Abstract
The invention relates to a chemical ionisation method, in particular an adduct ionisation method, for ionising a sample including analytes to be ionised, wherein ligand compound ions formed from reactant ions and a dopant substance are made available in a reaction volume (2), wherein said sample with said analytes is introduced into said reaction volume (2) to react with said ligand compound ions to form adduct ions and a neutral byproduct, said adduct ions including ionised analytes being adducts of said reactant ions and the respective said analytes, wherein said reactant ions and said dopant substance provide a higher binding energy when binding together to said ligand compound ions than a binding energy said reactant ions and a ligand forming substance provide when binding together, wherein said ligand forming substance is present at least in traces in said reaction volume (2) when said sample with said analytes react with said ligand compound ions to form said adduct ions and said neutral byproduct. Furthermore, the invention relates to An ion molecule reactor (1) for ionising a sample including analytes to be ionised with the chemical ionisation method according to one of claims 1 to 11, in particular for use with a mass spectrometer (100), including: a reaction volume (2) adapted for ionising inside said reaction volume (2)said sample including said analytes to be ionised by chemical ionisation, in particular adduct ionisation, wherein inside of said reaction volume (2) ligand compound ions formed from reactant ions and a dopant substance can be made available to react with said sample including said analytes to form adduct ions and a neutral byproduct, said adduct ions including ionised analytes being adducts of said reactant ions and the respective said analytes, at least one sample inlet (4) for introducing said sample including said analytes into said reaction volume (2); at least one reactant inlet (5, 6) for introducing at least one substance into said reaction volume (2) for making said ligand compound ions available inside said reaction volume (2); and an outlet (7) for letting out said adduct ions from said reaction volume (2).
Claims
1. A chemical ionisation method, for ionising a sample including analytes to be ionised, wherein ligand compound ions formed from reactant ions and a dopant substance are made available in a reaction volume, wherein said sample with said analytes is introduced into said reaction volume to react with said ligand compound ions to form adduct ions and a neutral byproduct, said adduct ions including ionised analytes being adducts of said reactant ions and the respective said analytes, wherein said reactant ions and said dopant substance provide a higher binding energy when binding together to said ligand compound ions than a binding energy said reactant ions and a ligand forming substance provide when binding together, wherein said ligand forming substance is present at least in traces in said reaction volume when said sample with said analytes react with said ligand compound ions to form said adduct ions and said neutral byproduct.
2. The chemical ionisation method as claimed in claim 1, wherein said sample includes at least traces of said ligand forming substance.
3. The chemical ionisation method as claimed in claim 2, wherein said sample consists of parts and includes at least one part, of said ligand forming substance per 10′000′000 parts, wherein said parts are atoms or molecules.
4. The chemical ionisation method as claimed in claim 1, wherein said ligand forming substance is one of water, ethanol, benzene, nitric acid and acetic acid or is any other molecule containing an acid, peroxide, alcohol or ketone moiety.
5. The chemical ionisation method as claimed in claim 1, wherein said reactant ions are one of I.sup.−, Br.sup.−, Cl.sup.−, CF.sub.3O.sup.−, NO.sub.3.sup.−, acetate.sup.−, NO.sup.+, NH.sub.4.sup.+, amine.sup.+, acetone.sup.+, ethanol.sup.+, H.sub.3O.sup.+ and benzene.sup.+.
6. The chemical ionisation method as claimed in claim 1, wherein said dopant substance is a molecule.
7. The chemical ionisation method as claimed in claim 1, wherein said dopant substance is one of water, ethanol, methanol, benzene, acetone, acetonitrile, formic acid, lactic acid, nitric acid, or is any other molecule containing an acid, peroxide, alcohol or ketone moiety, and in that said dopant substance and said reactant ions provide said higher binding energy when binding together to said ligand compound ions than said binding energy said reactant ions and said ligand forming substance provide when binding together.
8. The chemical ionisation method as claimed in claim 1, wherein said reactant ions and said dopant substance provide a lower binding energy when binding together than a binding energy said reactant ions and any of said analytes to be analysed provide when binding together.
9. The chemical ionisation method as claimed in claim 1, wherein in said reaction volume a gas pressure in a range from 1 mbar to 1′000 mbar, is maintained.
10. The chemical ionisation method as claimed in claim 1, wherein a temperature in said reaction volume is constantly maintained within a bandwidth of 2 degrees Celsius, during executing said chemical ionisation method.
11. The chemical ionisation method as claimed in claim 1, wherein the temperature in said reaction volume (2) is constantly maintained in a temperature range between 15° and 100° C.
12. A method for mass analysing analytes in a sample including said analytes, wherein said sample including said analytes is ionised with the chemical ionisation method as claimed in claim 1 and the resulting ions are transferred to a mass analyser and mass analysed with said mass analyser in order to mass analyse said analytes.
13. An ion molecule reactor for ionising a sample including analytes to be ionised with the chemical ionisation method according to claim 1, in particular for use with a mass spectrometer, including: a) a reaction volume adapted for ionising inside said reaction volume (2) said sample including said analytes to be ionised by chemical ionisation, wherein inside of said reaction volume ligand compound ions formed from reactant ions and a dopant substance can be made available to react with said sample including said analytes to form adduct ions and a neutral byproduct, said adduct ions including ionised analytes being adducts of said reactant ions and the respective said analytes, b) at least one sample inlet for introducing said sample including said analytes into said reaction volume; c) at least one reactant inlet for introducing at least one substance into said reaction volume for making said ligand compound ions available inside said reaction volume; and d) an outlet for letting out said adduct ions from said reaction volume.
14. A chemical ionisation ion source including an ion molecule reactor according to claim 13 for ionising a sample including analytes to be ionised with the chemical ionisation method according to claim 1, wherein said chemical ionisation ion source includes either a reactant ion ion source for ionising the reactant to reactant ions or a ligand compound ion ion source for ionising the ligand compound to ligand compound ions for making said ligand compound ions available in said reaction volume.
15. A mass spectrometer for mass analysing analytes in a sample including said analytes with the method as claimed in claim 12, wherein said mass spectrometer including a chemical ionisation ion source according to claim 14 for ionising said sample including said analytes to resulting ions, said mass spectrometer including a mass analyser for mass analysing said resulting ions in order to mass analyse said analytes, wherein said mass analyser is fluidly coupled to said chemical ionisation ion source for receiving the resulting ions.
16. The chemical ionisation method as claimed in claim 2, wherein said sample consists of parts and includes at least one molecule of said ligand forming substance per 10′000′000 parts, wherein said parts are molecules.
17. The chemical ionisation method as claimed in claim 1, wherein in said reaction volume a gas pressure in a range from 10 mbar to 1′000 mbar is maintained.
18. The chemical ionisation method as claimed in claim 1, wherein in said reaction volume a gas pressure in a range from 20 mbar to 1′000 mbar is maintained.
19. The chemical ionisation method as claimed in claim 1, wherein the temperature in said reaction volume is constantly maintained in a temperature range between 25° C. and 100° C.
20. The chemical ionisation method as claimed in claim 1, wherein the temperature in said reaction volume is constantly maintained in a temperature range between 40° C. and 100° C.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0071] The drawings used to explain the embodiments show:
[0072] FIG. 1 a simplified schematic view of an ion molecular reactor according to the invention for ionising a sample including analytes to be ionised with the method according to the invention, in particular for use with a mass spectrometer,
[0073] FIG. 2 a simplified schematic view of a chemical ionisation ion source which includes the ion molecule reactor shown in FIG. 1 for ionising a sample including analytes to be ionised with the method according to the invention,
[0074] FIG. 3 a simplified schematic view of a variant of the chemical ionisation ion source which includes the ion molecule reactor shown in FIG. 1 for ionising a sample including analytes to be ionised with the method according to the invention,
[0075] FIG. 4 a simplified schematic view of a mass spectrometer for mass analysing analytes in a sample including the analytes, the mass spectrometer including the chemical ionisation ion source shown in FIG. 2,
[0076] FIG. 5a, b, c calculated diagrams showing the ratios of iodide ions (I.sup.−) as reactant ions and ligand ions of these reactant ions (I.sup.−) formed with water (I(H.sub.2O).sup.−, I(H.sub.2O).sub.2.sup.− and I(H.sub.2O).sub.3.sup.−, respectively) in dependence of the partial gas pressure of water (pH2O) in the ion molecule reactor (IMR) i.e. the reaction volume, at a temperature of 25° C.,
[0077] FIG. 6 the same curves as FIG. 5a, calculated for a total gas pressure of 50 mbar at 25° C. in the reaction volume and a measurement of nitric acid, acrylic acid and formic acid in laboratory air at 25° C. and 50 mbar total gas pressure in the reaction volume at different partial gas pressures of water in the reaction volume, normalised to the amount of nitric acid, acrylic acid and formic acid measured in completely dry conditions where the partial gas pressure of water in the reaction volume was zero,
[0078] FIG. 7a, b measured diagrams for illustrating the chemical ionisation method according to the invention at a total gas pressure of 50 mbar in the reaction volume and at a temperature of 25° C. in the reaction volume, with a acetone as dopant substance,
[0079] FIG. 8a, b, c measured diagrams for illustrating the chemical ionisation method according to the invention at a total gas pressure of 50 mbar in the reaction volume and at a temperature of 25° C. in the reaction volume, with methanol as dopant substance,
[0080] FIG. 9a, b measured diagrams for illustrating the chemical ionisation method according to the invention at a total gas pressure of 50 mbar in the reaction volume and at a temperature of 25° C. in the reaction volume, with acetonitrile (ACN) as dopant substance, and
[0081] FIG. 10 the same two diagrams as FIG. 6, wherein the lower diagram of FIG. 10, however, additionally the same measurement of nitric acid, formic acid and acrylic acid in laboratory air performed under the same conditions but by using the chemical ionisation method according to the invention is shown with the data points being shown as filled points.
[0082] In the figures, the same components are given the same reference symbols.
PREFERRED EMBODIMENTS
[0083] FIG. 1 shows a simplified schematic view of an ion molecular reactor 1 according to the invention for ionising a sample including analytes to be ionised with the chemical ionisation method according to the invention, in particular for use with a mass spectrometer 100 (see FIG. 4). This ion molecular reactor 1 includes a reaction volume 2 which is defined by a chamber 3 of the ion molecule reactor 1. The reaction volume 2 is adapted for ionising inside the reaction volume 2 the sample including the analytes to be ionised by adduct ionisation, which is a type of chemical ionisation. Inside of the reaction volume 2, ligand compound ions formed from reactant ions and a dopant substance can be made available to react with the sample including the analytes to form adduct ions and a neutral byproduct, the adduct ions including ionised analytes being adducts of the reactant ions and the respective analytes.
[0084] The ion molecule reactor 1 includes a sample inlet 4 for introducing the sample including the analytes into the reaction volume 2 and two reactant inlets 5, 6. A first one of these two reactant inlets 5 is for introducing reactant ions into the reaction volume 2, while a second one of these two reactant inlets 6 is for introducing a dopant substance into the reaction volume 2 for forming ligand compound ions with the reactant ions in the reaction volume 2 in order to make available the ligand compound ions in the reaction volume 2. Thus, the ion molecule reactor 1 includes two reactant inlets 5, 6 for introducing at least one substance into the reaction volume 2 for making available the ligand compound ions inside the reaction volume 2. Furthermore, the ion molecule reactor 1 includes an outlet 7 for letting out the adduct ions from the reaction volume 2 and for enabling transferring the adduct ions from the reaction volume 2 to the mass analyser 101 of the mass spectrometer 100, when the ion molecule reactor 1 is used in the mass spectrometer 100.
[0085] FIG. 2 shows a simplified schematic view of a chemical ionisation ion source 50 which includes the ion molecule reactor 1 shown in FIG. 1 for ionising a sample including analytes to be ionised with the chemical ionisation method according to the invention, wherein the chemical ionisation ion source 50 further includes a reactant ion ion source 51 for ionising a reactant to reactant ions. This reactant ion ion source 51 is an ultraviolet ion source and is fluidly coupled to the first one of the two reactant inlets 5 of the ion molecule reactor 1 for introducing the reactant ions from the reactant ion ion source 51 into the reaction volume 2. The chemical ionisation ion source 50 furthermore includes a reservoir 52 of dopant substance fluidly coupled to the second one of the two reactant inlets 6 of the ion molecule reactor 1 for introducing the dopant substance in the reaction volume 2 in order to make the ligand compound ions available in the reaction volume 2.
[0086] Additionally, the chemical ionisation ion source 50 includes means 55 for achieving and maintaining a desired temperature in the reaction volume within a desired bandwidth. These means 55 are a temperature control unit with to a temperature sensor sensing the temperature in the reaction volume 2 and a heater for heating the reaction volume 2 for achieving and maintaining the temperature in the reaction volume within the respective bandwidth and range.
[0087] Furthermore, the chemical ionisation ion source 50 includes means 56 for achieving and maintaining the gas pressure in the reaction volume in the desired range. Since in the chemical ionisation ion source 50, the desired pressure ranges are below the air pressure on ground on earth and since the chemical ionisation ion source 50 is intended to be used on ground, the means for achieving and maintaining the gas pressure in the reaction volume is simply a vacuum pump.
[0088] In a variant shown in FIG. 3, the chemical ionisation ion source 50 includes a ligand compound ion ion source 54 instead of the reactant ion ion source 51. In this case, a ligand compound formed of the reactant and the dopant substance is ionised by the ligand compound ion ion source 54 to ligand compound ions. Thus, in this case, the ion molecular reactor 1 includes only one reactant inlet 8 which is fluidly coupled to the ligand compound ion ion source 54 for introducing the ligand compound ions from the ligand compound ion ion source 54 into the reaction volume 2 in order to make the ligand compound ions available in the reaction volume 2.
[0089] In both the cases shown in FIGS. 2 and 3, the chemical ionisation ion source 50 further includes a control unit 53 adapted for controlling the chemical ionisation ion source 50 and adapted for executing the chemical ionisation method according to the invention.
[0090] FIG. 4 shows a simplified schematic view of a mass spectrometer 100 for mass analysing analytes in a sample including the analytes. This mass spectrometer 100 includes the chemical ionisation ion source 50 shown in FIG. 2 for ionising the sample including the analytes to resulting ions. The mass spectrometer 100 further includes a mass analyser 101 for mass analysing the resulting ions in order to mass analyse the analytes. This mass analyser 101 is in the present embodiment a time of flight mass analyser. However, the mass analyser 101 can as well be any other type of mass analyser like for example a quadrupole mass analyser. In the mass spectrometer 100 shown in FIG. 4, the mass analyser 101 is fluidly coupled to the chemical ionisation ion source 50 for receiving the resulting ions. Thus, the mass spectrometer 100 is for mass analysing the analytes in the sample including the analytes with a method for mass analysing the analytes in the sample including the analytes where the sample including the analytes is ionised with the method according to the invention and the resulting ions are transferred to the mass analyser 101 and mass analysed with the mass analyser 101 in order to mass analyse the analytes.
[0091] The mass spectrometer 100 further includes a ion mobility separation cell 102 fluidly coupled between the chemical ionisation ion source 50 and the mass analyser 101 for separating the resulting ions received from the chemical ionisation ion source 50 according to their mobility before mass analysing the resulting ions in the mass analyser 101. Thus, in the method for mass analysing the analytes in the sample including the analytes, the resulting ions are separated according to their mobility in the ion mobility separation cell 102 before being mass analysed with the mass analyser 101 in order to mass analyse the analytes. In order to pass the resulting ions in a pulsed manner through the ion mobility separation cell 102, the mass spectrometer 100 includes an ion trap 104 arranged downstream of the chemical ionisation ion source 50 and upstream of the ion mobility separation cell 102. In this ion trap 104, the resulting ions received from the chemical ionisation ion source 50 are collected and released in pulses to be passed through the ion mobility separation cell 102 for being separated according to their mobility.
[0092] For the sake of completeness, it is mentioned here that the mass spectrometer 100 includes a control unit 103 adapted for controlling the mass spectrometer 100 and for controlling the mass spectrometer 100 to execute the methods described in the present text. In FIG. 4, this control unit 103 is shown schematically as a square in the mass spectrometer 100. However, the control unit 103 may as well be a separate computer connected to the rest of the mass spectrometer 100. Thereby, the control unit 103 may directly control the chemical ionisation ion source 50 or may control a control unit 53 of the chemical ionisation ion source 50. Since the control units 103 adapted for controlling a mass spectrometer are well known in the art, the control unit 103 of the mass spectrometer 100 shown in FIG. 4 is not further explained here.
[0093] FIGS. 5a, 5b and 5c show calculated diagrams showing the ratios of iodide ions (I.sup.−) as reactant ions and ligand ions of these reactant ions (I.sup.−) formed with water (I(H.sub.2O).sup.−, I(H.sub.2O).sub.2.sup.− and I(H.sub.2O).sub.3.sup.−, respectively) in dependence of the partial gas pressure of water (pH2O) in the ion molecule reactor (IMR) i.e. the reaction volume, at a temperature of 25° C. Thereby, the partial gas pressure of water in the reaction volume is shown in mbar on the x-axis, while the amounts of reactant ions (I.sup.−) and ligand ions are shown on the y-axis in units of their fraction of the total number of iodide in the reaction volume. For this reason, the y-axis is labelled “Fractional Reactant Ions” on the y-axis, while the partial gas pressure of water in the reaction volume is shown on the x-axis.
[0094] The diagram shown in FIG. 5a is calculated for a total gas pressure of 50 mbar in the reaction volume. Thereby, the partial gas pressure of water on the x-axis reaches from 0 mbar to 1.4 mbar, which is from zero to 2.8% of the total gas pressure in the reaction volume. The diagram shown in FIG. 5b is calculated for a total gas pressure of 150 mbar in the reaction volume. Thereby, the partial gas pressure of water on the x-axis reaches from 0 mbar to 4.2 mbar, which is as well from zero to 2.8% of the total gas pressure in the reaction volume. The diagram shown in FIG. 5c has been calculated for a total gas pressure of 500 mbar in the reaction volume. Thereby, the partial gas pressure of water on the x-axis reaches from 0 mbar to 14 mbar, which is as well from zero to 2.8% of the total gas pressure in the reaction volume.
[0095] The diagrams shown in FIGS. 5a, 5b and 5c illustrate on the example of iodide ions (I.sup.−) as reactant ions, how strongly the presence of water as ligand forming substance in the reaction volume influences the ratios between the pure reactant ions (I.sup.−) and the different ligand ions (I(H.sub.2O).sup.−, I(H.sub.2O).sub.2.sup.−, and I(H.sub.2O).sub.3.sup.−, respectively) formed from the reactant ions and the ligand forming substance. As illustrated, in case the sample includes a varying content of water as ligand forming substance, these ratios change considerably as the content of water varies. Since the pure reactant ions (I.sup.−) and the different types of ligand ions (I(H.sub.2O).sup.−, I(H.sub.2O).sub.2.sup.−, and I(H.sub.2O).sub.3.sup.−, respectively) provide a different likelihood for reacting with an analyte to form an adduct ion of one reactant ion and one analyte and in case of the ligand ions to form an adduct ion of one reactant ion and one analyte besides a neutral byproduct, the ionisation efficiencies of a prior art chemical ionisation ion source for different analytes chances dramatically as the amount of ligand forming substance changes in the sample.
[0096] As visible from FIGS. 5a, 5b and 5c, a total gas pressure of 50 mbar in the reaction volume and a partial gas pressure of water between 0.2 mbar and 0.4 mbar in the reaction volume provide the least changes in the ligand ions in particular in the ratio of pure reactant ions (I.sup.−) and the first ligand ions I(H.sub.2O).sup.−. For this reason, the prior art it teaches to aim at such conditions in the reaction volume in order to improve the quantitative results of the mass analysis of the analytes in the sample. This can be achieved by maintaining the total gas pressure in the reaction volume low enough while continuously adding some of the ligand forming substance to the reaction volume to achieve and maintain in the reaction volume a certain minimal partial gas pressure of the ligand forming substance, the minimal partial gas pressure being in a range where the sensitivity of reactant ion□adduct ionisation to many compounds shifts more gradually when the amount of ligand forming substance in the sample changes.
[0097] The upper diagram in FIG. 6 shows the same curves as FIG. 5a, calculated for a total gas pressure of 50 mbar at 25° C. in the reaction volume. In order to illustrate the changes of the sensitivity of reactant ion-adduct ionisation in the prior art chemical ionisation methods, the lower diagram of FIG. 6 shows a measurement of nitric acid, acrylic acid and formic acid in laboratory air at 25° C. and 50 mbar total gas pressure in the reaction volume at different partial gas pressures of water in the reaction volume, normalised to the amount of nitric acid, acrylic acid and formic acid measured in completely dry conditions where the partial gas pressure of water in the reaction volume was zero. The measurement has been performed by mass spectrometry, wherein the sample of laboratory air with the included analytes nitric acid, acrylic acid and formic acid was ionised with a prior art chemical ionisation method using iodide ions (I.sup.−). In order to simulate the different amounts of water as ligand forming substance in the sample, water vapour was introduced into the reaction volume for achieving the different partial gas pressures of water in the reaction volume.
[0098] As can be seen from the lower diagram in FIG. 6, the sensitivity for ionising nitric acid with the prior art chemical ionisation method increases by 100% from zero to 0.4 mbar partial gas pressure of water in the reaction volume. At the same time, the sensitivity for ionising acrylic acid decreases by about 70% from zero to 0.4 mbar partial gas pressure of water in the reaction volume and even decreases further towards higher partial gas pressures of water in the reaction volume. Even more, the sensitivity for ionising formic acid increases by about 70% from zero to 0.2 mbar partial gas pressure of water in the reaction volume and then decreases again at higher gas pressures of waters and even drops below the sensitivity achieved at zero partial gas pressure of water when the partial gas pressure of water in the reaction volume is increased to just above 1 mbar.
[0099] FIGS. 7a and 7b show measured diagrams for illustrating the chemical ionisation method according to the invention at a total gas pressure of 50 mbar in the reaction volume and at a temperature of 25° C. in the reaction volume (2). In this example, again, iodide ions (I.sup.−) are the reactant ions and water is the ligand forming substance. In order to simulate different amounts of ligand forming substance in the sample, water vapour was introduced into the reaction volume (2) for achieving the different partial gas pressures of water in the reaction volume (2). In contrast to the prior art, a dopant substance has additionally been introduced into the reaction volume (2) which reacts with the reactant ions and forms ligand compound ions in order to make ligand compound ions available in the reaction volume (2).
[0100] In the example of FIGS. 7a and 7b, the dopant substance is acetone. Thereby, curves measured for different amounts of dopant substance introduced into the reaction volume measured in sccm are shown. Again, the partial gas pressure of water in the reaction volume is shown on the x-axis of the three diagrams. In the top diagram of FIG. 7a, the amounts of pure reactant ions (I.sup.−) measured is shown on the y-axis in arbitrary units. In the centre diagram of FIG. 7a, the amounts of the first ligand ions I(H.sub.2O).sup.− measured is shown on the y-axis in the same arbitrary units. And in the lower diagram of FIG. 7a, the amounts of the ligand compound ions formed from the dopant substance acetone measured is shown on the y-axis in the same arbitrary units.
[0101] As can be seen from FIG. 7a, with increasing amount of the dopant substance acetone in the reaction volume (2), the ratio of ligand ions to ligand compound ions shifts in the favour of the ligand compound ions.
[0102] In FIG. 7b, diagrams are shown where the air in the laboratory has been sampled for nitric acid (top diagram), formic acid (centre diagram) and acrylic acid (lower diagram) by mass spectrometry, again with the different partial gas pressures of water in the reaction volume (2) and for different amounts of dopant substance introduced into the reaction volume (2). Thereby, in all three diagrams shown in FIG. 7b, the y-axis is normalised to the amount of the respective acid measured in the dry, i.e. at zero partial gas pressure of water.
[0103] As can be seen from FIG. 7b, with iodide ions (I.sup.−) as reactant ions and acetone as dopant substance, the dependency of the ionisation efficiency on water as changing ligand forming substance in the sample is reduced for nitric acid, formic acid and acrylic acid with the chemical ionisation method according to the invention. The reason for this effect is that acetone provides a slightly higher binding energy when binding to the iodide ions (I.sup.−) than water provides when binding to the iodide ions (I.sup.−).
[0104] FIGS. 8a and 8b show the same diagrams as FIGS. 7a and 7b measured essentially under the same conditions. However, in FIGS. 8a and 8b, methanol has been used as dopant substance instead of acetone. As can be seen, the dependency of the ionisation efficiency on water as changing ligand forming substance in the sample is reduced even further for nitric acid, formic acid and acrylic acid with the chemical ionisation method according to the invention in case methanol is used as dopant substance. The reason for this effect is that methanol provides a higher binding energy when binding to the iodide ions (I.sup.−) than acetone provides when binding to the iodide ions (I.sup.−) and than water provides when binding to the iodide ions (I.sup.−).
[0105] FIGS. 9a and 9b show the same diagrams as FIGS. 7a and 7b and FIGS. 8a and 8b, respectively, measured essentially under the same conditions. However, in FIGS. 9a and 9b, acetonitrile (ACN) has been used as dopant substance instead of acetone or methanol. As can be seen, the dependency of the ionisation efficiency on water as changing ligand forming substance in the sample is roughly the same for nitric acid and formic acid as in case methanol is used as dopant substance (see FIG. 8b). However, the dependency of the ionisation efficiency on water as changing ligand forming substance in the sample is reduced further for acrylic acid with the chemical ionisation method according to the invention in case acetonitrile (ACN) is used as dopant substance. The reason for this effect is that acetonitrile (ACN) provides a higher binding energy when binding to the iodide ions (I.sup.−) than methanol provides when binding to the iodide ions (I.sup.−), than acetone provides when binding to the iodide ions (I.sup.−) and than water provides when binding to the iodide ions (I.sup.−).
[0106] FIG. 10 shows the same two diagrams as FIG. 6. In the lower diagram of FIG. 10, however, additionally the same measurement of nitric acid, formic acid and acrylic acid in laboratory air performed under the same conditions but by using the chemical ionisation method according to the invention is shown with the data points being shown as filled points. In this additionally shown measurement, a flow of 30 sccm of acetonitrile (ACN) as dopant substance was introduced into the reaction volume (2) for making available the ligand compound ions in the reaction volume (2).
[0107] As can be seen from the lower diagram of FIG. 10, the chemical ionisation method according to the invention enables a considerably more precise and more reliable quantification of the analytes in the sample with mass spectrometry. The sensitivity for ionising nitric acid, formic acid and acrylic acid no longer varies in the order of 100% with changing water content in the sample. Rather, the changes of sensitivity for changing water content is reduced to 20% or even lower.
[0108] The invention is not limited to the examples illustrated in the context of the Figures. For example, the invention is not limited to iodide ions (I.sup.−) as reactant ions. Any of of I.sup.−, Br.sup.−, Cl.sup.−, CF.sub.3O.sup.−, NO.sub.3.sup.−, acetate.sup.−, NO.sup.+, NH.sub.4.sup.+, amine.sup.+, acetone.sup.+, ethanol.sup.+, H.sub.3O.sup.+ and benzene.sup.+ can be used as reactant ions. Even more, the invention is not limited to these reactant ions. Other reactant ions can be used as well. Furthermore, the dopant substance is not limited to acetone, methanol and acetonitrile (ACN). Any dopant substance of water, ethanol, methanol, benzene, acetone, acetonitrile (ACN), formic acid, lactic acid and nitric acid can be used. Even more, the invention is not limited to these dopant substances. Rather, any other dopant substance can be used as well. Additionally, the ligand forming substance is not required to be water as used in the examples illustrated in the context of the Figures. The ligand forming substance can by any one of water, ethanol, benzene, nitric acid and acetic acid. Even more, the invention is not limited to these ligand forming substances. Rather, any other ligand forming substance can be used as well. Important for the invention is only that the reactant ions and the dopant substance provide the higher binding energy when binding together to the ligand compound ions than the binding energy the reactant ions and a ligand forming substance provide when binding together. The chemical ionisation method according to the invention is particular advantageous, if at least traces of the ligand forming substance are present in the sample and the amount of ligand forming substance is likely to vary during one measurement or between two or more measurements which should be compared quantitatively afterwards. Thus, the chemical ionisation method according to the invention is particular advantageous in case the sample consists of parts and includes at least one part, in particular at least one molecule, of the ligand forming substance per 10′000′000 parts of the sample. Furthermore, the chemical ionisation method according to the invention is advantageous in case the sample consists of parts, wherein the parts are atoms or molecules, and wherein a concentration of the parts of ligand forming substance in the total parts of the sample varies at a rate of at least 10% of the initial concentration of the parts of ligand forming substance in the total parts of the sample within one hour, within one minute or even within one second.
[0109] Additionally, the chemical ionisation method according to the invention is particular advantageous in case the sample consists of parts, wherein the parts are atoms or molecules, and the amount of dopant substance provided in the reaction volume as dopant substance or already in the form of the ligand compound ions in the reaction volume is controlled to be at all times during executing the chemical ionisation method according to the invention more than 1 part of dopant substance per 10′000′000 parts of the sample, like for example 1 part per 10′000 parts of the sample, or even 1 part per 100 parts of the sample, that are present in the reaction volume. In the measurement obtained with the chemical ionization method according to the invention shown in the lower diagram of FIG. 10, the total gas pressure in the reaction volume was 50 mbar and the temperature was maintained at 25° C. within a bandwidth of 1 degree Celsius. This was chosen because these parameters are optimal for the measurement obtained with the prior art chemical ionization method which is shown in the diagram as well. In the chemical ionization method according to the invention, the total gas pressure in the reaction volume can be chosen to be higher or lower. In examples, the total gas pressure in the reaction volume is 10 mbar, 30 mbar, 100 mbar, 250 mbar, 500 mbar, 750 mbar and 900 mbar, respectively. Furthermore, the temperature in the reaction volume can be chosen to be higher or lower. In examples, the temperature in the reaction volume is 16° C., 20° C., 30° C., 50° C., 70° C., 100° C., 150° C. and 170° C., respectively.
[0110] In summary, it is to be noted that a chemical ionisation method, in particular an adduct ionisation method, and an ion molecule reactor pertaining to the technical field initially mentioned are provided that enable a more precise and more reliable quantification of the analytes in the sample with mass spectrometry.
