RU2608362C2 - Device of stable electro-spraying solutions of substances at atmospheric pressure for ion sources - Google Patents

Abstract

FIELD: physics; instrumentation.

SUBSTANCE: invention relates to ion-drift and mass spectrometry and will find a wide application when solving analytical tasks in organic and bioorganic chemistry, immunology, biotechnology, forensics, proteomics when investigating labile substances using the "electrospray" method. Device of stable electro-spraying solutions of substances at atmospheric pressure for ion sources is configured as a metallic capillary to feed the solution. At the end of that capillary a liquid meniscus is formed, from which there is an emission of charged particles made under the effect of electric voltage supplied to the counter electrode. Outside the metallic capillary there is a coaxial nozzle from a chemically stable, non-wettable, non-porous dielectric material. End of the nozzle on the side of the meniscus has the shape of a truncated cone with the section diameter and the inner channel both equal to two diameters of the capillary, onto which the meniscus rests. Inner channel is located along the axis of the straight truncated cone and has a variable cross-section, the length of the inner channel in its narrow part is equal to the diameter of the cone section and makes five its diameters. Inner channel in its wide part features a diameter much larger than that in its narrow part. Cone vertex has an angle of not more than 90 degrees. Flat counter electrode is electrically connected to a high-voltage power supply source, and the metallic capillary is grounded. Coaxial gap between the capillary and the nozzle is connected to an air extraction pump to eliminate excess non-sprayed solution together with the laboratory air.

EFFECT: longer stable mode of electro-spraying solutions of substances at atmospheric pressure for ion sources, reduced noise in the recorded spectra, absence of false peaks in the spectra due to electrochemical erosion, increased electric strength of the electro-spraying unit for breakdowns.

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Description

The present invention relates to the field of ion-drift and mass spectrometry and will find wide application in solving analytical problems in organic and bioorganic chemistry, immunology, biotechnology, forensics, proteomics in the study of labile substances 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 from solutions into the gas phase, for example, such as peptides, proteins, polynucleotides, drugs. However, existing atmospheric pressure electrospray devices for analyte solutions for ion sources have a number of factors that limit the stable operation of ion sources. The impossibility of precisely matching the flows supplied to the spray region of the analyzed solution in 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 non-evaporated microdrops entering the ion source in the gas-vapor stream as a rule, to clogging and clogging inlet diaphragms and conveying systems from atmospheric pressure to the high vacuum region of the ion analyzer, charging their elements, shorting the electrodes, passing under different potentials, increasing noise and the appearance of false 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 liquid accumulating on the outer side of the capillary, from the end of which the emission of charged microdrops occurs from the meniscus of the liquid, which is associated with inconsistency in 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 to the axis of the conveying system [3]. This device, in comparison with [1, 2], is supplemented with a coaxial capillary, through which a heated vaporizer gas is supplied to the zone of existence of the spray torch. The heated vaporizer gas is designed to more efficiently evaporate the resulting 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 due to 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. Electrospray significantly depends on the conductivity of the sprayed solution — the composition of the solvent and the concentration of the analyte, in addition, all these parameters affect the magnitude of the surface tension, and, accordingly, the electrospray mode. 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. This orientation of the electrospray device allows avoiding clogging or clogging of the inlet diaphragm of the system for transporting charged particles to the analyzer, since when using such a geometry of the solution electrospray assembly, large drops by inertia predominantly fly past the entrance to the analyzer.

The closest known, selected as a prototype, is an electrospray device for chromatographic streams of analyzed solutions of substances for ion sources [4]. This device, in comparison with [1, 2], is supplemented with a coaxial capillary, according to which a vapor-gas mixture is pumped from the meniscus region of the liquid, consisting of laboratory air and excess non-atomized solution that accumulates on the outside of the internal capillary through which the solution enters. The process of formation of charged particles in such a device occurs under normal conditions. Such a combination of electrospray and stimulated removal of the non-sprayed solution allows achieving relatively long-term spray stability (tens of minutes), but when using an external coaxial capillary from a metal, it electrolyzes, a film appears on the surface, the wettability of the inner wall of the coaxial capillary changes, which leads to a transition to a stable electrospray mode unstable and large droplet. A significant effect of the wettability of the inner surface of the external capillary in a small coaxial gap occurs under the action of capillary forces, and an unsteady liquid plug appears in the gap, which changes the stability of the flow of the vapor-gas mixture taken from the spraying region and also leads to some instability of the spraying. This is especially true for an extended coaxial channel with a small gap when the solution enters from a liquid chromatograph in a solvent gradient, which leads to a variable wettability and viscosity.

The objective of the invention is to eliminate the conditions of unstable electrospray of solutions with the possibility of increasing the flow and eliminating noise in the recorded spectra due to instability of spraying.

The problem is solved due to the fact that in the known device for stable electrospray at atmospheric pressure of solutions of substances for ion sources, 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 flat counter electrode, a coaxial gap between the capillaries is connected to air pumping pump, characterized in that the coaxial external capillary is made in the form of a coaxial nozzle of a chemically resistant in this case, the end face of the nozzle on the meniscus has the shape of a truncated cone with a section diameter and an inner channel equal to two capillary diameters on which the meniscus is located, the inner channel is aligned with the axis of the straight truncated cone and has a variable cross section, the length of the inner channel equal to the diameter the cross section of the cone is five of its diameters, then the diameter of the inner channel is much larger than the initial one, the top of the cone has an angle of no more than 90 degrees.

The inventive device is a stable electrospray at atmospheric pressure of solutions of substances for ion sources is shown schematically in figure 1. Through the inner metal capillary (1) a solution is supplied from a liquid micropump (2). This capillary is grounded. Coaxial to the capillary (1) is an external dielectric nozzle (3). Excess non-sprayed solution flowing down the outer wall of the capillary (1), together with the laboratory air, is pumped out by the air pump (4) through the gap between the capillary (1) and the coaxial nozzle (3). The use of an internal channel of variable cross-section in a coaxial nozzle makes it possible to obtain a high gas flow velocity at the beginning in its narrow part, which effectively carries away unsprayed liquid from the outside of the internal capillary, and then in the wide part reduces the linear velocity of the air flow without changing its volume velocity and reduces resistance in the inner channel. This allows you to more finely control the air flow in the coaxial gap, and hence the stable spraying mode. Opposite the end of the inner capillary (1) is a flat counter electrode (5) with a central hole, electrically connected to a high-voltage power source (6).

On the whole, the removal of non-atomized or condensed liquid from the spray region and the symmetry of the spray jet allow one to obtain charged particles of atomic size, which in turn allows one to localize the region of extraction of ions from the solution under normal conditions and to efficiently transport ions to the analyzer. Figure 2 shows the top of the coaxial nozzle used in the device. The coaxial nozzle is made of a chemically resistant, non-wettable, non-porous dielectric, for example, PEEK. The end face of the nozzle on the meniscus side has the shape of a truncated cone (1) with a section diameter and inner channel (2) equal to two diameters of the capillary on which the meniscus is located, the inner channel is aligned with the axis of the straight truncated cone and has a variable section, the length of the inner channel is equal to the diameter of the cross section of the cone is five of its diameters (3), then the diameter of the inner channel is much larger than the initial (4), the top of the cone has an angle of no more than 90 degrees.

The figure 3 shows the shape of the meniscus corresponding to the regime of stable electrospray of the solution obtained in compliance with the requirements of the described device. If the requirements are not met, the meniscus shape has the form shown in Figure 4 — droplet spray mode, which is characterized by extreme instability and a wide scatter in the size of microdrops, respectively, random signals are present in the spectrum.

Information sources

1. Alexandrov M.L., Gal L.N., Krasnov N.V., Nikolaev V.I., Pavlenko V.Α., Shkurov V.A. The extraction of ions from solutions at atmospheric pressure is a method of mass spectrometric analysis of bioorganic substances. // DAN, 1984, V.277, 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. www.agilent.com

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

Claims (1)

A device for stable electrospraying at atmospheric pressure of solutions of substances for ion sources, including a capillary, at the end of which there is a meniscus of the sprayed solution and coaxially to which there is an external capillary of a larger diameter, a flat counter electrode, a coaxial gap between the capillaries is connected to the air pump, characterized in that the external coaxial the capillary is made in the form of a coaxial nozzle of a chemically resistant, non-wettable, non-porous dielectric, with the end face of the nozzles the meniscus side has the shape of a truncated cone with a cross-sectional diameter and an inner channel equal to the two diameters of the capillary on which the meniscus is located, the inner channel is coaxial to the axis of the straight truncated cone and has a variable cross section, the length of the inner channel equal to the diameter of the cone section is five diameters, then the diameter of the inner channel is much larger than the initial one, the top of the cone has an angle of no more than 90 degrees, the flat counter electrode is electrically connected to the high-voltage power source, and the metal esky capillary grounded.

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