Method and device for removing chlorine from sample for determination of isotopic mass of water-soluble organic carbon in salt lake

Abstract

The application relates to a sampling and chlorine removing method and device for salt lake water soluble organic carbon isotope mass spectrum determination, and relates to a chlorine ion concentration determination method for salt lake water samples. If the chlorine ion concentration of the salt lake water sample is equal to or lower than the upper limit set value of the chlorine removing device, the gas sample prepared from the salt lake water sample is removed of chlorine through the chlorine removing device; the device is a filtering tube with a plurality of axial parallel silver wire bundle filters connected in series with a sampling needle capillary; the filtering tube is used in positive and reverse directions; if the chlorine ion concentration of the water sample is higher than the upper limit set value, the chlorine ion concentration of the water sample is reduced to below the upper limit set value through a chemical precipitation method, and then the chlorine is removed through the chlorine removing device. The method has the advantages of fully exerting the advantages of chemical precipitation in removing a large amount of chlorine, avoiding the adverse effects of AgNO3 excess on the water sample during chemical precipitation, avoiding the limitation of the filter in removing chlorine, and significantly reducing the cost of the silver wire in removing chlorine.

Description

Technical Field

[0001] This invention relates to a sample preparation method for isotope mass spectrometry determination, and particularly to a sample preparation and dechlorination method and apparatus for soluble organic carbon isotope mass spectrometry determination in salt lake water. Background Technology

[0002] Our stable isotope mass spectrometry laboratory is capable of determining the carbon isotopes of soluble organic carbon (DOC) in general water bodies. In recent years, a project team has been conducting carbon source and sink analysis of lakes on the Qinghai-Tibet Plateau, requiring the determination of DOC carbon isotopes in the lake water. Water samples collected from Qinghai-Tibet Plateau lakes underwent pretreatment similar to other water samples. However, after testing, we found that the probe became clogged after only a few samples. Furthermore, small, pale green water droplets appeared at the probe's insertion point on the sample pad, which was unusual, as the probe uses headspace air intake and does not come into contact with the liquid. Additionally, opening the bottle produced a pungent odor, which was not present in other water samples. The most significant difference between Qinghai-Tibet Plateau lake water and other water bodies is its extremely high salinity, which we suspect might be the cause affecting the measurements. We collected small green water droplets from the sample bottle pads and used inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine that the main elements in these droplets were iron and chromium, the main components of stainless steel. Analysis determined that the high chloride ion concentration in the saline lake water was the contributing factor. During pretreatment, a strong oxidant was added to oxidize DOC into carbon dioxide before mass spectrometry was used to measure isotopes. During oxidation, chloride ions were converted into chlorine gas. Chlorine gas has a strong, pungent odor and reacts with stainless steel. The injection needle, made of stainless steel, was corroded by chlorine gas, producing small green water droplets. The chlorine-corroded needle frequently became clogged. Furthermore, chlorine entering the mass spectrometer caused signal instability, affecting the accuracy of δ¹³C measurements. Therefore, a suitable method was needed to reduce the chloride ion concentration in the water during pretreatment, and to remove the generated chlorine gas before it entered the mass spectrometer.

[0003] The main methods for removing chloride ions from water are: 1. Adsorption: This method involves using an ion exchanger to exchange chloride ions with the water, thus fixing the chloride ions through adsorption. However, when lake water samples are passed through an adsorption column filled with an ion exchanger, the ion exchange capacity is limited, and saturation is easily reached. Using a larger column or connecting multiple columns can affect the soluble organic carbon in the brine, and this method is labor-intensive and costly, making it unsuitable for sample processing. 2. Evaporation: This method involves boiling and vaporizing water molecules at high temperatures, followed by condensation, separating the water molecules from the salt to remove chloride ions. Experiments have shown that this method is effective in removing chloride ions, but it also removes soluble organic carbon, making it unsuitable for this method as well. Therefore, there is a practical need for a simple, reliable, and easy-to-implement soluble organic carbon isotope mass spectrometry technique for chloride removal. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a simple, reliable and easy-to-implement sample injection and dechlorination method for determining soluble organic carbon isotopes in salt lake water by mass spectrometry. This invention also relates to the sample injection and dechlorination device used in the method of this invention.

[0005] To achieve the above objectives, the present invention provides a method for dechlorination of soluble organic carbon isotopes in salt lake water using mass spectrometry. The key feature is the determination of chloride ion concentration in the salt lake water sample. If the chloride ion concentration of the salt lake water sample is equal to or lower than the upper limit set value that allows the dechlorination device to operate within its reasonable lifespan, a gas sample prepared from the salt lake water sample is passed through the dechlorination device for dechlorination. This dechlorination device consists of a centrally disconnected capillary tube with its upstream and downstream ends sealed and connected to upstream and downstream thickened reducing pipe fittings. The thickened ends of the upstream and downstream thickened reducing pipe fittings are then connected together... The filter tube has a sealed connection with multiple axially parallel silver wire bundle filter elements. The filter tube is initially used in a forward connection with the head upstream and the tail downstream. After a certain number of filtration cycles, it is then used in a reverse connection with the tail upstream and the head downstream. In this way, when the sample gas is introduced from the upstream section of the middle-broken sample needle capillary during headspace intake, the silver wire bundle filter elements react with the chlorine in the sample gas to form silver chloride, which is then fixed. When the sample gas further flows into the downstream section of the middle-broken sample needle capillary, it will not contain chlorine, thus achieving a simple, reliable and easy sample dechlorination. Using the filter tubes in both forward and reverse directions allows for full utilization of the entire silver wire bundle filter element's chlorine removal function. However, after multiple forward uses, the chlorine removal intensity decreases sequentially from upstream to downstream, resulting in progressively increasing porosity within the filter tube, thus affecting upstream chlorine removal efficiency. Conversely, using the filter tubes in reverse order after multiple forward uses leverages the advantage of still having large porosity downstream and avoids the disadvantage of small porosity upstream. This reverse method maintains the high porosity upstream and low porosity downstream, maximizing the chlorine removal efficiency of the silver wire bundle. It offers the advantage of a simple, reliable, and easy-to-implement method for removing chlorine from gas-phase samples during soluble organic carbon isotope mass spectrometry determination.

[0006] If the chloride ion concentration in the water sample is higher than the set value, the following chemical precipitation method is first used to reduce the chloride ion concentration in the water sample to below the upper limit set value. Then, the gas sample made from the dechlorinated water sample is passed through the above-mentioned sample introduction dechlorination device for dechlorination. The chemical precipitation method involves adding an appropriate amount of AgNO3 to a quantitative salt lake water sample, mixing and reacting thoroughly, and filtering to remove the white AgCl precipitate. The appropriate amount is greater than the amount of AgNO3 required to reduce the chloride ion concentration in the water sample to the set value and less than the amount of AgNO3 required to reduce the chloride ion concentration in the water sample to zero. In this way, by first reducing the chloride ion concentration in the water sample to below the upper limit set value using chemical precipitation, and then passing the gas sample made from the dechlorinated water sample through the above-mentioned sample introduction dechlorination device for dechlorination, the advantages of large-volume dechlorination by chemical precipitation can be fully utilized while effectively avoiding the adverse effects of excessive AgNO3 on the water sample during chemical precipitation. It also fully utilizes the advantages of the sample introduction dechlorination device being simple, reliable, and easy to implement, and avoids the limitation of the dechlorination capacity of filter cartridges and significantly reduces the cost of silver wires for dechlorination of filter cartridges.

[0007] As an optimization, the chemical precipitation method involves quantitatively placing a salt lake water sample into a centrifuge tube, then adding an appropriate amount of AgNO3 to the centrifuge tube, and shaking to allow the Cl to settle. -1 The reaction with silver nitrate is complete, and the white precipitate of AgCl is removed by filtration. Shaking and precipitation in the same centrifuge tube ensures that the silver nitrate reaction is complete, and the operation is simple and reliable.

[0008] The upstream and downstream thickened reducing pipe fittings consist of an internally threaded pipe head seat that is sealed to the upstream and downstream ends of the capillary tube, an internally threaded pipe base that is sealed to the end of the filter tube, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. A downstream silver wire bundle filter element, which does not reverse synchronously with the filter tube, is installed in the outer narrow cavity of the downstream reducing externally threaded pipe section that is screwed into the internally threaded pipe head seat. This allows the downstream silver wire bundle filter element to filter out residual chlorine gas in the downstream end of the reverse filter tube and its associated fittings when the filter tube is used in reverse, ensuring the chlorine removal efficiency when the filter tube is used in reverse. The filter tube is a metal tube or a transparent glass tube. Metal tubes are durable, while transparent glass tubes allow for easy observation of the filling and filtration status.

[0009] As an optimization, the upstream and downstream ends of the metal capillary tube are respectively riveted, welded, or otherwise fixed to the outer opening of the upstream and downstream internally threaded tube head seats. This helps to ensure the strength of the sealing connection and provides good durability.

[0010] The inner openings of the upstream and downstream internally threaded pipe heads are respectively provided with internally threaded blind holes that extend into their inner cavities. The outer ends of the upstream and downstream reducing externally threaded pipe sections have externally threaded protrusions that mate with the internally threaded blind holes. The end face of the externally threaded protrusion is sealed to the end face of the internally threaded blind hole by the corrosion-resistant elastic sealing ring. This flexible connection facilitates disassembly, cleaning, and maintenance.

[0011] The metal upstream and downstream internally threaded pipe base is provided with a variable diameter cavity that is thinner inside and thicker outside. The thinner inner section of the metal upstream and downstream internally threaded pipe base is fitted with both ends of the filter pipe, and the thicker outer section of the internal thread is threaded with the outer threaded protrusion at the inner end of the metal upstream and downstream variable diameter externally threaded pipe section.

[0012] A corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube, the inner end face of the reducing cavity, and the outer periphery of the filter tube, allowing for independent disassembly, maintenance, and replacement of the filter tube; alternatively, both ends of the filter tube are provided with externally protruding baffles that abut against the inner end faces of the reducing cavities, with a corrosion-resistant elastic sealing ring provided between the inner end face of the externally threaded convex tube and the externally protruding baffles, providing high sealing strength and durability; or, in any of the upstream and downstream reducing externally threaded pipe sections, a corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube, the inner end face of one of the reducing cavities in the upstream and downstream internally threaded pipe bases, and the outer periphery of one end of the filter tube, while the other end of the filter tube is provided with an externally protruding baffle that abuts against the inner end face of the reducing cavity in another internally threaded pipe base, with a corrosion-resistant elastic sealing ring provided between the inner end face of the externally threaded convex tube and the externally protruding baffle. One end allows for independent disassembly, maintenance, and replacement of the filter tube, while the other end provides high sealing strength and durability.

[0013] As an optimization, the chemical precipitation method involves quantitatively placing collected high-salinity lake water into centrifuge tubes, then adding AgNO3 to the centrifuge tubes; and shaking the tubes in a shaker for 8-12 minutes to allow the Cl2 to settle. -1 The reaction with silver nitrate was complete, and the resulting white AgCl precipitate was removed by filtering the solution through a micron-sized filter membrane. Specifically, high-salinity lake water (Cl...) was used. -1 Add 5 ml of a solution (with an ion concentration of approximately 4500 mg / L) to a centrifuge tube, then add 0.11 g of AgNO3 to the centrifuge tube. The specific amount of silver nitrate added as a reactant can also be determined based on the Cl- concentration in the lake water. -1 Calculate the ion concentration and the reaction equation between silver nitrate and chloride ions, adding an appropriate amount of silver nitrate. Shake in a shaker for 6, 10, or 12 minutes to allow the chloride ions to react. -1 The reaction with silver nitrate is complete. The resulting white AgCl precipitate is removed by filtering the solution through a 0.45 or 1 micrometer filter membrane.

[0014] The applicant's existing technique for preparing gas from water samples involves placing 2 mL of filtered water sample into a clean 12 mL headspace vial (soaking in an acid bath for 24 hours to remove potential inorganic carbon, and then igniting in a muffle furnace at 500°C for 6 hours to remove potential organic carbon). Approximately 10 drops of melted pure phosphoric acid (pure phosphoric acid is solid at room temperature; it is melted in a 70°C water bath) are added. The vial is then heated at 45°C for 45 minutes on a dry thermostat to remove soluble inorganic carbon from the water. After cooling to room temperature, the vial is tightened with the gasketed cap to prevent leakage. High-purity helium is then used to purge the vial with headspace gas at a flow rate of 100 mL / min for 8 minutes to remove air and other impurities. At this point, the vial contains water sample with soluble inorganic carbon removed and high-purity helium. Inject 1 mL of reaction reagent (40 g / L potassium sulfate / sodium sulfate, 4 g high-purity potassium sulfate / sodium sulfate dissolved in 100 mL of water) into the sample vial that has been purged with He using a syringe. React for 1 hour in a 100°C water bath. Avoid adding sample to the vial walls; wipe any sample off the cap. Centrifuge at 4000 rpm for 2 minutes to remove moisture from the vial walls. Allow to equilibrate overnight at room temperature before isotope mass spectrometry analysis. This salt lake water sample contains chloride ions (Cl-). 1 The chloride ion concentration is approximately 4500 mg / L. Chloride ion concentrations in salt lakes range from several hundred to hundreds of thousands of mg / L.

[0015] The upstream and downstream sections of the injection needle capillary and the upstream thickened reducer are made of copper for ease of use, disassembly, and maintenance. The downstream thickened reducer is made of stainless steel for durability and high strength. The copper upstream and stainless steel downstream materials are used to distinguish the upstream and downstream fittings and prevent misuse. The filter tube is made of stainless steel or transparent glass. Stainless steel offers better durability, while transparent glass allows for easy observation of the filling and filtration status. The upstream and downstream sections of the injection needle capillary are made of red copper for ease of use; the upstream thickened reducer is made of brass for easy disassembly and maintenance.

[0016] As an optimization, the filter tube contains multiple loosely arranged, axially straight, parallel silver wire bundles, or multiple loosely arranged, axially intertwined, parallel silver wire bundles. The upper limit setting is 1 / (10-20) of the midpoint between the highest and lowest chloride ion concentrations in the salt lake water sample. This significantly reduces the filter tube load and extends its service life, while avoiding the adverse effects of chemical precipitation dechlorination on the soluble organic carbon isotope mass spectrometry determination of salt lake water. Typically, the chloride ion concentration in salt lake water ranges from several hundred to hundreds of thousands of mg / L. Taking the midpoint between the maximum and minimum chloride ion concentrations helps ensure and avoid unnecessary chemical precipitation dechlorination while reducing the dechlorination load on the filter tube.

[0017] The chlorine removal device used in the sample injection method for determining soluble organic carbon isotopes in salt lake water according to this invention is characterized by a centrally disconnected sample injection needle capillary. The upstream and downstream ends of the capillary are sealed and connected to upstream and downstream thickened reducing pipe fittings, respectively. The thickened ends of these fittings are then jointly sealed and connected to a filter tube containing multiple axially arranged parallel silver wire bundles. The filter tube is initially used in a forward connection with the head upstream and the tail downstream. After a certain number of filtration cycles, it is then used in a reverse connection with the tail upstream and the head downstream. In this way, during headspace intake, the sample gas introduced from the upstream section of the centrally disconnected sample injection needle capillary flows through the filter tube. The silver wire bundles react with the chlorine in the sample gas to form silver chloride, which is then fixed. When the sample gas further flows into the downstream section of the centrally disconnected sample injection needle capillary, it is chlorine-free, thus achieving a simple, reliable, and easy-to-use sample injection chlorine removal process. Using the filter tubes in both forward and reverse directions allows for full utilization of the entire silver wire bundle filter element's chlorine removal function. However, after multiple forward uses, the chlorine removal intensity decreases sequentially from upstream to downstream, resulting in progressively increasing porosity within the filter tube, thus affecting upstream chlorine removal efficiency. Conversely, using the filter tubes in reverse order after multiple forward uses leverages the advantage of still having large porosity downstream and avoids the disadvantage of small porosity upstream. This reverse method maintains the high porosity upstream and low porosity downstream, maximizing the chlorine removal efficiency of the silver wire bundle. It offers the advantage of a simple, reliable, and easy-to-implement method for removing chlorine from gas-phase samples during soluble organic carbon isotope mass spectrometry determination.

[0018] As an optimization, the upstream and downstream thickened reducing pipe fittings consist of an internally threaded pipe head seat that is sealed to the upstream and downstream ends of the capillary tube, an internally threaded pipe base that is sealed to the end of the filter tube, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. This facilitates thickening and reducing the diameter and makes it convenient to disassemble and replace the filter element and filter tube. The filter tube is a metal tube or a transparent glass tube. Metal tubes have good durability, while transparent glass tubes allow for easy observation of the filling and filtration status. The outer narrow cavity of the downstream reducing externally threaded pipe section, which is screwed into the internally threaded pipe head seat, is equipped with a downstream silver wire bundle filter element that does not reverse synchronously with the filter tube. This allows the downstream silver wire bundle filter element to filter out chlorine residue in the downstream end of the reverse filter tube and its auxiliary pipe fittings when the filter tube is used in reverse, ensuring the chlorine removal efficiency when the filter tube is used in reverse.

[0019] As an optimization, the upstream and downstream ends of the metal capillary tube are respectively riveted, welded, or otherwise fixed to the outer opening of the upstream and downstream internally threaded tube head seats. This helps to ensure the strength of the sealing connection and provides good durability.

[0020] The inner openings of the upstream and downstream internally threaded pipe heads are respectively provided with internally threaded blind holes that extend into their inner cavities. The outer ends of the upstream and downstream reducing externally threaded pipe sections have externally threaded protrusions that mate with the internally threaded blind holes. The end face of the externally threaded protrusion is sealed to the end face of the internally threaded blind hole by the corrosion-resistant elastic sealing ring. This flexible connection facilitates disassembly, cleaning, and maintenance.

[0021] The metal upstream and downstream internally threaded pipe base is provided with a variable diameter cavity that is thinner inside and thicker outside. The thinner inner section of the metal upstream and downstream internally threaded pipe base is fitted with both ends of the filter pipe, and the thicker outer section of the internal thread is threaded with the outer threaded protrusion at the inner end of the metal upstream and downstream variable diameter externally threaded pipe section.

[0022] A corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube, the inner end face of the reducing cavity, and the outer periphery of the filter tube, allowing for independent disassembly, maintenance, and replacement of the filter tube; alternatively, both ends of the filter tube are provided with externally protruding baffles that abut against the inner end faces of the reducing cavities, with a corrosion-resistant elastic sealing ring provided between the inner end face of the externally threaded convex tube and the externally protruding baffles, providing high sealing strength and durability; or, in any of the upstream and downstream reducing externally threaded pipe sections, a corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube, the inner end face of one of the reducing cavities in the upstream and downstream internally threaded pipe bases, and the outer periphery of one end of the filter tube, while the other end of the filter tube is provided with an externally protruding baffle that abuts against the inner end face of the reducing cavity in another internally threaded pipe base, with a corrosion-resistant elastic sealing ring provided between the inner end face of the externally threaded convex tube and the externally protruding baffle. One end allows for independent disassembly, maintenance, and replacement of the filter tube, while the other end provides high sealing strength and durability.

[0023] As an optimization, the upstream and downstream sections of the injection needle capillary and the upstream thickened reducer connector are made of copper for ease of use, disassembly, and maintenance. The downstream thickened reducer connector is made of stainless steel for better durability and strength. The copper upstream and stainless steel downstream materials are used to distinguish the upstream and downstream components and prevent misuse. The filter tube is made of stainless steel or transparent glass. Stainless steel offers better durability, while transparent glass allows for easy observation of the filling and filtration status. The upstream and downstream sections of the injection needle capillary are made of red copper for ease of use; the upstream thickened reducer connector is made of brass for easy disassembly and maintenance.

[0024] As an optimization, the filter tube contains multiple loosely arranged, axially aligned, parallel bundles of silver wires. The straight silver wires help ensure unobstructed filtration, while the loose arrangement enhances the chlorine removal capacity.

[0025] As an optimization, the straight silver wire is a variable diameter silver wire with successively thick and thin sections densely distributed along the axial direction. This significantly improves the scale-holding capacity and chlorine removal efficiency.

[0026] As an optimization, the filter tube contains multiple loosely arranged, axially twisted, parallel bundles of silver wire filter elements. This significantly enhances chlorine removal efficiency. The loose structure is beneficial for improving chlorine removal capacity.

[0027] In other words, this new type of instrument modification involves adding a sealed, transparent glass or metal filter tube filled with silver wire to the middle of the sample needle capillary by thickening and reducing its diameter. This filter removes residual chlorine from the sample gas. Since silver and chlorine react rapidly to form silver chloride, the silver wire must be tightly packed to ensure efficient removal of chlorine from the gas, maximizing contact between the chlorine and the silver wire. Furthermore, silicone gaskets are used to seal the connections between the filter tube and the sample needle and mass spectrometer peripherals to ensure no leakage.

[0028] After adopting the above technical solution, the sampling and dechlorination method and sampling and dechlorination device for determining soluble organic carbon isotopes in salt lake water of the present invention can give full play to the advantages of chemical precipitation for large-scale dechlorination and effectively avoid the adverse effects of excessive AgNO3 on water samples during chemical precipitation. It can also give full play to the advantages of the sampling and dechlorination device being simple, reliable and easy to implement. Furthermore, it can avoid the shortcomings of limited dechlorination capacity of filter cartridges and significantly reduce the cost of silver wire for dechlorination of filter cartridges. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the first embodiment of the sample introduction and dechlorination device used in the sample introduction and dechlorination method for determining soluble organic carbon isotopes in salt lake water according to the present invention. Figure 2 This is a schematic diagram of the second embodiment of the sample introduction and dechlorination device used in the sample introduction and dechlorination method for determining soluble organic carbon isotopes in salt lake water according to the present invention. Detailed Implementation

[0030] The present invention relates to a method for dechlorination of soluble organic carbon isotopes in salt lake water using mass spectrometry. The method involves measuring the chloride ion concentration of the salt lake water sample. If the chloride ion concentration is equal to or lower than the upper limit set value for the reasonable lifespan of the dechlorination device described below, a gas sample prepared from the salt lake water sample is passed through the dechlorination device. This device consists of a discontinuous capillary tube with its upstream and downstream ends sealed and connected to upstream and downstream thickened reducing pipe fittings. The thickened ends of these fittings are then jointly sealed and connected to multiple internally mounted... The filter tube uses axially parallel silver wire bundle filter elements. The filter tube is initially used in a forward connection with the head upstream and the tail downstream. After a certain number of filtration cycles, it is then used in a reverse connection with the tail upstream and the head downstream. In this way, when the sample gas is introduced through the upstream section of the middle-broken sample needle capillary during headspace intake, the silver wire bundle filter elements react with the chlorine in the sample gas to form silver chloride, which is then fixed. When the sample gas further flows into the downstream section of the middle-broken sample needle capillary, it will not contain chlorine, thus achieving a simple, reliable, and easy sample dechlorination. Using the filter tubes in both forward and reverse directions allows for full utilization of the entire silver wire bundle filter element's chlorine removal function. However, after multiple forward uses, the chlorine removal intensity decreases sequentially from upstream to downstream, resulting in progressively increasing porosity within the filter tube, thus affecting upstream chlorine removal efficiency. Conversely, using the filter tubes in reverse order after multiple forward uses leverages the advantage of still having large porosity downstream and avoids the disadvantage of small porosity upstream. This reverse method maintains the high porosity upstream and low porosity downstream, maximizing the chlorine removal efficiency of the silver wire bundle. It offers the advantage of a simple, reliable, and easy-to-implement method for removing chlorine from gas-phase samples during soluble organic carbon isotope mass spectrometry determination.

[0031] If the chloride ion concentration in the water sample is higher than the set value, the following chemical precipitation method is first used to reduce the chloride ion concentration in the water sample to below the upper limit set value. Then, the gas sample made from the dechlorinated water sample is passed through the above-mentioned sample introduction dechlorination device for dechlorination. The chemical precipitation method involves adding an appropriate amount of AgNO3 to a quantitative salt lake water sample, mixing and reacting thoroughly, and filtering to remove the white AgCl precipitate. The appropriate amount is greater than the amount of AgNO3 required to reduce the chloride ion concentration in the water sample to the set value and less than the amount of AgNO3 required to reduce the chloride ion concentration in the water sample to zero. In this way, by first reducing the chloride ion concentration in the water sample to below the upper limit set value using chemical precipitation, and then passing the gas sample made from the dechlorinated water sample through the above-mentioned sample introduction dechlorination device for dechlorination, the advantages of large-volume dechlorination by chemical precipitation can be fully utilized while effectively avoiding the adverse effects of excessive AgNO3 on the water sample during chemical precipitation. It also fully utilizes the advantages of the sample introduction dechlorination device being simple, reliable, and easy to implement, and avoids the limitation of the dechlorination capacity of filter cartridges and significantly reduces the cost of silver wires for dechlorination of filter cartridges.

[0032] Specifically, the chemical precipitation method involves quantitatively placing a salt lake water sample into a centrifuge tube, adding an appropriate amount of AgNO3, and shaking to allow the Cl to settle. -1The reaction with silver nitrate is complete, and the white precipitate of AgCl is removed by filtration. The upstream and downstream thickened reducing pipe fittings consist of an internally threaded pipe head seat that is sealed to the upstream and downstream ends of the capillary tube, an internally threaded pipe base that is sealed to the end of the filter tube, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. The downstream reducing externally threaded pipe section is fitted with a downstream silver wire bundle filter element that does not reverse synchronously with the filter tube in the outer narrow cavity of the downstream internally threaded pipe head seat. The filter tube is a metal tube or a transparent glass tube.

[0033] More specifically, the upstream and downstream ends of the metal capillary tube are riveted or welded to the outer openings of the upstream and downstream internally threaded pipe head seats. The inner openings of the upstream and downstream internally threaded pipe head seats are each provided with internally threaded blind holes extending into their inner cavities. The outer ends of the upstream and downstream reducing externally threaded pipe sections have externally threaded protrusions that mate with the internally threaded blind holes. The end face of the externally threaded protrusion is sealed to the end face of the internally threaded blind hole via the corrosion-resistant elastic sealing ring. The metal upstream and downstream internally threaded pipe base has a reducing cavity with a narrower inner diameter and a wider outer diameter. The metal upstream and downstream internally threaded pipe base also has a narrower inner section cavity that fits into both ends of the filter pipe and a wider inner thread section cavity that fits into the inner end of the externally threaded protrusion of the metal upstream and downstream externally threaded pipe section. A corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded protrusion of the inner end of the reducing cavity and the outer circumference of the filter pipe; alternatively, both ends of the filter pipe have externally convex baffles that abut against the inner end faces of the reducing cavity, and the internally convex externally threaded protrusion... A corrosion-resistant elastic sealing ring is provided between the pipe end face and the externally protruding baffle; or a corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex pipe on the inner side of any of the upstream and downstream reducing externally threaded pipe sections, the inner end face of a reducing cavity in the upstream and downstream internally threaded pipe base, and the outer periphery of one end of the filter pipe, and an externally protruding baffle is provided at the other end of the filter pipe to abut against the inner end face of the reducing cavity of another internally threaded pipe base, and a corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex pipe on the inner side and the externally protruding baffle.

[0034] Specifically, the chemical precipitation method involves quantitatively placing collected high-salinity lake water into centrifuge tubes, then adding AgNO3 to the tubes; and shaking the tubes for 8-12 minutes to allow the Cl2 to settle. -1 The reaction with silver nitrate is complete, and the resulting white AgCl precipitate is removed by filtering the solution using a micron-sized filter membrane. The upstream and downstream sections of the injection needle capillary and the upstream thickened reducer connector are made of copper, while the downstream thickened reducer connector is made of stainless steel. The filter tube is made of stainless steel or transparent glass. The upstream and downstream sections of the injection needle capillary are made of red copper, and the upstream thickened reducer connector is made of brass.

[0035] Specifically, the chemical precipitation method involves quantitatively placing collected high-salinity lake water into centrifuge tubes, then adding AgNO3 to the tubes; and shaking the tubes for 8-12 minutes to allow the Cl2 to settle. -1 The reaction with silver nitrate is complete, and the resulting solution is filtered through a micron-sized membrane to remove the white AgCl precipitate. More specifically, high-salinity lake water (Cl...) is used. -1 Add 5 ml of a solution (with an ion concentration of approximately 4500 mg / L) to a centrifuge tube, then add 0.11 g of AgNO3 to the centrifuge tube. The specific amount of silver nitrate added as a reactant can also be determined based on the Cl- concentration in the lake water. -1 Calculate the ion concentration and the reaction equation between silver nitrate and chloride ions, adding an appropriate amount of silver nitrate. Shake in a shaker for 6, 10, or 12 minutes to allow the chloride ions to react. -1 The reaction with silver nitrate was complete. The resulting white AgCl precipitate was removed by filtering the solution through a 0.45 or 1 micrometer filter membrane. This sample contained chloride ions (Cl-). 1 The chloride ion concentration is approximately 4500 mg / L. This salt lake water sample contains Cl- ions. 1 The chloride ion concentration is approximately 4500 mg / L. Chloride ion concentrations in salt lakes range from several hundred to hundreds of thousands of mg / L.

[0036] The applicant's existing technique for preparing gas from water samples involves placing 2 mL of filtered water sample into a clean 12 mL headspace vial (soaking in an acid bath for 24 hours to remove potential inorganic carbon, and then igniting in a muffle furnace at 500°C for 6 hours to remove potential organic carbon). Approximately 10 drops of melted pure phosphoric acid (pure phosphoric acid is solid at room temperature; it is melted in a 70°C water bath) are added. The vial is then heated at 45°C for 45 minutes on a dry thermostat to remove soluble inorganic carbon from the water. After cooling to room temperature, the vial is tightened with the gasketed cap to prevent leakage. High-purity helium is then used to purge the vial with headspace gas at a flow rate of 100 mL / min for 8 minutes to remove air and other impurities. At this point, the vial contains water sample with soluble inorganic carbon removed and high-purity helium. Inject 1 mL of reaction reagent (40 g / L potassium sulfate / sodium, 4 g high-purity potassium sulfate / sodium dissolved in 100 mL of water) into the sample vial that has been purged with He using a syringe. React for 1 hour in a 100°C water bath. Avoid adding sample to the vial walls and wipe any sample off the cap. Centrifuge at 4000 rpm for 2 minutes to remove moisture from the inner wall of the vial. After equilibration at room temperature overnight, determine the isotope mass spectrometry results.

[0037] The upstream and downstream sections of the injection needle capillary and the upstream thickened reducer are made of copper for ease of use, disassembly, and maintenance. The downstream thickened reducer is made of stainless steel for durability and high strength. The copper upstream and stainless steel downstream materials are used to distinguish the upstream and downstream fittings and prevent misuse. The filter tube is made of stainless steel or transparent glass. Stainless steel offers better durability, while transparent glass allows for easy observation of the filling and filtration status. The upstream and downstream sections of the injection needle capillary are made of red copper for ease of use; the upstream thickened reducer is made of brass for easy disassembly and maintenance.

[0038] Specifically, the filter tube contains multiple loosely arranged, axially straight, parallel silver wire bundles, or multiple loosely arranged, axially intertwined, parallel silver wire bundles. The upper limit setting is 1 / (10-20) of the midpoint between the highest and lowest chloride ion concentrations in the salt lake water sample. This significantly reduces the filter tube load and extends its service life, while avoiding the adverse effects of chemical precipitation dechlorination on the determination of soluble organic carbon isotopes in the salt lake water. Typically, the chloride ion concentration in salt lake water ranges from several hundred to hundreds of thousands of mg / L. Taking the midpoint between the maximum and minimum chloride ion concentrations helps ensure and avoid unnecessary chemical precipitation dechlorination while reducing the dechlorination load on the filter tube.

[0039] Example 1, as Figure 1 As shown, the chlorine removal device used in the sample injection method for determining soluble organic carbon isotopes in salt lake water according to the present invention consists of an upstream and downstream section 11 and 12 of a discontinuous injection needle capillary, which are respectively sealed and connected to upstream and downstream thickened reducing pipe fittings. The thickened ends of the upstream and downstream thickened reducing pipe fittings are then jointly sealed and connected to a filter tube 2 containing multiple axially parallel silver wire bundle filter elements. The filter tube 2 is initially used for filtration with the head upstream and the tail downstream in a forward connection. After a certain number of filtration cycles, it is then used for filtration with the tail upstream and the head downstream in a reverse connection. In this way, when the sample gas introduced from the upstream section of the discontinuous injection needle capillary passes through the filter tube during headspace intake, the silver wire bundle filter elements react with the chlorine in the sample gas to form silver chloride, which is then fixed. When the sample gas further flows into the downstream section of the discontinuous injection needle capillary, it will not contain chlorine, thus achieving a simple, reliable, and easy-to-use sample injection chlorine removal device. Using the filter tubes in both forward and reverse directions allows for full utilization of the entire silver wire bundle filter element's chlorine removal function. However, after multiple forward uses, the chlorine removal intensity decreases sequentially from upstream to downstream, resulting in progressively increasing porosity within the filter tube, thus affecting upstream chlorine removal efficiency. Conversely, using the filter tubes in reverse order after multiple forward uses leverages the advantage of still having large porosity downstream and avoids the disadvantage of small porosity upstream. This reverse method maintains the high porosity upstream and low porosity downstream, maximizing the chlorine removal efficiency of the silver wire bundle. It offers the advantage of a simple, reliable, and easy-to-implement method for removing chlorine from gas-phase samples during soluble organic carbon isotope mass spectrometry determination.

[0040] Specifically, the upstream and downstream thickened reducing pipe fitting consists of an internally threaded pipe head seat that is sealed to the upstream and downstream sections 11 and 12 of the capillary tube, an internally threaded pipe base that is sealed to the filter tube 2, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. The downstream reducing externally threaded pipe section 52 is fitted with the downstream internally threaded pipe head seat 32, and a downstream silver wire bundle filter element that does not switch forward and reverse synchronously with the filter tube is provided in the outer fine cavity.

[0041] More specifically, the upstream and downstream sections 11 and 12 of the metal capillary tube are riveted or welded to the outer openings of the upstream and downstream internally threaded pipe head seats 31 and 32, respectively. The inner openings of the upstream and downstream internally threaded pipe head seats 31 and 32 are respectively provided with internally threaded blind holes that extend into their inner cavities. The outer ends of the upstream and downstream reducing externally threaded pipe sections 51 and 52 have externally threaded protrusions that are threaded into the internally threaded blind holes. The end face of the externally threaded protrusions is sealed to the end face of the internally threaded blind holes through the corrosion-resistant elastic sealing ring.

[0042] The upstream and downstream internally threaded pipe bases 41 and 42 are provided with a variable diameter cavity with a narrow inner side and a wide outer side. The narrow inner section cavity of the upstream and downstream internally threaded pipe bases 41 and 42 is fitted with both ends of the filter pipe 2, and the wide outer section cavity is threaded with the inner end externally threaded convex pipe of the upstream and downstream externally threaded pipe sections 51 and 52. A corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube, the inner end face of the reducing cavity, and the outer periphery of the filter tube 2; alternatively, both ends of the filter tube may have externally protruding baffles that abut against the inner end faces of the reducing cavity, and a corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube and the externally protruding baffles; alternatively, any one of the upstream and downstream reducing externally threaded pipe sections may have a corrosion-resistant elastic sealing ring provided between the inner end face of the externally threaded convex tube, the inner end face of one of the reducing cavities in the upstream and downstream internally threaded pipe bases, and the outer periphery of one end of the filter tube, and the other end of the filter tube may have an externally protruding baffle that abuts against the inner end face of the reducing cavity of another internally threaded pipe base, and a corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded convex tube and the externally protruding baffles.

[0043] Specifically, the upstream and downstream sections 11 and 12 of the injection needle capillary and the upstream thickened reducer fitting are made of copper, while the downstream thickened reducer fitting and filter tube 2 are made of stainless steel. The upstream copper and downstream stainless steel materials are used to distinguish the upstream and downstream fittings and prevent them from being mixed up. More specifically, the upstream and downstream sections of the injection needle capillary are made of red copper, and the upstream thickened reducer fitting is made of brass.

[0044] Specifically, the filter tube 2 contains a bundle of loosely arranged, axially straight, parallel silver wires 61. Alternatively, the straight silver wires can be further preferably variable diameter silver wires with successively thick and thin sections densely distributed along the axial direction.

[0045] Example 2, as Figure 2 As shown, the sample dechlorination device used in the sample injection method for determining soluble organic carbon isotopes in salt lake water of the present invention differs from that in Example 1 above in that: the filter tube 2 contains multiple loosely arranged axially rope-like silver wire bundles 69.

[0046] In other words, this new type of instrument modification involves adding a sealed, transparent glass or metal filter tube filled with silver wire to the middle of the sample needle capillary by thickening and reducing its diameter. This filter removes residual chlorine from the sample gas. Since silver and chlorine react rapidly to form silver chloride, the silver wire must be tightly packed to ensure efficient removal of chlorine from the gas, maximizing contact between the chlorine and the silver wire. Furthermore, silicone gaskets are used to seal the connections between the filter tube and the sample needle and mass spectrometer peripherals to ensure no leakage.

[0047] In summary, the sampling and dechlorination method and device for determining soluble organic carbon isotopes in salt lake water according to the present invention can fully utilize the advantages of chemical precipitation for large-scale dechlorination and effectively avoid the adverse effects of excessive AgNO3 on the water sample during chemical precipitation. It can also fully utilize the advantages of the simple, reliable and easy-to-use sampling and dechlorination device, and avoid the shortcomings of limited dechlorination capacity of filter cartridges and significantly reduce the cost of silver wire for dechlorination of filter cartridges.

Claims

1. A method for sample injection and dechlorination for the determination of soluble organic carbon isotopes in salt lake water by mass spectrometry, characterized in that... Chloride ion concentration is measured on salt lake water samples. If the chloride ion concentration of the salt lake water sample is equal to or lower than the upper limit setting value that allows the following sample dechlorination device to dechlorinate within its reasonable lifespan, the gas sample made from the salt lake water sample is dechlorinated by the following sample dechlorination device. The sample dechlorination device consists of a sample needle capillary tube with the upstream and downstream ends sealed and connected to upstream and downstream thickened reducing pipe fittings, respectively. The thickened pipe ends of the upstream and downstream thickened reducing pipe fittings are then jointly sealed and connected to a filter tube containing multiple axially parallel silver wire bundle filter elements. The filter tube is initially used for filtration with the head upstream and the tail downstream in a forward connection. After a certain number of filtration cycles, it is then used for filtration with the tail upstream and the head downstream in a reverse connection. If the chloride ion concentration in the water sample is higher than the upper limit setting, the following chemical precipitation method is first used to reduce the chloride ion concentration in the water sample to below the upper limit setting. Then, the gas sample made from the dechlorinated water sample is passed through the above-mentioned sample introduction dechlorination device to remove chloride. The chemical precipitation method involves adding an appropriate amount of AgNO3 to a quantitative salt lake water sample, mixing and reacting thoroughly, and filtering to remove the white AgCl precipitate. The appropriate amount is the amount of AgNO3 greater than the amount needed to reduce the chloride ion concentration in the water sample to the upper limit setting and less than the amount needed to reduce the chloride ion concentration in the water sample to zero.

2. The method for sample injection and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 1, characterized in that... The chemical precipitation method involves quantitatively placing a salt lake water sample into a centrifuge tube, adding an appropriate amount of AgNO3, and shaking to allow the Cl to settle. -1 After reacting completely with silver nitrate, the white precipitate of AgCl was removed by filtration. The upstream and downstream thickened reducing pipe fitting consists of an internally threaded pipe head seat that is sealed to the upstream and downstream ends of the capillary tube, an internally threaded pipe base that is sealed to the end of the filter tube, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. The downstream reducing externally threaded pipe section is fitted with the downstream internally threaded pipe head seat in the outer narrow cavity, and a downstream silver wire bundle filter element that does not reverse synchronously with the filter tube is provided. The filter tube is a metal tube or a transparent glass tube.

3. The method for sample introduction and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 2, characterized in that... The upstream and downstream ends of the metal capillary tube are respectively riveted or welded to the outer pipe opening of the upstream and downstream internally threaded metal pipe head seat. The inner opening of the metal upstream and downstream internally threaded pipe head seat is provided with an internally threaded blind hole that extends into its inner cavity. The outer end of the metal upstream and downstream reducing externally threaded pipe section has an outer end externally threaded protrusion that is screwed into the internally threaded blind hole. The end face of the outer end externally threaded protrusion is sealed to the end face of the internally threaded blind hole through the corrosion-resistant elastic sealing ring. The metal upstream and downstream internally threaded pipe base is provided with a variable diameter cavity that is thinner inside and thicker outside. The metal upstream and downstream internally threaded pipe base is provided with an inner thin section cavity that fits with both ends of the filter pipe and an inner thread outer thick section cavity that fits with the inner end external threaded protrusion of the metal upstream and downstream variable diameter externally threaded pipe section.

4. The method for sample injection and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 3, characterized in that... A corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded protruding tube, the inner end face of the variable diameter cavity, and the outer periphery of the filter tube.

5. The method for sample injection and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 3, characterized in that... The filter tube has externally protruding baffles at both ends that abut against the inner end face of the variable diameter cavity, and a corrosion-resistant elastic sealing ring is provided between the inner end of the externally threaded protruding tube and the externally protruding baffle.

6. The method for sample introduction and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 3, characterized in that... A corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex tube on the inner side of any one of the upstream and downstream reducing externally threaded pipe sections, the inner end face of a reducing cavity in one of the upstream and downstream internally threaded pipe bases, and the outer periphery of one end of the filter tube. The other end of the filter tube is provided with an externally convex baffle that abuts against the inner end face of the reducing cavity of another internally threaded pipe base. A corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex tube on the inner side and the externally convex baffle.

7. The method for sample introduction and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 1, characterized in that... The chemical precipitation method involves quantitatively placing collected high-salinity lake water into centrifuge tubes, then adding AgNO3 to the tubes; and shaking the tubes for 8-12 minutes to allow the Cl2 to settle. -1 The reaction with silver nitrate was completed, and the resulting white AgCl precipitate was removed by filtering the solution through a micron-sized filter membrane. The upstream and downstream sections of the injection needle capillary and the upstream thickened reducer connector are made of copper, while the downstream thickened reducer connector is made of stainless steel; the filter tube is made of stainless steel or transparent glass.

8. The method for sample injection and dechlorination for determining soluble organic carbon isotopes in salt lake water according to claim 1, characterized in that... The filter tube contains multiple loosely arranged, axially straight, parallel silver wire bundles, or the filter tube contains multiple loosely arranged, axially rope-like, intertwined, parallel silver wire bundles; the upper limit setting value is 1 / (10-20) of the median value between the highest and lowest chloride ion concentrations in the salt lake water sample.

9. The sample introduction dechlorination device used in the sample introduction and dechlorination method for determining soluble organic carbon isotopes in salt lake water according to claim 1, characterized in that... The upstream and downstream ends of the discontinuous injection needle capillary are sealed and connected to the upstream and downstream thickened reducing tube fittings, respectively. The thickened tube ends of the upstream and downstream thickened reducing tube fittings are then jointly sealed and connected to the filter tube containing multiple axially parallel silver wire bundle filter elements. The filter tube is first used for filtration with the head upstream and the tail downstream in a forward connection. After a certain number of filtrations, it is then used for filtration with the tail upstream and the head downstream in a reverse connection.

10. The sample introduction dechlorination device according to claim 9, characterized in that... The upstream and downstream thickened reducing pipe fitting consists of an internally threaded pipe head seat that is sealed to the upstream and downstream ends of the capillary tube, an internally threaded pipe base that is sealed to the end of the filter tube, and a reducing externally threaded pipe section whose two ends are respectively sealed and screwed to the internally threaded pipe holes of the internally threaded pipe head seat and the internally threaded pipe base by corrosion-resistant elastic sealing rings. The downstream reducing externally threaded pipe section is fitted with the downstream internally threaded pipe head seat in the outer narrow cavity, and a downstream silver wire bundle filter element that does not reverse synchronously with the filter tube is provided. The filter tube is a metal tube or a transparent glass tube.

11. The sample introduction dechlorination device according to claim 10, characterized in that... The upstream and downstream ends of the metal capillary tube are respectively riveted or welded to the outer pipe opening of the upstream and downstream internally threaded metal pipe head seat. The inner opening of the metal upstream and downstream internally threaded pipe head seat is provided with an internally threaded blind hole that extends into its inner cavity. The outer end of the metal upstream and downstream reducing externally threaded pipe section has an outer end externally threaded protrusion that is screwed into the internally threaded blind hole. The end face of the outer end externally threaded protrusion is sealed to the end face of the internally threaded blind hole through the corrosion-resistant elastic sealing ring. The metal upstream and downstream internally threaded pipe base is provided with a variable diameter cavity that is thinner inside and thicker outside. The metal upstream and downstream internally threaded pipe base is provided with an inner thin section cavity that fits with both ends of the filter pipe and an inner thread outer thick section cavity that fits with the inner end external threaded protrusion of the metal upstream and downstream variable diameter externally threaded pipe section.

12. The sample introduction dechlorination device according to claim 11, characterized in that... A corrosion-resistant elastic sealing ring is provided between the inner end face of the externally threaded protruding tube, the inner end face of the variable diameter cavity, and the outer periphery of the filter tube.

13. The sample introduction dechlorination device according to claim 11, characterized in that... The filter tube has externally protruding baffles at both ends that abut against the inner end face of the variable diameter cavity, and a corrosion-resistant elastic sealing ring is provided between the inner end of the externally threaded protruding tube and the externally protruding baffle.

14. The sample introduction dechlorination device according to claim 11, characterized in that... A corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex tube on the inner side of any one of the upstream and downstream reducing externally threaded pipe sections, the inner end face of a reducing cavity in one of the upstream and downstream internally threaded pipe bases, and the outer periphery of one end of the filter tube. The other end of the filter tube is provided with an externally convex baffle that abuts against the inner end face of the reducing cavity of another internally threaded pipe base. A corrosion-resistant elastic sealing ring is provided between the end face of the externally threaded convex tube on the inner side and the externally convex baffle.

15. The sample introduction dechlorination device according to claim 9, characterized in that... The upstream and downstream sections of the injection needle capillary and the upstream thickened reducer connector are made of copper, while the downstream thickened reducer connector is made of stainless steel; the filter tube is made of stainless steel or transparent glass.

16. The sample introduction dechlorination device according to claim 9, characterized in that... The filter tube contains multiple loosely arranged, axially straight, parallel silver wire bundles, or multiple loosely arranged, axially rope-like, intertwined, parallel silver wire bundles.

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