the injection valve to the chromatographic column, and then flows into the sandwich-type liquid core waveguide detection cell, working in the fluorescence detector mode.

Start the HPLC infusion system, light up a column of light-emitting diodes 3, and adjust the chemiluminescence detector so that the reading is 0. Inject pure water (triple distilled water or ultrapure water) into the flow cell body through the water inlet 6 on the flow cell body, stop adding water and close the water inlet 6 and water outlet 7 after confirming that the water is full and there are no residual air bubbles. At this point, the liquid core optical fiber has been completely immersed in pure water. Since the refractive index of water (1.33) is smaller than that of the liquid-core fiber wall (1.29), a sandwich structure with a dense-dense-dense refractive index is formed inside the flow cell body, that is, a dense-dense sandwich structure is formed outside the liquid-core fiber. Another layer of liquid wall structure with total internal reflection capability. The total internal reflection layer on the outside can prevent most of the side light from entering the liquid core fiber, thereby greatly reducing the intensity of scattered light and improving the signal-to-noise ratio of detection. At this time, the reading of the chemiluminescence detector has dropped to -1920; and the display range of the chemiluminescence detector is ±1999.

Example 2

Use the device shown in Example 1 to start the HPLC infusion system, use fluorescein as a sample and methanol as ^a solvent to prepare a ^10-6-10-9 mol/L fluorescein solution, and inject the fluorescein solution through the injection valve Inject into the HPLC system, and detect with the apparatus described in Example 1, with an injection volume of 10 μl. Figure 2 shows a typical chromatogram. Samples with the same concentration were injected 3 times, and the arithmetic mean value was calculated to obtain a linear range of: 6.02×10 ^-9 mol/L-3.01×10 ^-7 mol/(R ² =0.997). It can be known by calculation that when the signal-to-noise ratio is 3, the minimum detection concentration of fluorescein by this device is 3.95×10 ^-10 mol/L.

Chromatography and detection conditions: PMT working voltage is -730V; mobile phase: methanol; flow rate: 1.0ml/min;

Fluorescein concentration: 3.01×10 ^-8 mol/L; injection volume: 10 μL; LEDs: 100, working voltage: 3.1V.

Claims (10)

1. a sandwich liquid core waveguide structure investigating pond mainly is made up of liquid-core optical fibre, flow cell body, three-way connection, wherein:

The circulation pool center traverses a liquid-core optical fibre, and flow cell body both sides are provided with one can feed liquid outlet and liquid inlet, axially offers light source hole on the flow cell body wall, and the light direct beam that light source hole sent is on the liquid-core optical fibre sidewall; Flow cell body two ends respectively connects a three-way connection, and one of them has flow cell inlet this three-way connection, and flow cell outlet is arranged on another, in order to connect external discrete or analytic system;

The liquid that injects through flow cell body water inlet wherein, its refraction index should be greater than the refraction index 1.31 of employed liquid core waveguide material, to be the sandwich type structure of close-thin-Mi at the inner formation of flow cell body refraction index, promptly form the liquid wall structure that another layer has the total internal reflection ability in the liquid-core optical fibre outside, the light that the total internal reflection layer in this outside can stop side to be penetrated enters liquid-core optical fibre inside, thereby the reduction scattered intensity improves the signal to noise ratio (S/N ratio) that detects.

2. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, wherein liquid-core optical fibre is a Teflon AF kapillary.

3. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, body termination, circulate among pond is connected with threeway with the pond body joint that has the plastics tapered sleeve.

4. sandwich liquid core waveguide structure investigating pond as claimed in claim 3 is characterized in that, wherein threeway is that stainless steel or PEEK engineering plastics are made.

5. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, circulate among pond body is that metal or nonmetal engineering plastics are made.

6. sandwich liquid core waveguide structure investigating pond as claimed in claim 5 is characterized in that, circulate among pond body is that stainless steel is made.

7. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, the light source hole on the body of circulate among pond is installed optical fiber or light emitting diode.

8. sandwich liquid core waveguide structure investigating pond as claimed in claim 7, it is characterized in that the light source that adopts when wherein optical fiber being installed is: the broad band light that filters without the white light of beam split, through optical filter, through the monochromatic light of the monochromatic light of optical splitter beam split or laser instrument, hollow cathode lamp.

9. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, wherein the two ends of liquid-core optical fibre utilize ordinary optic fibre to liquid-core optical fibre lead-in light or derivation light signal by three-way connection and ordinary optic fibre coupling connection.

10. sandwich liquid core waveguide structure investigating pond as claimed in claim 1 is characterized in that, wherein this ordinary optic fibre is silica fibre or plastic optical fiber.

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