CN103681204A - Ion transmission system for inductively coupled plasma mass spectrometry - Google Patents

Abstract

The invention belongs to the technical field of mass spectrographies, and relates to an ion transmission system for an inductively coupled plasma mass spectrometry. The ion transmission system comprises an ion sampling cone, an interception cone, an extraction lens, an ion deflecting electrode and ion focusing lenses, wherein the centers of all the parts are on coaxial horizontal lines; space electric field distribution is generated under a DC voltage; ions deflect, focus and are transmitted under the action of the electric field; photons and neutral particles in a sample are free from the action of the electric field, transmitted linearly, and blocked while meeting the ion deflecting electrode; electrified ions are guided by the electric field, bypass the ion deflecting electrode, and focus into an ion beam under the action of the electric field of the focusing lenses, and then are transmitted to a mass analyzer. The ion transmission system has the advantages that the structure is simple; the use is convenient; interference signals generated due to the entering of the photons and the neutral particles can be removed effectively; the ion transmission efficiency and the sensitivity of the inductively coupled plasma mass spectrometry are improved.

Description

Inductively Coupled Plasma Mass Spectrometry Ion Transport System

technical field

The invention belongs to the technical field of mass spectrometry, and relates to an inductively coupled plasma mass spectrometry ion transmission system, in particular to a novel ion transmission device and method for inductively coupled plasma mass spectrometry.

Background technique

Inductively coupled plasma mass spectrometry (ICP-MS) is an analytical and testing technology developed rapidly in the 1970s. Its principle is to use inductively coupled plasma to ionize the elements contained in the analysis sample into charged ions, and pass through the ion transmission system Charged ions are introduced into the mass analyzer and separated according to different mass-to-charge ratios. After the ion current is amplified by the detector, the measurement and control system processes and gives the analysis results. Compared with other analytical techniques, the ICP-MS has the advantages of low detection limit, wide linear range, rapid and simultaneous detection of various elements, and the like. With the expansion of the scope of application, ICP-MS has developed into a routine analysis and testing technique in this field.

Usually, inductively coupled plasma mass spectrometry (ICP-MS) is mainly composed of ICP ion sampling system, interface system, ion optical transmission system, and mass analysis and detection system. Among them, the ion optical transmission system is a key part of ICP-MS technology, which determines the transmission of ions from the interface part of the instrument to the mass analyzer. It is an important bridge between the inductively coupled plasma ion source and the mass analyzer, and its performance is also directly It determines the most critical performance indicators such as sensitivity and detection limit of ICP-MS.

In the ICPMS instrument, the ICP plasma generated by the torch enters the ion transmission system through the sampling cone and skimmer cone of the interface part to reach the mass analyzer. ICP plasma ions are composed of electrons, ions, photons and neutral particles. The function of the ion lens in the ion transmission system is to accelerate the ion flow, focus it into an ion beam, and then transmit it to the mass analyzer, while blocking the photons and neutral particles. sex particles. Since ions are charged particles, the electric field can deflect them, while photons and neutral particles are not affected by the electric field and propagate in a straight line. Therefore, photon baffles or off-axis deflection methods are generally used to separate ions and photons and neutral particles ( uncharged particles) are separated.

At present, the ion transport systems used in the mainstream products of ICPMS manufacturers have their specific designs and their own characteristics. Basically, they can achieve electric field deflection and separate charged particles from photons and neutral particles. The overall ion optical transmission system can be divided into three types: photon baffle type, ion axis type, and 90-degree deflection type.

The photon baffle type refers to placing a metal sheet between the skimmer cone and the ion lens coaxially, the photons and neutral particles passing through the skimmer cone are blocked by the metal baffle, and the charged positive ions in the ICP plasma are received by the ion lens The guidance of the photon, bypassing the photon baffle and then reuniting, while the electrons are blocked by the repulsion by the electric field of the ion lens, the neutral particles encounter the baffle during the transmission process and stop the transmission, and the charged positive ions are under the action of the electric field of the ion lens Next, the ion beam focused into the smallest divergence angle bypasses the baffle and enters the mass analyzer. Although this structural design prevents the photons and neutral particles in the ICP plasma from directly entering the detector to cause a signal response, it also causes nearly 80% ion loss, resulting in low efficiency of ion transmission and mass discrimination.

The ion axis deflection type is that the ion flow is extracted by the extraction lens after the skimmer cone, and after the focusing of the lens group and the electric field action of the deflection lens, the ion beam leaves the optical axis and passes through the small hole deviated from the optical axis on the differential plate to enter the mass The analyzer uses the characteristic that neutral particles and photons are not affected by the electric field and still advances along the optical axis to separate from the ions. The transmission efficiency of the ions is improved and the sensitivity is improved. However, the design of the entire ion optical system is extremely complicated, making the ions The cleaning and maintenance of the lens and other components becomes extremely difficult. At the same time, the sample matrix will directly hit the ion lens with high voltage to form a capacitive effect, which makes the instrument prone to drift.

The 90-degree deflection type deflects the ion beam by 90 degrees through the parabolic electric field, so that the background noise of photons and neutrons generated by the ICP ion source is quickly extracted by the vacuum system, thereby ensuring that the entire system has very high sensitivity. The focus of the 90-degree corner is not very stable, the speed and reproducibility are not high, and the structure of the ion optical system of the whole instrument is too complicated, which makes the overall maintenance and disassembly more difficult.

To sum up, the ion transmission system is in the middle hub between the sample ion source and the mass analyzer. Its importance is to efficiently transmit the sample ions generated by the ion source to the mass analyzer. Among them, there are a large number of neutral particles in the ICP sample ions And photons, the ion transmission system effectively removes neutral particles and photons in the sample ions during the transmission process. In view of the significant impact of the ion optical transmission system of ICP-MS on the analytical performance of the instrument, in order to increase the ion transmission efficiency, eliminate the influence of photons and neutral particles on the instrument, and improve the sensitivity of the instrument, various instrument manufacturers in this field plan to provide various Same ion optics structure.

Contents of the invention

The object of the present invention is to provide a novel ion transmission system for inductively coupled plasma mass spectrometry aiming at the defects of the prior art. The transmission system can effectively realize the ion deflection path, remove neutral particles and photons, and at the same time collect and focus the sample ions entering the mass analyzer, and enter the mass analyzer with appropriate kinetic energy and angle. The transmission system device can improve the transmission efficiency of ions, effectively improve the sensitivity of ions, has a simple structure, and is easy to assemble, disassemble and wash.

Specifically, the present invention provides an inductively coupled plasma mass spectrometry ion transmission system, which is characterized in that it mainly includes a sampling cone 101, a skimmer cone 102, an extraction lens 103, an ion deflection electrode 104, and an ion focusing lens group 105-109 The sample ions formed in the ICP torch are respectively transmitted to the mass spectrometer detection system (mass analyzer) through the sampling cone 101, skimmer cone 102, extraction lens 103, ion deflection electrode 104, and ion focusing lens group 105-109. More specifically, different operating voltages are applied to each component to form an effective electric field distribution, and the ions are deflected, focused, and transmitted under the action of this electric field; among them, photons and neutral particles are not affected by the electric field and are transmitted in a straight line. The ion deflection electrode is blocked; the charged ions are guided by the electric field, bypass the ion deflection electrode, focus into an ion beam under the electric field of the focusing lens group, and transmit it to the mass analyzer.

The DC voltage applied to each component in the system device of the present invention is distributed in a trapezoidal shape, which facilitates ion transmission and can effectively improve ion transmission efficiency.

In the present invention, the centers of the sampling cone, skimmer cone, extraction lens, ion deflection electrode, and ion focusing lens group are located on the coaxial horizontal line.

In the present invention, different operating voltages are respectively applied to the sampling cone, skimmer cone, extraction lens, ion deflection electrode, and ion focusing lens group to form an effective electric field distribution; ions are deflected, focused, and transmitted under the action of this electric field , wherein, the voltage value of the direct current voltage applied on the ion deflection electrode is lower than the direct voltage value of the extraction lens, forming a potential difference with the extraction lens voltage to facilitate ion transmission.

In the present invention, the ion deflection electrode is arranged behind the ion extraction lens and between the front half of the ion focusing lens group; its shape can be a cone, ellipse or rhombus. The ion deflection electrode of the present invention has a conical, elliptical or rhombus structure;

The shape of the cone includes a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, a cone with any angle, and a conical shape.

In the present invention, the sampling cone and the skimmer cone make the instrument transition from atmospheric pressure to a vacuum system, and simultaneously extract sample ions from the ICP plasma and enter the mass spectrometer. The taper of the sampling cone is larger than that of the skimmer cone, and the sampling cone The aperture is within 2mm, and the aperture of the skimmer cone is within 1mm, forming an effective differential vacuum system to facilitate ion transmission.

The extraction lens of the present invention is closely attached to the back of the skimmer cone, and a corresponding DC voltage is applied to the extraction lens to form a certain electric field to extract sample ions, which can defocus and focus the sample ions passing through the skimmer cone , forming an effective ion beam to reach the ion deflection electrode behind.

In the present invention, the shape of the ion focusing lens group is flat or cylindrical, consisting of two or more lens barrels, and the lenses are not connected to each other to maintain electrical insulation. An implementation of the present invention In the example, each lens barrel in the ion focusing lens group is isolated by ceramics;

In the present invention, different DC voltage values are loaded on each lens barrel to form an effective ladder potential with the DC voltage values of the extraction lens and the ion deflection electrode, which can achieve the purpose of extracting, defocusing and focusing the charged ions of the sample.

The ion transmission system of the present invention can be used in other types of mass spectrometers, or in any ion optical transmission system arrangement in the analytical field.

In actual operation, different DC voltage values are applied to the sampling cone, skimmer cone, extraction lens, ion deflection electrode, and ion focusing lens group to form an effective step potential difference; the sample ions formed in the ICP torch are formed by the analyte Charged ions, neutral particles and photons; sample ions pass through the sampling cone, interceptor cone, and extraction lens to reach the ion deflection electrode, where the neutral particles and photons are not affected by the electric field and are transmitted in a straight line; The cone and the extraction lens are on the coaxial line, the neutral particles and photons are blocked by the ion deflection electrode and cannot pass through, while the charged ions of the analyte are guided and controlled by the electric field of the ion lens, bypass the ion deflection electrode and then meet again, the ions The structure of the deflection electrode is more conducive to the transmission of ions, while the electrons will no longer exist due to the electric field repulsion of the ion lens, and the neutral particles will be excluded by the vacuum pump, eliminating the photons and neutral particles in the ICP plasma directly entering the detector. In response to the signal, the ion focusing lens transmits a certain directional velocity to the ions, and focuses them into an ion beam with the smallest possible divergence angle to enter the mass analyzer, which increases the ion transmission efficiency, eliminates the influence of photons and neutral particles, and achieves improved purpose of sensitivity.

The ICP-MS ion transmission system of the present invention has the following advantages:

The structure is simple and easy to use, and can effectively remove the interference signal generated by photons and neutral particles entering the detector; improve the ion transmission efficiency and the sensitivity of the mass spectrometer.

For ease of understanding, the ICP-MS ion transmission system of the present invention will be described in detail below through specific drawings and embodiments. It should be pointed out that the specific examples and accompanying drawings are only for illustration. Obviously, those skilled in the art can make various amendments and changes within the scope of the present invention according to the description herein. These amendments and Modifications are also included within the scope of the present invention.

Description of drawings

Figure 1(a) is a schematic diagram of the structure of the ion transport system;

Figure 1(b) is a schematic diagram of the triangular cone structure of the ion deflection electrode of the ion transport system;

Figure 1(c) is a schematic diagram of the quadrangular pyramid structure of the ion deflection electrode of the ion transport system;

Figure 1(d) is a schematic diagram of the pentagonal pyramid structure of the ion deflection electrode of the ion transport system.

Figure 2 is a diagram of the theoretical simulation calculation results in the ion transport system.

Fig. 3 is a schematic diagram of the overall application structure of the ion transport system.

Detailed ways

Example 1

As shown in Figures 1 to 3, the novel ion transmission system device of the inductively coupled plasma mass spectrometry (as shown in Figure 1 ) of the present invention has a structure consisting of a sampling cone 101, a skimmer cone 102, an extraction lens 103, an ion deflection electrode 104, Composed of ion focusing lens groups 105-109, the ion deflection electrode 104 is in the shape of a triangular cone as shown in Figure 1(b), a quadrangular cone as shown in Figure 1(c) or a pentagonal cone as shown in Figure 1(d); its 101～ The centers of 109 are all on the coaxial horizontal line, and DC voltage values are respectively applied to 101-109 to form an effective electric potential field, and the sample ions formed in the ICP torch respectively pass through the sampling cone 101, the skimmer cone 102, the extraction lens 103, and the ion The deflection electrode 104 and the ion focusing lens group 105-109 are transmitted to the mass spectrometry detection system, and the photons and neutral particles in the sample ions are not affected by the electric field during transmission and are still transmitted along the optical axis and are blocked by the ion deflection electrode 104; Photons and neutral particles cannot pass through the ion deflection electrode 104, thereby avoiding signal response interference caused by photons and neutral particles directly entering the detector, and the analyte ions in the sample ions are transmitted under the guidance and control of the ion electric field, After bypassing the ion deflection electrode 104 and then reuniting, under the action of the electric field of the focusing lens group 105-109, the analyte ions are focused into an ion beam and enter the mass analyzer; according to the design plan of the ion transmission system, it is established by simulation software Theoretical calculation simulation model, the simulation calculation results are shown in Figure 2. The voltage in the theoretical calculation process is according to the applied voltage method described in the embodiment. For a better description, this embodiment lists one of the example parameters to describe the entire simulation calculation process; during the theoretical simulation calculation modeling process, the sampling cone 201 taper hole The diameter is 1.5 mm, the aperture of the skimmer cone 202 is 1.1 mm, the inner diameter of the extraction lens 203 is 1 mm, the ion deflection electrode 204 adopts a triangular shape, and the ion focusing lens group 105-109 adopts a cylindrical shape with an inner diameter of 24 mm. The distance between each focusing lens barrel is 2 mm, and the DC voltage values +40V, +35V, +32V, + 30V, +30V, +25V, +20V, +18V, +15V, the charged ions are affected by the electric field, transmit along the optical axis, bypass the ion deflection electrode 204 and converge to the ion focusing lens group to focus to form a beam, transmit into the mass analyzer and finally to the detector. The results of theoretical simulation calculations show that the ion transmission rate of this ion transmission system device is more than 95%, and the DC voltage value on each electrode is adjusted according to different ion mass numbers to form an effective electric potential field, which is convenient for ion transmission and improves ion transmission. transmission efficiency and stability.

Claims (8)

1. An inductively coupled plasma mass spectrometry ion transmission system, characterized in that it consists of a sampling cone (101), a skimmer cone (102), an extraction lens (103), an ion deflection electrode (104), and an ion focusing lens group (105) ~(109) composition; The centers of the sampling cone, skimmer cone, extraction lens, ion deflection electrode, and ion focus lens group are located on the coaxial horizontal line, and the ion deflection electrode is placed behind the ion extraction lens, between the front half of the ion focus lens group, and the extraction lens is close to the the back of the skimmer cone; Different operating voltages are applied to each of the components to form an effective electric field distribution, and the ions are deflected, focused, and transmitted under the action of the electric field; among them, photons and neutral particles are transmitted in a straight line without being affected by the electric field. The ion deflection electrode is blocked; the charged ions are guided by the electric field, bypass the ion deflection electrode, focus into an ion beam under the action of the electric field of the focusing lens group, and transmit it to the mass analyzer. 2. The inductively coupled plasma mass spectrometry ion transmission system according to claim 1, characterized in that, the operating voltage applied to each component in the system device is a direct current voltage and is distributed in a trapezoidal shape. 3. by the described inductively coupled plasma mass spectrometry ion transmission system of claim 1 or 2, it is characterized in that, the voltage value of the DC voltage applied on the described ion deflection electrode is lower than the extraction lens DC voltage value, forms with extraction lens voltage a potential difference. 4. The inductively coupled plasma mass spectrometry ion transmission system according to claim 1, wherein the shape of the ion deflection electrode is cone, ellipse or rhombus. 5. by the described inductively coupled plasma mass spectrometry ion transport system of claim 4, it is characterized in that, described conical shape comprises triangular conic shape, quadrangular conic shape, pentagonal conic shape and the conic shape of any angle, and conical . 6. The inductively coupled plasma mass spectrometry ion transmission system according to claim 1, wherein the shape of the ion focusing lens group is flat or cylindrical, and consists of two or more lens barrels, The lenses are not connected to each other and are isolated and insulated by ceramics. 7. by the described inductively coupled plasma mass spectrometry ion transmission system of claim 6, it is characterized in that, load different DC voltage values on each lens barrel, form an effective ladder potential with extraction lens and ion deflection electrode DC voltage value , to extract, defocus and focus sample charged ions. 8. The use of the inductively coupled plasma mass spectrometry ion transmission system of claim 1 in any mass spectrometry instrument or ion optical transmission system.

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