Pulse type solution cathode glow discharge device and method with controllable lifting anode

Abstract

The invention relates to a pulse type solution cathode glow discharge device with a lifting-controllable anode, in the device, a metal anode and a graphite cathode are respectively connected with a high-voltage direct-current power supply, a sample is conveyed by a capillary tube and is in contact with the graphite cathode to form a liquid cathode, and glow discharge can be excited between the metal anode and the liquid cathode after high voltage is applied. And the metal anode is fixed on a working platform capable of moving along the guide rail and can move towards the direction close to or far away from the sample. The control box regulates and controls the movement of the working platform and guides the metal anode to complete a series of periodic operations including four stages of anode descending, short-range discharging, anode lifting and long-range discharging, so that the discharging current is in pulse type fluctuation. And the spectrum detection system collects an emission spectrum generated in a glow discharge area between the metal anode and the liquid cathode, and detects the sample. Due to the controllable periodic lifting design of the anode, the anti-interference capability of the cathode glow discharge device is enhanced, and the measurement precision and sensitivity are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of plasma spectral analysis, and particularly relates to a pulsed solution cathode glow discharge device and method with controllable lifting of the anode. Background Art

[0002] Traditional analytical instruments, including inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), and atomic fluorescence spectrometry (AFS), have been widely used in elemental analysis, covering various fields such as environment, biology, and chemical industry. However, due to their large equipment size, high power requirements, large gas consumption, and high operating costs, these traditional atomic spectrometers / mass spectrometers are difficult to meet the requirements of rapid detection and on-site analysis.

[0003] Solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) has attracted extensive attention from researchers around the world due to its excellent characteristics of simple device, low power consumption, operation at atmospheric pressure, and real-time analysis. Since it does not require an atomization system and can meet the characteristics of simultaneous determination of multiple elements, SCGD-AES has become an ideal choice for portable instruments to directly analyze liquids and has developed rapidly in the past decade.

[0004] Although SCGD-AES has been successfully applied to the detection of various actual samples, due to its low power and limited excitation ability, the sensitivity of some elements still cannot meet the detection requirements. At the same time, it is easily affected by the coexisting matrix in the actual sample to a certain extent, resulting in a decrease in accuracy. Summary of the Invention

[0005] Aiming at the problems of low sensitivity and poor anti-interference ability in the existing solution cathode glow discharge, the present invention provides a pulsed solution cathode glow discharge device and method with controllable lifting of the anode, which is configured with a capillary coaxial with the metal anode. The sample to be measured overflowing from the opening of the capillary contacts the graphite cathode to form a liquid cathode, and a glow discharge region is formed between the liquid cathode and the metal anode. When the plasma in this region is ignited, the computer controls the operation of the displacement system to control the metal anode to perform periodic operations, including: anode descent stage, short-range discharge stage, anode lift stage, and long-range discharge stage. The detection of the composition of the sample solution to be measured is realized by collecting and detecting the emission spectrum generated during the short-range discharge process. Compared with the traditional fixed anode type solution cathode glow discharge device, the pulsed discharge technology with controllable lifting of the anode is adopted, and this device can more efficiently excite the elements in the sample and enhance the intensity of the spectral signal. At the same time, this innovative design significantly enhances the anti-interference ability and improves the measurement accuracy. In addition, this design shows excellent adaptability and can better meet various different analysis requirements.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A pulsed solution cathode glow discharge device with a controllable anode lift, comprising: a glow discharge light source system, a displacement system, a spectral detection system, and a computer; the glow discharge light source system includes: a sampling unit, a metal anode, a graphite cathode, and a high-voltage DC power supply, the sampling unit includes: a capillary for transporting a sample to be measured, the capillary is coaxially arranged with the metal anode and has an opening opposite to one end of the metal anode, the capillary penetrates through the graphite cathode, and the sample to be measured overflows from the opening and contacts the graphite cathode to form a liquid cathode; the metal anode and the graphite cathode are respectively connected to the positive and negative electrodes of the high-voltage DC power supply, so as to form a glow discharge region between the liquid cathode and the metal anode; the displacement system includes an electric displacement stage and a control box, the electric displacement stage includes a working platform and a guide rail suitable for the working platform to move, the metal anode is fixed on the working platform, the control box is connected to the working platform for control, and the working platform drives the metal anode to move periodically along the guide rail under the control of the control box; the computer is connected to the control box, and the control box operates according to a set program, and further controls the metal anode to perform periodic operations, including: an anode descent stage, a short-range discharge stage, an anode lift stage, and a long-range discharge stage, the anode descent stage is the metal anode moving towards the direction close to the opening, and the anode lift stage is the metal anode moving towards the direction away from the opening; the spectral detection system is used to collect the emission spectrum in the glow discharge region.

[0008] In some embodiments, the sampling unit further includes: a sampling tube and a sampling pump, the sampling tube is connected to the capillary, and the sampling pump pumps the sample in the sampling tube into the capillary; a small hole is provided in the length direction of the graphite cathode, the capillary vertically penetrates through the graphite cathode through the small hole, and the vertical distance between the opening and the graphite cathode is 2-4 mm.

[0009] In some embodiments, when a high voltage is applied to the metal anode and the graphite cathode, and the metal anode moves towards the direction close to the liquid cathode, the metal anode moves to a position at a certain distance from the surface of the solution at the opening of the sampling tube, so as to ignite the plasma in the glow discharge region, and the distance is less than the electrode distance corresponding to the air breakdown field strength.

[0010] In some embodiments, the spectral detection system includes: a condenser lens, an optical fiber probe, and a detector; the condenser lens is used to collect and focus the emission spectrum in the glow discharge region;

[0011] The optical fiber probe is used to transmit the emission spectrum signal collected by the condenser lens to the detector; the detector is used to convert the emission spectrum signal into an electrical signal and transmit it to the computer for outputting the result; the center of the glow discharge region, the center of the condenser lens, and the optical fiber probe are located on the same straight line.

[0012] In some embodiments, the glow discharge light source system further includes: a ballast resistor, which is connected in series between the negative electrode of the high-voltage DC power supply and the graphite cathode or between the positive electrode of the high-voltage DC power supply and the metal anode.

[0013] In some embodiments, the metal anode is arranged vertically, the graphite cathode is arranged horizontally, and the metal anode can move periodically in the vertical direction away from or towards the opening; and / or, the diameter of the metal anode is 1.5 - 3 mm, the length is 40 - 100 mm, and one end of the metal anode corresponding to the opening is ground into a sharp angle of 30 - 60°, and the material of the metal anode is one or several of tungsten, titanium, and molybdenum; and / or, the diameter of the graphite cathode is 5 - 6 mm; and / or, the inner diameter of the capillary is 0.3 - 1 mm, and the wall thickness is 0.4 - 0.8 mm; and / or, it further includes: a liquid discharge unit, including a waste discharge pipe and a liquid discharge pump arranged on the waste discharge pipe, the waste discharge pipe is used to discharge the sample after glow discharge; it further includes: a waste liquid pool, the waste liquid pool is used to hold the sample after glow discharge; the graphite cathode vertically penetrates the side wall of the waste liquid pool and is arranged parallel to the bottom of the waste liquid pool.

[0014] The present invention also provides a pulsed solution cathode glow discharge method with controllable anode lifting, using the above-mentioned pulsed solution cathode glow discharge device. The steps include: the sample to be tested overflows from the opening of the capillary and contacts the graphite cathode to form the liquid cathode, and a glow discharge region is formed between the liquid cathode and the metal anode; the high-voltage DC power supply applies a high voltage, and the displacement system controls the metal anode to move towards the opening, waiting for the gas in the glow discharge region to be ionized and generate plasma; after the plasma is ignited, the metal anode performs periodic operations under the control of the computer and the displacement system. One cycle includes four stages: the anode descending stage, the short-range discharge stage, the anode lifting stage, and the long-range discharge stage; the metal ions to be tested in the sample to be tested enter the plasma and are excited to generate an emission spectrum; the spectral detection system collects the emission spectrum and transmits it to the computer for outputting the result.

[0015] In some embodiments, during the short-range discharge stage, the distance between the metal anode and the surface of the solution of the sample to be measured at the opening is 0.5 - 1.5 mm; during the long-range discharge stage, the distance between the metal anode and the surface of the solution of the sample to be measured at the opening is 3 - 5 mm.

[0016] In some embodiments, the duration of the short-range discharge is longer than the integration time of the spectral detection system and shorter than the overheating time of the discharge end of the metal anode.

[0017] The present invention also provides a control system, including a memory and a processor. The memory is used to store a computer program, and the processor is used to execute the computer program to control the periodic operation of the metal anode in the above solution cathode glow discharge method, or to control the periodic operation of the metal anode in the above pulsed solution cathode glow discharge device.

[0018] Compared with the prior art, the pulsed solution cathode glow discharge device and method with controllable anode lifting provided by the present invention have the following beneficial effects:

[0019] 1. For the pulsed solution cathode glow discharge device provided by the present invention, the computer periodically regulates the action of the metal anode by manipulating the displacement device. The actions of the metal anode in one cycle include an anode descent stage, a short-range discharge stage, an anode lifting stage, and a long-range discharge stage. During this periodic process, the emission spectral signal collected in the short-range discharge stage is used as the detection basis. Compared with the traditional fixed anode type solution cathode glow discharge device, this device shows significant advantages in detecting multiple element signals, improving the sensitivity and accuracy of the spectral signal; in addition, due to the design of controllable anode lifting, the anti-interference ability of the solution cathode glow discharge spectrometry to the coexisting salt matrix in the sample is significantly improved, thus greatly improving the measurement accuracy of the sample, and it also has a wider applicability, capable of meeting different types of samples and analysis requirements, thereby broadening its application range;

[0020] 2. For the pulsed solution cathode glow discharge device provided by the present invention, compared with the pulsed discharge driven by a pulsed power supply, it does not require corresponding circuit design, control algorithm, and high-power components, so the cost is relatively lower;

[0021] 3. In the pulsed solution cathode glow discharge device and the device provided by the present invention, the long-range discharge stage can ensure the continuous operation of the plasma, keep the discharge area at a high electron temperature, gas temperature, and electron density, and ensure the signal sensitivity of the short-range discharge; in the short-range discharge stage, the distance between the two electrodes is shorter than that of the conventional discharge, the plasma size is smaller, and it is less likely to be interfered by the surrounding environment;

[0022] 4. The displacement system in the pulsed solution cathode glow discharge device provided by the present invention adopts programmed automation technology, and precisely and orderly controls the glow discharge process and the periodic movement process of the metal anode through a preset program, avoiding problems such as uncertainty and poor consistency caused by manual operation, and ensuring high-precision and repeatability of detection. Description of the Drawings

[0023] The present invention will be further described below in conjunction with the drawings and embodiments.

[0024] Figure 1 It is a schematic structural diagram of the pulsed solution cathode glow discharge device provided by the present invention;

[0025] Figure 2 It is four stages of one movement cycle of the metal anode provided by the present invention;

[0026] Figure 3 It is a Cd signal timing diagram when the pulsed solution cathode glow discharge device provided by the present invention is operating;

[0027] Figure 4 It is a comparison diagram of Cd recovery rates between the pulsed solution cathode glow discharge device provided by the present invention and a conventional anode-fixed solution cathode glow discharge device under the same concentration of sodium salt matrix content.

[0028] The meanings of the reference symbols in the drawings are as follows:

[0029] 1 - High-voltage DC power supply; 2 - Metal anode; 3 - Graphite cathode; 4 - Plasma; 5 - Ballast resistor; 6 - Waste liquid pool; 7 - Capillary; 8 - Waste discharge pipe; 9 - Working platform; 10 - Guide rail; 11 - Fixing part; 12 - Control box; 13 - Condensing lens; 14 - Optical fiber probe; 15 - Detector; 16 - Computer. Detailed Embodiments

[0030] The present invention will be further explained in detail below in conjunction with the description of the drawings and specific embodiments. However, the following description including the embodiments is only used to enable those of ordinary skill in the technical field to which the present invention belongs to more clearly understand the principles and essence of the present invention, and does not mean any form of limitation to the present invention.

[0031] Embodiment 1

[0032] As Figure 1 shown, the present invention provides a pulsed solution cathode glow discharge device with controllable anode lifting, including: a glow discharge light source system, a displacement system, a spectral detection system, and a computer.

[0033] The above-mentioned glow discharge light source system includes: a sample injection unit, a metal anode 2, a graphite cathode 3, and a high-voltage DC power supply 1.

[0034] The above-mentioned sample injection unit includes: a capillary 7 for transporting the sample to be measured. The capillary 7 is coaxially arranged with the metal anode 2. The capillary 7 has an opening opposite to one end of the metal anode 2. The capillary 7 penetrates through the graphite cathode 3. The sample to be measured overflows from the opening and contacts the graphite cathode 3 to form a liquid cathode (conductive path). The capillary 7 is preferably a ceramic capillary.

[0035] The metal anode 2 and the graphite cathode 3 are respectively connected to the positive and negative electrodes of the high-voltage DC power supply 1, and a glow discharge region is formed between the liquid cathode and the metal anode 2.

[0036] The above-mentioned displacement system includes an electric displacement stage and a control box 12. The electric displacement stage includes a working platform 9 and a guide rail 10 suitable for the working platform 9 to move. The metal anode 2 is fixed on the working platform 9 through a fixing member 11. The control box 12 is connected to the working platform 9 for control. Under the control of the control box 12, the working platform 9 drives the metal anode 2 to move periodically along the guide rail 10, that is, to move periodically in the direction of approaching or moving away from the sample to be measured.

[0037] Preferably, the control box 12 is connected by an RS232 interface.

[0038] The above-mentioned computer is connected to the control box 12 of the displacement system. The computer 16 issues control instructions to the control box according to the set program. The control box controls the movement of the working platform 9 according to the instructions, so as to realize the periodic operation of the metal anode 2. The operations within one cycle include the following four stages: the anode descent stage, the short-range discharge stage, the anode lift stage, and the long-range discharge stage. The anode descent stage refers to the movement of the metal anode 2 in the direction of approaching the opening of the capillary, and the anode lift stage refers to the movement of the metal anode 2 in the direction of moving away from the opening of the capillary.

[0039] Preferably, the computer 16 is connected by a USB interface for software processing and display, and issues instructions. The operation programs of the displacement system and the high-voltage DC power supply and the display of their interfaces are written through virtual instrument software, programming software, etc., so that the operator can directly adjust the periodic operation parameters of the metal anode 2 on the computer 16, and control the operation of the device more conveniently and intuitively.

[0040] The above-mentioned spectral detection system is used to collect the emission spectrum generated in the glow discharge region.

[0041] In some embodiments, the diameter of the above-mentioned metal anode 2 is 1.5 - 3 mm, the length is 40 - 100 mm, one end of the metal anode 2 corresponding to the opening is ground into a sharp angle of 30 - 60°, and the material of the metal anode 2 is one or several of tungsten, titanium, and molybdenum.

[0042] Further, the diameter of the above-mentioned graphite cathode 3 is 5 - 6 mm.

[0043] Further, the inner diameter of the capillary 7 is 0.3 - 1 mm, and the wall thickness is 0.4 - 0.8 mm.

[0044] In some embodiments, when a high voltage is applied to the metal anode 2 and the graphite cathode 3, and the metal anode 2 is in the anode descent stage, the metal anode 2 descends to a position at a certain distance from the liquid surface at the opening of the capillary 7, and this distance is less than the electrode distance corresponding to the air breakdown field strength.

[0045] In some embodiments, the above-mentioned sample injection unit further includes: a sample injection tube and a sample injection pump. The sample injection tube is connected to the capillary 7, and the sample injection pump can pump the sample in the sample injection tube into the capillary 7.

[0046] In some embodiments, the pulsed solution cathode glow discharge device further includes a waste liquid pool 6, which can hold the sample after glow discharge.

[0047] In this embodiment, a preferred structural design of the pulsed solution cathode glow discharge device is provided: as Figure 1 shown, a small hole is opened along the length direction of the graphite cathode 3, the capillary 7 vertically penetrates through the graphite cathode 3 through this small hole, the vertical distance between the opening of the capillary 7 and the graphite cathode 3 is 2 - 4 mm, the graphite cathode 3 vertically penetrates through the side wall of the waste liquid pool 6 and is arranged parallel to the bottom of the waste liquid pool 6.

[0048] The metal anode 2 is arranged vertically, the graphite cathode 3 is arranged horizontally, the metal anode 2 and the graphite cathode 3 are perpendicular to each other, and the metal anode 2 can move periodically in the vertical direction towards or away from the opening under the control of the displacement system.

[0049] Preferably, the material of the waste liquid pool 6 is polytetrafluoroethylene, and it can also be polyether ether ketone, as long as it meets the requirements of high temperature resistance and electrical insulation.

[0050] Further, the material of the fixing part 11 near the fixing position of the metal anode 2 should have good heat resistance and electrical insulation.

[0051] Preferably, in combination with the preferred structural design of the pulsed solution cathode glow discharge device provided above, the guide rail 10 is placed vertically, that is, the guide rail 10 is perpendicular to the graphite cathode 3 and parallel to the metal anode 2, so as to realize the periodic movement of the metal anode 2 approaching or departing from the graphite cathode 3 in a perpendicular form.

[0052] After the plasma 4 in the glow discharge area is ignited, the metal anode 2 performs periodic movement, as Figure 2As shown, one cycle includes four stages: anode descent, short-range discharge, anode lift, and long-range discharge. During the short-range discharge stage, the metal anode 2 is located 0.5 - 1.5 mm directly above the surface of the solution of the sample to be tested. The short-range discharge stage is a high-current discharge, and the spectral signal during the short-range discharge stage is recorded for sample detection, which has better sensitivity and detection limit. During the long-range discharge stage, the metal anode 2 is located 3 - 5 mm directly above the surface of the solution of the sample to be tested. The long-range discharge stage is a conventional DC solution cathode glow discharge mode, which is used to maintain the stable operation of the plasma 4 without extinguishing.

[0053] In some embodiments, the above spectral detection system includes: a condenser lens 13, an optical fiber probe 14, and a detector 15. The condenser lens 13 collects and focuses the emission spectrum of the glow discharge region. The optical fiber probe 14 transmits the emission spectrum signal collected by the condenser lens 13 to the detector 15. The detector 15 is used to convert the emission spectrum signal into an electrical signal and transmit it to the computer 16, and the test results are visually displayed on the screen of the computer 16, facilitating the operator to monitor and record data in real time. The detector 15 is preferably a charge-coupled detector.

[0054] The center of the above glow discharge region, the center of the condenser lens 13, and the optical fiber probe 14 are located on the same straight line.

[0055] The above optical fiber probe 14 is fixed on a three-dimensional platform (not shown in the figure) with an adjustable precision of 2 μm in the X, Y, and Z directions. Through debugging, the best spectral acquisition effect during the short-range discharge stage is obtained, and no optical path adjustment is made for the three stages of anode descent, anode lift, and long-range discharge.

[0056] In some embodiments, the high-voltage DC power supply 11 can provide a DC high voltage of 0 - 1500 V and a DC current of 0 - 200 mA.

[0057] Preferably, in order to better achieve the excitation of the liquid cathode glow discharge micro-plasma 4, the working voltage of the high-voltage DC power supply 1 is 900 - 1150 V, and the working current is 40 - 150 mA.

[0058] In some embodiments, the glow discharge light source system further includes: a ballast resistor 5. The ballast resistor 5 is connected in series between the negative electrode of the high-voltage DC power supply 1 and the graphite cathode 3 or between the positive electrode of the high-voltage DC power supply 1 and the metal anode 2.

[0059] Preferably, the resistance value of the ballast resistor 5 is 1 - 1.5 kΩ, so as to greatly reduce the probability of the glow discharge turning into arc discharge and improve the stability of the glow discharge.

[0060] In some embodiments, the pulsed solution cathode glow discharge device further has a liquid discharge unit, including a waste discharge pipe 8 and a liquid discharge pump arranged on the waste discharge pipe 8. The waste discharge pipe 8 is used to discharge the sample after glow discharge. Preferably, the waste discharge pipe 8 has the same structural setting as the capillary 7 and vertically penetrates the bottom of the waste liquid pool 6. The liquid discharge pump pumps the sample in the waste liquid pool 6 into the waste discharge pipe 8 and discharges it from the waste liquid pool 6.

[0061] Preferably, the liquid inlet pump and the liquid discharge pump can be the same peristaltic pump.

[0062] Example 2

[0063] Combined Figure 1 and Figure 2 As shown, the present invention also provides a pulsed solution cathode glow discharge method with controllable anode lifting, using the pulsed solution cathode glow discharge device described in Example 1. The steps include:

[0064] The sample to be measured overflows from the opening of the capillary 7 and contacts the graphite cathode 3 to form a liquid cathode. A glow discharge region is formed between the liquid cathode and the metal anode 2.

[0065] The computer 16 and the displacement system control the metal anode 2 to move along the guide rail 10 in the direction approaching the opening, and the gas in the glow discharge region is ionized to generate plasma 4.

[0066] The metal anode 2 quickly moves downward, that is, quickly moves in the direction approaching the liquid cathode. When the metal anode reaches a position at a specific distance from the surface of the solution at the top opening of the capillary 7, it can trigger the instantaneous ignition of the plasma 4 in the glow discharge region. This distance is less than the electrode distance corresponding to the air breakdown field strength.

[0067] After the plasma 4 is ignited, the metal anode 2 first rises (moves in the direction away from the opening) to a specific height, and then the displacement system controls the metal anode 2 to perform a periodic operation. One cycle includes four stages: anode descent, short-range discharge, anode lift, and long-range discharge.

[0068] At the same time, the metal ions to be measured in the sample to be measured enter the plasma 4 and are excited to generate an emission spectrum. The metal anode 2 reciprocates at a certain time interval, so that the distance between the metal anode 2 and the surface of the solution of the sample to be measured changes periodically, the length of the plasma 4 changes periodically, and the discharge current changes in a pulsed manner, thereby causing the corresponding change in the emission spectrum.

[0069] The spectral detection system collects the emission spectrum and transmits it to the computer 16 for display.

[0070] Preferably, the injection flow rate of the sample to be measured is 2-5 mL / min, and the pH value is 0.5-1.5.

[0071] Preferably, the duration of the short-range discharge is longer than the integration time of the spectral detection system, so as to ensure that the signal of the short-range discharge is completely collected, and this duration also needs to be shorter than the overheating time of the discharge end of the metal anode 2 to ensure the service life of the metal anode 2 and the normal operation of the microplasma 4.

[0072] Furthermore, when in the stage of short-range discharge, the distance between the metal anode 2 and directly above the liquid surface of the sample to be measured at the opening is 0.5-1.5 mm.

[0073] When in the stage of long-range discharge, the distance from directly above the liquid surface of the sample to be measured at the opening is 3-5 mm.

[0074] The optical fiber probe 14 obtains the best spectral acquisition effect in the short-range discharge stage through debugging, and no optical path adjustment is made in the three stages of anode descent, anode lift, and long-range discharge.

[0075] Record the spectral signal in the short-range discharge stage for sample detection.

[0076] Example 3

[0077] Based on Example 1 and Example 2, the present invention further provides a control system, including a memory and a processor. The memory is used to store a computer program, and the processor is used to execute the computer program to control the periodic operation of the metal anode in the pulsed solution cathode glow discharge method in Example 2, or control the periodic operation of the metal anode in the pulsed solution cathode glow discharge device in Example 1, that is, control the periodic movement process of the working platform 9 driving the metal anode 2 along the guide rail 10 to realize the four stages of the periodic operation.

[0078] The above-mentioned processor can be a central processing unit CPU, a microprocessor MCU, etc., and the memory is a medium that can store program codes, such as ROM (read-only memory), RAM (random access memory), non-volatile memory such as a hard disk, etc.

[0079] Combined with Example 1 and Example 2, the following provides some specific examples to illustrate the pulsed solution cathode glow discharge device and method provided by the present invention:

[0080] Example 4

[0081] In this embodiment, the metal anode 2 is a tungsten rod with a diameter of 2.5 mm, and its tip is ground into a sharp angle of 30 - 60°; the graphite cathode 3 has a diameter of 5 mm and a length of 60 mm; the capillary is a ceramic capillary with an inner diameter of 0.3 mm and an outer diameter of 1.2 mm. The sample solution to be measured is pumped into the capillary 7 by an injection pump and overflows from the opening at the upper end of the capillary 7 to contact the graphite cathode 3 to form a liquid cathode (conductive path). The injection flow rate of the sample solution to be measured is 3 mL / min, the pH value is 1, and the acid matrix is nitric acid.

[0082] In the short-range discharge stage, the vertical distance between the metal anode 2 and the surface of the sample solution at the opening is 1 mm; in the long-range discharge stage, the vertical distance between the metal anode 2 and the surface of the sample solution at the opening is 4 mm; the DC voltage for maintaining the discharge operation of the microplasma 4 is 1140 V, and the resistance value of the ballast resistor 5 is 1.2 kΩ; the spectral integration time is 300 ms.

[0083] Prepare a standard solution containing 0.5 mg / L Cd, and continuously pump it into the capillary 7 by a peristaltic pump. Turn on the high-voltage DC power supply 1. First, control the metal anode 2 to move downward. After a glow discharge microplasma 4 is formed between the electrodes, after the plasma 4 is ignited, control the metal anode 2 to move upward until the metal anode 2 is 3 mm directly above the surface of the sample solution at the opening. Cyclically execute the four stages of anode descent, short-range discharge, anode lift, and long-range discharge, and record the signal changes at 228.80 nm and 229.38 nm. Among them, the signal at 229.38 nm is used as the background, and the net signal of Cd is the signal difference between the two wavelengths. The experimental results are obtained as Figure 3 shown. The results show that through the short-range discharge stage of the pulsed SCGD device, higher signal intensity can be obtained, which is approximately 5 times that of the long-range discharge signal and far exceeds the signal of the conventional SCGD device.

[0084] Example 5

[0085] In this embodiment, the metal anode 2 is a tungsten rod with a diameter of 2.5 mm, and its tip is ground into a sharp angle of 30 - 60°; the graphite cathode 3 has a diameter of 5 mm and a length of 60 mm; the capillary 7 is a ceramic capillary with an inner diameter of 0.3 mm and an outer diameter of 1.2 mm. The sample solution to be measured is pumped into the capillary 7 by a peristaltic pump and overflows from the opening at the upper end of the capillary 7 to contact the graphite cathode 3 to form a liquid cathode (conductive path). The injection flow rate of the sample solution to be measured is 3 mL / min, the pH value is 1, and the acid matrix is nitric acid.

[0086] During the short-range discharge stage, the vertical distance between the metal anode 2 and the surface of the sample solution at the opening is 1 mm; during the long-range discharge stage, the vertical distance between the metal anode 2 and the surface of the sample solution at the opening is 3 mm; the DC voltage for maintaining the discharge operation of the microplasma 4 is 1040 V, and the resistance value of the ballast resistor 5 is 1.2 kΩ; the spectral integration time is 300 ms.

[0087] Sodium salts were selected for the salt matrix effect test. A series of mixed solutions containing 1 mg / L Cd and a certain concentration of Na were prepared, and the concentrations of Na were 0 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, 500 mg / L, 700 mg / L, and 900 mg / L, respectively. They were pumped into the capillary 7 by a peristaltic pump respectively. Taking the signal of the solution containing 0 mg / L Na as the reference, the ratio of the signal of the solution containing the remaining concentration of Na to the reference was defined as the recovery rate of Cd at different sodium salt concentrations. The experimental results are as Figure 4 shown. The results show that a higher recovery rate can be obtained through the short-range discharge stage of the pulsed SCGD device, far exceeding that of the conventional SCGD device. That is to say, when analyzing samples containing a certain content of salt matrix, the pulsed solution cathode glow discharge device with controllable anode lifting provided by the present invention has higher accuracy.

[0088] Inspired by the ideal embodiments of the present invention, through the above description, relevant staff can make various changes and modifications completely within the scope not deviating from the technical idea of this invention.

[0089] The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A pulsed solution cathode glow discharge device with controllable anode lifting and lowering, It is characterized in that include: Glow discharge light source system, displacement system, spectrum detection system, computer; The glow discharge light source system comprises: a sample injection unit, a metal anode, a graphite cathode and a high-voltage DC power supply. The sample injection unit comprises: a capillary for conveying a sample to be tested, the capillary being coaxially arranged with the metal anode and having an opening arranged opposite to one end of the metal anode, the capillary penetrating the graphite cathode, the sample to be tested overflowing from the opening and contacting the graphite cathode to form a liquid cathode; The metal anode and the graphite cathode are connected to the positive electrode and the negative electrode of the high voltage DC power supply respectively, so that a glow discharge region is formed between the liquid cathode and the metal anode; The displacement system comprises an electric displacement platform and a control box, wherein the electric displacement platform comprises a working platform and a guide rail suitable for the working platform to move, the metal anode is fixed on the working platform, the control box is control-connected with the working platform, and the working platform drives the metal anode to move periodically along the guide rail under the control of the control box; The computer is connected to the control box, and the control box runs according to the setting program of the computer, thereby controlling the metal anode to perform periodic operations, including: an anode descending stage, a short-range discharge stage, an anode lifting stage, and a long-range discharge stage. The anode descending stage is when the metal anode moves toward a direction close to the opening, and the anode lifting stage is when the metal anode moves away from the opening; The spectrum detection system is used to collect the emission spectrum in the glow discharge region.

2. The pulsed solution cathode glow discharge device according to claim 1, characterized in that: The sampling unit further comprises: a sampling tube and a sampling pump, wherein the sampling tube is connected to the capillary tube, and the sampling pump pumps the sample in the sampling tube into the capillary tube; A small hole is provided in the length direction of the graphite cathode, the capillary passes through the small hole vertically through the graphite cathode, and the vertical distance between the opening and the graphite cathode is 2-4 mm.

3. The pulsed solution cathode glow discharge device according to claim 1, characterized in that: When high voltage is applied to the metal anode and the graphite cathode and the metal anode moves toward the liquid cathode, the metal anode moves to a position a distance away from the surface of the solution at the opening of the capillary, thereby igniting the plasma in the glow discharge region, and the distance is smaller than the electrode spacing corresponding to the field strength required for air breakdown.

4. The pulsed solution cathode glow discharge device according to claim 1, characterized in that: The spectrum detection system comprises: a condenser lens, an optical fiber probe and a detector; The condenser lens is used to collect and focus the emission spectrum of the glow discharge area; The optical fiber probe is used to transmit the emission spectrum signal collected by the focusing lens to the detector; The detector is used to convert the emission spectrum signal into an electrical signal and transmit it to the computer to output the result; The center of the glow discharge region, the center of the condenser lens and the optical fiber probe are located on the same straight line.

5. The pulsed solution cathode glow discharge device according to claim 1, characterized in that: The glow discharge light source system further comprises: a ballast resistor, which is connected in series between the negative electrode of the high-voltage DC power supply and the graphite cathode or between the positive electrode of the high-voltage DC power supply and the metal anode.

6. The pulsed solution cathode glow discharge device according to any one of claims 1 to 5, characterized in that: The metal anode is arranged in a vertical direction, the graphite cathode is arranged in a horizontal direction, and the metal anode can periodically move in a vertical direction away from or close to the opening; and / or, The metal anode has a diameter of 1.5 to 3 mm and a length of 40 to 100 mm, one end of the metal anode corresponding to the opening is polished into a sharp angle of 30 to 60 degrees, and the material of the metal anode is one or more of tungsten, titanium and molybdenum; and / or, The diameter of the graphite cathode is 5 to 6 mm; and / or, The inner diameter of the capillary is 0.3-1 mm, and the wall thickness is 0.4-0.8 mm; and / or, It also includes: a liquid discharge unit, including a waste discharge pipe and a liquid discharge pump arranged on the waste discharge pipe, wherein the waste discharge pipe is used to discharge the sample after the glow discharge; It also includes: a waste liquid pool, which is used to hold samples after glow discharge; the graphite cathode vertically penetrates the side wall of the waste liquid pool and is arranged parallel to the bottom of the waste liquid pool.

7. A pulsed solution cathode glow discharge method with controllable anode lifting and lowering, characterized in that: The pulsed solution cathode glow discharge device according to any one of claims 1 to 6 is used, and the steps include: The sample to be tested overflows from the opening of the capillary and contacts the graphite cathode to form the liquid cathode, and the glow discharge region is formed between the liquid cathode and the metal anode; The high-voltage DC power supply applies high voltage, and the displacement system controls the metal anode to move toward the direction close to the opening, until the gas in the glow discharge region is ionized and plasma is generated; After the plasma is ignited, the metal anode is periodically operated under the control of the displacement system and the computer, and one cycle includes four stages: an anode descending stage, a short-range discharge stage, an anode raising stage, and a long-range discharge stage; The metal ions to be tested in the sample to be tested enter the plasma and are excited to generate an emission spectrum; The emission spectrum is collected by the spectrum detection system and transmitted to the computer for output.

8. The solution cathode glow discharge method according to claim 7, characterized in that: When in the short-range discharge stage, the distance between the metal anode and the surface of the solution of the sample to be tested at the opening is 0.5 to 1.5 mm; When in the long-range discharge stage, the distance between the surface of the solution of the sample to be tested at the opening and the surface is 3 to 5 mm.

9. The solution cathode glow discharge method according to claim 7, characterized in that: The duration of the short-range discharge is longer than the integration time of the spectrum detection system and shorter than the overheating time of the discharge end of the metal anode.

10. A control system, characterized in that: It comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor is used to execute the computer program to realize the periodic operation of the metal anode in the solution cathode glow discharge method described in any one of claims 7 to 9, or to control the periodic operation of the metal anode in the pulsed solution cathode glow discharge device described in any one of claims 1 to 6.

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