Karl Fischer method automatic sample injection moisture determination system and Karl Fischer method automatic sample injection moisture determination method

Abstract

According to the system and the method, a titration cup is purged through a shielding gas inlet and a shielding gas outlet, a solvent is added into the titration cup, liquid in the titration cup passes through a sample introduction cavity through a sample introduction circulating pump, then is pumped back and drips into the titration cup, and the titration cup is subjected to automatic sample introduction; the method comprises the following steps of: driving a sample injection needle through a transverse guide rail to realize the circulation of a solvent in a titration cup, a sample injection cavity and a pipeline system thereof, realizing a pre-titration and drifting program, driving the sample injection needle through the transverse guide rail on the basis, cleaning the solvent, the balance solution and the sample on the sample injection needle, subsequently sucking a liquid sample with a set volume through the sample injection needle, and injecting the liquid sample into the sample injection cavity; and titrating to obtain the water content of the sample, controlling to discharge waste liquid, and starting the determination of the next sample.

Description

Technical Field

[0001] The invention belongs to the technical field of water content determination, and in particular relates to a Karl Fischer automatic sampling water content determination system and method. Background Art

[0002] The Karl Fischer method has the advantages of fast analysis speed, accurate measurement, high sensitivity and low detection limit, and has become a classic method for measuring moisture in various industries. According to its titration principle, it is divided into coulometric method and volumetric method. The coulometric method uses electrolysis to produce elemental iodine, which reacts quantitatively with water. The volumetric method uses the addition of a certain concentration of Karl Fischer solution to achieve quantitative analysis.

[0003] At present, the headspace principle is often used to achieve automatic sample injection. The principle is to use a heating furnace to heat the water in the sample into a gaseous state, carry it into the titration cup with a carrier gas for absorption, and then use the coulometric method or volumetric method for analysis. This automatic sampler is called a headspace Karl Fischer moisture sample heating processor, or a heating furnace automatic sampler.

[0004] The heating furnace autosampler pre-separates the sample matrix and water by heating, thereby eliminating the interference of the sample matrix, reducing the probability of side reactions, and improving the specificity and accuracy of water measurement. However, for samples that can form azeotropes or form steam under heating conditions, the heating furnace autosampler cannot achieve injection. This type of sample will evaporate and condense in the needle or transmission pipeline, causing the needle or pipeline to be blocked. Therefore, the heating furnace autosampler cannot achieve automatic injection analysis of water in organic solvents such as methanol and ethanol. Karl Fischer coulometric method or volumetric method generally uses methanol water standard substances or pure water to calibrate the system, quality control, etc., and the heating furnace autosampler cannot achieve automatic injection.

[0005] Based on the above problems, a Karl Fischer automatic sampling water content determination system and method are needed to realize direct sampling analysis of liquid samples and post-dissolution analysis of solid samples. Summary of the invention

[0006] In order to overcome the above problems, the inventors have conducted intensive research and designed a Karl Fischer method automatic sampling water content determination system and method, in which the titration cup is purged through the protective gas inlet and outlet, solvent is added to the titration cup, and the liquid in the titration cup is pumped back through the sampling chamber by the sampling circulation pump and dripped into the titration cup, so that the solvent circulates in the titration cup and the sampling chamber and its pipeline system, and the pre-titration and drift program is realized. On this basis, the sampling needle is driven by the transverse guide rail to complete the solvent cleaning, equilibrium solution cleaning and sample cleaning of the sampling needle, and then a set volume of liquid sample is sucked by the sampling needle and injected into the sampling chamber; then the water content of the sample is obtained by titration, the waste liquid is controlled to be discharged, and the determination of the next sample is started, thereby completing the present invention.

[0007] Specifically, the object of the present invention is to provide a Karl Fischer method automatic sampling water content determination system, the system comprising:

[0008] A titration cup 5, a sample injection chamber 10 and a sample injection circulation pump 6 connected by a pipeline;

[0009] The titration operation is performed in the titration cup 5, and the injection chamber 10 is a closed chamber. The liquid in the titration cup 5 is pumped back through the injection chamber 10 by the injection circulation pump 6 and drips into the titration cup 5, thereby realizing the circulation of the solvent in the titration cup 5, the injection chamber 10 and their pipeline system.

[0010] The system further comprises a sample injection needle 9, which is fixed on a sample injection needle seat 8, and the extraction and ejection operations of the sample injection needle 9 are controlled by the sample injection needle seat 8;

[0011] The injection needle seat 8 is fixed on the automatic injection tower 7, and the injection needle seat 8 can rise and fall in the automatic injection tower 7, thereby driving the injection needle 9 to rise and fall.

[0012] The system further comprises a transverse guide rail 12, and the automatic injection tower 7 can reciprocate on the transverse guide rail 12.

[0013] The injection chamber 10 is arranged below the transverse guide rail 12.

[0014] A waste liquid chamber 13 and a sample tray 15 are also provided below the transverse guide rail 12; sample bottles and cleaning solvent bottles are placed on the sample tray 15;

[0015] Under the driving control of the transverse guide rail 12 and the automatic injection tower 7, the injection needle 9 can be inserted into the injection chamber 10, the waste liquid chamber 13, the sample bottle and the cleaning solvent bottle in any order, and under the driving control of the injection needle seat 8, the extraction and ejection operations are performed;

[0016] Preferably, the waste liquid chamber 13 is a closed chamber.

[0017] The system further comprises a waste liquid pump 11 and a waste liquid bottle 14.

[0018] One end of the waste liquid pump 11 is connected to the bottom of the titration cup 5 through a pipeline, and the other end of the waste liquid pump 11 is connected to the waste liquid chamber 13 through a pipeline;

[0019] The waste liquid chamber 13 is connected to the waste liquid bottle 14 through a pipeline.

[0020] The system further comprises a protective gas inlet and outlet 4, which are arranged in parallel, all penetrate into the titration cup 5, and are all located above the liquid surface.

[0021] The system further comprises a volumetric liquid feeding device 1 and an electrolysis generating device;

[0022] Wherein, when the system uses the volumetric method, the volumetric method liquid feeding device 1 is connected to the titration cup 5 through a pipeline;

[0023] When the system uses the coulometric method, the electrolysis generating device is electrically connected to the titration cup 5 .

[0024] The present invention also provides a method for determining water content by automatic sampling using the Karl Fischer method.

[0025] The method is implemented by the Karl Fischer automatic sampling water determination system described above;

[0026] Preferably, the method comprises the following steps:

[0027] Purging, adding solvent, pre-titration and drift, needle washing and sampling, titration analysis, and draining waste liquid.

[0028] In the pre-titration and drift step, the sample circulation pump 6 is started, so that the solvent in the titration cup 5 drips back into the titration cup 5 after passing through the sample injection chamber 10, so that the solvent circulates in the titration cup and the sample injection chamber and its pipeline system;

[0029] Preferably, when the volumetric method is used, the system is maintained at a titration endpoint equilibrium state by the volumetric method liquid feeding device 1;

[0030] When the coulometric method is used, the system is maintained at the equilibrium state at the titration endpoint by electrolysis;

[0031] More preferably, the system realizes pre-titration when the equilibrium state is reached at the titration endpoint, and maintains the equilibrium state for a certain period of time to complete the determination of the system drift value.

[0032] The needle washing and sampling steps specifically include the following sub-steps:

[0033] Sub-step 1, the automatic injection tower 7 moves to the cleaning solvent bottle position of the sample tray 15 through the transverse guide rail 12, the injection needle seat 8 descends from the highest position, the injection needle 9 is inserted into the cleaning solvent bottle, and the set volume of the cleaning solvent is absorbed. The injection needle seat 8 rises to the highest position, washes the injection needle according to the full volume or partial volume, and moves to the waste liquid chamber 13 to inject the needle washing waste liquid into the waste liquid bottle 14;

[0034] Sub-step 2, the automatic injection tower 7 moves to the injection chamber 10, absorbs the equilibrium solution in the titration cup 5, and eliminates the water in the injection needle;

[0035] Sub-step 3, the automatic injection tower 7 moves to the liquid sample position, and uses the liquid sample to clean the injection needle 9, that is, the injection needle 9 draws and ejects in the sample bottle to achieve further cleaning and remove bubbles;

[0036] Sub-step 4, the injection needle 9 draws a set volume of liquid sample and injects it into the injection chamber 10;

[0037] Preferably, in the above sub-step 1, sub-step 2 and sub-step 3, the number of solvent washing, equilibrium solution washing and sample washing can be set to 0 to 10 times, and each washing volume can be set to 0% to 100%;

[0038] Preferably, in the above sub-step 4, the sample volume can be set to 0.001 mL to 1.000 mL;

[0039] Preferably, when the water content of a solid sample needs to be determined, the equilibrium solution in the titration cup 5 is sucked by the injection needle 9 to fully extract and dissolve the water in the solid sample, or anhydrous methanol is used to extract and dissolve the solid sample, and then the sample is injected through the above sub-step 4.

[0040] Wherein, in the titration analysis step, when the Karl Fischer volumetric method is used, the volumetric method liquid feeding device 1 is started to titrate to the end point, and the water content of the sample is obtained by calculating the consumed volume, titration time and drift value;

[0041] When the Karl Fischer coulometric method is used, the electrolytic generator is started and titrated to the endpoint, and the water content of the sample is obtained by calculating the electrolytic coulometric value, titration time and drift value.

[0042] The beneficial effects of the present invention include:

[0043] (1) According to the present invention, the automatic sampling system and method for determining water content by Karl Fischer method can realize automatic sampling of liquid by Karl Fischer coulometric method and volumetric method;

[0044] (2) The Karl Fischer automatic sampling water content determination system and method provided by the present invention are suitable for direct sampling analysis of liquid samples, and can also be used for analysis of solid samples after dissolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The schematic diagram of the structure of the automatic sampling water content determination system of the Karl Fischer volumetric method of the present application is shown;

[0046] Figure 2 The schematic diagram of the structure of the automatic sampling water content determination system of the Karl Fischer coulometric method of the present application is shown;

[0047] Figure 3 A schematic diagram showing the cavity structure of the sampling cavity or waste liquid cavity of the automatic sampling water determination system of the Karl Fischer method of the present application;

[0048] Figure 4 A schematic diagram showing the workflow of the automatic sampling water determination method of the Karl Fischer method of the present application is shown.

[0049] Description of Reference Numerals

[0050] 1-Volumetric feeding device

[0051] 2-Solvent bottle

[0052] 3-Solvent pump

[0053] 4-Protective gas inlet and outlet

[0054] 5-Titration cup

[0055] 6-Injection circulation pump

[0056] 7-Automatic injection tower

[0057] 8-Injection needle seat

[0058] 9-Injection needle

[0059] 10-Injection chamber

[0060] 11-Waste pump

[0061] 12- Horizontal guide rail

[0062] 13-Waste chamber

[0063] 14-Waste liquid bottle

[0064] 15-Sample tray

[0065] 16-Sealing nut

[0066] 17-Sealing gasket

[0067] 18-Cavity Base DETAILED DESCRIPTION

[0068] The present invention will be further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present invention will become more clear and distinct.

[0069] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0070] The present invention provides a Karl Fischer method automatic sampling water content determination system, such as Figure 1 and Figure 2 As shown in , the system includes: a titration cup 5, a sample injection chamber 10 and a sample injection circulation pump 6 connected by a pipeline;

[0071] The titration operation is performed in the titration cup 5, and the injection chamber 10 is a closed chamber. The liquid in the titration cup 5 is pumped back through the injection chamber 10 by the injection circulation pump 6 and drips into the titration cup 5, thereby realizing the circulation of the solvent in the titration cup 5, the injection chamber 10 and their pipeline system.

[0072] In the prior art, the common sample port of the titration cup is far from the liquid surface (more than 5 cm), which requires a longer needle. However, the longer needle is prone to bending and damage when inserted into the titration cup. In addition, the sample port of the titration cup has limited space and cannot accommodate an automatic sampling device. Moreover, the sizes of the titration cups for the Karl Fischer coulometric method and the volumetric method are different, and the fixing methods are also different. It is impossible to design an automatic sampling device for the titration cup that is compatible with both. Based on this, the above-mentioned separate sample chamber 10 is designed in the present application, which makes the design of a shorter needle length possible, provides sufficient design space for the sampling device, and achieves compatibility with the Karl Fischer coulometric method and the volumetric method. Furthermore, in order to achieve the connection between the sample chamber and the titration cup and transfer the sample in the sample chamber into the titration cup, an internal circulation system is also designed and provided in the present application.

[0073] Preferably, the side of the sample injection chamber 10 is connected with two pipelines, wherein the pipeline located at the bottom is connected to the titration cup 5, and the pipeline located at the top is connected to the sample injection circulation pump 6, thereby forming an internal circulation system.

[0074] In a preferred embodiment, the system also includes an injection needle 9, which is fixed on the injection needle seat 8, and the extraction and ejection operations of the injection needle 9 are controlled by the injection needle seat 8; preferably, a stepper motor, an optical coupling limiter and a longitudinal guide rail are arranged in the injection needle seat 8, so that the extraction and ejection operations of the injection needle 9 are realized by providing power through the stepper motor and providing a limit through the guide rail, and the extraction and ejection operations of the injection needle 9 are provided. The optical coupling limiter is provided to provide a precise control amount for the extraction and ejection operations of the injection needle 9, that is, the driving distance during extraction and ejection can be controlled, and the optical coupling limiter is used to ensure timely and accurate parking when the preset distance is reached.

[0075] The injection needle seat 8 is fixed on the automatic injection tower 7, and the injection needle seat 8 can rise and fall in the automatic injection tower 7, thereby driving the injection needle 9 to rise and fall, so that the injection needle 9 can be inserted into the cavity or sample bottle. Preferably, a stepper motor, an optical coupling limiter and a guide rail are arranged inside the automatic injection tower 7, and the stepper motor provides power and the guide rail provides a limit, so that the injection needle seat 8 can reciprocate in the vertical direction, and the optical coupling limiter controls the precise definition of the moving position of the injection needle seat 8 to ensure that the injection needle seat 8 can be moved according to the predetermined height and distance.

[0076] In a preferred embodiment, Figure 1 and Figure 2As shown in FIG. , the system further comprises a transverse guide rail 12, on which the automatic injection tower 7 can reciprocate.

[0077] The injection chamber 10 is arranged below the transverse guide rail 12.

[0078] A waste liquid chamber 13 and a sample tray 15 are also provided below the transverse guide rail 12 ; sample bottles and cleaning solvent bottles are placed on the sample tray 15 ; the sample bottles store liquid samples, and the cleaning solvent bottles store cleaning solvents.

[0079] Under the driving control of the transverse guide rail 12 and the automatic injection tower 7, the injection needle 9 can be inserted into the injection chamber 10, the waste liquid chamber 13, the sample bottle and the cleaning solvent bottle in any order, and under the driving control of the injection needle seat 8, the extraction and ejection operations are performed;

[0080] Preferably, the waste liquid chamber 13 is a closed chamber.

[0081] Preferably, a stepper motor, an optical coupling stopper and a guide rail are provided on the transverse guide rail 12, so that the automatic injection tower 7 can be controlled to move in the horizontal direction, so that the automatic injection tower 7 can move over the injection chamber 10, the waste liquid chamber 13, the sample bottle and the cleaning solvent bottle, and under the action of the optical coupling stopper, the automatic injection tower 7 can accurately stay at any position. Furthermore, based on the polar coordinate principle, different samples are located at corresponding positions of the transverse guide rail 12, so that the transverse guide rail can quickly and accurately send the automatic injection tower 7 to the desired position.

[0082] In a preferred embodiment, Figure 3 As shown in the figure, the injection chamber 10 and the waste liquid chamber 13 in the present application have the same structure and are both closed chambers; preferably, the injection chamber 10 and the waste liquid chamber 13 both include a sealing nut 16, a sealing septum 17 and a chamber base 18;

[0083] The sealing nut 16 and the cavity base 18 are screwed together via a threaded structure; the sealing nut 16 and the cavity base 18 are made of polytetrafluoroethylene, and the sealing gasket 17 is made of silicone rubber or fluororubber.

[0084] The sealing nut 16 and the sealing gasket 17 in the present application can be pierced by the injection needle 9, and can be sealed again by themselves after the injection needle 9 is withdrawn, so that the injection circulation pump 6 and the waste liquid pump 11 can continue to work and perform the suction operation.

[0085] In a preferred embodiment, the system further comprises a waste liquid pump 11 and a waste liquid bottle 14.

[0086] One end of the waste liquid pump 11 is connected to the bottom of the titration cup 5 through a pipeline, and the other end of the waste liquid pump 11 is connected to the waste liquid chamber 13 through a pipeline;

[0087] The waste liquid chamber 13 is connected to the waste liquid bottle 14 through a pipeline.

[0088] The waste liquid chamber 13 in the present application can also provide a needle washing function, and can collect and discharge waste liquid generated during the operation process and the needle washing process.

[0089] In a preferred embodiment, the system further includes a protective gas inlet and outlet 4, which are arranged in parallel, all extend into the titration cup 5, and are all located above the liquid surface. In the present application, the protective gas inlet and outlet 4 include an air inlet and an air outlet, and the protective gas inlet and outlet 4 just extends into the titration cup from the inner wall of the titration cup, and the protective gas inlet and outlet 4 is located at the center of the titration cup. During operation, the protective gas is blown in from the air inlet, circling to replace the gas in the titration cup, and then blown out from the air outlet.

[0090] In a preferred embodiment, the system further comprises a volumetric liquid feeding device 1 and an electrolytic generating device;

[0091] Wherein, when the system uses the volumetric method, the volumetric method liquid feeding device 1 is connected to the titration cup 5 through a pipeline;

[0092] When the system uses the coulometric method, the electrolysis generating device is electrically connected to the titration cup 5 .

[0093] The electrolysis generating device may be an electrolytic cell of a common Karl Fischer coulometer.

[0094] The present invention also provides a method for determining water content by Karl Fischer automatic sampling, which is implemented by the above-mentioned system for determining water content by Karl Fischer automatic sampling;

[0095] Preferably, the method comprises the following operating steps: purging, adding solvent, pre-titration and drifting, needle washing and sampling, titration analysis, and draining waste liquid.

[0096] Preferably, in the purging step, dry nitrogen or air is used as a carrier gas to purge the system through the protective gas inlet and outlet 4 to maintain a dry environment of the system, and the purging is stopped after a period of time; preferably, the purging time can be set to 0min to 10min, and the purging flow rate can be set to 100mL / min to 500mL / min. The purging and drying gas in this application only dries the titration cup and the gas inlet and outlet, and does not dry other pipelines.

[0097] Preferably, in the solvent adding step, the solvent pump 3 pumps an appropriate solvent from the solvent bottle 2 into the titration cup 5. The volumetric method generally uses anhydrous methanol as the solvent, and the coulometric method directly uses a pyridine-free coulometric Karl Fischer electrolyte as the solvent. In order to improve the solubility of some samples or reduce the side reactions, a certain proportion of ethanol, chloroform, benzene, etc. can be added as solvents. The total volume of the pumped solvent is generally 100mL to 150mL.

[0098] Preferably, in the pre-titration and drift step, the sample circulation pump 6 is started, so that the solvent in the titration cup 5 drips back into the titration cup 5 after passing through the sample injection chamber 10, so that the solvent circulates in the titration cup and the sample injection chamber and their pipeline system;

[0099] Preferably, when the volumetric method is used, the system is maintained at a titration endpoint equilibrium state by the volumetric method liquid feeding device 1;

[0100] When the coulometric method is used, the system is maintained at the equilibrium state at the titration endpoint by electrolysis;

[0101] More preferably, the system realizes pre-titration when the equilibrium state is reached at the titration endpoint, and maintains the equilibrium state for a certain period of time to complete the determination of the system drift value.

[0102] Preferably, the needle washing and sampling steps specifically include the following sub-steps:

[0103] Sub-step 1, the automatic injection tower 7 moves to the cleaning solvent bottle position of the sample tray 15 through the transverse guide rail 12, the injection needle seat 8 descends from the highest position, the injection needle 9 is inserted into the cleaning solvent bottle, and the set volume of the cleaning solvent is absorbed. The injection needle seat 8 rises to the highest position, washes the injection needle according to the full volume or partial volume, and moves to the waste liquid chamber 13 to inject the needle washing waste liquid into the waste liquid bottle 14;

[0104] Sub-step 2, the automatic injection tower 7 moves to the injection chamber 10 position, absorbs the equilibrium solution in the titration cup 5, and eliminates the moisture in the injection needle; preferably, the equilibrium solution absorbed into the injection needle is finally injected into the waste liquid chamber 13. Since the waste liquid pump 11 is a peristaltic pump, it has a trapping effect, and the solution will enter the waste liquid chamber 13. If the system is in the pre-titration preparation state, it can also directly return to the injection chamber. The advantage of this is to save titration solvent, but the disadvantage is that it destroys the system balance and brings more contaminants that may exist in the needle. The specific control can be selected according to the experimental needs of the operator.

[0105] Sub-step 3, the automatic injection tower 7 moves to the liquid sample position, uses the liquid sample to clean the injection needle 9, and the waste liquid of the first few cleanings is injected into the waste liquid chamber 13. The number of sample cleaning times can be set; after the sample is cleaned, the bubbles are discharged, that is, the injection needle 9 draws and ejects in the sample bottle;

[0106] Sub-step 4, the injection needle 9 draws a set volume of liquid sample and injects it into the injection chamber 10;

[0107] Preferably, in the above sub-step 1, sub-step 2 and sub-step 3, the number of solvent cleaning, equilibrium solution cleaning and sample cleaning can be set to 0 to 10 times, and each cleaning volume can be set to 0% to 100%; the cleaning volume refers to the full-scale volume of the injection needle;

[0108] In the present application, by setting the above-mentioned cleaning process, it can be ensured that the sample and the titration cup are not contaminated, and the sample is quantitatively injected into the titration cup while maintaining its original properties.

[0109] Specifically, sub-step 1 is to clean the residual substances in the needle to ensure that the titration cup is not contaminated; sub-step 2 is to clean the cleaning solvent in the needle. The solvent may contain water to prevent it from contaminating the sample; sub-step 3 is to ensure that the solution in the injection needle is consistent with the original sample solution; sub-step 4 is to quantitatively absorb the sample solution.

[0110] Preferably, in the above sub-step 4, the sample volume can be set to 0.001 mL to 1.000 mL;

[0111] Preferably, when it is necessary to determine the water content of a solid sample, the equilibrium solution in the titration cup 5 is sucked by the injection needle 9 to fully extract and dissolve the water in the solid sample, or anhydrous methanol is used to extract and dissolve it, and then the sample is injected through the above sub-step 4, that is, the liquid obtained after the above extraction and dissolution is the liquid sample.

[0112] Preferably, in the titration analysis step, when the Karl Fischer volumetric method is used, the volumetric method liquid feeding device 1 is started to titrate to the end point, and the water content of the sample is obtained by calculating the consumed volume, titration time and drift value;

[0113]

[0114] Where: ω represents the water content of the sample, in grams per hundred grams (g / 100g) or grams per hundred milliliters (g / 100mL);

[0115] c represents the titer of the Karl Fischer volumetric titration solution, in milligrams per milliliter (mg / mL);

[0116] V represents the volume of Karl Fischer volumetric titration solution consumed by the sample, in milliliters (mL);

[0117] m represents the amount of sample, in milligrams (mg) or microliters (μ);

[0118] t represents the total time of a single measurement, in seconds (s);

[0119] D represents the most recently measured drift value of the titration system, in microliters per minute (μL / min).

[0120] When the Karl Fischer coulometric method is used, the electrolytic generator is started and titrated to the endpoint, and the water content of the sample is obtained by calculating the electrolytic coulometric value, titration time and drift value.

[0121]

[0122] Where: μgH2O represents the mass of water measured at a single time, in micrograms of water (μgH2O);

[0123] N A represents Avogadro's constant, 6.02214076×10 23 mol -1 ;

[0124] e represents the electron charge, 1.602176634×10 -19 C;

[0125] i represents the current, in coulomb per second (C / s);

[0126] t represents the total time of a single measurement, in seconds (s);

[0127] D represents the most recently measured drift value of the titration system, in micrograms of water per minute (μgH2O / min).

[0128] Preferably, in the waste liquid discharge step, when the solution in the titration cup 5 can still be used and the volume of the solution is also within an appropriate range, the needle washing and sampling steps and the titration analysis step are repeated to perform water analysis of the next sample;

[0129] When the solution in the titration cup 5 can still be used, but the volume of the solution is too large, the waste liquid pump 11 is started to discharge the appropriate solution in the titration cup 5 into the waste liquid bottle 14, so that the volume of the solution in the titration cup 5 reaches an appropriate range, and then the above needle washing and sampling steps and titration analysis steps are repeated to perform the moisture analysis of the next sample;

[0130] When the solution in the titration cup cannot be used, the waste liquid pump 11 is started to discharge all the waste liquid in the titration cup 5 into the waste liquid bottle 14, and then the above steps are repeated from the purge step to start the next sample analysis;

[0131] Preferably, the replacement frequency of the solution in the titration cup 5 is related to the sample properties. If the sample has a large water content and a low solubility, it will be used less frequently. Therefore, the frequency of replacing the titration solution can be set according to the actual situation.

[0132] In the present application, compared with the common dissolution transfer method and back titration method, the automatic quantitative addition of the sample solution is realized; the sample in the same bottle can be sampled and analyzed multiple times; if the standard aqueous solution is used, the system calibration, quality control, and titration solution calibration can be automatically performed; the use of a sealed headspace bottle to hold the sample can ensure that the sample is not affected by the outside world and its water content is stable.

[0133] Example 1

[0134] The Karl Fischer volumetric automatic sampling water determination system determines the water content in ethanol, specifically including the following steps:

[0135] Through the protective gas inlet and outlet, use dry air to purge the system at a rate of 150 mL / min for 5 min;

[0136] Pump 130 mL of anhydrous methanol from the solvent bottle into the titration cup using the solvent pump;

[0137] Start the sample circulation pump; start pre-titration to eliminate the solvent methanol and residual water in the system; automatically start the drift measurement, the drift evaluation time is 4 minutes, and the measured drift value is 5.09μL / min;

[0138] Directly use the equilibrium solution in the titration cup to clean the injection needle, the cleaning volume is 0.300mL, clean the whole process, and clean it 3 times; then use the ethanol sample to clean the injection needle, the cleaning volume is 0.300mL, clean the whole process, and clean it 3 times; the injection needle draws in and out of the ethanol sample bottle, the volume is 1.000mL, back and forth 3 times; the injection volume is 1.000mL; titrate to the endpoint, record the consumed volume and titration time.

[0139] The measurement was repeated 6 times.

[0140] Preparation of standard methanol water standard sample: Add 200mL of anhydrous methanol to the titration cup, use the pre-titration method, titrate until the system is balanced, and maintain the calcium balance state. Accurately pipette 0μL, 10μL, 20μL, 50μL, 80μL and 100μL of distilled water into a 10mL dry volumetric flask, and dilute to the scale with the equilibrium solution in the titration cup. Immediately transfer the solution in the volumetric flask to a dry and clean 10mL headspace bottle and seal it for storage. Considering the density of water to be 1.00g / mL, the above concentrations are 0.00mg / mL, 1.00mg / mL, 2.00mg / mL, 5.00mg / mL, 8.00mg / mL and 10.00mg / mL respectively.

[0141] Similarly, 1.000 mL of standard methanol water standard samples with water contents of 0.00 mg / mL, 1.00 mg / mL, 2.00 mg / mL, 5.00 mg / mL, 8.00 mg / mL and 10.00 mg / mL were aspirated, and a standard curve was established with water content (mg) as the horizontal axis and the endpoint consumption volume minus the product of the drift value and time as the vertical axis.

[0142] The linear regression equation is y=0.1804x+0.0032, and the linear correlation coefficient is R 2 =1.0000, with good linear relationship, and can be used to determine the moisture content of ethanol samples.

[0143]

[0144]

[0145] The water content of the ethanol sample was 4.26 mg / mL, and the relative standard deviation was 0.57% (n=6).

[0146]

[0147] Embodiment 2:

[0148] The Karl Fischer coulometric automatic sampling moisture determination system determines the moisture content in tobacco, specifically including the following steps:

[0149] Through the protective gas inlet and outlet, use dry air to purge the system at a rate of 150 mL / min for 5 min;

[0150] Add 140 mL of pyridine-free coulometric Karl Fischer electrolyte to the titration cup via a solvent pump, using a diaphragm-free electrolytic electrode;

[0151] Start the sample circulation pump and start the pre-titration. The system is in the "iodine-permeated" state. Add 70 μL of pure water to put the system in the "water-permeated" state. Start the pre-titration again to eliminate the residual water in the system. Automatically start the drift determination. The drift evaluation time is 2 minutes. The measured drift value is 2.97 μg water / min.

[0152] Take 0.5g~1g of uniform tobacco (water content of 50mg~100mg) and put it into a 50mL water-free volumetric flask, and record the tobacco mass m, accurate to 0.0001g. Add anhydrous methanol to make up the volume, extract for 5min, and take the supernatant for testing. Repeat 3 times. At the same time, make an anhydrous methanol blank.

[0153] Directly use the equilibrium solution in the titration cup to clean the injection needle, the cleaning volume is 0.250mL, the whole process is cleaned, and the cleaning is repeated 3 times; then use anhydrous methanol extract to clean the injection needle, the cleaning volume is 0.250mL, the whole process is cleaned, and the cleaning is repeated 3 times; the injection needle draws in and out of the sample bottle of anhydrous methanol extract, the volume is 0.250mL, back and forth 3 times; the injection volume is 1.000mL. Titrate to the endpoint and record the titration result (in terms of the percentage of moisture in tobacco g / 100g).

[0154] The water content in anhydrous methanol is 188.25 μg / mL

[0155] The moisture content of the tobacco shreds was 11.8 g / 100 g, with a relative standard deviation of 1.46% (n=3).

[0156]

[0157] The above embodiments illustrate that the automatic sampling water content determination method of the Karl Fischer method provided in the present application can accurately implement direct sampling analysis of liquid samples and post-dissolution analysis of solid samples.

[0158] The present invention has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve only as an illustration. On this basis, the present invention may be subjected to a variety of substitutions and improvements, all of which fall within the scope of protection of the present invention.

Claims

1. A Karl Fischer automatic sampling water determination system, It is characterized in that The system includes: A titration cup (5), a sample injection chamber (10) and a sample injection circulation pump (6) connected by pipelines; The titration operation is performed in the titration cup (5), the injection chamber (10) is a closed chamber, and the liquid in the titration cup (5) is pumped back through the injection chamber (10) by the injection circulation pump (6) and drips into the titration cup (5), thereby realizing the circulation of the solvent in the titration cup (5), the injection chamber (10) and their pipeline system.

2. The Karl Fischer automatic sampling water content determination system according to claim 1, It is characterized in that The system also includes an injection needle (9) which is fixed on the injection needle seat (8), and the extraction and ejection operations of the injection needle (9) are controlled by the injection needle seat (8); The injection needle seat (8) is fixed on the automatic injection tower (7), and the injection needle seat (8) can rise and fall in the automatic injection tower (7), thereby driving the injection needle (9) to rise and fall.

3. The Karl Fischer automatic sampling water content determination system according to claim 2, It is characterized in that The system also includes a transverse guide rail (12), on which the automatic injection tower (7) can reciprocate. The injection chamber (10) is arranged below the transverse guide rail (12). A waste liquid chamber (13) and a sample tray (15) are also provided below the transverse guide rail (12); a sample bottle and a cleaning solvent bottle are placed on the sample tray (15); Under the driving control of the transverse guide rail (12) and the automatic injection tower (7), the injection needle (9) can be inserted into the injection chamber (10), the waste liquid chamber (13), the sample bottle and the cleaning solvent bottle in any order, and under the driving control of the injection needle seat (8), the extraction and ejection operations are performed; Preferably, the waste liquid chamber (13) is a closed chamber.

4. The Karl Fischer automatic sampling water content determination system according to claim 3, It is characterized in that The system also includes a waste liquid pump (11) and a waste liquid bottle (14). One end of the waste liquid pump (11) is connected to the bottom of the titration cup (5) through a pipeline, and the other end of the waste liquid pump (11) is connected to the waste liquid chamber (13) through a pipeline; The waste liquid chamber (13) is connected to the waste liquid bottle (14) via a pipeline.

5. The Karl Fischer automatic sampling water content determination system according to claim 1, It is characterized in that The system also comprises a protective gas inlet and outlet (4), which are arranged in parallel, both penetrate into the titration cup (5), and both are located above the liquid surface.

6. The Karl Fischer automatic sampling water content determination system according to claim 1, It is characterized in that The system also includes a volumetric liquid feeding device (1) and an electrolytic generating device; Wherein, when the system uses the volumetric method, the volumetric method liquid feeding device (1) is connected to the titration cup (5) through a pipeline; When the system uses the coulometric method, the electrolytic generating device is electrically connected to the titration cup (5).

7. A method for determining moisture content by Karl Fischer automatic sampling. It is characterized in that The method is implemented by the Karl Fischer automatic sampling water content determination system according to any one of claims 1 to 6; Preferably, the method comprises the following steps: Purging, adding solvent, pre-titration and drift, needle washing and sampling, titration analysis, and draining waste liquid.

8. The method for determining water content by automatic sampling using the Karl Fischer method according to claim 7, It is characterized in that In the pre-titration and drift step, the injection circulation pump (6) is started, so that the solvent in the titration cup (5) drips back into the titration cup (5) after passing through the injection chamber (10), thereby realizing the circulation of the solvent in the titration cup, the injection chamber and the pipeline system thereof; Preferably, when the volumetric method is used, the system is maintained at a titration endpoint equilibrium state by means of the volumetric method liquid feeding device (1); When the coulometric method is used, the system is maintained at the equilibrium state at the titration endpoint by electrolysis; More preferably, the system realizes pre-titration when the equilibrium state is reached at the titration endpoint, and maintains the equilibrium state for a certain period of time to complete the determination of the system drift value.

9. The method for determining water content by automatic sampling using the Karl Fischer method according to claim 7, It is characterized in that The needle washing and sampling steps specifically include the following sub-steps: Sub-step 1, the automatic injection tower (7) moves to the cleaning solvent bottle position of the sample tray (15) through the transverse guide rail (12), the injection needle seat (8) descends from the highest position, the injection needle (9) is inserted into the cleaning solvent bottle, and a set volume of cleaning solvent is absorbed. The injection needle seat (8) rises to the highest position, washes the injection needle according to the full volume or partial volume, and moves to the waste liquid chamber (13) and injects the needle washing waste liquid into the waste liquid bottle (14); Sub-step 2, the automatic injection tower (7) moves to the injection chamber (10) to absorb the equilibrium solution in the titration cup (5) to eliminate the water in the injection needle; Sub-step 3, the automatic injection tower (7) moves to the liquid sample position, uses the liquid sample to clean the injection needle (9), and the waste liquid from the first few cleanings is injected into the waste liquid chamber 13; after the sample is cleaned, the bubbles are discharged, that is, the injection needle (9) draws and ejects in the sample bottle; Sub-step 4, the injection needle (9) draws a set volume of liquid sample and injects it into the injection chamber (10); Preferably, in the above sub-step 1, sub-step 2 and sub-step 3, the number of solvent washing, equilibrium solution washing and sample washing can be set to 0 to 10 times, and each washing volume can be set to 0% to 100%; Preferably, in the above sub-step 4, the sample volume can be set to 0.001 mL to 1.000 mL; Preferably, when it is necessary to determine the water content of a solid sample, the sample is injected using a sampling needle (9) to absorb the equilibrium solution in the titration cup (5) to fully extract and dissolve the water in the solid sample, or after extraction and dissolution using anhydrous methanol, the sample is injected according to the above sub-step 4.

10. The method for determining water content by automatic sampling using the Karl Fischer method according to claim 7, It is characterized in that In the titration analysis step, when the Karl Fischer volumetric method is used, the volumetric liquid feeding device (1) is started to titrate to the endpoint, and the water content of the sample is obtained by calculating the consumed volume, titration time and drift value; When the Karl Fischer coulometric method is used, the electrolytic generator is started and titrated to the endpoint, and the water content of the sample is obtained by calculating the electrolytic coulometric value, titration time and drift value.

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