A continuous sampling ion trap mass spectrometer and analysis method

Abstract

The present invention discloses a continuous sampling ion trap mass spectrometer and an analysis method. The present invention realizes two-stage vacuum differential from atmospheric pressure to vacuum through a continuous atmospheric pressure interface and an aperture electrode, and is equipped with a side-illuminated VUV lamp and an ion transmission hexapole in the first-stage vacuum chamber. Ions are generated by the VUV lamp or directly generated by an external ionization source after the gas molecules to be measured pass through the capillary outlet, enter the ion transmission hexapole for focusing through the action of the airflow field, and finally enter the second-stage vacuum chamber through the aperture electrode for analysis. The ion transmission hexapole can increase the signal intensity by an order of magnitude and is simple to assemble. The device has a simple structure and can achieve high-sensitivity qualitative and quantitative analysis of samples. It has great application potential in the fields of national defense security and environmental monitoring.

Description

Technical Field

[0001] The present invention relates to a continuous-injection ion trap mass spectrometer and analysis method. This patent discusses the composition, structure, and usage of the mass spectrometer. The side-illuminated VUV lamp, used as an ionization source, has high ionization efficiency, enabling highly sensitive detection of volatile organic compounds. Furthermore, the side-illuminated lamp is designed to be perpendicular to the axis of the continuous atmospheric pressure interface, which does not affect the coupling of the rear-end ion trap with an external ionization source, broadening the instrument's application range. The patent combines hexapole transmission with a continuous-injection ion trap mass spectrometer for the first time, increasing signal strength by an order of magnitude. Background Art

[0002] Mass spectrometry is widely used in chemical analysis due to its high sensitivity, selectivity, and ability to analyze a vast majority of compounds. Ion trap mass spectrometry, in particular, is a hot topic in this field due to its compact size, high operating pressure, and time-series mass spectrometry capabilities. However, most common micro-ion trap mass spectrometers are equipped with a discontinuous atmospheric pressure interface, which limits the stability and robustness of the instruments and restricts their application.

[0003] This invention proposes a continuous-injection ion trap mass spectrometer equipped with a side-illuminated VUV lamp and hexapole transmission. Hexapole transmission significantly focuses ions at a pressure of 133 Pa, boosting signal intensity by an order of magnitude and enabling highly sensitive detection. After passing through the capillary outlet, the gas sample is ionized by the VUV lamp and focused by hexapole transmission before entering the ion trap chamber for detection. Ions generated by an external ionization source, such as an electrospray ionization source, can directly enter the instrument through the capillary for detection, broadening the instrument's application range.

[0004] In the literature, Zhai, YB; Feng, Y.; Wei, YZ; Wang, YZ; Xu, W., Development of aminiature mass spectrometer with continuous atmospheric pressure interface. Analyst 2015, 140 (10), 3406-3414. first proposed a micro ion trap mass spectrometer equipped with a continuous atmospheric pressure interface, and in subsequent work, an ion funnel was configured in the first-stage vacuum chamber for transmission, which increased the signal intensity by an order of magnitude (Analytical chemistry 2017, 89 (7), 4177-4183.). Currently, the radio frequency transmission devices used in micro continuous sampling ion trap mass spectrometers are all ion funnels, but the ion funnel has multiple capacitors and resistors, and the assembly is relatively complicated. The hexapole transmission device has a simple structure and is currently widely used in commercial mass spectrometers to focus ions. However, the current working pressure of the hexapole is 0.1Pa-10Pa, and few people use the hexapole for focusing at a pressure of 100Pa. In addition, the center of the built-in ionization source in the current continuous sampling ion trap mass spectrometer is on the same axis as the center of the continuous atmospheric pressure interface. Ions cannot enter the first-stage vacuum chamber through the continuous atmospheric pressure interface, so it can only work in external ionization source or built-in ionization source mode (Journal of the American Society for Mass Spectrometry 2020, 31(4), 961-968.), and the combination of the two cannot be achieved.

[0005] To address the complex assembly of the ion funnel in these instruments, the present invention proposes a continuous-injection ion trap mass spectrometer equipped with a side-illuminated VUV lamp and an ion-transmitting hexapole. The hexapole transmission boosts signal intensity by an order of magnitude, enabling highly sensitive qualitative and quantitative analysis with high detection stability. This instrument, capable of operating in two modes, has a wide range of applications and holds great promise for applications in chemical warfare agent simulants detection and environmental monitoring. Summary of the Invention

[0006] The present invention relates to a continuous-injection ion trap mass spectrometer and analysis method. The ion transmission hexapole effectively focuses ions, increasing signal intensity by an order of magnitude and enabling highly sensitive qualitative and quantitative analysis of samples. The side-illuminated VUV lamp design enables the mass spectrometer to operate in low-pressure photoionization mode or in an external ionization source mode, broadening the instrument's application range and showing great potential in fields such as national defense security and environmental monitoring.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A continuous sampling ion trap mass spectrometer comprises two connected vacuum chambers, wherein a first-stage vacuum chamber (2) and a second-stage vacuum chamber (7) are connected via an aperture electrode (6) (also known as a skimmer or vacuum differential electrode), an injection port (1) connected to the atmosphere, an annular focusing electrode (4) and an ion transmission hexapole (5) are provided in the first-stage vacuum chamber (2), the injection port (1) and the ion transmission hexapole (5) are respectively located on both sides of the annular focusing electrode (4), and an annular extraction electrode (8), an ion trap (9) and an ion detector (10) are provided in the second-stage vacuum chamber (7);

[0009] The first-stage vacuum chamber (2) and the second-stage vacuum chamber (7) are respectively connected to the air inlet of the mechanical pump (11) through pipelines, and the second-stage vacuum chamber (7) is connected to the air inlet of the molecular pump (12) through a pipeline.

[0010] A VUV lamp (3) is provided on the side wall of the first-stage vacuum chamber (2), with the light outlet of the VUV lamp (2) facing the interior of the chamber. The emitted light of the VUV lamp is transmitted in the chamber along an axis perpendicular to the annular focusing electrode (4), forming an ionization zone in the chamber. The ionization zone and the ion transmission hexapole (5) are respectively located on both sides of the annular focusing electrode (4).

[0011] The air pressure of the first-stage vacuum chamber (2) is higher than that of the second-stage vacuum chamber (7), and the air pressure in the first-stage vacuum chamber (2) is between 1-103Pa, while the air pressure in the second-stage vacuum chamber (7) is between 10-3-1Pa.

[0012] A capillary serving as an injection tube is inserted into the injection port, and the distance between the capillary outlet and the ion transmission hexapole inlet is 2-6 mm.

[0013] Different voltages V1 and V2 are applied to the annular focusing electrode and the aperture electrode in descending order, with a voltage difference of 10-50V.

[0014] The RF voltage frequency applied to the ion transmission hexapole is 1-2.5MHz, the peak-to-peak value Vp-p is adjustable from 100-340V, 5MHz, and the RF phase difference between adjacent rods is 180°; a DC voltage V3 is superimposed on the applied RF voltage, and the voltage of V3 is between V1 and V2 to ensure the smooth extraction of ions.

[0015] A ring-shaped extraction electrode is added between the aperture electrode and the ion entrance electrode of the ion trap. Together with the aperture electrode and the ion entrance electrode, it forms an electrostatic lens to focus the ions. The distances between the aperture electrode and the ring-shaped extraction electrode, and between the ring-shaped extraction electrode and the ion entrance electrode of the ion trap, are equal, at 2-4 mm. Different voltages, V4, V5, and V6, are applied to the aperture electrode, the ring-shaped extraction electrode, and the ion trap entrance electrode, in descending order.

[0016] The injection port, the annular focusing electrode, the ion transmission hexapole, the middle through hole of the aperture electrode, the annular extraction electrode (8), and the ion entrance electrode of the ion trap (9) are located on the same axis.

[0017] The ion trap (9) is a rectangular ion trap.

[0018] The sample is passively sucked into the first-stage vacuum chamber by negative pressure. After being focused by the ion transmission hexapole, the ions pass through the electrostatic lens composed of the aperture electrode, the annular extraction electrode and the ion trap entrance electrode and then enter the ion trap for detection.

[0019] The mass spectrometer can operate in either of two modes:

[0020] Low-pressure photoionization mode: The gas sample is passively sucked into the first-stage vacuum chamber by negative pressure, ionized by the VUV lamp, and then detected after passing through the ion guide device;

[0021] External ionization source mode: The ions generated by the external ionization source represented by the electrospray ionization source are passively sucked into the first-stage vacuum chamber under negative pressure and then detected after passing through the ion guide device.

[0022] The advantages of the present invention are:

[0023] 1. The outstanding advantages of this invention are: it increases the operating pressure of the ion transmission hexapole, introduces the ion transmission hexapole into a continuous injection ion trap mass spectrometer for the first time, and improves signal strength by an order of magnitude. The ion transmission hexapole has a simple structure, is easy to assemble, and is suitable for miniaturization.

[0024] 2. The side-illuminated VUV lamp design of the present invention achieves compatibility between low-pressure photoionization mode and external ionization source mode. For volatile organic compounds, the gas sample directly enters the first-stage vacuum chamber and is photoionized, with high photoionization efficiency and simple spectra. For liquid or fixed samples such as drugs and pesticides, an external ionization source such as an electrospray ionization source can effectively ionize the sample. After entering the first-stage vacuum, the ions pass through the ion transmission hexapole to reach the ion trap chamber for detection. The compatibility of the two modes broadens the application range of the instrument, and it has great application potential in areas such as national defense security and the environment.

[0025] 3. The mass spectrometer can achieve collision-induced dissociation in the first-stage vacuum chamber by increasing the radio frequency voltage amplitude of the ion transmission hexapole, generating fragment ions and improving qualitative accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0027] Figure 1This is a structural schematic diagram of a continuous sampling ion trap mass spectrometer involved in the present invention, wherein 1 is an inlet connected to the atmosphere, 2 is a first-stage vacuum chamber, 3 is a VUV lamp, 4 is an annular focusing electrode, 5 is an ion transmission hexapole, 6 is an aperture electrode, 7 is a second-stage vacuum chamber, 8 is an annular extraction electrode, 9 is an ion trap, 10 is an ion detector, 11 is a mechanical pump, and 12 is a molecular pump.

[0028] Figure 2 The present invention relates to a continuous injection ion trap mass spectrometer (such as Figure 1 ) Test results of the ion transmission hexapole for improving signal intensity.

[0029] Figure 3 The present invention relates to a continuous injection ion trap mass spectrometer (such as Figure 1 ) Test results for 500 ppb dimethyl methyl phosphate (DMMP).

[0030] Figure 4 The present invention relates to a continuous injection ion trap mass spectrometer (such as Figure 1 ) Test results of signal strength stability.

[0031] Figure 5 The present invention relates to a continuous injection ion trap mass spectrometer (such as Figure 1 ) Test results of collision-induced dissociation of 5ug / ml DMMP in the first-stage vacuum chamber.

[0032] Figure 6 The present invention relates to a continuous injection ion trap mass spectrometer (such as Figure 1 ) Test results of 100ug / ml heroin detected using an electrospray ionization source. DETAILED DESCRIPTION

[0033] Example 1

[0034] In order to make the contents of the present invention clearer and easier to understand, the contents of the present invention are described in detail below with reference to specific embodiments and drawings.

[0035] The mass spectrometer includes two connected vacuum chambers, wherein the first vacuum chamber 2 and the second vacuum chamber 7 are connected via an aperture electrode 6. An inlet 1 connected to the atmosphere, an annular focusing electrode 4, and an ion transmission hexapole 5 are provided in the first vacuum chamber 2. The inlet 1 and the ion transmission hexapole 5 are located on either side of the annular focusing electrode 4. An annular extraction electrode 8, an ion trap 9, and an ion detector 10 are provided in the second vacuum chamber 7.

[0036] A VUV lamp 3 is provided on the side wall of the first-stage vacuum chamber 2, with the light outlet of the VUV lamp 3 facing the interior of the chamber. The emitted light of the VUV lamp is transmitted inside the chamber along the axis direction perpendicular to the annular focusing electrode 4, forming an ionization zone in the chamber. The ionization zone and the ion transmission hexapole 5 are respectively located on both sides of the annular focusing electrode 4.

[0037] The air pressure in the first vacuum chamber 2 is higher than that in the second vacuum chamber 7, and the air pressure in the first vacuum chamber 2 is between 1 and 10 3 Pa, the pressure in the second vacuum chamber 7 is between 10 -3 -1Pa.

[0038] A capillary serving as an injection tube is inserted into the injection port, and the distance between the capillary outlet and the ion transmission hexapole inlet is 2-6 mm.

[0039] Different voltages V1 and V2 are applied to the annular focusing electrode and the aperture electrode in descending order, with a voltage difference of 10-50V.

[0040] The RF voltage frequency applied to the ion transmission hexapole is 1-2.5MHz, the peak-to-peak value Vp-p is adjustable from 100-340V, 5MHz, and the RF phase difference between adjacent rods is 180°; a DC voltage V3 is superimposed on the applied RF voltage, and the voltage of V3 is between V1 and V2 to ensure the smooth extraction of ions.

[0041] A ring-shaped extraction electrode is added between the aperture electrode and the ion entrance electrode of the ion trap. Together with the aperture electrode and the ion entrance electrode, it forms an electrostatic lens to focus the ions. The distances between the aperture electrode and the ring-shaped extraction electrode, and between the ring-shaped extraction electrode and the ion entrance electrode of the ion trap, are equal, at 2-4 mm. Different voltages, V4, V5, and V6, are applied to the aperture electrode, the ring-shaped extraction electrode, and the ion trap entrance electrode, in descending order.

[0042] The injection port, the annular focusing electrode, the ion transmission hexapole, the middle through hole of the aperture electrode, the annular extraction electrode (8), and the ion entrance electrode of the ion trap (9) are located on the same axis.

[0043] The ion trap 9 is a rectangular ion trap.

[0044] The sample is passively sucked into the first-stage vacuum chamber by negative pressure. After being focused by the ion transmission hexapole, the ions pass through the electrostatic lens composed of the aperture electrode, the annular extraction electrode and the ion trap entrance electrode and then enter the ion trap for detection.

[0045] The mass spectrometer of the present invention can operate in either of two modes:

[0046] The mass spectrometer can operate in either of two modes:

[0047] Low-pressure photoionization mode: The gas sample is passively sucked into the first-stage vacuum chamber by negative pressure, ionized by the VUV lamp, and then detected after passing through the ion guide device;

[0048] External ionization source mode: The ions generated by the external ionization source represented by the electrospray ionization source are passively sucked into the first-stage vacuum chamber under negative pressure and then detected after passing through the ion guide device.

[0049] The mass spectrometer of the present invention uses an ion transmission hexapole 5 to focus ions. In the low-pressure photoionization mode, two chemical warfare agent simulants, 100 μg / ml dimethyl methyl phosphate (DMMP, the same below) (N2) and 100 μg / ml dipropylene glycol methyl ether (N2), were used as samples to test the improvement of the ion transmission hexapole on signal intensity. The specific parameters are: the first stage vacuum chamber pressure is 133 Pa, the second stage vacuum chamber pressure is 6*10 -4 Pa, the distance between the capillary outlet and the ion transmission hexapole entrance is 6 mm, V1-V5 are 14 V, 14 V, 11 V, -10 V, and 1 V respectively, the RF voltage frequency applied to the ion transmission hexapole is 2.35 MHz, and the peak-to-peak value V p- The p is 280V, and the distance between the opening electrode and the ring extraction electrode, and the distance between the ring extraction electrode and the ion entrance electrode of the ion trap are all 3mm. Figure 3 As shown in the figure, the signal enhancement times of the two samples were 16 times and 33 times respectively.

[0050] The mass spectrometer of the present invention has the characteristics of high sensitivity and good stability. In the low pressure photoionization mode, the minimum detection limit for DMMP is 0.5ug / ml ( Figure 4 ). 100 consecutive tests were performed using 10ug / ml dipropylene glycol methyl ether as the sample, and the RSD of the instrument was 5.34% ( Figure 5 ), which proves that the instrument has good stability.

[0051] The mass spectrometer of the present invention can achieve collision-induced dissociation in the first-stage vacuum chamber by increasing the RF voltage amplitude of the ion transmission hexapole, generating fragment ions and improving qualitative accuracy. Taking 5ug / ml DMMP as the sample, the hexapole peak-to-peak value is set to 340V. p-p , the test results are as follows Figure 6 As shown. DMMP fragment ion [M+H-CH2] + ,[M+H-2CH2] + ,[M+H-2CH2-H2O] + It can be successfully detected, which improves the accuracy of qualitative analysis.

[0052] The mass spectrometer described in the present invention can operate in external ionization source mode. Using a 100 μg / mL sample of heroin (methanol / water = 1:1) and applying a voltage of 1200 V to the electrospray ionization source, fragment ions of heroin were successfully detected under electrospray ionization conditions. This demonstrates the successful combination of the mass spectrometer and the external ionization source, broadening the instrument's application range.

Claims

1. A continuous-injection ion trap mass spectrometer, characterized in that: The mass spectrometer comprises two connected vacuum chambers, wherein the first vacuum chamber (2) and the second vacuum chamber (7) are connected via an opening electrode (6), and an injection port (1) connected to the atmosphere, an annular focusing electrode (4) and an ion transmission hexapole (5) are provided in the first vacuum chamber (2), the injection port (1) and the ion transmission hexapole (5) are respectively located on both sides of the annular focusing electrode (4), and an annular extraction electrode (8), an ion trap (9) and an ion detector (10) are provided in the second vacuum chamber (7); The first-stage vacuum chamber (2) and the second-stage vacuum chamber (7) are respectively connected to the air inlet of the mechanical pump (11) through pipelines, and the second-stage vacuum chamber (7) is connected to the air inlet of the molecular pump (12) through pipelines; A VUV lamp (3) is provided on the side wall of the first-stage vacuum chamber (2), with the light outlet of the VUV lamp (3) facing the interior of the chamber. The light emitted by the VUV lamp is transmitted in the chamber along an axis perpendicular to the annular focusing electrode (4), forming an ionization zone in the chamber. The ionization zone and the ion transmission hexapole (5) are respectively located on both sides of the annular focusing electrode (4). An annular extraction electrode is added between the aperture electrode and the ion entrance electrode of the ion trap to form an electrostatic lens with the aperture electrode and the ion entrance electrode to focus the ions. The distances between the aperture electrode and the annular extraction electrode, and between the annular extraction electrode and the ion entrance electrode of the ion trap are equal, both of which are 2-4 mm. Different voltages V4, V5 and V6 are loaded on the aperture electrode, the annular extraction electrode and the ion trap entrance electrode in the order from high to low and then to high.

2. The mass spectrometer according to claim 1, wherein: The air pressure of the first stage vacuum chamber (2) is higher than that of the second stage vacuum chamber (7), and the air pressure in the first stage vacuum chamber (2) is between 1 and 10 3 Pa, the pressure in the second vacuum chamber (7) is 10 -3 -1Pa.

3. The mass spectrometer according to claim 1, wherein: A capillary serving as an injection tube is inserted into the injection port, and the distance between the capillary outlet and the ion transmission hexapole inlet is 2-6 mm.

4. The mass spectrometer according to claim 1, wherein: Apply different voltages V1 and V2 to the annular focusing electrode and the aperture electrode in descending order, with a voltage difference of 10-50V. The RF voltage applied to the ion transmission hexapole has a frequency of 1-2.5 MHz and a peak-to-peak value of V p-p It is adjustable from 100-340V, 5MHz, and the RF phase difference between adjacent rods is 180°; a DC voltage V3 is superimposed on the applied RF voltage, and the voltage of V3 is between V1 and V2 to ensure the smooth extraction of ions.

5. The mass spectrometer according to claim 4, wherein: The injection port, the annular focusing electrode, the ion transmission hexapole, the middle through hole of the aperture electrode, the annular extraction electrode (8), and the ion entrance electrode of the ion trap (9) are located on the same axis.

6. The mass spectrometer according to claim 1, wherein: The ion trap (9) is a rectangular ion trap.

7. An analysis method using the mass spectrometer according to any one of claims 1 to 6, characterized in that: The sample is passively sucked into the first-stage vacuum chamber by negative pressure. After being focused by the ion transmission hexapole, the ions pass through the electrostatic lens composed of the aperture electrode, the annular extraction electrode and the ion trap entrance electrode and then enter the ion trap for detection.

8. The analysis method according to claim 7, characterized in that: The mass spectrometer can operate in either of two modes: Low-pressure photoionization mode: The gas sample is passively sucked into the first-stage vacuum chamber by negative pressure, and then ionized by the VUV lamp and detected after passing through the ion guide device; External ionization source mode: The ions generated by the external ionization source represented by the electrospray ionization source are passively sucked into the first-stage vacuum chamber under negative pressure and then detected after passing through the ion guide device.

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