EP1566829B1 - Method for the production of an output-ion-stream - Google Patents

Abstract

An output ion current of a single ionic species is produced by reacting ions formed in ionization of a source gas and/or ions extracted from ionization region, in a region in which source gas is located until source ionic species that do not react with the source gas are present. A reactant gas different from the source gas reacts with the ions of the source ionic species to convert the ions of the source ionic species into the single ionic species. The production of output ion current comprised of a single ionic species, involves reacting ions formed in ionization of a source gas in an ionization region (A) and/or ions extracted from the ionization region in a region in which source gas is located, until source ionic species are present that do not react with the source gas. A reactant gas different from the source gas is supplied to a reaction region (C) located outside of the ionization region and in which ions of the source ionic species are present. It reacts with the ions of the one or several source ionic species to convert the ions of the source ionic species into the single ionic species forming the output ion current.

Description

The invention relates to a method for obtaining an essentially only one single ion species existing source ion current, wherein in the ionization of a source gas in an ionization region formed ions and / or extracted from the ionization ion ions in a region in which there is source gas, be reacted until essentially only one or more source ion types are present that do not react with the source gas.

Such a method is for example from the AT 001 637 U1 known. This document describes a process for obtaining an ion stream consisting essentially of H ₃ O ⁺ ions. For this purpose, water vapor is ionized in an ionization region by means of an ion source, whereby various ions are formed (O ⁺ , OH ⁺ , H ⁺ , H ₂ ⁺ , .....). These ions are extracted by means of a weak electric field into a region outside the ionization region and are left in this region, in which H ₂ O is at a pressure above 0.01 Torr, until the first of H ₃ O ⁺ ions have converted various ions by subsequent reactions in H ₃ O ⁺ ions. In this region and / or in an adjoining region, the ion current is also passed through an electric field whose field strength is sufficiently high, so that H ₃ O ⁺ . (H ₂ O) _n cluster ions formed by association reactions with neutral ions occur between two successive bursts Shock partners have acquired sufficient kinetic energy, so that these shocks are predominantly dissociative. It prevents the formation of such cluster ions or largely reversed. To improve these dissociation reactions, H ₂ O may also be admixed with an additional gas, such as Ar, Kr or N ₂ , which serves as cluster partner for the cluster ions but does not react chemically with the H ₃ O ⁺ ions.

Such an ion stream consisting essentially of H ₃ O ⁺ ions can be used in particular as a primary ion stream for the chemical ionization of a sample gas by proton exchange reactions in order to mass spectrometrically examine the ions formed in the sample gas. This proton exchange reaction mass spectrometry, short PTR-MS, is in the AT 001 637 U1 and the references cited therein. It is a special one Type of Ion Molecule Reaction Mass Spectrometry (IMR-MS), which is also described in the AT 001 637 U1 and the references cited therein.

In the AT 406 206 B is also a procedural ago from the AT 001 637 U1 known methods analogous to obtain a substantially consisting of NH ₄ ⁺ ions ionic current. For this purpose, ammonia (NH ₃ ) is ionized as the source gas and the ions formed are left after extraction from the ionization area in a range with an ammonia pressure of above 0.01 Torr (1.33 Pascal) until the substantially only NH ₄ ⁺ ion has formed ion current (to prevent or reverse the formation of cluster ions again a sufficiently high electric field strength is applied to induce shocks).

From the AT 403 214 B It is further known to introduce different source gases into an ion source and to filter out all but one of the primary ion species from the source ion species generated in the ion source from various neutral atoms or molecules of the source gases by means of a filter device. The remaining primary ion species is allowed to pass into the reaction space and allowed to react with a sample gas in the reaction space, whereby the reaction products formed by ion molecule reactions (eg, proton exchange reactions) are examined with a mass spectrometer. The disadvantage here is the additionally required, the filter device forming mass spectrometer.

The recovery of only one ion species existing output ion streams without such mass spectrometric filtering, as shown in AT 403 214 B is known is through the process of AT 001 637 U1 respectively. AT 406 206 B only possible for a few types of ions, in particular for H ₃ O ⁺ ions, NH ₄ ⁺ ions and H ₃ ⁺ ions. Only in the case of a few source gases do output-ion streams, which essentially consist of only one single ionic species, form in the manner described in these two publications. Such source gases are described in the literature as "Cl Reagent Gases".

In the EP 000 865 A1 describes the investigation of a substance gas, which is ionized for this purpose by ion-molecule reactions. The chemical ionization of the substance gas takes place here as an ionization chamber described space (which is commonly referred to as "drift tube"). The ionization chamber is supplied partially ionized primary gas from an ion source, which is designed here as a gas discharge chamber. The ionization chamber is also supplied with a reactant gas in addition to the substance gas, which reacts with the ions entering the ionization chamber from the ion source and in turn ionizes the substance gas. In the ionization chamber is thus a mixture of the more or less ionized components of the primary gas, reactant gas and the gas of substance. An extraction of an essentially only one single ion species existing initial ion current is not apparent from this document. For the exit opening of the ionization chamber, both the ionized primary particles and the reactant gas and substance ions are conducted.

The object of the invention is to expand the range of producible output ion currents, which consist essentially of only a single type of ion, without requiring a mass spectrometric filtering (as in AT 403 214 B described) is required. According to the invention, this is achieved by a method having the features of patent claim 1.

By the method according to the invention, it is possible in particular to produce substantially only one single ion species existing output ion currents, which by direct addition of the reactant gas in the primary ionization due to the various species present in this area (ions, electrons, atoms, molecules, radicals , excited atoms, excited molecules) would not arise in this form. If, for example, nitrogen (N ₂ ) were added to the source gas H ₂ , then neutral NH ₃ would be produced in the plasma of the primary ionization region (cf. ref1: Fuji et al., Int. J. Mass Spectrom. 216, 169, 2002 ). H ₃ ⁺ would thus preferentially react with NH ₃ in the reaction H ₃ ⁺ + NH ₃ → NH ₄ ⁺ + H ₂ and the generation of an N ₂ H ⁺ leaving ion current (as explained below) would not be possible.

The addition of the reactant gas in a spatially separated from the primary ionization reaction area also has the advantage that gases can be added, the presence of which would be problematic in the primary ionization, z. NO in filament ion sources (leads to rapid filament breakage) or carbon-containing gases in plasma ion sources (leading to carbon deposits).

Preferably, suitable measures are taken so that a backflow of the reactant gas from the reaction zone into the ionization zone is substantially prevented, ie. H. less than 10%, preferably less than 5%, of the partial pressure in the ionization zone should originate from the reactant gas or from products formed therefrom. For this purpose, for example, the spaces forming the ionization region and the reaction region may be separated by one or more intermediate walls, wherein a diaphragm opening is arranged in a respective intermediate wall, and a gas flow pointing in the direction from the ionization region to the reaction region through at least one of the diaphragm openings is maintained by appropriate pumping devices , Also Zwischenabpumpungen between the areas are conceivable and possible.

In principle, it would be conceivable and possible, at least in some applications, to lead the ions extracted from the ionization zone directly into the reaction zone. However, it is preferred to first guide the ions extracted from the ionization region into an intermediate region in which they are left until the ions, which are still initially different from the one or more source ion species, essentially (ie more than 90%) , preferably more than 95%) in ions of one or more source ion species. From this intermediate region, ions of the one or more source ion species can subsequently be extracted into the reaction zone in which they are substantially (ie more than 90%, preferably more than 95%, by adding the reactant gas into the single ion species of the parent ion stream. ) being transformed.

If the extraction of ions from the ionization region takes place directly into the reaction region, the reactions of the ions formed in the ionization to the ions of the one or more source ion species are essentially already in the ionization region or these reactions take place mainly or partly in the reaction region , It must be to source gas with a sufficient pressure (for example, more than 1 Pascal) in the reaction area. Furthermore, if possible, the reactant gas should not react with ions that have not yet been converted into ions of one or more source ion species. This is the case for some combinations of source gases and reactant gases. It would be conceivable and possible, in special cases, for the primary ions and / or secondary products to disrupt interfering ion types (which are undesirable with the reactant gas) ion species) by adding a suitable additional gas into non-interfering ions to convert.

As a source gas, a clean gas or a gas mixture can be used. For the reactant gas, the use of a clean gas is preferred, wherein the use of gas mixtures would also be conceivable and possible.

Hereinafter, embodiments of the invention will be explained with reference to the accompanying drawings. In this, the only Fig. Shows a highly schematic representation of a device with which the inventive method is feasible.

The device shown schematically in the figure for carrying out the method according to the invention has three areas. The primary ionization area A is supplied with a source gas through a feed 1. In the ionization region A, an ion source or ionization device 2, not shown in detail, is arranged. The primary ionization of the source gas takes place z. By electron emission from a filament, by ionizing radiation (eg, α-particles), by an electrical discharge, or other ionization techniques. The choice of the primary ionization method is not relevant to the subject invention.

The source gas used is a clean gas, for example hydrogen (H ₂ ), or a gas mixture, for example H ₂ argon (Ar) or nitrogen (N ₂ ) nitrous oxide (N ₂ O). Total pressure and partial pressures depend on the choice of ionization method (low pressure or high pressure ion source).

In the primary ionization region A, there are a variety of species (ions, electrons, atoms, molecules, radicals, excited atoms, excited molecules).

• Im Fall von H₂ als Quellgas besteht der extrahierbare positive lonenstrom einfach geladener lonen aus H⁺, H₂ ⁺, H₃ ⁺ und H₃ ⁺·H₂.
• Im Fall eines H₂-Ar-Gemisches besteht der extrahierbare positive lonenstrom einfach geladener lonen aus Ar⁺, Ar₂ ⁺, ArH⁺, ArH₂ ⁺, ArH₂ ⁺, H⁺, H₂ ⁺, H₃ ⁺, H₃ ⁺•H₂.
• Im Fall eines N₂-N₂O-Gemisches besteht der extrahierbare negative lonenstrom aus vornehmlich O^--lonen, mit Spuren von NO^--lonen. (vgl. ref2: A.P. Bruins et al., Adv. Mass Spectrom. 7, 355, 1978 )

By applying an electric field of suitable polarity, either positive or negative ions are extracted through an aperture 3 in an intermediate wall 4 into the intermediate region B. The generated ionic current is usually non-selective, ie it generally consists of different types of ions:

• In the case of H ₂ as a source gas, the extractable positive ionic current of singly charged ions consists of H ⁺ , H ₂ ⁺ , H ₃ ⁺ and H ₃ ⁺ · H ₂ .
• In the case of an H ₂ -Ar mixture, the extractable positive ion current of singly charged ions consists of Ar ⁺ , Ar ₂ ⁺ , ArH ⁺ , ArH ₂ ⁺ , ArH ₂ ⁺ , H ⁺ , H ₂ ⁺ , H ₃ ⁺ , H ₃ ⁺ • H ₂ .
• In the case of an N ₂ -N ₂ O mixture, the extractable negative ionic current consists primarily of O ^- ions, with traces of NO ^- ions. (see ref2: Bruins AP et al., Adv. Mass Spectrom. 7, 355, 1978 )

The relative proportions of the exemplified, extractable ion species depend on various source parameters (total pressure of the source gas or partial pressures of the various source gas components, temperature, etc.). In addition to singly charged ions, multiply charged ions can also occur and be extracted, depending on the ion source and the source gas.

The intermediate region B is fed with the source gas (total pressure> 0.01 mbar, particle gas density N _B ). The feed can be done by flowing out of the ionization region A in the intermediate region of source gas. There may also be a separate feeder, not shown in the figure. The pressure of the source gas in the intermediate region B may be similar or equal to the pressure of the source gas in the ionization region A. In the intermediate region B, an electric field of field strength E _{B is} applied by electrodes 5. The intermediate region is at a temperature T _B.

In the intermediate region B, the ions extracted from the primary ionization region A interact with the source gas. The spectrum of interactions includes binary ion-molecule reactions (eg H ₂ ⁺ + H ₂ → H ₃ ⁺ + H), ternary ion-molecule reactions (eg H ⁺ + H ₂ + H ₂ → H ₃ ⁺ + H ₂ ), collision-induced dissociation reactions (eg H ₃ ⁺ • H ₂ + H ₂ → H ₃ ⁺ + H ₂ + H ₂ ), as well as activation and deactivation reactions (eg (H ₂ ⁺ ) ^* + H ₂ → H ₂ ⁺ + H ₂ )

The parameters E _B / N _B and T _B define the reaction conditions, ie by varying these parameters it is possible to prefer or suppress certain reaction channels.

By suitable choice of the reaction conditions, the ion stream consisting of numerous ion species and extracted from the primary ionization region A is extracted is converted into a selective ionic stream substantially of an ion species not reacting with the source gas, or an ionic stream of essentially a plurality of non-source-reactive ion species. These one or more ion species which do not react with the source gas, ie they are "stable" to the source gas, are referred to in this document as "source ion species". At the exit of the intermediate region B, to which the ion current is passed through the electric field E _B , the ionic current is preferably at least 90% of the one or more source ion species, with a value of at least 95% being particularly preferred.

At the exit of the intermediate region, the proportion of ions of the source ion species could also be lower than the stated value of preferably 90% or 95%, for example if a proportion of cluster ions (eg H ₃ ⁺ .H ₂ ) is present, which is converted into dissociation reactions in ions of the one or more source ion species (plus neutral source gas) only in reaction region C described below by applying an electric field with a sufficient field strength in the reaction region C to carry out the required collision-induced dissociation reactions becomes.

The values of E _B / N _B and T _B vary depending on the application example. It would also be conceivable and possible to improve the efficiency of the dissociation reactions taking place in the intermediate region B by adding an additional gas (eg Ar, Kr or N ₂ ) to the source gas which does not react with the ions extracted in the intermediate region via ion molecule reactions but instead only serves as collision partner.

$${\mathrm{H}}^{+}+{\mathrm{H}}_{\mathrm{2}}\mathrm{+}{\mathrm{H}}_{\mathrm{2}}\mathrm{\to }{{\mathrm{H}}_{\mathrm{3}}}^{\mathrm{+}}\mathrm{+}{\mathrm{H}}_{\mathrm{2}}$$

In the case of H ₂ as the source gas, a selective H ₃ ⁺ ionic current is generated. Here are ion-molecule reactions of the following nature: $${{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{2}}}^{\mathrm{+}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{2}}\mathrm{\to }{{\mathrm{<figure-callout\; id="3"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{3}}}^{\mathrm{+}}\mathrm{+}\mathrm{H}$$

$${\mathrm{H}}^{+}+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{2}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{2}}\mathrm{\to }{{\mathrm{<figure-callout\; id="3"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{3}}}^{\mathrm{+}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_{\mathrm{2}}$$

The applied electric field also leads to dissociation reactions, which predominate over the association reactions and which largely reverse the formation of cluster ions, or prevent their formation from the outset: $${{\mathrm{<figure-callout\; id="3"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_3}^{+}•{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_2+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\to {{\mathrm{<figure-callout\; id="3"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_3}^{+}+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_2+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_2$$

In the case of an H ₂ -Ar mixture as the source gas, a selective H ₃ ⁺ ion stream is also formed (cf. Praxmarer et al., J. Chem. Phys. 100 (12), 8884-8889, 1994 ). In other source gas mixtures of H ₂ with a pure gas X, whose proton affinity is smaller than that of H ₂ is formed as source ion type H ₃ ⁺ . If the proton affinity of component X is greater than that of H ₂ , XH ⁺ ions are formed as source ion species.

In the case of the N ₂ -N ₂ O source gas mixture, the reaction conditions are chosen so that a selective O ^- ion current is maintained (ref2).

The intermediate region B is already known from conventional methods and devices for obtaining a selective ion current (it corresponds to the regions B and C of FIG AT 001 637 U1 and AT 406 206 B ) and is also called "source drift region". The intermediate region B could also be divided into two subregions B1 and B2. In the area B1, the source gas would then be present, but the electric field strength would be too small for dissociation reactions. In the subsequent area B2, a higher field strength would be present to cause the dissociation reactions.

By applying an electric field, the resulting ions of the one or more source ion species are extracted through an aperture 6 in an intermediate wall 7 in the reaction region C.

In the reaction region C, an additional, different from the source gas in its chemical composition, reactive collision partner is added, which is referred to in the context of this document as a reactant gas. The reactant gas can be formed by a clean gas or a gas mixture. The total pressure in the reaction region C is more than 0.01 mbar (particle gas density N _c ). The partial pressures of source gas and reactant gas vary depending on the source and reactant gas used. The admixture of the reactant gas is effected by a feed 8 shown schematically in the figure. By means of electrodes 9, an electric field of the field strength E _{c is} applied. The reaction region C is at a temperature T _c .

By ion-molecule reactions with the reactant gas, the ion stream extracted from the intermediate region B, preferably consisting essentially of the one or more source ion species, is converted into an output ion stream which is substantially, i. H. more than 90%, preferably more than 95%, of a single type of ion. In practice, values of up to more than 99% can be achieved. If the ion stream extracted from the intermediate region B consists of more than one source ion species, the conversion into the starting ion stream comprising essentially only one single ion species is achieved by the fact that only the reactions of the various source ion species with the reactant gas a single production variety emerges.

The parameters E _c / N _c and T _c define the reaction conditions, ie by varying these parameters it is possible to favor certain reaction channels and suppress others to produce a selective ion source ion stream. For example, by suitable choice of the field strength of the field E _c dissociation reactions can be effected in order to reverse the formation of cluster ions or to prevent their formation from the outset. To improve the efficiency of such dissociation reactions, an additional gas could also be mixed into the reaction region C, which does not react with the ions present in the reaction region C via ion molecule reactions, but serves only as a collision partner.

By the electric field E _c , the ions are passed through the reaction region C to the output 10.

By the electrodes 5 in the intermediate region B and / or by the electrodes 9 in the reaction region C, an electrostatic potential is preferably generated. It is hereby preferred that in the intermediate region B and / or in the reaction region C, a homogeneous electric field E _B or E _{c is} generated. Due to the homogeneity of the electric field E _B or E _c , the reaction conditions can be manipulated in an advantageous manner, ie, certain reaction channels are preferred or suppressed.

By changing the reactant gas, different selective output ion streams (ie, essentially only one ionic sort of output ion streams) can be generated in a simple, fast way. which can be used, for example, as primary ions for chemical ionization processes. Such chemical ionization methods are used, for example, in ion-molecule reaction mass spectrometry (IMR-MS) or in proton exchange reaction mass spectrometry (PTR-MS). In this case, a substance gas to be examined is ionized by means of the initial ion current in a drift tube and subsequently analyzed by mass spectrometry. However, the reaction region C remains substantially free of the substance gas to be examined, ie the partial pressure of the substance gas in the reaction region C is less than 1/10 of the partial pressure of the substance gas in the drift tube. In the reaction region C, apart from the components of the source and reaction gases, preferably less than 50 ppm of other reactive components (= reactive impurities) are present (formed, for example, by backflowing components of a substance gas to be analyzed), with a value of less than 25 ppm is particularly preferred. Non-reactive components (eg nitrogen) can be present with higher proportions.

The type of ion at the exit 10 differs from the one or more source ion types.

If BH ₃ ⁺ ions are extracted as source ion species at the exit of the intermediate region, they can be used to generate, for example, initial ion currents which have the following ions in each case as substantially single ion species: N ₂ H ⁺ , H ₃ O ⁺ , NO ⁺ , NH ₄ ⁺ . Reactant gases which react with the H ₃ ⁺ ion stream from intermediate region B to the single ion species forming the parent ion stream are: Nitrogen (N ₂ ) H ₃ ⁺ + N ₂ → N ₂ H ⁺ + H ₂ resulting selective output ion current N ₂ H ⁺ Water (H ₂ O) H ₃ ⁺ + H ₂ O → H ₃ O ⁺ + H ₂ resulting selective output ion current H ₃ O ⁺ Nitric oxide (NO) H ₃ ⁺ + NO → HNO ⁺ + H ₂
ENT ⁺ + NO → NO ⁺ + ENT resulting selective output ion current NO ⁺ Ammonia (NH ₃ ) H ₃ ⁺ + NH ₃ → NH ₄ ⁺ + H ₂ resulting selective ion current: NH ₄ ⁺

$${\mathrm{O}}^{\mathrm{-}}\mathrm{+}{\mathrm{H}}_2\mathrm{\to }{\mathrm{OH}}^{\mathrm{-}}\mathrm{+}\mathrm{H}$$

A selective OH ^- exit ion current can be obtained from the O ^- ion stream extracted from the intermediate region B by means of the reactant gases methane (CH ₄ ) or H ₂ : $${\mathrm{O}}^{\mathrm{-}}\mathrm{+}\mathrm{<figure-callout\; id="4"\; label="C\; \; H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C\; </figure-callout>}{\mathrm{H}}_{}{\mathrm{}}_{\mathrm{4}}\mathrm{\to }{\mathrm{OH}}^{\mathrm{-}}\mathrm{+}\mathrm{C}{\mathrm{H}}_{\mathrm{4}}$$

$${\mathrm{O}}^{\mathrm{-}}\mathrm{+}{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0001.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\mathrm{\to }{\mathrm{OH}}^{\mathrm{-}}\mathrm{+}\mathrm{H}$$

If XH ⁺ ions are present as the source ion species, X being a component of the source gas whose proton affinity is greater than H ₂ , then N ₂ H ⁺ is formed as N ₂ reactant gas as the starting ion current, if the proton affinity of component X is smaller than that of N ₂ . With H ₂ O as the reactant gas, if the proton affinity of X is less than the proton affinity of H ₂ O, then the essentially single ion species of the H ₂ O ⁺ source ion current is formed.

In principle, it would also be conceivable and possible for the intermediate area B to be omitted. The reactions of the ions formed in the ionization region to the source ion species which does not react with the source gas or the plurality of source ion species which do not react with the source gas could then either proceed essentially completely already in the ionization region and / or after the extraction of the (not or only partially reacted to the one or more source ion species) continue ions from the ionization in the reaction region C in this by the existing partial pressure of source gas. There should be such conditions that the reactant gas does not react with the precursor products of the one or more source ion species and / or precursor products reacting with the reactant gas are allowed to react with non-interfering ions with a suitable additional gas.

Even with an existing intermediate region B, it would be conceivable and possible that the completion of the reactions to the one or more source ion species takes place only in the reaction region C.

Thus, areas A and B can at least partially overlap or areas B and C can partially overlap, as long as B does not overlap with A. In any case, the reaction region C is located outside the ionization region A (ie outside the region in which the plasma formed during the ionization of the source gas is present). The reaction area C is thus spatially separated from the ionization region A and it is a feedback of reactant gas from the reaction region C in the ionization A substantially suppressed.

Legend to the reference numbers:

1

feed

2

ionization device

3

aperture

4

partition

5

electrode

6

aperture

7

partition

8th

feed

9

electrode

10

output

Claims (13)

1. Method for obtaining an output ion stream consisting substantially only of a single type of ion, ions formed in the ionization of a source gas in an ionization region (A) and/or ions extracted from the ionization region (A) being allowed to react in a region (A, B, C) in which source gas is present until substantially only one or more types of source ions which do not react with the source gas are present, characterized in that a reactant gas differing from the source gas is fed to a reaction region (C) which is present outside the ionization region (A) and in which ions of the one or more types of source ions are present, which reactant gas reacts with the ions of the one or more types of source ions, the ions of the one or more types of source ions being substantially converted into the single type of ions which forms the output ion stream.
2. Method according to Claim 1, characterized in that backflow of the reactant gas from the reaction region (C) into the ionization region (A) is substantially suppressed.
3. Method according to Claim 1 or Claim 2, characterized in that the ions extracted from the ionization region (A) are fed into an intermediate region (B) in which they are left until the ions initially still differing from the one or more types of source ions have also been substantially converted into ions of the one or more types of source ions or cluster ions thereof by ion-molecule reactions with source gas present in the intermediate region.
4. Method according to Claim 3, characterized in that ions of the one or more types of source ions or cluster ions thereof are extracted from the intermediate region (B) into the reaction region (C).
5. Method according to Claim 1 or Claim 2, characterized in that the ions extracted from the ionization region are fed directly into the reaction region (C).
6. Method according to any of Claims 1 to 5, characterized in that source gas is also fed to the reaction region (C).
7. Method according to any of Claims 1 to 6, characterized in that an electric field (E_c) having a strength by means of which the formation of cluster ions from the ion type of the output ion stream is prevented or reversed is applied at least in a section adjacent to the output of the reaction region (C).
8. Process according to either of Claims 3 and 4, characterized in that an electric field (E_B) having a strength by means of which formation of cluster ions from the one or more types of source ions is prevented or reversed is applied at least in a section adjacent to the output of the intermediate region (B).
9. Method according to any of Claims 1 to 8, characterized in that only one type of source ion is formed.
10. Method according to any of Claims 1 to 9, characterized in that source gas having a pressure of at least one Pascal is present in the region (A, B, C) in which the ions formed in the ionization region (A) and/or ions extracted from the ionization region (A) are allowed to react to form the one or more types of source ions.
11. Method according to any of Claims 1 to 9, characterized in that, for obtaining in each case output ion streams which consist substantially only of a single type of ion and differ in the type of ion, different reactant gasses are fed to the reaction region (C) depending on that ion type of the output ion stream which is to be formed, the reaction region (C) being pumped out to remove previously used different reactant gas before a respective reactant gas is fed in.
12. Method according to any of Claims 7 to 11, characterized in that the electric field (E_c) applied in the reaction region (C) is electrostatic and homogeneous.
13. Method according to any of Claims 8 to 12, characterized in that the electric field (E_B) applied in the intermediate region (B) is electrostatic and homogeneous.

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