RU2613429C2 - Method of drop-free ion flow forming at analyzed electric spraying solutions in ions sources with atmospheric pressure - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to mass-spectrometry. Method of forming drip-free continuous stable ion flow during analytes solutions electric spraying in sources of ions with atmospheric pressure is characterized by absence of drops formation in the beginning of electric spraying process, which substantially simplifies process of continuous and stable mono-dispersed flow of charged particles in wide range of sprayed liquid volumetric flow rates and, consequently, stable ion current of analyzed substances entering analyzer, as well as ion source long-term operation without disassembly and cleaning. Method features are: presence of solid controlled sliding gate valve from conducting material electrically connected to counter electrode, wherein counter electrode in initial state is closed by shutter. Besides, gas flow value pumped through coaxial channel before the beginning of electric spraying process, is set more than needed to obtain stable drop-free ion flow. At ions to analyzer inlet axis horizontal orientation meniscus from vertices of which charged particles emission in mode of drop-free continuous stable ion stream takes place, is installed at an angle to horizontal plane on ions to analyzer inlet axis.

EFFECT: enabling formation of drop-free continuous stable ion flow during analytes solutions electric spraying in ions sources with atmospheric pressure under normal conditions at the beginning and termination of solution spraying with taking into account of liquid meniscus deformation under action of gravity.

1 cl, 2 dwg

Description

The present invention relates to the field of mass spectrometry, namely to ion sources with a soft ionization method using electrospray of the analyzed solutions in a nonuniform constant electric field at atmospheric pressure, and will find wide application in mass spectrometry, ion mobility spectrometry in solving problems of organic and bioorganic chemistry, immunology, medicine, disease diagnosis, biochemical research, pharmaceuticals, proteomics, metabolomics e and forensics: the study of proteins, trace analysis of biochemical markers, drugs and their metabolites in biological tissues and fluids.

In the process of electrospray of analyzed solutions of substances for ion sources with an inhomogeneous constant electric field at atmospheric pressure, satellite gas is used to obtain ions of the studied substances from charged microdrops.

A well-known method for extracting ions from solutions at atmospheric pressure [1] is that at the end of the metal capillary through which the solution of the substance flows, a meniscus of liquid is formed under the influence of a nonuniform constant electric field, from which the emission of charged microdrops evaporates under normal conditions with the formation of ions transported by an electric field or satellite gas to an ion analyzer. The flow of the analyzed solution was 0.05-5 μl / min. This method has much in common with other spray methods [2-6]. In all these methods, the analyzed solution is converted into a finely dispersed charged aerosol, which evaporates in the region with atmospheric gas pressure, and evaporation products, including charged ions, are taken into the chamber of the ion analyzer through a gas-dynamic conveying system. The difference in the methods used for dispersing and charging microdrops does not change the essence of the physical processes leading to the extraction of ions from an evaporating charged aerosol. This is confirmed by the similarity of mass spectra for different spray methods. All these methods are aimed at increasing the flow of the sprayed solution to match the flow of eluent from the chromatographic column, i.e. 50-200 μl / min.

As the latest examples in this direction of the development of the ion source for solutions of labile substances, one can cite [7–8]. In these devices, electrospray plays an auxiliary role, as a way of charging micro-droplets of liquid sprayed by an additional stream of atomizing gas, usually nitrogen. For the greatest extraction of the charged component from the obtained microdrops, another auxiliary stream of hot gas-vaporizer began to be used. Thus, in the design of the ion source with electrospray of the solution, only the charging of the sprayed microdrops remained from the method itself, and the microdrops in the form of a “shower” are received and their evaporation occurs gasdynamically in gas flows. The main drawback of these methods is the non-monodispersity of the emitted charged microdrops and, accordingly, the unstable ion current, which affects the shape of the recorded spectra, as shown by the example of the ion mobility spectrum in [9].

The best characteristics in the range of the space velocity of the analyzed solution using electrospray and ion current stability were obtained in [10]. The method of spraying large volumes of the analyzed solution for ion sources of electrospray with a stable ion current proposed in [11] is selected as a prototype in this patent.

There is a method of electrospraying chromatographic flows of analyte solutions of substances for ion sources with atmospheric pressure, based on the formation of a meniscus of the analyzed fluid in a strong electric field with the emission of charged particles from the top of the meniscus, and the unsprayed solution is removed from the spraying area by countercurrent of the surrounding gas through a coaxial channel under normal conditions.

The disadvantage of this method is that it is not possible to completely avoid the appearance of large drops both at the initial stage of obtaining stable spraying and at the end of the spraying process. The consequence of this significant drawback is the need to clean the elements of the transportation system due to the deposition of non-volatile components (not become ions) from non-evaporated droplets.

The aim of the proposed method is the formation of a droplet-free ion flow during electrospray of the analyzed solutions in ion sources with atmospheric pressure for the chromatographic flows of the analyzed solutions of substances, with the exception of the appearance of large drops during the spraying time, based on the fact that a sample stream is established before the solution is supplied to the electrospray area from the area of atomization of the surrounding gas through the coaxial channel is more than necessary to obtain a stable atomization tions under normal conditions, and the hole in the counter electrode conductive closed sliding gate valve electrically connected with the counter. As an example embodiment of the invention, the following actions can be considered. After the solution arrives through the capillary into the electrospray area, a regulated electric voltage is applied to the counter electrode, which creates the necessary electric field strength for spraying the solution with the used geometry of the atomization unit. Varying the magnitude of the pumped gas flow and electric voltage, they enter the stable spraying mode. Obtaining a stable atomization mode is determined by the stability of the current of charged particles entering the sliding gate valve of Figure 1. Upon reaching the optimal atomization mode, the current of charged particles has no jumps. The presence of hysteresis of the parameter settings, especially with respect to the voltage, allows displacing the sliding gate valve without disturbing the steady-state spraying process, opening a hole in the counter electrode to allow the ion flux to enter the analyzer. Thus, droplets of the sprayed solution do not get into the analyzer at the initial stage of spraying until a stable current of charged particles is obtained. After entering the stable spraying mode, the settings (voltage at the counter electrode and the volume of the countercurrent of the surrounding gas through the coaxial channel) do not change when the fluid flow is continuously introduced into the supply channel to the spraying area. When spraying the solution is complete, the sliding gate valve is set to its original position, closing the hole in the counter electrode and eliminating the possibility of droplets entering the analyzer when exiting the spraying mode. After this, the flow of the solution to the spraying area is stopped, the electric voltage is turned off, and gas pumping from the spraying area through the coaxial channel is stopped.

With a horizontal orientation of the entrance of the ion analyzer, the meniscus of the sprayed solution is oriented at an angle to the horizontal along the axis of entry into the analyzer. This orientation of the meniscus is due to the influence of gravity on the liquid meniscus and, accordingly, the deformation of its conical symmetrical shape. In this case, the top of the meniscus, from which the emission of charged particles occurs, is shifted from the axis of symmetry (figure 2). To obtain the maximum current of charged particles (passing through the hole in the counter electrode), an angular correction is introduced depending on the distance from the meniscus to the counter electrode.

This embodiment of the invention allows to reproduce and control the production of a drop-free ion stream with continuous stable electrospray of solutions in an ion source at atmospheric pressure at all stages of the electrospray process.

Information sources

1. Alexandrov M.L., Gal L.N., Krasnov N.V., Nikolaev V.I., Pavlenko V.A., Shkurov V.A. DAN T. 277, No. 2. Physical chemistry, p. 379-383, (1984).

2. Iribarne J.V., Thomson B.A. Int. J. Mass-spectrom. Ion phys. V. 50, p. 331, (1982).

3. Fenn J. B., Whitehouse S. M., Dreyer R. N., Yamashita M. Anal. Chem. V. 57, p. 675 (1985).

4. Covey T.R., Bruins A.P., Henion J.D. Anal. Chem. V. 59, p. 2642, (1984).

5. Pilesot D., Kin H.Y., Diches D.F., Vestal M. Anal. Chem. V. 56, p. 1236, (1984).

6. Kambara H. Anal. Hem. V. 54., p. 143 (1982).

7. Shimadzu Corp. (www.Shimadzu.com).

8. Thermo Scientific (www.tectronica.com).

9. V.A. Samokish, H.B. Krasnov, M.Z. Muradymov. Electrospray ion source with a dynamic divider of fluid flow // Scientific Instrument Making. 2012, T. 22, No. 3, S. 5-12

10. N. Arseniev, N.V. Krasnov, M.Z. Muradymov. Investigations of electrospray stability during dynamic division of a fluid flow // Mass Spectrometry, 2014, T. 11, No. 1, P. 36-38.

11. N.V. Krasnov, M.Z. Muradymov, Samokish V.A. Patent for invention №2530782 from 08/15/2014. Method for electrospraying chromatographic streams of analyzed solutions of substances for ion sources.

Claims (2)

1. The method of formation of a droplet-free ion flow during electrospray of the analyzed solutions in ion sources with atmospheric pressure, based on the formation of the meniscus of the analyzed liquid in an inhomogeneous constant electric field with the emission of charged particles from the top of the meniscus, while the unsprayed eluent is removed from the spraying area by countercurrent ambient gas through coaxial channel under normal conditions, characterized in that the counter electrode in the initial state is closed by a continuous controlled sliding backward with a conductive material connected electrically to the counter electrode, and the flow of gas pumped through the coaxial channel before the start of the electrospray process is set higher than that necessary to obtain a stable, drop-free ion flow. 2. The method according to p. 1, characterized in that the meniscus is oriented at an angle to the horizontal plane on the axis of entry into the ion analyzer.

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