An inductively coupled plasma mass spectrometry interface device

Abstract

The present invention discloses an inductively coupled plasma mass spectrometer interface device, comprising a sampling cone, a skimmer cone, a negative ion lens and a shell, wherein the sampling cone, the skimmer cone and the negative ion lens are sequentially arranged in the shell, a first through hole is arranged at the center of the sampling cone, a second through hole, a third through hole and a fourth through hole are sequentially arranged in the skimmer cone, the length of the second through hole is less than the length of the third through hole and the fourth through hole, and a diameter-changing device is arranged in the third through hole for changing the inner diameter of the third through hole. The advantages of the present invention are: 1. The design of the skimmer cone speeds up the extraction speed of ions, reduces the accumulation of high-matrix and high-salt samples at the skimmer cone mouth, and improves the phenomenon of signal drift; 2. The secondary pressure reduction of the skimmer cone and the involvement of the first slope and the second slope suppress the divergence of the ion beam after the skimmer cone, greatly improving the sensitivity of the instrument.

Description

Technical Field

[0001] The invention relates to the field of laboratory analytical instruments, and in particular to an interface device of an inductively coupled plasma mass spectrometer. Background Art

[0002] ICP-MS has now become a routine analytical method for trace and ultra-trace elements in aqueous solutions in analytical testing laboratories, and has been widely used in the fields of environment, semiconductors, medical treatment, food, etc. In the development of ICP-MS, the extraction interface has always been one of the focuses of researchers, and its transmission characteristics directly affect the analytical performance of ICP-MS instruments. Foreign instrument manufacturers have different designs for interfaces, each with its own advantages. For example, a sampling cone with a copper chassis is mainly related to heat dissipation; a cutting cone with an insert with a side hole affects the transmission path of the aerosol and improves the salt accumulation characteristics of the cone mouth; a design that uses different thicknesses for the central channel of the insert directly affects the convergence of ions, improves ion transmission, and increases the sensitivity of the instrument; a designed three-cone interface adds a cutting cone called a super cutting cone, which uses two-step pressure reduction and two-step sharp angles to intercept ions, and the third cone has a smaller angle, which effectively reduces the divergence of the ion beam after the cone and reduces the contamination of the mass spectrometry system after the cone; a sampling cone and a cutting cone with a slit are specially designed cone mouths, and the slit is used to input collision / reaction gas.

[0003] Domestic manufacturers rarely have their own designs for cone ports, and mainly use imported interface devices. As a result, two problems arise: (1) the operating cost of ICP-MS instruments is greatly increased, hindering the social service of domestic instruments; (2) the key design parameters of the cone are the aperture and shape, which are related to the design of the ion lens and the configuration of the vacuum system. The imported interface is not compatible with domestic instruments, which greatly reduces the sensitivity of the instrument and limits the development of domestic instruments into the application market. Summary of the invention

[0004] The object of the present invention is to provide an inductively coupled plasma mass spectrometry interface device.

[0005] In order to solve the above technical problems, the present invention is achieved through the following technical solutions: an inductively coupled plasma mass spectrometry interface device, comprising a sampling cone, a skimmer cone, a negative ion lens and a shell, wherein the sampling cone, the skimmer cone and the negative ion lens are arranged in sequence in the shell, a first through hole is arranged at the center of the sampling cone, a second through hole, a third through hole and a fourth through hole are arranged in sequence in the skimmer cone, the length of the second through hole is smaller than the length of the third through hole and the fourth through hole, and a diameter-changing device is installed in the third through hole for changing the inner diameter of the third through hole.

[0006] Preferably, the first through hole is a cylindrical through hole with a hole diameter of 1.0 mm to 1.1 mm.

[0007] Preferably, the second through hole is a tapered hole, and the distance between the second through hole and the air inlet end of the first through hole is , where δ is the mean free path of the collected particles, D0 is the aperture of the sampling cone, P0 is the atmospheric pressure, P1 is the low pressure after passing through the sampling cone, and the aperture of one end of the conical hole is 0.45mm to 0.75mm, and the aperture of the other end is 2.50mm to 3.50mm.

[0008] Preferably, the aperture of the second through hole is the same as the maximum value of the aperture of the first through hole, and the aperture of the third through hole is larger than the aperture of the second through hole.

[0009] Preferably, the diameter-changing device is a circular ring structure, with a diameter-changing through hole provided inside, and a first inclined surface and a second inclined surface are respectively provided at two ends of the diameter-changing through hole.

[0010] Preferably, the reducing device is installed in the third through hole, and the distance between the reducing device and the air inlet end of the second through hole is d1*tan(a)*k1, d1 is the hole length of the second through hole, a is half of the taper of the second through hole, and k1 is the coefficient.

[0011] Preferably, the angle between the first slope and the inner surface of the reducer is 30-60 degrees, the angle between the second slope and the inner surface of the reducer is 30-60 degrees, the length of the first slope and the second slope is 0.15m to 0.5m, and the length and height of the first slope and the second slope are d1*tan(a)*k3, where k3 is a coefficient.

[0012] Preferably, the length of the third through hole is equal to the length of the fourth through hole.

[0013] Compared with the prior art, the advantages of the present invention are:

[0014] 1. The design of the interceptor cone speeds up the extraction of ions, reduces the accumulation of high-matrix and high-salt samples at the interceptor cone mouth, and improves the phenomenon of signal drift;

[0015] 2. The design of the secondary pressure reduction of the skimmer cone and the first and second slopes suppresses the divergence of the ion beam after the skimmer cone, greatly improving the sensitivity of the instrument;

[0016] 3. The faster extraction speed of the intercepting cone reduces the deposition of plasma gas flow at the cone mouth and improves the signal drift caused by high-matrix and high-salt samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the present invention;

[0018] Figure 2 It is a schematic diagram of the diameter-changing device of the present invention;

[0019] Figure 3 It is a closed boundary area simulated by MATLAB of the present invention;

[0020] Figure 4 The charge density distribution behind the second through hole of the present invention;

[0021] Figure 5 is the space charge field distribution on the yz plane of the present invention;

[0022] Figure 6 It is the space charge field distribution at various locations on the xy cross section of the present invention.

[0023] 1-sampling cone, 11-first through hole, 2-intercepting cone, 21-second through hole, 22-third through hole, 23-fourth through hole, 3-negative ion lens, 4-diameter reducing device, 41-first inclined plane, 42-diameter reducing through hole, 43-second inclined plane. DETAILED DESCRIPTION

[0024] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0025] like Figure 1 and Figure 2 As shown: an inductively coupled plasma mass spectrometer interface device, including a sampling cone, a skimmer cone, a negative ion lens and a shell, wherein the sampling cone, the skimmer cone and the negative ion lens are arranged in sequence in the shell.

[0026] The sampling cone is provided with a first through hole at the center, which is a cylindrical through hole. According to the Debye length formula:

[0027] ;

[0028] Where ε0 is the vacuum dielectric constant, Te is the electron temperature, k B is the Boltzmann constant, n e is the electron density. When the Debye length is much smaller than the spatial size, the plasma is quasi-neutral. It can be seen that the Debye length of the plasma gas flow at the sampling cone is about 10-5mm. In order to ensure quasi-neutrality, the Debye length must be much smaller than the sampling cone aperture. Generally, the aperture of the first through hole is 1.0mm to 1.1mm.

[0029] The intercepting cone is provided with a second through hole, a third through hole and a fourth through hole in sequence, the length of the second through hole is smaller than the length of the third through hole and the fourth through hole, and the third through hole is provided with a diameter reducing device for changing the inner diameter of the third through hole. Because the position of the Mach disk affects the best position of the test result, when the second through hole is located at two-thirds of the distance from the first through hole to the Mach disk, the best ion response can be obtained. At this time, the position Xs of the second through hole (i.e., the distance between the second through hole and the air inlet end of the first through hole) can be calculated by the following formula:

[0030] ;

[0031] Where δ is the mean free path of the collected particles, D0 is the aperture of the sampling cone, P0 is the atmospheric pressure, and P1 is the low pressure after passing through the sampling cone. The position of the intercepting cone is calculated to be approximately in the range of 10mm to 11mm. The second through hole is a conical hole, and the aperture of one end of the conical hole is 0.45mm to 0.75mm, and the aperture of the other end is 2.5mm to 3.5mm.

[0032] After the plasma gas flow passes through the interceptor cone, as the electron density decreases, the Debye length increases, the quasi-neutral state is destroyed, and the space charge effect is obvious. The closed boundary region constructed by MATLAB is used to simulate the space charge effect. Figure 3 This model assumes that the ion beam has no losses. Figure 3 The ions are evenly distributed on the same cross section. Since the sample ion content is much smaller than that of argon ions, only the argon ion flow is considered here. The relationship between the charge density ρ and the distance z behind the interceptor cone can be calculated from the charge continuity and ion movement speed. Figure 4 Calculations show that the distribution of equipotential lines of the electric field formed by space charges is as follows: Figure 5 As shown: The space charge field distribution on the cross section is obtained from (z = 250), and the result is as follows Figure 6 As shown. The area with serious space charge effect is mainly concentrated in the area where the ion beam is just formed. The electric field strength formed by the space charge is radially outward, and the sample ions with small mass are more easily pushed outward, while the sample ions with large mass are not easily repelled. As a result, the loss of light ions is more serious than that of heavy ions, which is the light mass discrimination phenomenon. In summary, the position of the third through hole is at a distance of d1*tan(a)*k2 from the air inlet end of the second through hole, d1 is the hole length of the second through hole, a is half of the taper of the second through hole, and k2 is the coefficient. After experiments, it was found that when k2 is in the range of 14 to 20, the device effect is best.

[0033] The third through hole is provided with a diameter reducing device, which is a circular ring structure, and a diameter reducing through hole is provided inside. The two ends of the diameter reducing through hole are provided with a first inclined surface and a second inclined surface respectively. The distance between the diameter reducing device and the air inlet end of the second through hole is d1*tan(a)*k1, d1 is the hole length of the second through hole, a is half of the taper of the second through hole, and k1 is the distance coefficient. After testing, it was found that the device effect is best when k1 is in the range of 25 to 40. The diameter reducing through hole is 10 to 18 times the size of the second through hole. The angle between the first inclined surface and the inner surface of the diameter reducing device is 30-60 degrees, the angle between the second inclined surface and the inner surface of the diameter reducing device is 30-60 degrees, the length of the first inclined surface and the second inclined surface is 0.15m to 0.5m, and the height of the first inclined surface and the second inclined surface is d1*tan(a)*k3, k3 is the coefficient. After testing, it was found that the device effect is best when k3 is in the range of 0.45 to 1.85.

[0034] The above description is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. An inductively coupled plasma mass spectrometer interface device, comprising a sampling cone, a skimmer cone, a negative ion lens and a housing, characterized in that: The housing is provided with a sampling cone, a skimmer cone and a negative ion lens in sequence, the sampling cone is provided with a first through hole at its center, the skimmer cone is provided with a second through hole, a third through hole and a fourth through hole in sequence, the second through hole is shorter than the third through hole and the fourth through hole, the third through hole is provided with a diameter-changing device for changing the inner diameter of the third through hole, and the third through hole includes an inner diameter-reducing section, an inner diameter-unchanging section and an inner diameter-enlarging section; The second through hole is a tapered hole, and the distance between the second through hole and the air inlet end of the first through hole is , where δ is the mean free path of the collected particles, D0 is the aperture of the sampling cone, P0 is the atmospheric pressure, P1 is the low pressure after passing through the sampling cone, and the aperture of one end of the conical hole is 0.45mm to 0.75mm, and the aperture of the other end is 2.50mm to 3.50mm.

2. The inductively coupled plasma mass spectrometry interface device according to claim 1, characterized in that: The first through hole is a cylindrical through hole with a hole diameter of 1.0 mm to 1.1 mm.

3. The inductively coupled plasma mass spectrometry interface device according to claim 1, characterized in that: The aperture of the third through hole is the same as the maximum value of the aperture of the second through hole, and the aperture of the fourth through hole is larger than the aperture of the third through hole.

4. The inductively coupled plasma mass spectrometry interface device according to claim 1, characterized in that: The diameter-changing device is a circular ring structure, and a diameter-changing through hole is arranged inside. The two ends of the diameter-changing through hole are respectively provided with a first inclined surface and a second inclined surface.

5. The inductively coupled plasma mass spectrometry interface device according to claim 4, characterized in that: The reducing device is installed in the third through hole, and the distance between the reducing device and the air inlet end of the second through hole is d1*tan(a)*k1, d1 is the hole length of the second through hole, a is half of the taper of the second through hole, and k1 is the coefficient.

6. The inductively coupled plasma mass spectrometry interface device according to claim 4, characterized in that: The angle between the first slope and the inner surface of the reducing device is 30-60 degrees, the angle between the second slope and the inner surface of the reducing device is 30-60 degrees, the length of the first slope and the second slope is 0.15m to 0.5m, and the height of the first slope and the second slope is d1*tan(a)*k3, d1 is the hole length of the second through hole, a is half of the taper of the second through hole, and k3 is the coefficient.

7. The inductively coupled plasma mass spectrometry interface device according to claim 1, characterized in that: The length of the third through hole is equal to the length of the fourth through hole.

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