CN109632937B - Wood capillary electrospray ionization device and analysis method - Google Patents
Wood capillary electrospray ionization device and analysis method Download PDFInfo
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Abstract
An electrospray ionization device for a wooden capillary tube and an analysis method thereof are disclosed, wherein the device is composed of the wooden capillary tube, a three-way connecting piece, a gas tube and a sample tube. The wood capillary tube adopted by the invention is made of non-metal materials and is non-conductive, so that ionization inhibition caused by discharge is greatly reduced in the electrospray process, sample complication caused by electrochemical reaction is reduced, and the detection result is closer to the real condition of the sample.
Description
Technical Field
The invention relates to the technical field of analysis, in particular to an electrospray ionization device for a wood capillary and an analysis method.
Background
Because various compounds can be analyzed, especially the analysis of thermally unstable and nonvolatile biomacromolecules becomes practical, electrospray ionization mass spectrometry becomes one of the most widely applied mass spectrometry technologies at present. The electrospray ionization method adopts a capillary as a nozzle (emitter), a sample solution enters the nozzle through a pipeline, high voltage is applied to the inside of the nozzle, the sample solution forms spray at the tip of the nozzle under the action of an electric field, the spray forms small droplets, the solvent in the small droplets is continuously evaporated to cause the small droplets to be continuously burst, and finally ions are formed to enter a mass spectrum to be detected. Because metals have ductility, high hardness, easy processing and good conductivity, the current commercial mass spectrometers all use stainless steel capillaries as electrospray nozzles. But metal capillaries as electrospray nozzles have the following disadvantages:
(1) metal jets tend to cause signal suppression. The tip of the metal showerhead is susceptible to discharge at high voltage, which results in signal suppression and reduced detection sensitivity. Especially, the discharge voltage and the spray voltage are very close in the negative ion mode, so that mass spectrum signals in the negative ion mode are severely inhibited, the signal intensity is usually 1 to 2 orders of magnitude lower than that in the positive ion mode, and the application of the negative ion mode electrospray mass spectrum is far lower than that in the positive ion mode.
(2) Metal jets lead to spectrum complications. The sample solution may have electrochemical reaction in the metal nozzle unrelated to analysis, resulting in hydrolysis, polymerization and other reactions of the compound in the sample solution, so that the spectrogram cannot accurately reflect the real condition of the sample solution. In addition, a part of the current generated by the applied voltage is used for electrochemical reaction unrelated to analysis, thereby reducing spray current, causing insufficient ionization and reducing detection sensitivity.
(3) At high flow rates or high water phase conditions, the signal is severely reduced. The metal surface is smooth and not easy to be wetted by the solvent, and has no micropores, which also reduces the contact area of the solution and the metal and reduces the ionization efficiency. These properties result in larger spray droplets, reducing detection sensitivity, and are more severe in the case of high flow rates or high water phases, which severely affects the sensitivity of liquid chromatography mass spectrometry.
Disclosure of Invention
Aiming at the problems, the invention provides an electrospray ionization device and an analysis method for a wooden capillary tube, and the technical concept of the invention has the following characteristics:
the method has the characteristics that: the use of non-conductive materials as the showerhead may reduce signal rejection. The wood material is not an electric conductor, and the wood material as an electrospray nozzle material can not cause discharge inhibition of signals, so that the detection sensitivity is improved.
The method has the following characteristics: the non-metal material is adopted as the spray head, so that the spectrogram is simple. The wood capillary tube as the electrospray nozzle can greatly reduce the complex reaction caused by the electrochemical reaction, so that the spectrogram becomes simple, the current generated by the external voltage is completely used for spraying, the ionization efficiency is greatly improved, and the detection sensitivity is greatly improved.
The characteristics are three: can resist high flow rate or high water phase samples. The wooden capillary tube is not conductive, but becomes a good electric conductor after being wetted by the solvent, the surface of the wooden capillary tube is of a porous structure, the contact area of the solution and the spray head is greatly increased, and the ionization efficiency is improved. These properties result in smaller spray droplets, increased sensitivity, and a strong signal at high flow rates or high water phases.
In order to realize the purpose of the invention, the invention adopts the following technical scheme:
the method comprises the following steps: a wooden capillary tube (2) with the inner diameter of 10-250 mu m, the outer diameter of the tip close to the inner diameter and the length of 1-5cm is arranged at a position 0.1-6cm away from the mass spectrometer inlet (1), and the included angle between the spray head of the wooden capillary tube (2) and the axis of the mass spectrometer inlet (1) is 0-90 degrees.
Step two: the wooden capillary (2) is wetted by water, and is applied with voltage to form a loop with a mass spectrometer. The sample solution and nitrogen are delivered to the wood capillary (2) at a flow rate of 0-600L/h. The sample solution is ionized inside the wood capillary (2), under the assistance of gas, a spray is formed at the tip of the wood capillary (2), and generated ions enter the mass spectrometer through the mass spectrometer inlet (1) to be detected.
In order to realize the electrospray ionization mass spectrometry method for the wood capillary provided by the invention, the invention provides an electrospray ionization device for the wood capillary (shown in figure 1):
the device consists of a wooden capillary tube (2), a three-way connecting piece (3), a gas tube (4) and a sample tube (5).
The mass spectrometer inlet (1) is positioned at the rightmost end; the left end is wooden capillary (2), and the most advanced of wooden capillary (2) is placed in mass spectrometer entry (1) department, and the distance that gets into mass spectrometer entry (1) is 0.1-6cm, and the contained angle of wooden capillary shower nozzle (2) and mass spectrometer entry (1) axis is 0-90. The inner diameter of the wood capillary (2) is 10-250 mu m, the length is 1-5cm, the outer diameter of the tip is close to the inner diameter, the shape and the size of the tail end of the capillary (2) can be connected with a solution pipeline, and the middle part of the capillary (2) can be in any shape. The tail part of the wooden capillary tube (2) is connected with the three-way connecting piece (3), the other two ends of the three-way connecting piece (3) are respectively used as gas and sample inlets and are connected with the gas tube (4) and the sample tube (5), and high voltage is directly applied to the wooden capillary tube (2).
The specific test analysis process is as follows:
1) wetting a wood capillary tube with water, and applying voltage;
2) turning on the mass spectrometer, and scanning mass spectrum signals;
3) opening a sample introduction system, conveying a sample solution to the wood capillary (2) through a sample tube (5) and a three-way connecting piece (3), opening a gas switch, conveying nitrogen to the wood capillary (2) through a gas tube (4) and the three-way connecting piece (3), and adjusting the position and the gas flow of the wood capillary (2) to enable a signal to be strongest;
3) and recording the scanning data to obtain a mass spectrogram of the sample ions.
Description of the technology
Description 1: step one, the inner diameter of the wood capillary (2) is 10-250 mu m, the electrospray airflow is relatively stable in the range, and the requirements of different sample flow rates can be met. Not only does the inner diameter of the capillary influence the spray, but the outer diameter also influences the spray, increasing the spray voltage threshold, and in the case of a large solution flow rate, the spray droplets generated by the capillary with a large outer diameter are also large, which leads to a reduction in the signal, so the front end of the wooden capillary is trimmed to a point as much as possible, and the outer diameter is made to approach the inner diameter as much as possible. The capillary electrospray is only related to the inner diameter and the outer diameter of the tip of the capillary, so that the shape of the rest part of the wood capillary is not important, and the wood capillary is convenient to operate as long as the wood capillary can be connected with a three-way connecting piece (3).
The length of the wooden capillary (2) also influences the electrospray, the long capillary does not improve the performance, but the solution pressure in the capillary is increased, so that the technical requirement on the capillary manufacturing is improved, and in addition, a longer pipeline can generate a larger dead volume in the liquid chromatography-mass spectrometry combined analysis, so that the peak is widened, and the analysis sensitivity is reduced. Therefore, the length of the wood capillary tube (2) is limited below 5cm, so that large pressure and dead volume cannot be generated, and the wood capillary tube is also inconvenient to operate due to too short length, so that the length of the wood capillary tube is only in the range of 1-5 cm.
The distance between the tip of the capillary nozzle and the mass spectrometer inlet (1) is related to parameters such as voltage, sample solution flow rate, sample solution composition, inner diameter and outer diameter of the capillary tip and the like, so that optimization is needed according to actual conditions, and the distance from the tip of the capillary nozzle to the mass spectrometer inlet (1) is usually 0.1-6 cm.
The included angle between the spray head of the wooden capillary tube (2) and the axis of the mass spectrometer inlet (1) can be 0-90 degrees, under the conditions that the flow rate of sample solution is low and the solution matrix is less, the spray head of the wooden capillary tube (2) and the axis of the mass spectrometer inlet can be on the same straight line, the tip of the spray head (2) is over against the mass spectrometer inlet (1), namely the included angle is equal to 0 degree. However, in the case of a large solution flow rate and a complex matrix, this arrangement may lead to contamination of the ion source. When the included angle between the wood capillary (2) and the axis of the mass spectrum inlet (1) is more than 0 degree, the matrix particles, the liquid drops which are not gasified and the substances which are not ionized can be deflected out and cannot enter the ion source, so that the pollution to the ion source and the interference to target compounds are reduced.
Description 2: and step two, wetting the wood capillary tube (2) by using water, enabling the water to enter the wood micropores, enabling the wood capillary tube (2) to have electric conduction capability, and applying a high voltage to enable the wood capillary tube and the mass spectrometer inlet (1) to form a potential difference to form an electric field, which is the premise that a sample in the wood capillary tube (2) is ionized. Wood is not conductive, but is well conductive after being wetted by a solvent, so that it is very convenient to apply voltage as a metal capillary tube, as long as it is clamped on a wooden capillary tube (2) by using an electric clamp.
Under the condition of high solution flow rate or high water ratio, the solution can not generate spray simply depending on electric field force, and the nitrogen is introduced to assist gasification. The flow rate of nitrogen is related to the ease of vaporization of the sample solution, and generally the flow rate is greater with a higher proportion of water, whereas the flow rate of nitrogen may be smaller or even completely closed.
The nitrogen gas is mixed with the sample solution which is ionized in the wood capillary (2), a spray is formed at the tip of the wood capillary (2), the spray is a series of charged small droplets, the charged small droplets move to the inlet (1) of the mass spectrometer under the action of an electric field, in the process, the solvent on the surface of the droplets is continuously evaporated, the diameter of the droplets is reduced, the quantity of the charges on the surface of the droplets is unchanged, when the repulsion force of the charges on the surface of the droplets is equal to the surface tension of the droplets, namely the Rayleigh limit, the droplets begin to burst, smaller droplets are formed, the process is repeated, finally, sample ions are formed, and the sample ions enter the inlet (1) of the mass spectrometer to be detected.
Has the advantages that:
1. the invention adopts the non-conductive material wood capillary as the electrospray nozzle, and can greatly reduce the signal inhibition caused by discharge. Compared with a metal nozzle, the positive ion signal intensity of wood capillary electrospray is one order of magnitude higher than that of the metal capillary nozzle, and the negative ion signal intensity is 2 orders of magnitude higher than that of the metal capillary nozzle, so that the problem of low negative ion mode signal of electrospray mass spectrometry for a long time is solved, and the performance and the use efficiency of the instrument are improved.
2. Compared with metal capillary electrospray, the wood capillary as an electrospray nozzle can greatly reduce complex chemical reaction caused by electrochemical reaction, and the spectrogram becomes simple. In addition, the electrospray energy of the wood capillary is higher than that of the metal capillary, so that various additive reactions generated in the process of gasifying and ionizing sample molecules are reduced, and the sample information is reflected more truly.
3. The wood porosity characteristic enables the wood capillary to have higher ionization efficiency, smaller spray liquid drops and better resistance to high sample flow rate and high proportion water phase than metal capillary electrospray, thereby solving the problem of mass spectrum signal reduction caused by high sample flow rate and high water phase in the process of liquid chromatography-mass spectrometry combination at present.
Drawings
Fig. 1 is a schematic structural diagram of an electrospray ionization device for a wood capillary tube.
In the figure, 1-mass spectrometer inlet; 2-a wood capillary; 3-a three-way connection; 4-a gas pipe; 5-sample tube.
FIG. 2 is an electrospray mass spectrum of baicalein metal capillary in positive ion mode;
FIG. 3 is an electrospray mass spectrum of baicalein in positive ion mode by using a wooden capillary;
FIG. 4 is an emodin metal capillary negative ion mode electrospray mass spectrogram;
FIG. 5 is an emodin wood capillary negative ion mode electrospray mass spectrogram;
FIG. 6 is an electrospray mass spectrum of myoglobin metal capillary in positive ion mode;
FIG. 7 is an electrospray mass spectrum of myoglobin capillary positive ion mode;
FIG. 8 is a graph of ion signal intensity versus electrospray from a metal capillary and a wood capillary at different flow rates;
FIG. 9 is a graph of ion signal intensity versus electrospray from wood capillary and metal capillary at different solvent ratios
Detailed Description
Example 1
Manufacturing a wooden capillary tube (2): taking a small wood stick, longitudinally splitting, using a nicking tool or laser to carve a small groove in the center, then combining the wood sticks together again according to the situation before splitting, and using an adhesive tape for fixing, thus forming the wooden capillary (2). The front end of the wood capillary (2) is trimmed to be sharp, so that the outer diameter of the wood capillary is as close as possible to the inner diameter. The tail end of the wood capillary (2) is also trimmed to be sharp, so that the wood capillary can be connected with a solution pipeline.
An electrospray ionization device for a wooden capillary (as shown in figure 1): the device consists of a wooden capillary tube (2), a three-way connecting piece (3), a gas tube (4) and a sample tube (5).
The mass spectrometer inlet (1) is positioned at the rightmost end; the left end is wooden capillary (2), and the most advanced of wooden capillary (2) is placed in mass spectrometer entry (1) department, and the distance that gets into mass spectrometer entry (1) is 0.1-6cm, and the contained angle of wooden capillary (2) and mass spectrometer entry (1) axis is 0-90. The inner diameter of the wood capillary (2) is 10-250 μm, the length is 1-5cm, and the outer diameter of the tip is close to the inner diameter. The tail end of the capillary (2) is sharpened so that it can be connected with the three-way connection piece (3). The middle part of the capillary (2) can be in any shape. The tail part of the wooden capillary tube (2) is connected with the three-way connecting piece (3), the other two ends of the three-way connecting piece (3) are respectively used as gas and sample inlets and are connected with the gas tube (4) and the sample tube (5), and high voltage is directly applied to the wooden capillary tube (2).
The specific test analysis process is as follows:
1) wetting a wood capillary tube with water, and applying voltage;
2) turning on the mass spectrometer, and scanning mass spectrum signals;
3) opening a sample introduction system, conveying a sample solution to the wood capillary (2) through a sample tube (5) and a three-way connecting piece (3), opening a gas switch, conveying nitrogen to the wood capillary (2) through a gas tube (4) and the three-way connecting piece (3), and adjusting the position and the gas flow of the wood capillary (2) to enable a signal to be strongest;
4) and recording the scanning data to obtain a mass spectrogram of the sample ions.
Example 2
In this example, a wood capillary electrospray ionization device was used in combination with a mass spectrometry system (Thermo LCQ speed) to analyze astragalin, and compared with metal capillary electrospray. The wood capillary electrospray ionization device was the wood capillary electrospray ionization device described in example 1 (fig. 1), and the metal capillary electrospray device was the electrospray device (stainless steel) provided by a commercial electrospray mass spectrometer (Thermo LCQ speed).
The sample solution is placed in an injector and is injected into the wood capillary tube (2) or the metal capillary tube through the sample tube (5) and the three-way connecting piece (3), and the flow rate of the sample is 5 mu L/min. In order to compare the performance of the two, the auxiliary gas is not turned on, and other parameters are adjusted to the strongest signal. The wood capillary electrospray was performed in the same manner as in example 1, using a positive ion electrospray mode.
From FIG. 2, it can be observed that the peaks generated by electrospray of metal capillary are relatively complex, and the protonated peak ([ M + H ] of baicalein) exists]+M/z 271), plus sodium peak ([ M + Na ]]+M/z 293), sodium addition peak of dimer ([ 2M + Na)]+M/z 563), potassium peak of dimer ([ 2M + K)]+M/z 579), sodium peak of trimer ([ 3M + Na ]]+M/z 833) and the tripolymer Potassium Peak ([ 3M + K)]+M/z 849), where the signal for the dimeric ions is strongest and the signal for the trimeric ions is also evident. However, the peak generated by wood capillary electrospray (fig. 3) is relatively simple, the protonated peak of baicalein is the only strong peak, and the signal of the polymeric ion is very low, which indicates that the energy generated by the wood capillary spray head is higher than that of the metal material, and the polymerization of the target compound is inhibited, so that the signal (90000) generated by wood capillary electrospray is obviously stronger than the signal (10000) generated by metal capillary electrospray.
Example 3
In this example, emodin was analyzed using a wood capillary electrospray ionization device in combination with a mass spectrometry system (Thermo LCQ speed) and compared with metal capillary electrospray. The wood capillary electrospray ionization device was the wood capillary electrospray ionization device described in example 1 (fig. 1), and the metal capillary electrospray device was the electrospray device (stainless steel) provided by a commercial electrospray mass spectrometer (Thermo LCQ speed).
The sample solution is placed in an injector and is injected into the wood capillary tube (2) or the metal capillary tube through the sample tube (5) and the three-way connecting piece (3), and the flow rate of the sample is 5 mu L/min. In order to compare the performance of the two, the auxiliary gas is not turned on, and other parameters are adjusted to the strongest signal. The wood capillary electrospray was performed in the same manner as in example 1, using a negative ion electrospray mode.
The signal for emodin woodcapillary electrospray (fig. 5) was much stronger than for metal capillary electrospray (fig. 4), with signal intensity approximately 2 orders of magnitude higher. Generally, a metal capillary tube is easy to generate discharge phenomena in an electrospray negative ion mode, and the discharge can seriously inhibit mass spectrum signals, so that the negative ion mode is usually smaller than a positive ion mode electrospray signal by one order of magnitude. Wood is a poor electrical conductor, wood conductivity comes from the analyzed sample solution, so its discharge phenomenon is weaker than metal, signal suppression is not as severe as metal capillary electrospray, just as evidenced by wood capillary electrospray (figure 5) producing a very significant emodin dimer deprotonated ion (m/z 539). From an examination of fig. 4, it can be seen that metal capillary electrospray generates a complex electrolytic reaction, producing a series of small peaks, whereas wood capillary electrospray (fig. 5) does not. The wood capillary tube generates a high-intensity mass spectrum signal in a negative ion mode, and does not generate signal inhibition and complex chemical reaction like metal capillary tube electrospray, so that the problem of low signal of the conventional negative ion mode electrospray mass spectrum is well solved, and the performance and efficiency of the electrospray mass spectrum can be further improved.
Example 4
This example uses a wood capillary electrospray ionization device in combination with a mass spectrometry system (Thermo LCQ speed) to analyze proteins and compares them to metal capillary electrospray. The wood capillary electrospray device was the wood capillary electrospray device described in example 1 (fig. 1), and the metal capillary electrospray device was the electrospray device (stainless steel) provided by a commercial electrospray mass spectrometer (Thermo LCQ speed).
Myoglobin is used as a sample, a sample solution is placed in an injector and is injected into a wood capillary tube (2) or a metal capillary tube through a sample tube (5) and a three-way connecting piece (3), and the flow rate of the sample is 5 mu L/min. In order to compare the performance of the two, the auxiliary gas is not turned on, and other parameters are adjusted to the strongest signal. The wood capillary electrospray was performed in the same manner as in example 1, using a positive ion electrospray mode.
Fig. 6 and 7 are positive ion mode mass spectra of myoglobin metal capillary electrospray and wood capillary electrospray, respectively. It can be observed from the figure that myoglobin produces a series of ions of different charges. The peak of multi-charge ions generated by wood capillary electrospray moves to a high charge position, the strongest peak of the mass spectrum is +16 peak (m/z 1060), and the strongest peak of the metal capillary electrospray (figure 6) is +14 peak (m/z 1211), which shows that the charging efficiency of the wood capillary electrospray is higher than that of the metal capillary electrospray. The wood has porosity which can increase the electrode area, thereby improving the ionization efficiency. The signal intensity generated by wood capillary electrospray is one order of magnitude higher than that of metal capillary electrospray, which is of great significance to the research in the field of life science.
Example 5
This example examines the resistance of a wood capillary electrospray ionization device to high sample flow rates and compares it to metal capillary electrospray. The wood capillary electrospray device was the wood capillary electrospray device described in example 1 (fig. 1) in combination with a mass spectrometry system (Thermo LCQ speed), and the metal capillary electrospray device was the electrospray device (stainless steel) provided by a commercial electrospray mass spectrometer (Thermo LCQ speed).
Betaine is used as a sample, a sample solution is placed in an injector, and is injected into a wood capillary tube (2) or a metal capillary tube through a sample tube (5) and a three-way connecting piece (3). In order to compare the performance of the two, the auxiliary gas is not turned on, and other parameters are adjusted to the strongest signal. The flow rates of the betaine methanol solutions of 0.1mg/ml were set to 5. mu.l/min, 10. mu.l/min, 15. mu.l/min, 20. mu.l/min, 25. mu.l/min, 30. mu.l/min, 35. mu.l/min, and 40. mu.l/min, respectively. The wood capillary electrospray was performed in the same manner as in example 1, using a positive ion electrospray mode.
As shown in fig. 8, at the same flow rate, the wood capillary electrospray signal was significantly stronger than the metal capillary electrospray. As the flow rate increases, the signal generated by electrospray from the wood capillary increases, while the signal generated by electrospray from the metal capillary gradually decreases. The wood capillary electrospray ionization is suitable for detecting a sample with large flow rate, and can tolerate higher sample flow rate. Although wood is not conductive, the porosity results in good conductivity when transporting sample solutions, and the porosity increases the area of the wood capillary and increases ionization efficiency. In addition, the porosity can also effectively reduce the diameter of the spray droplets, thereby being beneficial to improving the ionization efficiency. Secondly, wood does not generate electrochemical reaction per se, all current is used for ionizing compounds in the sample, metal generates electrochemical reaction per se, only a part of current is used for ionizing the sample, and therefore the ionization efficiency is not as good as that of wood. In the case where discharge suppression does not occur, the stronger the current, the stronger the mass spectrum signal. Therefore, wood capillary electrospray is more suitable than metal capillary electrospray for integration with liquid chromatography techniques. When a sample is detected, the high separation capacity of liquid chromatography is firstly utilized, then the high flow rate resistance characteristic of wood capillary electrospray is utilized, and gas-assisted gasification is combined, so that the detection sensitivity of the high flow rate sample can be effectively improved, and the problem of the sensitivity reduction of the conventional liquid chromatography-mass spectrometry combined high flow rate sample is solved.
Example 6
This example examines the tolerance of a wood capillary electrospray ionization device to high water phase samples and compares it to metal capillary electrospray. The wood capillary electrospray ionization device was the wood capillary electrospray ionization device described in example 1 (fig. 1) in combination with a mass spectrometry system (Thermo LCQ speed), and the metal capillary electrospray device was the electrospray device (stainless steel) provided by a commercial electrospray mass spectrometer (Thermo LCQ speed).
The sample solution is placed in an injector and is injected into the wood capillary tube (2) or the metal capillary tube through the sample tube (5) and the three-way connecting piece (3). In order to compare the performance of the two, the auxiliary gas is not turned on, and other parameters are adjusted to the strongest signal. Dissolving betaine standard substance in methanol, methanol water containing 0.1% glacial acetic acid (80: 20, V/V), methanol water containing 0.1% glacial acetic acid (60: 40, V/V), methanol water containing 0.1% glacial acetic acid (40: 60, V/V), methanol water containing 0.1% glacial acetic acid (20: 80, V/V), and pure water containing 0.1% glacial acetic acid to obtain 0.1mg/ml betaine solution, and performing sample injection detection by metal capillary electrospray and wood capillary electrospray respectively. The wood capillary electrospray was performed in the same manner as in example 1, using a positive ion electrospray mode.
The betaine standards dissolved in solvents (methanol/water) of different proportions were tested by metal capillary electrospray and wood capillary electrospray, and the analysis results shown in fig. 9 were obtained. As shown in fig. 9, the mass spectra signals for both metal capillary electrospray and wood capillary electrospray decreased as the proportion of water increased. This is because the surface tension of water is large, which results in the formation of large spray droplets, which are detrimental to the vaporization of the sample, and thus, the signal is reduced. It can also be observed from fig. 9 that the mass spectrum signal of electrospray from the wood capillary is stronger than that of electrospray from the metal capillary for the same water phase ratio sample. The signal is stronger because the porous structure of the wood capillary allows smaller spray droplets to be generated, which facilitates the formation of sample ions. It can also be observed that the signal intensity generated by electrospray from wooden capillary is almost the same as that generated by electrospray from metal capillary when the water content in the solvent is 20%, 40% and 60%. At a water ratio of 80%, the mass spectrum signal begins to decrease. However, even in the case of pure water, the signal intensity generated by electrospray from wooden capillaries is still considerable, while that from metal capillaries is very low. At present, gradient elution is often adopted in liquid chromatography-mass spectrometry, but when the gradient is large, the sensitivity of the existing metal capillary electrospray is too low when the high-water-phase effluent is detected, and the characteristic of a high-water-phase-resistant sample of wood capillary electrospray just can solve the problem.
Claims (3)
1. An electrospray mass spectrometry method for a wood capillary tube comprises the following steps:
the method comprises the following steps: a wooden capillary (2) is placed at the inlet of the mass spectrometer,
step two: a voltage is applied to the wood capillary (2) to form a loop with the inlet (1) of the mass spectrometer;
conveying a sample solution and nitrogen into a wood capillary (2), ionizing the sample solution in the wood capillary (2), forming spray at the tip of the wood capillary (2) under the assistance of gas, and enabling generated ions to enter a mass spectrometer through a mass spectrometer inlet (1) to be detected;
wherein the inner diameter of the wood capillary tube (2) is 10-250 mu m, the length is 1-5cm, the tail end of the wood capillary tube (2) is processed into a tip, the outer diameter of the tip is close to the inner diameter, the tip of the wood capillary tube (2) is placed at the inlet (1) of the mass spectrometer, the distance from the inlet (1) of the mass spectrometer is 0.1-6cm, and the included angle between the wood capillary tube (2) and the axis of the inlet (1) of the mass spectrometer is 0-90 degrees.
2. An electrospray mass spectrometry method for a wood capillary as claimed in claim 1, wherein: the gas adopted in the second step is nitrogen, and the flow rate is 0-600L/h.
3. An electrospray ionization device for a wooden capillary tube comprises four parts, namely a wooden capillary tube (2), a three-way connecting piece (3), a gas tube (4) and a sample tube (5);
the mass spectrometer inlet (1) is positioned at the rightmost end; the left end is a wood capillary (2), the tip of the wood capillary (2) is placed at the inlet (1) of the mass spectrometer, the distance from the inlet (1) of the mass spectrometer is 0.1-6cm, and the included angle between the wood capillary (2) and the axis of the inlet (1) of the mass spectrometer is 0-90 degrees; the tail part of the wooden capillary tube (2) is connected with the three-way connecting piece (3), the other two ends of the three-way connecting piece (3) are respectively connected with the gas tube (4) and the sample tube (5), and high voltage is directly applied to the wooden capillary tube (2);
wherein the inner diameter of the wood capillary (2) is 10-250 μm, the length is 1-5cm, the outer diameter of the tip is close to the inner diameter, and the tail end of the wood capillary (2) is processed into a tip so as to be connected with the three-way connecting piece (3).
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