RU2451364C1 - Apparatus for orthogonal input of ions into ion-drift or mass-spectrometer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apparatus for separation and orthogonal input of ions is in form of a T-shaped coupling of a gas-dynamic and an input channel, wherein the input channel consists of a diaphragm and an electrostatic lens system. The electrostatic field of the lens system of the orthogonal channel draws ions into the drift region and big droplets fly in the initial direction.

EFFECT: reduced clogging of input interface elements, charging of said elements and reduced noise in the detected spectrum.

2 cl, 3 dwg

Description

The alleged invention relates to the field of ion-drift and mass spectrometry and will find wide application in solving problems of organic and bioorganic chemistry, immunology, biotechnology and medicine in the ionization of the studied substances by the method of "electrospray" and others. The method of "electrospray" is one of the modern methods of "soft" ionization, which allows you to translate into the gas phase and simultaneously ionize large biological molecules such as peptides, proteins and polynucleotides. However, the existing mass and ion drift spectrometers with direct coaxial ion input have a number of factors limiting their operability. The presence of large unevaporated droplets flying from the source leads, as a rule, to clogging and clogging of the input interfaces, charging of their elements, and an increase in noise in the recorded spectrum.

Known ion-drift spectrometer with a source of ions of the type "electrospray" [1], where the source and the drift region are located on the same axis. In this case, large drops fall into the ion-drift spectrometer, which complicates the analysis, as well as the operation of the device.

The closest known one, chosen as a prototype, is an orthogonal ion input device [2] - non-axial configuration of the electrospray when the source axis is at an angle to the input. Such an input device avoids clogging or clogging of the inlet when introducing ions into the mass spectrometer analyzer, since when using an off-axis configuration of the electrospray, large droplets fly by. Thus, the mass spectrometer is prevented from dropping large droplets inside, and the ions are pulled by an electric field. However, in this device, ions are introduced directly into the pumped area of the mass spectrometer without preliminary ion separation.

The presence of curved channels behind the input skimmer of the mass spectrometer [3] also helps to solve the problem. In the presence of curved channels, heavy drops, due to greater inertia, cannot fit into the rotation and are lost on the channel wall. However, due to the reduced pressure in the system, the effectiveness of this method is not fully implemented.

The objective of the invention is to significantly reduce the degree of contamination of the input system of both the ion-drift spectrometer and the mass spectrometer with solvent droplets, with the possibility of increasing the flow intensity and reducing noise in the recorded drift spectrum.

The problem is solved by separating ions directly at atmospheric pressure in the area in front of the input devices of ion-drift or mass spectrometers. The ion input device is made orthogonal in the form of a T-shaped joint of the gas-dynamic and input channels, the latter consists of a diaphragm and elements of an electrostatic lens system. In this case, large atomized droplets are carried by the gas stream further down the channel and thereby do not enter the input system, and the ions are drawn into it by the electric field.

Figure 1 shows a General view (in section) of the device orthogonal separation and input of ions into the ion-drift or mass spectrometer together with the characteristic trajectories of the ions.

Figure 2 shows a diagram of the proposed device. The ion input device (FIGS. 1, 2) consists of an electrospray type ion source (not shown), a cylindrical channel 1, an orthogonal input channel with a diaphragm 2, a lens system 3-7, and a grid 8 (Bradbury-Nielsen ion-drift shutter spectrometer or in place of the grid is the input skimmer of the mass spectrometer).

Figure 3 illustrates the physical principle of the device: the characteristic ion paths are shown depending on their proximity to the entrance of the drift region at different values of the applied pulling potential.

The proposed device operates as follows (figure 2, 3). Ions and large atomized droplets formed in the electrospray source move in a gas stream along a cylindrical channel — tube 1. At atmospheric pressure, the ion velocity is taken to be equal to the gas gas velocity U _gas . Perpendicular to the axis of the tube is the input channel of an ion-drift or mass spectrometer. A pulling electrostatic potential is supplied to the input diaphragm 2 (Fig. 2) of the ion-drift channel. Behind the input diaphragm is a lens system 3-7 (figure 2). When the ions carried away by the gas flow approach the region of the inlet of the ion-drift channel, the electric field E of the input diaphragm 2 begins to act on them. A component of the velocity of motion appears, determined by the ion mobility coefficient k ₀ - U = k ₀ E. Thus, total velocity of ion motion will consist of the motion in the gas stream and motion in an electric field input system - U _ion = U _gas + k ₀ E. characteristic resulting ion trajectories obtained by SIMION program [4] and podprog Amma [5] are shown in Figure 2. For definiteness, the ion mobility coefficient is assumed to be 2 cm ² / (V · s). In this example, the gas flow velocity U _gas = 12 cm / s, the potential of the input diaphragm 2 relative to the tube potential V ₂ = -100 V, respectively V ₃ = -500 V, V ₄ = -600 V, V ₅ = -700 V, V ₆ = -800 V, V ₇ = -900 V. The potential of grid 8 (the Bradbury-Nielsen gate of the ion-drift spectrometer or the input skimmer of the mass spectrometer located in place of the grid) is V ₈ = -1000 V. The diffusion of the ion in the gas is determined from the Einstein relation [6], which relates the mobility coefficient k ₀ to the diffusion coefficient D:

where k _B is the Boltzmann constant, T is the temperature, Ze is the ion charge. Then, the ion displacement beyond Δt due to diffusion equiprobable in directions will be equal to (6DΔf) ^½ . Diffusion leads to a slight distortion of the trajectory of the ion.

The “falling through” electric field of the input system will not have a significant effect on heavy or uncharged droplets and they, carried away by the gas stream, will pass by. In this case, the ions will be drawn into the input system. The spatial configuration of an electric field falling into the gas-dynamic channel facilitates the focusing of ions on the axis, regardless of the ordinate of the ion in the flow. It can be seen that following the field lines of force, the ions envelope the edge of the input system. The efficiency of ion capture by an electric field depends both on the applied potential and on the coordinate of motion of the ion relative to the channel cross section. Figure 3 shows the efficiency of ion capture, depending on their initial position and the magnitude of the addictive electric field (-90, -150, -180, -210 V at the input diaphragm, the potential of the cylindrical channel 0 V) and a constant gas flow rate of 24 cm / from. It can be seen that ions moving along the far wall are weaker deflected in the electric field that sinks into the channel. As the potential of the input system grows, the efficiency of ion capture over the cross section increases. At a potential of -210 V (FIG. 3), all ions enter the input system of an ion-drift or mass spectrometer. However, too strong a field can lead to pulling in large drops, which is undesirable.

Thus, the proposed device for orthogonal input of ions into the input system of an ion-drift or mass spectrometer helps to achieve this goal, namely, to reduce clogging of the elements of the input interfaces, charging their elements, and reducing noise in the recorded spectrum.

Information sources

1. Tang X., Bruce J.E., Hill H.H. Characterizing electrospray ionization using atmospheric pressure ion mobility spectrometry // Anal. Chem. 2006, v. 78, p. 7751-7760.

2. Apffel J.A., Werlich M.H., Bertsch J.L., Goodley P.C. Orthogonal ion sampling for electrospray LC / MS. US patent: 5495108, date of patent Feb. 27, 1996. (prototype)

3. Bajic S. Electrospray and atmospheric pressure chemical ionization mass spectrometer and ion source. US patent: 5756994, date of patent May 26.1998.

4. Dahl D.A. SEMION 7 User's Manual. Idaho National Engineering Lab., 2000, 657 p.

5. Kurnin I.V., Samokish V.A., Krasnov H.B. Modeling the work of an ion-drift spectrometer with a Bradbury-Nielsen shutter // Scientific Instrument Engineering, 2010, v.20, No. 3 (in press).

6. Smirnov B.M. Diffusion and mobility of ions in a gas.// UFN, 1967, vol. 92, issue 1, pp. 75-103.

Claims (2)

1. A device for orthogonal ion input into an ion-drift or mass spectrometer, including an electrospray ion source, characterized in that the orthogonal ion input is made in the form of a T-shaped joint of the gas-dynamic and input channels, while the input channel consists of a diaphragm and elements of an electrostatic lens system. 2. The device according to claim 1, characterized in that the gas-dynamic channel has a cylindrical shape.

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