DE10007498A1 - Electrospray device - Google Patents

Abstract

The invention relates to a device for spraying liquids using agents for providing a liquid with an electric potential. A plurality of agents are provided. The liquid which is provided with the potential is mechanically dispersed or sprayed using said agents. The mechanical dispersing or spraying agents are configured in such a way that the discharge region of the liquid from the mechanical spraying agents is formed from a majority of conical, tubular or thread-shaped elements. The surfaces of the conical, tubular or thread-shaped elements preferably consist of a material at least in the region of the open ends thereof, whereby said material involves only little adhesive forces between the liquid and the material. Threads which protrude from a metal tube especially serve as a dispersing agent. A liquid having an important flow can be sprayed in a particularly fine manner by means of said device.

Description

The invention relates to a device for atomizing electrically charged Liquids.

A sample solution is known from the prior art solution, i.e. a liquid through a metal capillary to pump that against high electrical potential lies over a counter electrode. Under these conditions The sample solution is charged electrochemically and electro at the end of the capillary at atmospheric pressure hydrodynamically charged droplets in an aerosol atomized.

Such a device is used for example in the Electrospray mass spectroscopy used. Successor decay of the charged, atomized drops ren, with constant evaporation of the solvent, finally to release ions. Those ions who to a mass analyzer via a pump system leads.

In electrospray mass spectroscopy, the In nominal diameter of the capillaries is usually around 100 µm, the applied potential difference at 3-6 kV and the Flow rates at 1-10 µl / min. The difference will be in the be with nano electrospray mass spectroscopy drawn method capillaries with an inner diameter 1 µm. The applied voltage is below 1 kV and the flow rates below approx. 20 nl / min. Electrospray mass spectroscopy is both today in research as well as in analytical application,  one of the most widely used mass spectrometry techniques.

Electrospray mass spectroscopy is from the following Reasons of particular importance for the proof ther mixed labile and high molecular substances such. B. of biomolecules (peptides, proteins, nucleic acids, Carbohydrates and Lipids - Richard B. Cole; "Electrospray Ionization Mass Spectrometry: Fundamentals tals, Instrumentation & Applications "; John Wiley & Sons Inc., New York, 1997).

The transfer of analyte ions from the liquid state in the gas phase is gentle and induced in comparison little fragmentation compared to other ionization methods.

The mass spectrometric detection of substances is essentially determined only by the solubility in a polar solvent and sufficient ana lyt concentration according to the efficiency of the cer dust and the detection sensitivity of the mas spectrometer. However, the crowd can range of the spectrometer.

For molecules with many polar groups, the Mas range of a spectrometer continues that the analyte ions are uploaded in a Condition to be desolvated. N-fold charged molecules appear on their 1 / nth mass. So z. B. Albumin with a molecular weight of 66,430 Da still with a quadrupole mass spectrometer the.  

In the case of nano-electrospray mass spectroscopy the flow rates and consequently the required ones Sample amounts much less. It shows, that at these small diameters the ionization effi ciency is higher.

The electrospray mass spectrometer is of particular importance in recent years as a detector for the Liquid chromatography (LC) and the capillary electrophoresis (CE) achieved because the separated Pro solution immediately after leaving the separation medium in the electrospray capillary passed on, and such can be detected by mass spectrometry. Also for the future is of increasing spread this method. This coupling requires that the flow rate through the electrospray capillary the flow rate of the separation column is adjusted.

Currently, electrospray is subject to mass spectrometry However, some restrictions apply even wider application range and performance conflict with this method of analysis. This one restrictions are briefly described below: The flow rates of the analyte to be separated chromatographically Solutions are in liquid chromatography (e.g. HPLC) in the range of 1000 µl / min. The Flussra However, electrospray mass spectrometry not higher than 10 µl / min. To the flow rates of the ur original electrospray mass spectroscopy, which at 2-10 µl / min are based on these HPLC requirements to fit, is now the pneumatically under supported electrospray - also called ion spray det, which allows flow rates from 5 to 1000 µl / min light. With the IonSpray the atomization of the liquid  through and around a stream of nitrogen gas the capillary supports (sheat gas). Indeed can be achieved with electrospray at high flow rates (1000 µl / min) only about the same ion intensity as at low flow rates (5 µl / min). Through the Adaptation to the flow rates used in HPLC must be one for electrospray mass spectroscopy Loss of sensitivity by a factor of 100 in Purchase.

The ion current signal in the electrospray mass spectrometer scopia initially grows at low concentrations proportional to the analyte concentration only up to egg at a certain point in order to avoid high analyte concentrations can even be removed again.

Become strong in electrospray mass spectroscopy solutions containing salt or buffer are used in usually the analyte signal at the expense of the electrolyte suppressed. To avoid this undesirable effect It is often necessary to remove the sample solutions before the Desalt measurement. This suppressive effect is in nano-electrospray mass spectrometry wrestler.

Generally, masses of electrospray are over spectroscopy of only relatively polar analyte solutions Measurement accessible. When using electrolyte free analyte solutions in the electrospray masses spectroscopy (e.g. non-polar analytes in non-polar sol resources) are the prerequisites for production sufficient quantity of excess charges no longer given because ion formation in electrospray mass spectroscopy  with the electrochemical The analyte solution starts charging. To bypass this Difficulties must often be attributed to the APCI (atmospheric pressure chemical ionization) in which the analyte solution ver in a corona discharge is sprayed. However, this is not a mild Ionisa tion like electrospray mass spectroscopy possible.

The nano-electrospray mass spectroscopy is a Va riante of electrospray mass spectroscopy, in which significantly thinner, z. B. gold-plated glass capillaries (0 approx. 2 µm) can be used (MS Wilm, M: Mann; "Electrospray and taylor-cone-theory, dole's beam of macromolecules at last?"; Int. J. Mass Spectrom. Ion Proc .; 136; 167-180, 1994; Wolf D. Lehmann; "Mass Spectrometry in Biochemistry"; Spectrum Academic Agreement; Heidelberg; 111; 1996). Since these thin capillaries only allow flow rates of approx. 20 nl / min, coupling to the usual liquid chromatography at flow rates of 100-1000 µl / min proves to be very difficult. Furthermore, the handling of these thin capillaries is problematic in routine analysis because they easily clog. Nevertheless, the use of these thinner capillaries brings various advantages that make their use interesting in some areas:

• - Nano electrospray mass spectroscopy can can also be operated with the smallest sample quantities.
• - With the help of nano electrospray mass spectrosco pie become about at flow rates of about 20 nl / min achieves the same ion intensities as with the Electrospray mass spectroscopy at flow rates of approx. 5 µl / min and the TonSpray with flow rates  of about 1000 µl / min. The sensitivity of the Nano-electrospray mass spectroscopy is accordingly about four decades higher than that of the TonSpray. This higher sensitivity of both nano- Electrospray mass spectroscopy is on it attributed that, on the one hand, smaller droplets arise (drop diameter in the IonSpray in Micrometer range with nano electrospray Mass spectroscopy by an order of magnitude less), on the other hand these arising Droplets have a relatively high surface charge sit. Both factors support an effi efficient ion release.
• - Compared to the IonSpray, the nano-electro can spray mass spectroscopy at a size order of magnitude higher electrolyte concentrations (e.g. Salt contamination, buffer) in the analyte solution be operated without causing problems through Suppression effects is coming. To order at the IonSpray from the initially larger drops to the point the ion release must get more sol evaporate than the smaller, Uploaded drops in the nano electrospray Mass spectroscopy is necessary. Here comes there is a concentration of electrolytes in the Drops, causing the release of the analyte ions is suppressed [R. Juraschek, Th. Düicks, M. Karas; "Nanoelectrospray - more than just a minimized-flow electrospray ionization source "; J. At the. Soc. Mass Spectrom .; 10; 300-308; 1999].

From US 5,975,426 it is known to provide a porous ball at the end of a capillary. A liquid brought to potential is atomized through the porous ball. The ball consists of SiO ₂ .

The spraying of finely atomized liquids is furthermore always of economic importance if thin layers should be applied evenly. Such layers can be, for example Trade paints.

The object of the invention is to provide a device tion of the type mentioned at the beginning, with the high river drainage very good atomizations are possible.

The object of the invention is achieved by a device solved with the features of the first claim. Advantage harsh configurations result from the subclaims chen.

The claimed device comprises means to to change the electrical potential of a liquid that the liquid is thereby (under certain circumstances further) is charged electrically. The number of positive or negative electrical charge carrier increased by the mean.

With the means to the electrical potential of the rivers to change liquidity in the aforementioned manner is, for example, an electrode on which the rivers liquid is passed by. Through this electrode and through a counter electrode is then by applying a Voltage creates a strong electric field. Depending on Geometry, a voltage of 800 V is sufficient  his. Typically, the voltage applied is we at least 3 kV.

The liquid is absorbed by the aforementioned means electrochemically charged. At least it is always the case when a polar liquid was set. Non-polar liquids are less suitable like benzene, hexane or toluene. Are suitable aqueous or methanolic solutions, for example Salt or sugar solutions. An aqueous solution with Proteins dissolved in it are another example for a polar and therefore well suited solution.

A metal tube can be used as the electrode seen through which the liquid is passed. Alternatively, the electrode is in the liquid speed. For example, it is washed around by it.

There must be such contact between the electrode and the liquid present that a charge exchange can be done to bring the liquid to potential bring

The claimed device further comprises a variety of means by which the liquid brought to potential is mechanically finely divided or atomized. This can be a multitude of capillaries with very thin diameters of a few µm. The surface of these mechanical dividing or atomizing means consist in particular of a material in which there are only slight adhesive forces between the liquid and the material. Examples of suitable materials are fluorine compounds such as PTFE (Teflon®) and FEP, polyethylene or polypropylene. Materials with high adhesive forces are SiO ₂ , glasses or metals.

The adhesion forces between the liquid speed and mechanical division or atomization agents are preferably low in order to prevent that the liquid droplets emerge after exiting reunite the mechanical atomizers.

The mechanical atomizers are designed that the exit area of the liquid from the mechanical atomizers by a plurality of conical, tubular or thread-like elements are formed becomes. The liquid flows through or along the headed above elements. The cone, tube or thread-like elements finally have open ends on, from which the liquid from the mechanical Atomizer emerges.

An example of a plurality of tubular elements ten is a plurality of capillaries. These are in the we substantial parallel to each other or brush-like arranges. The capillary enables the potential to be reached brought liquid through for atomization tet.

An example of conical elements is a Membrane representing a variety of conical fro highlights to one side. Those on pots liquid brought into the conical form becomes conical Structures. At the tips of the cones occurs then the liquid out.  

The thread-like variant is particularly preferred. A bundle of threads ends in the form of a brush. The on Potential brought liquid is along the thread bundled and exits at the end of the brush. This variant is not only particularly easy to use but also enables particularly good ones Atomization of the liquid.

The conical, tubular or thread-like elements have between their open ends, from which those on Po potential brought liquid from the mechanical Zer dusts emerge, gaps arise. So are the ends of the threads ending in a brush shape spatially from separated from each other. The atomization then succeeds in white ter improved way.

In order to improve the atomization again, the run the aforesaid open ends, from which those on pots fluid brought from mechanical parts dusts emerge, pointy. This is esp especially advantageous for the threads.

It is sufficient if the liquid in the area of the out emerges from the mechanical atomizers on Po potential is brought.

To further improve the device in egg ner embodiment of the invention, a heating means, through which the liquid especially in front of the mechani atomization is heated. The atomization succeeds so even better.  

The invention is illustrated below using an example explained in more detail.

Fig. 1 shows in section the basic structure of a particularly suitable device of the type mentioned.

A methanolic sugar solution is passed through a thin tube 1 . The tube is made of metal and serves as an electrode. The inside of the tube is filled with a plurality of threads 2 , which consist of poly tetrafluoroethylene. The threads 2 run essentially parallel in the tube and emerge in the form of a brush at one end of the tube. The threads are pointed at the end of the "brush".

A counter electrode 3 is provided. This is placed in such a way that the liquid, which is passed through the tube 1 , emerges at the brush-shaped ends from the atomizing device in the direction of the counter electrode.

Additionally or alternatively, the threads can be made of metal wires exist in the area of the open ends with Fluoropolymer such as polytetrafluoroethylene (PTFE) or with Graphite fluoride are coated. On the wires then the voltage applied to the liquid Bring potential. The wires then serve as Electrode. The open ends are the ends of which from the liquid the disintegration or atomization means leaves.

With the help of the invention in electrospray  Mass spectroscopy high sensitivity as well as high Flow rates enabled. The process can even can be combined with liquid chromatography, which requires high flow rates.

The limits of electrospray mass spectroscopy analytical applications are state of the art mainly due to insufficient ionization efficiency at higher flow rates, d. H. larger capilla diameter, given. Since a high ionization ef efficiency of atomization of the analyte solution in possible depends on small and uploaded drops Conditions are chosen under which atomization the solution at the end of the capillary not just through one "thick" spray cone but about the formation of many fine spray conist takes place. This is achieved that the analyte solution is at the end of the capillary field-reinforcing structures that take a breakdown the liquid in many jet streams. Here, however, the areas of high field strength should not to the occurrence of gas discharges (e.g. a Ko rona discharge) cause this the mild electrospray Counteract ionization conditions.

The metal capillary of FIG. 1, for example, has an inner diameter of 600 microns. The outside diameter is z. B. 900 microns. In the capillary there are, for example, 600 threads or fibers, each with a diameter of 21 µm and made of Teflon. The threads protrude from the capillary from one end by approx. 1-2 mm and have open ends here

At least 5 of the aforementioned threads should be provided in a capillary in order to achieve noticeable desired results. For example, 2000 threads are also possible without any problems.

The following effects could be obtained with the embodiment shown in Fig. 1 compared to a conventional electrospray capillary.

• 1. 1.) Instead of a single "thick" so-called Taylor Cone created many fine Taylor Cones on the company serenden.
• 2. 2.) A more stable spray behavior even with watery Solutions could be achieved. When using conventional capillaries, the Taylor Cone trembles again and again and partly breaks down completely.
• 3. 3.) Even at higher flow rates is a stable spray possible. With conventional capillaries, the breaks Spray together at higher rivers.
• 4. 4.) More ions can be made from the same solvent amount generated.
• 5. 5.) A higher detection sensitivity can be achieved become. An improvement by about a factor of 100 was made achieved so far.
• 6. 6.) So far there has been no disadvantageous corona plan observed.
• 7. 7.) A mild ionization with little fragment formation, as with nano-electrospray mass spectroscopy possible.
• 8. 8.) A higher tolerance to salt contamination (e.g. solutions with a high buffer content) is in many Cases possible.
• 9. 9.) A greatly reduced neutral noise in the ver became the normal electrospray at  Spectroscopy observed.

The behavior resembles a variety of nano-electro sprays without the disadvantages of difficult to handle speed, the blockage of the nano-capillaries and the ge struggle to accept flow rates.

For the first time, a "multi-nano electrospray Mass Spectroscopy "to realize, in which we significant advantages of normal electrospray mas sens spectroscopy with those of the nano electrospray mas are connected to spectroscopy.

A coupling to standard liquid chromatography Methods (100-1000 µl / min) are therefore possible because of the high Flow rates can be used.

According to the current status of the Knowledge of particular importance.

• - Field-strengthening structures (thin fiber ends according to FIG. 1): At high field strengths, which are very limited in space (on pointed needles), spraying sprykoni can form particularly effectively. In addition, the conditions for the formation of a corona discharge are limited to a spatially so small area that disadvantageous corona discharges can hardly occur.
• - non-polar and non- wetting surface of the Teflon fibers: the from the Any liquid that escapes through the capillary individual fibers split. Usually would the liquid is closed again by cohesive forces a single liquid cone (can happen, for example, if you are pure Metal fiber brush or fiberglass brush used); due to the non-wetting surface of the PTFE  This largely prevents fibers. Separate small droplets of analyte migrate towards the field and then spray at the end of the fiber.
• - metal capillary or any other contact, past which the analyte solution flows: Here the flowing analyte solution charged (also glass Capillaries or plastic capillaries can be used be detected if the analyte sol solution is being charged.

Other advantages of this construction:

• - Low dead volume, so that the chromatographic Resolution in liquid chromatography or not affected by electrophoretic separation processes should be pregnant.
• - Fluoropolymers like PTFE are resistant to all common solvent.
• - Fluoropolymers like PTFE also show when measuring different samples in a row none Memory effect on.
• - Long durability even under heavy use: The PTFE fibers are compared to electrochemical corrosion sion processes with the analyte solution and under atmosphere spherical pressure inert and thus allow a long measuring time ten.
• - Gas discharges only occur between, if at all the counter electrode and the metal capillary (or contact point), so that the Teflon fibers are not changed the.

The invention becomes efficient among other things Ion formation, for the uniform coating of Surfaces or used for effective atomization.  An effective atomization is for example fuel injection in Inte engines resse.

Polyethylene, nylon, natural fibers Polymers also showed good properties. PTFE however, proved to be the best material.

The use of a capillary with an edge opening with threads, fibers or needles was also successful. The na made of carbon. The needles could itself in front of the outlet opening of a capillary compared to a noticeable improvement to achieve the state of the art. A little ver the worse embodiment was the provision of sharp edges or slits instead of spit zen at the end of the mechanical atomizer.

The invention can also be used in combination with "sheat gas" be used.

In Fig. 2, the influence of the material M, which forms the surface at the open ends of the mechanical disintegrating or atomizing agents, is illustrated by the example of various solutions. The greater the signal intensity I, the better the desired result is achieved. PTFE is therefore very suitable. Iron is the least suitable.

In FIG. 3, results are shown, the prior art has been made with a normal electrospray capillary and with the inventive device. The signal intensities I as a measure of the desired effects could be increased considerably by the invention. In both cases, 10-4 mol / l raffinose in methanol was used as the solution.

Claims (10)

1. Device for atomizing liquids with means ( 1 , 3 ) to bring a liquid to an electrical potential, with a variety of means by which the liquid brought to potential is mechanically divided or atomized, the mechanical parting or Atomizers are such that the outlet area of the liquid from the mechanical atomizer is formed by a plurality of conical, tubular or thread-like elements. 2. Device according to claim 1, wherein the surface of conical, tubular or thread-like elements at least in the area of their open ends from one Material exist for which only small ad adhesive forces between the liquid and the Material occur. 3. The device of claim 2, wherein the surface the open ends made of fluoropolymers such as PTFE, Polyethylene, graphite fluoride, pyrocarbon or Nylon exist. 4. Apparatus according to claim 1, 2 or 3, wherein the surface material of the conical, tubular or thread-like elements ( 2 ) is PTFE. 5. Device according to one of the preceding Claims where as the means to a  Liquid towards an electrical potential bring, electrodes are inserted. 6. Device according to one of the preceding claims, wherein an electrode is a capillary ( 1 ). 7. Device according to one of the preceding claims, in which in a tube ( 1 ) a plurality of fibers or threads run parallel, the fibers or threads ( 2 ) protruding at one end of the tube. 8. Device according to one of the preceding Claims where a voltage source is connected to an as Electrode serving tube as well as to a Counter electrode is connected. 9. Device according to one of the preceding claims, in which fibers or filaments ( 2 ) provided as a dividing or atomizing agent taper at at least one end. 10. Device according to one of the preceding claims, in which fibers or filaments ( 2 ) provided as a dividing or atomizing agent consist of metal wires provided as electrodes, which are coated at least at one open end with PTFE, nylon, polypropylene, polyethylene or carbon.