RU2608361C2 - Device for formation of drop-free ion flow at electrospraying of analyzed solutions in ion sources with atmospheric pressure - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to ion-drift and mass spectrometry and can be widely used in solving analytical tasks of organic and bioorganic chemistry, immunology, biotechnology, forensics science, proteomics, metabolomics at electrospraying of solutions of analyzed labile substances. Device for formation of drop-free ion stream during electrospraying of analyzed solutions in ion sources with atmospheric pressure is made in form of coaxial capillaries. Inner metal capillary is under ground potential, fluid pump supplies analyzed solution through it. At end of that capillary meniscus is formed, from surface of which ion flow is formed by electrospraying. Coaxial gap between capillaries is connected to air controlled extraction pump. Opposite to meniscus there is flat counter electrode with hole in center closed with sliding shutter, which are electrically connected to each other and are connected to high-voltage controlled source of supply. Sliding shutter shuts off penetration of drops in ion flow analyzer at beginning of electrospraying process and at its completion if process is not stationary. In version of horizontal orientation of hole axis in opposite electrode capillary, in end of which there is meniscus of sprayed solution is installed at angle to axis in horizontal plane for compensation of symmetry deformation of conical shape of meniscus under action of gravity.

EFFECT: obtaining drop-free ion flow at electrospraying of analyzed solutions in ion sources with atmospheric pressure under normal conditions, hence continuous stable spraying, stable operation of analyzer and stability of recorded spectra, reduced frequency of servicing of ion flow transfer device into analyzer for its cleaning.

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Description

The invention relates to the field of ion-drift and mass spectrometry and will find wide application in solving analytical problems of organic and bioorganic chemistry, immunology, biotechnology, forensics, proteomics, metabolomics during ionization of labile substances under study using the electrospray method. The method of "electrospray" is one of the modern methods of "soft" ionization, which allows you to transfer the ions of the studied labile substances, for example, such as peptides, proteins, polynucleotides, drugs, directly from solution into the gas phase. However, existing devices for the formation of a droplet-free ion flux during the electrospray of the analyzed solutions in ion sources with atmospheric pressure have a number of factors limiting the operability of ion sources. The impossibility of precisely matching the flows of the analyzed solution supplied to the spraying region over a wide range of space velocities (5 μl / min - 2000 μl / min) and its complete atomization with the formation of analyte ions without the presence of unevaporated microdrops entering the ion source in the gas-vapor stream, especially at the initial and final stages of spraying, as a rule, lead to clogging and clogging of the inlet diaphragms and conveying systems from the atmospheric pressure region to the high-vacuum region of the analyzer ion charging their elements, increase of noise and spurious signals in the recorded spectra.

Known electrospray devices for analyzed flows of solutions of substances [1, 2], where the electrospray device, the ion transport system of the source and the entrance to the ion analyzer are located on the same axis. In this case, large drops fall into the ion analyzer, which are formed from a liquid that accumulates on the outer side of the capillary, from the end of which the emission of charged microdrops occurs, which is due to the inconsistency of the flows of the incoming and sprayed solution. The ingress of large drops into the transporting system of the ion source and into the analyzer complicates the operation of the device and the analysis. Also known device orthogonal electrospray of the analyzed solution relative to the axis of input of charged particles into the analyzer transportation system [3]. This orientation of the electrospray device allows avoiding clogging or clogging of the input diaphragm of the system for transporting charged particles to the analyzer, since when using such a geometry of the solution electrospray assembly, large droplets by inertia predominantly fly past the entrance to the analyzer.

An improved device for orthogonal electrospray is [4] compared with [1, 2] supplemented with a coaxial capillary, through which a heated vaporizer gas is supplied to the zone of existence of the spray of the sprayed solution. The heated gas evaporator is designed to more efficiently evaporate the formed microdrops and, accordingly, increase the current of the analyzed ions from the solution. This combination of electrospray and stimulated evaporation of microdrops does not affect the existence of large droplets formed as a result of the unsteadiness of the spraying process. In turn, the non-stationary nature of the process of electrospray of the analyzed solution is mainly associated with the inability to coordinate the flow of the sprayed solution with the flow of the solution entering the spraying area — the meniscus at the end of the metal capillary. Excess solution wets the outside of the capillary, where a large drop begins to accumulate, until the electric field overcomes the wettability of the solution and tears it from the capillary. The size of such a drop is 100-1000 μm, which is much larger than the size of the droplets (≥1 μm), from which it is possible to extract ions of the substance. Such giant drops significantly complicate the work of the analyzer and lead to a distortion of analytical information (mobility spectra or mass spectra). A significant increase in the current of the analyzed ions entering the analyzer, a multiple increase in the flow of the sprayed solution, does not occur due to the influence of the space charge in the area of sputtering and extraction of ions from microdrops under normal conditions.

The closest known, selected as a prototype, is an electrospray device for chromatographic streams of analyzed solutions of substances for ion sources with atmospheric pressure [5].

In this device, compared with [4], a gas flow is used under normal conditions directed along a coaxial gap from the zone of existence of the spray of the sprayed solution. Such a combination of electrospraying and pumping out a vapor-gas mixture of an unsprayed solution avoids the appearance of microdrops in the ion stream in an ion source with atmospheric pressure under a steady-state spraying mode. In such a device for generating an ion flux during electrospray of analytes of solutions at atmospheric pressure, microdrops are formed as a result of the non-stationary state of the sputtering process at the initial and final stages of sputtering. The non-stationary nature of the electrospray process of the analyzed solution is mainly related to the inconsistency of the stream of the sprayed solution with the flow of the pumped gas mixture from the spraying area — the meniscus at the end of the metal capillary, which leads to instability of the ion flow (Fig. 1) [6].

The objective of the invention is to eliminate the conditions for the formation of droplets of a solution in the ion stream at the initial and final stages of the electrospray process in a wide range of spray flow rates, allowing long-term operation of the ion source and, accordingly, noise reduction in the recorded spectra caused by large drops.

The problem is solved due to the fact that in the known device for the formation of a droplet-free ion flow during electrospray of the analyzed solutions in an ion source with atmospheric pressure, the capillary, at the end of which the meniscus of the sprayed solution is located, is at zero potential - it is “grounded”, the outer capillary is larger diameter, the coaxial gap between the capillaries is connected to an air adjustable pump, a flat counter electrode with a hole in the center is closed sliding s flap, which are electrically connected together and connected to the high voltage regulated power supply. If the axis of the hole in the counter electrode is oriented horizontally, then the capillary, at the end of which the meniscus of the sprayed solution is located, is installed at an angle to the axis in the horizontal plane.

The inventive device for the formation of a droplet-free ion flow during electrospray of the analyzed solutions in ion sources with atmospheric pressure is shown schematically in FIG. 2. The internal metal capillary (1) is at zero potential - “grounded” (2), and a solution from a liquid micropump (3) is supplied through it. At the end of the capillary (1), a meniscus (4) is formed, from the surface of which an electrospray occurs with the formation of a droplet-free ion stream. Coaxial to the capillary (1) is an external dielectric capillary (5) with an inner diameter larger than the outer diameter of the capillary (1). Excess non-sprayed solution flowing down the outer wall of the capillary (1), together with the laboratory air, is pumped out by an air pump (6) through the gap between the coaxial capillaries (1) and (5). Opposite the end of the inner capillary (1) there is a flat counter electrode (7) with a central hole closed by a sliding controlled valve (8), an electrically counter electrode (7) and a sliding valve (8) are interconnected and connected to an adjustable high-voltage power supply (9). At the beginning of the electrospray process and at its completion, when the process is unsteady, a sliding gate valve closes the central hole of the counter electrode and does not pass the ion flow in the mixture with drops into the analyzer. If the axis of the hole in the counter electrode (7) is oriented horizontally, then the capillary (1), at the end of which the meniscus of the sprayed solution (4) is located, is installed at an angle to the axis in the horizontal plane to compensate for the symmetry deformation of the conical shape of the meniscus (4) under the influence of gravity .

In general, the removal of non-atomized or condensed liquid from the spray area, the use of adjustable parameters of the air pump and high-voltage power supply, the movement of the sliding gate along the counter electrode depending on the stage of electro-atomization make it possible to obtain a drop-free ion flow of substances from the analyzed solutions in ion sources with atmospheric pressure under normal conditions and efficiently transport the ion stream to the analyzer through the hole in the counter electrode. At the same time, during the analysis, there is no violation of the stability of the ion flux and the elements of the ion source and the interface of the analyzer are not contaminated with non-dispersed non-volatile substances.

Information sources

1. Alexandrov M.L., Gal L.N., Krasnov N.V., Nikolaev V.I., Pavlenko V.A., Shkurov V.A. The extraction of ions from solutions at atmospheric pressure is a method of mass spectrometric analysis of bioorganic substances. // DAN, 1984, T. 211, No. 2. Physical chemistry, p. 379-383.

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

3. Apffel J.A., Werlich M.H., Bertsch J.I., Goodly P.C. Ortogonal ion sampling for electrospray LC / MS. US patent: 5495108, date of patent Feb. 27, 1996.

4. www.agilent.com

5. H.B. Krasnov, M.Z. Muradymov, Samokish B.A. Patent for invention No. 2530783 dated 08/15/2014. Electrospray device for chromatographic streams of analyzed solutions of substances for ion sources.

6. A.N. Arseniev, N.V. Krasnov, M.Z. Muradymov. Field desorption of ions from the tip on the liquid meniscus during EHD spraying // Scientific Instrument Making. 2014.Vol. 24, No. 3, S. 21-26

Claims (2)

1. A device for the formation of a droplet-free ion flow during electrospray of the analyzed solutions in ion sources with atmospheric pressure, including a capillary, at the end of which there is a meniscus of the sprayed solution and coaxially to which there is an outer capillary of a larger diameter, a coaxial gap connected to the air pump, a flat counter electrode, different the fact that the capillary with the meniscus of the sprayed solution is at zero potential, the counter electrode with the hole in the center is closed a damper, which are electrically interconnected and connected to a high-voltage regulated power source. 2. The device according to claim 1, characterized in that the meniscus is oriented at an angle to the horizontal plane of the axis of the counter electrode hole.

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