Direct ionization device and method, mass spectrum system and application

Abstract

The invention belongs to a mass spectrometry technology, and particularly provides a direct ionization device and method, a mass spectrometry system and application, the ionization device comprises a direct ionization unit, one end of a liquid pipeline is inserted into the direct ionization unit, and the liquid pipeline and the direct ionization unit are sealed; the first through hole is formed in the part, extending into the direct ionization unit, of the liquid pipeline, and the projection of the first through hole on a plane containing the central axis of the liquid pipeline completely falls in the projection of the first electrode on the plane. The method has the advantages of high sensitivity and the like.

Description

Direct ionization devices and methods, mass spectrometry systems and applications Technical Field

[0001] This invention relates to mass spectrometry, and particularly to direct ionization apparatus and methods, mass spectrometry systems and applications. Background Technology

[0002] Liquid chromatography-mass spectrometry (LC-MS) has become the mainstream method for organic analysis due to its high specificity (accounting for more than 65% of the global mass spectrometry market). However, it relies on electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), which has inherent defects: 1) Ion suppression effect: the ionization efficiency of analytes in complex matrices is interfered with (such as salt competition); 2) Polarity discrimination: non-polar compounds are difficult to ionize; 3) Lengthy pretreatment: LC separation is time-consuming and cannot meet the needs of rapid on-site detection.

[0003] Direct ionization techniques (such as DBDI, DESI, DART, etc.) improve detection speed by omitting chromatographic steps, but key problems still exist: ions in the air between the ionization zone and the mass spectrometer inlet suffer significant loss due to diffusion / recombination, and existing techniques require pre-immobilization or vaporization of the sample, which compromises the homogeneity of the liquid sample.

[0004] DBDI, as a common flow-through ion source, has unique applications in gas flow-through sample introduction studies due to its advantage of being able to discharge and ionize air within a hollow dielectric tube. Currently, the integration of DBDI with LC-MS mainly adopts two approaches: 1. External ion beam, where the LC effluent is ionized on the surface or inside the DBDI plasma beam. This approach has low ionization efficiency, is significantly affected by ambient humidity, and causes significant environmental pollution.

[0005] 2. Back-end vaporization introduction, that is, the LC effluent is heated and vaporized and then introduced into the DBDI discharge region. The sample thermal decomposition loss is large and the energy consumption is high. The vaporization process leads to low sample utilization of microLC / nanoLC. In addition, the vaporization device increases the system volume and has poor compatibility with miniaturized mass spectrometers.

[0006] On-site testing requires lightweight equipment (≤20kg) and rapid response, but existing DBDI-LC-MS coupling solutions are complex and energy-intensive, which is not conducive to the simple integration and application of miniaturized mass spectrometers. Summary of the Invention

[0007] To address the shortcomings of the existing technical solutions, the present invention provides a direct ionization device, a mass spectrometry system, and a method.

[0008] The objective of this invention is achieved through the following technical solution: a direct ionization device, comprising a direct ionization unit, the ionization device further comprising: a liquid pipe, one end of which is inserted into the direct ionization unit and sealed to the direct ionization unit; a first through hole, the first through hole being disposed on the portion of the pipe wall into which the liquid pipe extends into the direct ionization unit, wherein the projection of the first through hole onto a plane including the central axis of the liquid pipe falls entirely within the projection area of ​​the first electrode of the direct ionization unit on the plane.

[0009] The present invention also aims to provide a mass spectrometry system, which is achieved through the following technical solution: a mass spectrometry system, including a miniaturized mass spectrometer with a weight ≤20kg; the ionization device is installed at the front end of the sample inlet cone of the miniaturized mass spectrometer.

[0010] The present invention also aims to provide a direct ionization method, which is achieved through the following technical solution: a direct ionization method, wherein the ionization method comprises: passing a liquid sample into the liquid pipeline; applying a voltage to the first electrode to discharge it, the generated charge being concentrated on the outer surface of the liquid pipeline and permeating through the first through hole, thereby charging the liquid pipeline and generating a Taylor cone at its end, causing the liquid sample to undergo a Coulomb explosion, thus achieving direct spray ionization.

[0011] The present invention also aims to provide an ionization control method based on mass spectrometry signal feedback. This objective is achieved through the following technical solution: an ionization control method based on mass spectrometry signal feedback, applied to the ionization device of this application, comprising the following steps: acquiring the spectral signal of the mass spectrometer in real time; determining whether the decrease in the signal intensity within three consecutive scanning cycles exceeds a preset threshold of 25%; if it exceeds, immediately triggering the second electrode to operate with a voltage of 5-8 kV and a pulse width of 10-100 ms.

[0012] The present invention also aims to provide a method for direct ionization mass spectrometry in rapid on-site detection. This objective is achieved through the following technical solution: for direct mass spectrometry analysis of liquid samples that have not undergone chromatographic separation or simple pretreatment.

[0013] The core of this invention lies in proposing a novel direct ionization mechanism for liquid samples. Its key innovation is that the liquid pipe 1 carrying the sample is directly inserted into the low-temperature plasma discharge region generated by the excitation of the first electrode 4, rather than interacting with it outside of it.

[0014] In this configuration, the first through-hole 3, located on the pipe wall within the discharge zone, plays a crucial role. This through-hole disrupts the axisymmetry of the original system, causing the electric field to concentrate highly in the region with an extremely small radius of curvature at the edge of the hole, resulting in a significant electric field curvature effect. This strong local electric field effectively weakens the surface tension of the liquid film, thereby greatly stabilizing and promoting the formation of a Taylor cone at the tip of the pipe end and the subsequent Coulomb explosion process, realizing the physical basis for the direct and efficient conversion of the liquid phase into gaseous ions.

[0015] At the same time, active charged particles (such as electrons and ions) in the discharge region can be reverse-permeated into the liquid flow in the pipe through the first through hole 3, and undergo in-situ gas-liquid interface chemical reactions (such as proton transfer) with the molecules of the analyte. This pathway significantly enhances the ionization efficiency, especially for nonpolar compounds that have a weak response to traditional ESI technology.

[0016] To optimize the ionization process and improve system robustness, this invention introduces two synergistic designs: First, a drive unit allows the liquid pipe 1 to rotate around its axis. This not only dynamically adjusts the wall charge and liquid film distribution through centrifugal force to regulate ionization energy but also provides a mechanical self-cleaning effect, preventing sample residue blockage. Second, an innovative real-time feedback system consisting of a second electrode 5 and a control module is incorporated. When the mass spectrometry signal attenuates due to an increase in unionized droplets, the system automatically triggers a high-intensity pulse discharge for "secondary ionization," thereby ensuring continuous high sensitivity and stability of the detection signal and forming an intelligent closed-loop control.

[0017] Compared with the prior art, the present invention has the following beneficial effects.

[0018] This invention patent discloses a novel ionization and integration system and application method for micro, nano, and picosecond-level liquid chromatography coupled with DBDI-miniature mass spectrometry. It achieves direct ionization of the liquid phase within the direct discharge region, overcoming the limitation that liquid-plasma integration can only be achieved through gas sample introduction. Compared to existing technologies, it offers the following advantages: 1. It is the first high-throughput miniaturized mass spectrometer detection method under a novel ionization mechanism; 2. Utilizing short ion channels, negative pressure self-absorption, and a relatively closed environment, it forms an ion interaction-dominated external electric field control technology, resulting in higher detection sensitivity; 3. The system has a simple structure, good miniaturization compatibility, is easy to disassemble and maintain, and can be fabricated as a consumable disposable ion source; 4. It offers fast analysis time, good continuity, low analyte consumption, and increased utilization rate. Attached Figure Description

[0019] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are merely illustrative of the technical solutions of this invention and are not intended to limit the scope of protection of this invention. In the drawings: Figure 1 is a simplified structural diagram of the ionization device of Embodiment 1 of this invention.

[0020] Figure 2 shows the standard curve of the present invention applied to the detection of valproic acid spiked in serum matrix.

[0021] As shown in the figure, 1-liquid pipe, 2-second through hole, 3-first through hole, 4-first electrode, 5-second electrode, 6-mass spectrometer cone, 7-third through hole, 8-dielectric tube. Detailed Implementation

[0022] Figure 1 and the following description illustrate optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. For the purpose of teaching the technical solutions of the invention, some conventional aspects have been simplified or omitted. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the following optional embodiments, but is defined only by the claims and their equivalents.

[0023] Example 1

[0024] The mass spectrometry system in this embodiment includes a direct ionization device and a mass spectrometer, with a distance between them ≤1 mm.

[0025] As shown in Figure 1, the direct ionization device includes a direct ionization unit, such as DBDI, DART, etc., which are all existing technologies in this field.

[0026] One end of the liquid pipe 1 is inserted into the direct ionization unit and sealed with the direct ionization unit.

[0027] The first through-hole 3 is disposed on the portion of the liquid pipe 1 that extends into the direct ionization unit. The projection of the first through-hole 3 (diameter between 10 μm and 50 μm) onto the plane containing the central axis of the liquid pipe 1 falls entirely within the projection of the first electrode 4 of the direct ionization unit onto that plane. Utilizing the design of the first through-hole 3, during discharge, the asymmetry alters the electric field distribution on the outer surface of the liquid pipe 1, generating a curvature effect, reducing surface tension, accelerating Taylor cone formation, and promoting spraying and ionization. Simultaneously, charge permeates back into the liquid pipe 1, reacting with the ejected droplets at the interface to form gas-phase protonation.

[0028] To address the decline in mass spectrometry signal, as shown in Figure 1, the direct ionization unit further includes a dielectric tube 8, a first electrode 4, and a power supply, wherein the power supply applies a first voltage to the first electrode 4.

[0029] The ionization device further includes a second electrode 5 and a controller. The second electrode 5 is disposed around the dielectric tube 8 and is located downstream of the first electrode 4. The power supply applies a second voltage to the second electrode 5, which is higher than the first voltage.

[0030] The controller controls whether the second voltage is applied based on the mass spectrometry signal. For example, if the mass spectrometry signal drops beyond a threshold within multiple scan cycles, a pulsed second voltage is applied; otherwise, the second voltage is turned off.

[0031] For use in micro, nano, and picoscale liquid phase flow discharge, the driving unit is used to drive the liquid pipeline to rotate, and the discharge energy is controlled by changing the local accumulation of charge on the outer surface.

[0032] The power supply uses lithium batteries to power the ionization device and the mass spectrometer.

[0033] The direct ionization method of this embodiment, that is, the working method of the ionization device of this embodiment, is as follows: the liquid sample is introduced into the liquid pipeline 1 at a flow rate of 0.05 nL / min-500 nL / min.

[0034] A first voltage is applied to the first electrode 4, and a charge is transferred to the surface of the liquid pipe 1 in the discharge area and penetrates into the liquid pipe 1 through the first through hole 3.

[0035] The liquid pipeline 1 is energized, generating a spray to achieve sample ionization.

[0036] An ionization control method based on mass spectrometry signal feedback, applied to the ionization device of this embodiment, includes the following steps: real-time acquisition of the spectral signal of the mass spectrometer.

[0037] Determine whether the decrease in signal strength over three consecutive scan cycles exceeds a preset threshold of 25%.

[0038] If the voltage exceeds the limit, the second electrode 5 will be immediately triggered to operate with a voltage of 5-8 kV and a pulse width of 10-100 ms.

[0039] Example 2

[0040] An example of the application of the mass spectrometry system and method in rapid on-site detection according to Example 1.

[0041] As shown in Figure 1, the direct ionization unit adopts DBDI, which includes a quartz dielectric tube 8 with an inner diameter of 2 mm, a first electrode 4, and a power supply (using a lithium battery). The power supply applies a first voltage to the first electrode 4.

[0042] Liquid pipe 1 is a metal pipe with an inner diameter of 100μm. One end of the part that extends into the medium pipe 8 is pointed and has a length of 10mm.

[0043] The first through hole 3 is disposed on the portion of the liquid pipe 1 that extends into the direct ionization unit. The projection of the first through hole 3 (with a diameter of 20 μm) onto the plane containing the central axis of the liquid pipe 1 falls completely within the projection of the first electrode 4 onto the plane.

[0044] A second through hole 2 and a third through hole 7 are provided on the liquid pipe 1 located outside the medium pipe 8, and the second through hole 2 and the third through hole 7 are symmetrical about the central axis.

[0045] The second electrode 5 is disposed around the dielectric tube 8 and is located downstream of the first electrode 4; the power source is the second electrode 5, which applies a second voltage higher than the first voltage.

[0046] The controller controls whether the second voltage is applied based on the mass spectrometry signal. For example, if the mass spectrometry signal drops beyond a threshold within multiple scan cycles, a pulsed second voltage is applied; otherwise, the second voltage is turned off.

[0047] The mass spectrometer cone 6 extends into the medium tube 8 and remains sealed, making the inside of the medium tube 8 a closed space that allows only liquid samples to enter and ions to exit.

[0048] The working method of the mass spectrometry system in this embodiment is as follows: the sample separated by nanoLC is introduced through liquid pipe 1 at a flow rate of 200 nL / min.

[0049] A voltage of 3.5kV is applied to the first electrode 4, and charge accumulates on the surface of the liquid pipe 1.

[0050] The tip generates a Taylor cone and sprays ionization, which enters the mass spectrometer cone 6.

[0051] Enter the linear ion trap for analysis (mass range 50-2000 m / z) to obtain the mass spectrometry signal.

[0052] When the mass spectrometry signal amplitude drops by more than 25% within 3 scan cycles, the mass spectrometry signal triggers the second electrode 5 to perform intermittent discharge. The second voltage is 5kV and the pulse width is 10ms.

[0053] Example 3

[0054] To verify the superiority of the present invention, the following comparative experiment was conducted: A methanol-water solution containing 1 ppm methamphetamine standard was introduced into a liquid pipeline at a flow rate of 100 nL / min, and mass spectrometry signal was detected under the ionization device and mass spectrometry parameter settings of Example 2.

[0055] The conventional external ion beam DBDI device is used to generate plasma that ionizes the sample ejected from the LC below at a flow rate of 200 nL / min.

[0056] Under the same mass spectrometry conditions, the signal-to-noise ratio (S / N) of the target analyte (m / z 150) in the experimental group was 1250, while the S / N of the control group was only 105. The limit of detection (LOD) of the experimental group reached 0.1 ppb, which was 10 times higher than that of the control group (1 ppb).

[0057] By measuring the ion current intensity and sample consumption rate, it was estimated that the effective ionization efficiency (sample utilization rate) of the experimental group exceeded 90%, while the efficiency of the control group was less than 50% due to droplet sputtering and ion diffusion loss.

[0058] Example 4

[0059] This embodiment demonstrates the ability of the present invention to directly analyze complex biological fluids without the need for liquid chromatography separation.

[0060] A drop of capillary blood (approximately 5 μL) was diluted 5-fold with methanol and centrifuged to obtain the supernatant. Using the mass spectrometry system of this invention, with nanoLC disabled, the processed blood sample supernatant was directly injected into the liquid pipeline at a flow rate of 500 nL / min. The liquid pipeline was set to low-speed rotation (200 rpm) to optimize charge distribution, successfully detecting multiple endogenous metabolites simultaneously in a single mass spectrometry scan, such as glucose (m / z 203.05).

[0061] Quantitative analysis of the added valproic acid was performed, as shown in Figure 2, achieving a broad linear range (R0) of 20-200 µg / mL in the blood sample. 2 >0.99), CV less than 2.09%. This demonstrates the powerful direct analytical capability of this invention for complex, high-matrix samples, with a linear range covering the actual effective blood drug concentration range, and R... 2 Both CV and CV meet the testing requirements.

Claims

1. A direct ionization device, comprising a direct ionization unit; characterized in that, The ionization device further includes: a liquid pipe, one end of which is inserted into the direct ionization unit and sealed to the direct ionization unit; and a first through hole, which is disposed on the portion of the liquid pipe extending into the direct ionization unit, wherein the projection of the first through hole onto a plane including the central axis of the liquid pipe falls entirely within the projection area of ​​the first electrode of the direct ionization unit onto the plane.

2. The ionization device according to claim 1, characterized in that, The diameter or length of the first through hole is between 10μm and 50μm.

3. The ionization device according to claim 1, characterized in that, The ionization device further includes a driving unit for driving the liquid pipeline to rotate around its center.

4. The ionization device according to claim 1, characterized in that, The ionization device further includes a second electrode and a controller. The second electrode surrounds the dielectric tube of the direct ionization unit and is located downstream of the first electrode. The controller controls the second electrode to operate intermittently in a pulse mode based on the mass spectrometry signal.

5. The ionization device according to claim 4, characterized in that, The controller operates by dynamically triggering the second electrode to operate in pulse voltage mode based on the intensity change of the real-time detection signal.

6. The ionization device according to claim 1, characterized in that, A second through hole and a third through hole are provided on the liquid pipe located outside the medium pipe, and the second through hole and the third through hole are symmetrical about the central axis.

7. A mass spectrometry system, characterized in that, include: Miniaturized mass spectrometer, weighing ≤20kg; The ion source is the ionization device according to any one of claims 1-6, which is installed at the front end of the sample inlet cone of the miniaturized mass spectrometer.

8. A direct ionization method, using the ionization apparatus according to any one of claims 1-6, characterized in that, The process includes the following steps: introducing a liquid sample into the liquid pipeline; applying a voltage to the first electrode to cause it to discharge, the resulting charge accumulating on the outer surface of the liquid pipeline and penetrating through the first through hole, thereby charging the liquid pipeline and generating a Taylor cone at its end, causing the liquid sample to undergo a Coulomb explosion, thus achieving direct spray ionization.

9. An ionization control method based on mass spectrometry signal feedback, applied to the ionization device as described in claim 4 or 5, characterized in that, The process includes the following steps: acquiring the spectral signal from the mass spectrometer in real time; determining whether the decrease in signal intensity over three consecutive scan cycles exceeds a preset threshold of 25%; If the voltage exceeds the limit, the second electrode will be immediately triggered to operate with a voltage of 5-8 kV and a pulse width of 10-100 ms.

10. An application of the mass spectrometry system as described in claim 7 in rapid on-site detection, characterized in that, Used for direct mass spectrometry analysis of liquid samples that have not undergone chromatographic separation or simple pretreatment.

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