METHOD AND APPARATUS OF MASS ANALYSING POSITIVELY CHARGED IONS AND NEGATIVELY CHARGED IONS

Abstract

The invention relates to a method for mass analysing positively charged ions and negatively charged ions with a mass analyser arrangement (10). The method includes inserting the positively charged ions and the negatively charged ions via an intake (13) of the mass analyser arrangement (10) into a mass analysis chamber (14) of the mass analyser arrangement (10). Furthermore, the method includes transferring inside the mass analysis chamber (14) the positively charged ions from the intake (13) to a first mass analyser (11) of the mass analyser arrangement (10) and mass analysing the positively charged ions with the first mass analyser (11) and transferring inside the mass analysis chamber (14) the negatively charged ions from the intake (13) to a second mass analyser (12) of the mass analyser arrangement (10) and mass analysing the negatively charged ions with the second mass analyser (12). The invention furthermore relates to the mass analyser arrangement (10) for mass analysing positively charged ions and negatively charged ions with the method according to the invention.

Claims

1. A method for mass analysing positively charged ions and negatively charged ions with a mass analyser arrangement, said method including a) inserting said positively charged ions and said negatively charged ions via an intake of said mass analyser arrangement into a mass analysis chamber of said mass analyser arrangement, and b) transferring inside said mass analysis chamber said positively charged ions from said intake to a first mass analyser of said mass analyser arrangement and mass analysing said positively charged ions with said first mass analyser and transferring inside said mass analysis chamber said negatively charged ions from said intake to a second mass analyser of said mass analyser arrangement and mass analysing said negatively charged ions with said second mass analyser.

2. The method according to claim 1, wherein insertion of said positively charged ions and said negatively charged ions via said intake into said mass analysis chamber is controlled with a switchable ion gate of said mass analyser arrangement, wherein said switchable ion gate is arranged in front of said intake, wherein said switchable ion gate is switched between a) a positive ions insertion mode where said positively charged ions are allowed to pass through said intake into said mass analysis chamber while said negatively charged ions are prevented from passing through said intake into said mass analysis chamber, and b) a negative ions insertion mode where said negatively charged ions are allowed to pass through said intake into said mass analysis chamber while said positively charged ions are prevented from passing through said intake into said mass analysis chamber.

3. The method according to claim 2, wherein said switchable ion gate is switched between said positive ions insertion mode and said negative ions insertion mode and back within 100 ms or less, preferably within 20 ms or less, particular preferably within 10 ms or less, more preferably within 200 μs or less, even more preferably within 50 μs or less, and most preferably within 15 μs or less.

4. A method for mass analysing a sample, wherein said sample is ionised with at least one ion source to positively charged ions and negatively charged ions, wherein said positively charged ions and said negatively charged ions are mass analysed with the method according to claim 1.

5. A mass analyser arrangement for mass analysing positively charged ions and negatively charged ions with the method according to claim 1, said mass analyser arrangement including a) a first mass analyser for mass analysing said positively charged ions, b) a second mass analyser for mass analysing said negatively charged ions, and c) an intake for inserting said positively charged ions and said negatively charged ions into a mass analysis chamber of said mass analyser arrangement for mass analysing said positively charged ions with said first mass analyser and for mass analysing said negatively charged ions with said second mass analyser, wherein said intake is fluidly coupled with said first mass analyser for transferring said positively charged ions from said intake to said first mass analyser for mass analysing said positively charged ions and wherein said intake is fluidly coupled with said second mass analyser for transferring said negatively charged ions from said intake to said second mass analyser for mass analysing said negatively charged ions.

6. The mass analyser arrangement according to claim 5, wherein said mass analyser arrangement includes a chamber housing surrounding said mass analysis chamber.

7. The mass analyser arrangement according to claim 5, wherein said mass analyser arrangement includes at least one transfer electrode for generating an electric field for transferring said positively charged ions inside said mass analysis chamber from said intake to said first mass analyser for being mass analysed with said first mass analyser and for transferring said negatively charged ions inside said mass analysis chamber from said intake to said second mass analyser for being mass analysed with said second mass analyser.

8. The mass analyser arrangement according to claim 5, wherein at least one of said first mass analyser and said second mass analyser is a time-of-flight mass analyser.

9. The mass analyser arrangement according to claim 5, wherein said mass analyser arrangement includes a switchable ion gate arranged in front of said intake for controlling an insertion of said positively charged ions and said negatively charged ions via said intake into said mass analysis chamber of said mass analyser arrangement for enabling mass analysis of said positively charged ions with said first mass analyser and said negatively charged ions with said second mass analyser.

10. The mass analyser arrangement according to claim 9, wherein said switchable ion gate is adapted for being switching between a positive ions insertion mode where said positively charged ions are allowed to pass through said intake into said mass analysis chamber while said negatively charged ions are prevented from passing through said intake into said mass analysis chamber, and a negative ions insertion mode where said negatively charged ions are allowed to pass through said intake into said mass analysis chamber while said positively charged ions are prevented from passing through said intake into said mass analysis chamber.

11. The mass analyser arrangement according to claim 10, wherein said mass analyser arrangement includes an ion path housing section for housing a section of an ion path of said positively charged ions and said negatively charged ions leading to said switchable ion gate and via said switchable ion gate to said intake, wherein said ion path housing section enables achieving and maintaining inside said ion path housing section a gas pressure of 10.sup.−2 mbar or less.

12. The mass analyser arrangement according to claim 5, wherein said mass analyser arrangement includes an ion trap for trapping said positively charged ions and/or said negatively charged ions, said ion trap being arranged in front of said intake into said mass analysis chamber.

13. The mass analyser arrangement according to claim 9 or according to claim 12, wherein said switchable ion gate is arranged at one end of said ion trap for releasing said positively charged ions and/or said negatively charged ions in a controlled manner from said ion trap and thus controlling said insertion of said positively charged ions and said negatively charged ions via said intake into said mass analysis chamber of said mass analyser arrangement for enabling mass analysis of said positively charged ions with said first mass analyser and said negatively charged ions with said second mass analyser.

14. The mass analyser arrangement according to claim 13, wherein said switchable ion gate and said ion trap are operable with voltages of less than 200 V for controlling an insertion of said positively charged ions and said negatively charged ions via said intake into said mass analysis chamber of said mass analyser arrangement for enabling mass analysis of said positively charged ions with said first mass analyser and said negatively charged ions with said second mass analyser.

15. An apparatus for mass analysing a sample with the method according to claim 4, said apparatus including a) at least one ion source for ionising said sample to positively charged ions and negatively charged ions and b) the mass analyser arrangement of claim 5, the mass analyser arrangement including the first mass analyser and the intake for inserting said positively charged ions and said negatively charged ions into said mass analysis chamber of said mass analyser arrangement, wherein said at least one ion source is fluidly coupled to said intake for transferring said positively charged ions and said negatively charged ions, respectively, from said at least one ion source to said intake for inserting said positively charged ions and said negatively charged ions into the mass analysis chamber of the mass analyser arrangement for enabling the mass analysis of said positively charged ions with the first mass analyser and for enabling the mass analysis of said negatively charged ions with the second mass analyser.

16. The method according to claim 3, wherein said switchable ion gate is switched between said positive ions insertion mode and said negative ions insertion mode and back within preferably within 10 ms or less.

17. The method according to claim 3, wherein said switchable ion gate is switched between said positive ions insertion mode and said negative ions insertion mode and back within 200 μs or less.

18. The method according to claim 3, wherein said switchable ion gate is switched between said positive ions insertion mode and said negative ions insertion mode and back within preferably within 15 μs or less.

19. The mass analyser arrangement according to claim 11, wherein said ion path housing section enables achieving and maintaining inside said ion path housing section a gas pressure of 10.sup.−3 mbar or less.

20. The mass analyser arrangement according to claim 14, wherein said switchable ion gate and said ion trap are operable with voltages of less than 100 V for controlling an insertion of said positively charged ions and said negatively charged ions via said intake into said mass analysis chamber of said mass analyser arrangement for enabling mass analysis of said positively charged ions with said first mass analyser and said negatively charged ions with said second mass analyser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] The drawings used to explain the embodiments show:

[0087] FIG. 1 a simplified schematic view of an apparatus 1 for mass analysing a sample with a method for mass analysing the sample, wherein the apparatus includes a mass analyser arrangement according to the invention for mass analysing positively charged ions and negatively charged ions and wherein in the method for mass analysing the sample, the method according to the invention for mass analysing positively charged ions and negatively charged ions is employed, and

[0088] FIG. 2 a simplified schematic view of a mass analysis chamber together with a first orthogonal time-of-flight mass analyser and a second orthogonal time-of-flight mass analyser, the view being a cutout of a mass analyser arrangement according to the invention.

[0089] In the figures, the same components are given the same reference symbols.

PREFERRED EMBODIMENTS

[0090] FIG. 1 shows a simplified schematic view of an apparatus 1 for mass analysing a sample with a method for mass analysing the sample. The apparatus 1 includes one ion source 2 for ionising the sample to positively charged ions and negatively charged ions. In a variant which is not shown here, the apparatus 1 includes a first ion source for generating the positively charged ions from the sample and a second ion source for generating the negatively charged ions from the sample. In this variant, an assay from the sample is fed to the first ion source and another assay from the sample is fed to the second ion source for ionising the sample to the positively charged ions and the negatively charged ions. In either variant, the one ion source or two ion sources include a sample inlet for inserting the sample into the respective ion source for being ionised to the positively charged ions and/or negatively charged ions, respectively.

[0091] Besides the one or more ion sources, the apparatus 1 includes a mass analyser arrangement 10 according to the invention for mass analysing the positively charged ions and the negatively charged ions with the method according to the invention for mass analysing the positively charged ions and the negatively charged ions. The mass analyser arrangement 10 includes a first mass analyser 11 and a second mass analyser 12 which are both time-of-flight mass analysers. In variants, one of the first mass analyser 11 and the second mass analyser 12 or both the first mass analyser 11 and the second mass analyser 12 are a different type of mass analyser than a time-of-flight mass analyser. Examples of different types of mass analysers are sector mass analysers, quadrupole mass analysers and Orbitraps.

[0092] The mass analyser arrangement 10 furthermore includes an intake 13 for inserting the positively charged ions and the negatively charged ions into a mass analysis chamber 14 of the mass analyser arrangement 10 for mass analysing the positively charged ions with the first mass analyser 11 and for mass analysing the negatively charged ions with the second mass analyser 12. Thereby, the intake 13 is fluidly coupled with the first mass analyser 11 for transferring the positively charged ions from the intake 13 to the first mass analyser 11 for mass analysing the positively charged ions. Furthermore, the intake 13 is fluidly coupled with the second mass analyser 12 for transferring the negatively charged ions from the intake 13 to the second mass analyser 12 for mass analysing the negatively charged ions. Thereby, the mass analyser arrangement 10 includes a chamber housing 15 surrounding the mass analysis chamber 14 and two transfer electrodes 16.1, 16.2 for generating an electrostatic field for transferring the positively charged ions inside the mass analysis chamber 14 from the intake 13 into a first mass analyser ion inlet 17 of the first mass analyser 11 and thus to the first mass analyser 11 for being mass analysed with the first mass analyser 11 and for transferring the negatively charged ions inside the mass analysis chamber 14 from the intake 13 into a second mass analyser ion inlet 18 of the second mass analyser 12 and thus to the second mass analyser 12 for being mass analysed with the second mass analyser 12. Both transfer electrodes 16.1, 16.2 are arranged inside the mass analysis chamber 14.

[0093] The mass analyser arrangement 10 is adapted for being operated with the mass analysis chamber 14 at a gas pressure of 8-10.sup.−5 mbar and thus less than 10.sup.−4 mbar during execution of the method according to the invention for mass analysing the positively charged ions and the negatively charged ions with the mass analyser arrangement 10. Thereby, the chamber housing 14 is sufficient gas tight that with a suitable vacuum pump, a gas pressure of 8-10.sup.−5 mbar and thus less than 10.sup.−4 mbar can be achieved and maintained in the mass analysis chamber 14. In a variant however, the mass analyser arrangement 10 is even adapted for being operated with the mass analysis chamber 14 at a gas pressure of 8.Math.10.sup.−6 mbar and thus less than 10.sup.−5 mbar during executing the method according to the invention for mass analysing the positively charged ions and the negatively charged ions with the mass analyser arrangement 10. In this latter variant, the chamber housing 14 is sufficient gas tight that with a suitable vacuum pump, a gas pressure of 8.Math.10.sup.−6 mbar and thus less than 10.sup.−5 mbar can be achieved and maintained in the mass analysis chamber 14.

[0094] In FIG. 1, no vacuum pump is shown because the vacuum pump is not required to be part of the mass analyser arrangement 10. More specifically, the vacuum pump may be included in the mass analyser arrangement 10 or the mass analyser arrangement 10 may include a connector for connecting an external suitable vacuum pump to the mass analyser arrangement 10. Such an external suitable vacuum pump may for example be part of a laboratory buildings' vacuum system or may be a mobile vacuum pump.

[0095] As visible in FIG. 1, the mass analyser arrangement 10 includes a switchable ion gate 19 arranged in front of the intake 13 for controlling an insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 for enabling mass analysis of the positively charged ions with the first mass analyser 11 and mass analysis of the negatively charged ions with the second mass analyser 12. Thereby, the switchable ion gate 19 is adapted for being switched between a positive ions insertion mode where the positively charged ions are allowed to pass through the intake 13 into the mass analysis chamber 14 while the negatively charged ions are prevented from passing through the intake 13 into the mass analysis chamber 14, and a negative ions insertion mode where the negatively charged ions are allowed to pass through the intake 13 into the mass analysis chamber 14 while the positively charged ions are prevented from passing through the intake 13 into the mass analysis chamber 14. Thereby, the switchable ion gate 19 is switchable between the positive ions insertion mode and the negative ion insertion mode by reversing a sign of an ion gate voltage applied to the switchable ion gate 19, wherein in both the positive ion insertion mode and the negative ion insertion mode, the ion gate voltage has an absolute value of 4 V and thus in a range from 1 V to about 5 V. In a variant, the ion gate voltage has an absolute value of 8 V and thus in a range from 1 V to about 10 V. In either variant, the switchable ion gate 19 is thus adapted to be operated with an ion gate voltage having an absolute value of less than 20 V being applied to the switchable ion gate 19 for controlling insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 for enabling mass analysis of the positively charged ions with the first mass analyser 11 and mass analysis of the negatively charged ions with the second mass analyser 12.

[0096] The mass analyser arrangement 10 furthermore includes an ion path housing section 20 for housing a section of an ion path of the positively charged ions and the negatively charged ions leading to the switchable ion gate 19 and via the switchable ion gate 19 to the intake 13, wherein the ion path housing section 20 enables achieving and maintaining inside the ion path housing section 20 a gas pressure of 10.sup.−2 mbar or less. In a variant however, the ion path housing section 20 enables achieving and maintaining inside the ion path housing section 20 a gas pressure of 10.sup.−3 mbar or less. Thus, the ion path housing section 20 is sufficiently gas tight that with a suitable vacuum pump, a gas pressure of 10.sup.−2 mbar or less, or a gas pressure of 10.sup.−3 mbar, respectively or less, respectively, can be achieved and maintained inside the ion path housing section 20. Again, in FIG. 1, no such vacuum pump is shown because the mass analyser arrangement 10 may include such a vacuum pump or may go without such a vacuum pump and include instead a connector for connecting the mass analyser arrangement 10 to an external suitable vacuum pump. Such an external suitable vacuum pump may for example be part of a laboratory buildings' vacuum system or may by a separate, mobile vacuum pump.

[0097] As visible in FIG. 1, the mass analyser arrangement 10 includes an ion trap 21 for trapping the positively charged ions and the negatively charged ions, the ion trap 21 being arranged in front of the intake 13 into the mass analysis chamber 14. The ion trap 21 is arranged inside the ion path housing section 20 as the switchable ion gate 19 is and is thus operated at the same gas pressure as the switchable ion gate 19 is.

[0098] The ion trap 21 includes a quadrupole electrode 22 for generating a radiofrequency electromagnetic field for confining the positively charged ions and the negatively charged ions to a space along an axis of the ion trap 21. Thereby, the mass analyser arrangement 10 includes a radiofrequency AC voltage source 23 for applying a radiofrequency AC voltage to the quadrupole electrode 22 for generating the radiofrequency electromagnetic field for confining the positively charged ions and the negatively charged ions to the space along the axis of the ion trap 21. This radiofrequency AC voltage has a maximum amplitude of 9 V and thus less than 10 V. In a variant however, the radiofrequency AC voltage has a maximum amplitude of 19 V and thus less than 20 V. In yet another variant, the radiofrequency AC voltage has a maximum amplitude of 45 V and thus less than 50 V.

[0099] The ion trap 21 furthermore includes two drive electrodes 24.1, 24.2 for generating a reversible DC electric field along the axis of the ion trap 21 for driving in one state of the DC electric field the positively charged ions to one end of the ion trap 21 and the negatively charged ions to the other end of the ion trap 21 and for driving in the reversed state of the DC electric field the negatively charged ions to the one end of the ion trap 21 and the positively charged ions to the other end of the ion trap 21. Thereby, the mass analyser arrangement 10 includes a DC voltage source 25 for applying a reversible DC voltage to the two drive electrodes 24.1, 24.2 for generating the reversible DC electric field along the axis of the ion trap 21 for driving in the one state of the DC electric field the positively charged ions to one end of the ion trap 1 and the negatively charged ions to the other end of the ion trap 21 and for driving in the reversed state of the DC electric field the negatively charged ions to the one end of the ion trap 21 and the positively charged ions to the other end of the ion trap 21. The reversible DC voltage has a maximum amplitude of 5 V and thus less than 10 V. In a variant, the reversible DC voltage has a maximum amplitude of 19 V and thus less than 20 V. In yet another variant, the reversible DC voltage has a maximum amplitude of 48 V and thus less than 50 V. Thus, the switchable ion gate 19 and the ion trap 21 are both adapted to be operated with voltages of less than 200 V and even less than 100 V for controlling the insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 for enabling mass analysis of the positively charged ions with the first mass analyser 11 and mass analysis of the negatively charged ions with the second mass analyser 12. Thus, in the method according to the invention for mass analysing positively charged ions and negatively charged ions with the mass analyser arrangement 10, the switchable ion gate 19 and the ion trap 21 are operated with voltages of less than 200 V, even less than 100 V, for controlling the insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 for enabling mass analysis of the positively charged ions with the first mass analyser 11 and mass analysis of the negatively charged ions with the second mass analyser 12.

[0100] As visible in FIG. 1, the switchable ion gate 19 is arranged at one end of the ion trap 21 for releasing the positively charged ions and the negatively charged ions in a controlled manner from the ion trap 21 and thus controlling the insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 of the mass analyser arrangement 10 for enabling mass analysis of the positively charged ions with the first mass analyser 11 and mass analysis of the negatively charged ions with the second mass analyser 12.

[0101] In the mass analysis arrangement 10, the switchable ion gate 19 is adapted for a fast switching. More precisely, the ion gate voltage can easily be switched at rates of up to 100 kHz or more with a comparably simple voltage supply and, which does not alter the electric fields inside the mass analysis chamber 14 because the switchable ion gate 19 is arranged in front of the intake 13 and not inside the mass analysis chamber 14. More precisely, the switchable ion gate 19 is adapted to be switched at switching rates of 0.004 Hz, 0.01 Hz, 0.1 Hz, 1 Hz, 10 Hz, 50 Hz, 100 Hz, 5 kHz, 20 kHz, 66.6667 kHz and 100 kHz.

[0102] When executing the method according to the invention for mass analysing the positively charged ions and the negatively charged ions with the mass analyser arrangement 10 shown in FIG. 1, the method includes inserting the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 of the mass analyser arrangement 10, and transferring inside the mass analysis chamber 14 the positively charged ions from the intake 13 to the first mass analyser 11 and mass analysing the positively charged ions with the first mass analyser 11 and transferring inside the mass analysis chamber 14 the negatively charged ions from the intake 13 to the second mass analyser 12 and mass analysing the negatively charged ions with the second mass analyser 12. Thereby, the insertion of the positively charged ions and the negatively charged ions via the intake 13 into the mass analysis chamber 14 is controlled with the switchable ion gate 19, wherein the switchable ion gate 19 is switched between the positive ions insertion mode where the positively charged ions are allowed to pass through the intake 13 into the mass analysis chamber 14 while the negatively charged ions are prevented from passing through the intake 13 into the mass analysis chamber 14 and the negative ions insertion mode where the negatively charged ions are allowed to pass through the intake 13 into the mass analysis chamber 14 while the positively charged ions are prevented from passing through the intake 13 into the mass analysis chamber 14. Thereby, depending on the needs of the specific measurement, the switchable ion gate 19 is switched between the positive ions insertion mode and the negative ions insertion mode and back within 250 s, 100 s, 10 s, 1 s, 100 ms, 20 ms, 10 ms, 200 μs, 50 μs or 15 μs or even less. Switching between the positive ions insertion mode and the negative ions insertion mode and back within 100 ms or less has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables a time resolved mass analysis of positively charged ions and negatively charged ions obtained by ionisation from an output of a gas chromatography column, wherein the time resolution is sufficient for obtaining the gas chromatogram from the gas chromatography column, too. Switching between the positive ions insertion mode and the negative ions insertion mode and back within 20 ms or less has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables a time resolved mass analysis of positively charged ions and negatively charged ions obtained by ionisation from an output of a fast gas chromatography column, wherein the time resolution is sufficient for obtaining the gas chromatogram from the fast gas chromatography column, too.

[0103] Furthermore, switching between the positive ions insertion mode and the negative ions insertion mode and back within 20 ms or less has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables a time resolved mass analysis of positively charged ions and negatively charged ions obtained by ionisation from a gaseous sample at atmospheric pressure, wherein the time resolution is sufficient for resolving changes in the gaseous sample, too. Switching between the positive ions insertion mode and the negative ions insertion mode and back within 10 ms or less has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables a time resolved mass analysis of positively charged ions and negatively charged ions obtained by ionisation from an output of an ion molecule reactor at a pressure of 50 mbar, wherein the time resolution is sufficient for resolving changes in the output of the ion molecule reactor, too.

[0104] Switching between the positive ions insertion mode and the negative ions insertion mode and back within 200 μs or less has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables a time resolved mass analysis of positively charged ions and negatively charged ions where at least one of the positively charged ions and the negatively charged ions are separated according to their mobility in an ion mobility separation chamber, wherein the time resolution is sufficient for obtaining the ion mobility spectrum of the positively charged ions and/or negatively charged ions, respectively, too.

[0105] Switching between the positive ions insertion mode and the negative ions insertion mode and back within 50 μs or less, in particular or 15 μs or less, has the advantage that the method for mass analysing the positively charged ions and the negatively charged ions enables obtaining with a high time resolution and very high time resolution, respectively, for analysing any time dependent changes in a sample. Too short switching times however may become disadvantageous as well. For example, switching the switchable ion gate 19 between the positive ions insertion mode and the negative ions insertion mode and back after a longer time period than 10 μs can be advantageous because this ensures that a mass spectra from 0 Th to at least 300 Th can be obtained with the first mass analyser 11 and the second mass analyser 12.

[0106] Switching the switchable ion gate 19 between the positive ions insertion mode and the negative ions insertion mode and back after a longer time period than 32 μs can as well be advantageous because it ensures that a mass spectra from 0 Th to at least 3'000 Th can be obtained with the first mass analyser 11 and the second mass analyser 12.

[0107] In the method for mass analysing the positively charged ions and the negatively charged ions with the mass analyser arrangement 10, the above mentioned electrostatic field is generated with the two transfer electrodes 16.1, 16.2 for transferring the positively charged ions inside the mass analysis chamber 14 from the intake 13 to the first mass analyser 11 for being mass analysed with the first mass analyser 11 and for transferring the negatively charged ions inside the mass analysis chamber 14 from the intake 13 to the second mass analyser 12 for being mass analysed with the second mass analyser 12. Furthermore, for mass analysing the positively charged ions and the negatively charged ions, a gas pressure of 8-10.sup.−6 mbar and thus less than 10.sup.−5 mbar or, in a variant, 8.Math.10.sup.−5 mbar and thus less than 10.sup.−4 mbar, is maintained in the mass analysis chamber 14 during inserting the positively charged ions and negatively charged ions via the intake 13 into the mass analysis chamber 14 and during transferring the positively charged ions inside the mass analysis chamber 14 from the intake 13 to the first mass analyser 11 and mass analysing the positively charged ions with the first mass analyser 11 and during transferring the negatively charged ions inside the mass analysis chamber 14 from the intake 13 to the second mass analyser 12 and mass analysing the negatively charged ions with the second mass analyser 12. Furthermore, in the ion path housing section 20, a gas pressure of 10.sup.−2 mbar or less, in particular a gas pressure of 10.sup.−3 mbar or less, is maintained during inserting the positively charged ions and negatively charged ions via the intake 13 into the mass analysis chamber 14.

[0108] In the method, before being inserted via the intake 13 into the mass analysis chamber 14, the positively charged ions and the negatively charged ions are trapped in the ion trap 21 in that the radiofrequency AC voltage is applied to the quadrupole electrode 22 for generating the radiofrequency electromagnetic field for confining the positively charged ions and the negatively charged ions to the space along an axis of the ion trap 21 and in that the reversible DC voltage is applied to the two drive electrodes 24.1, 24.2 and repeatedly reversed for generating the reversible DC electric field along the axis of the ion trap 21 for driving in the one state of the DC electric field the positively charged ions to one end of the ion trap 21 and the negatively charged ions to the other end of the ion trap 21 and for driving in the reversed state of the DC electric field the negatively charged ions to the one end of the ion trap 21 and the positively charged ions to the other end of the ion trap 21. Thereby, the reversible DC voltage is reversed at a rate which corresponds to the switching rate of the switchable ion gate 19 such that the ion trap 21 and the switchable ion gate 19 are synchronised. Every time when the reversible DC voltage is such that the DC electric field drives the positively charged ions in the ion trap 21 to the end of the ion trap 21 where the switchable ion gate 19 is located, the switchable ion gate 19 is switched to the positive ions insertion mode such that the positively charged ions are inserted into via the intake 13 into the mass analysis chamber 14. And every time when the reversible DC voltage is reversed such that the DC electric field is reversed and drives the negatively charged ions in the ion trap 21 to the end of the ion trap 21 where the switchable ion gate 19 is located, the switchable ion gate 19 is switched to the negative ions insertion mode such that the negatively charged ions are inserted into via the intake 13 into the mass analysis chamber 14.

[0109] In the apparatus 1 shown in FIG. 1, the ion source 2 is fluidly coupled to the intake 13 for transferring the positively charged ions and the negatively charged ions, respectively, from the ion source 2 to the intake 13 for inserting the positively charged ions and the negatively charged ions into the mass analysis chamber 14 for enabling the mass analysis of the positively charged ions with the first mass analyser 11 and for enabling the mass analysis of the negatively charged ions with the second mass analyser 12. Thereby, since the mass analysis arrangement 10 includes the ion trap 21 and the switchable ion gate 19, the ion source 2 is even fluidly coupled to the intake 13 for transferring the positively charged ions and the negatively charged ions, respectively, from the ion source 2 via the ion trap 21 and the switchable ion gate 19 to the intake 13 for inserting the positively charged ions and the negatively charged ions into the mass analysis chamber 14.

[0110] As mentioned, the apparatus 1 is for mass analysing a sample with a method for mass analysing the sample. Thereby, in the method for mass analysing the sample, the sample is ionised with the ion source 2 to positively charged ions and negatively charged ions. After this ionisation, the positively charged ions and the negatively charged ions are mass analysed with the mass analyser arrangement 10 of the apparatus 1 with the method according to the invention for mass analysing positively charged ions and negatively charged ions with the mass analyser arrangement 10 as described.

[0111] The apparatus 1 shown in FIG. 1 includes a control unit 26 adapted to control the apparatus 1 for executing the method for mass analysing the sample. Thereby, the control unit 26 is at the same part of the mass analyser arrangement 10 and adapted for controlling the mass analyser arrangement 10 for executing the method according to the invention for mass analysing positively charged ions and negatively charged ions. The control unit 26 may be a personal computer or any other computing device adapted for executing the respective method. Thereby, the instructions for executing the respective method may be hard wired in the computing device or may be a computer software running on the computing device. In a variant, however, the apparatus 1 goes without control unit 1. In this case, the apparatus 1 is connectable to a separate control unit like a personal computer for being operated and controlled to execute the method for analysing the sample.

[0112] In the mass analyser arrangement 10 of the apparatus 1 shown in FIG. 1, the first mass analyser 11 and a second mass analyser 12 are both time-of-flight mass analysers. Thereby, the first mass analyser and the second mass analyser can for example both be orthogonal time-of-flight mass analysers. In order to illustrate such a variant with the first mass analyser and the second mass analyser both being orthogonal time-of-flight mass analysers, FIG. 2 shows a simplified schematic view of a mass analysis chamber 114 together with a first orthogonal time-of-flight mass analyser 111 and a second orthogonal time-of-flight mass analyser 112. Thus, FIG. 2 essentially shows a cutout of a mass analyser arrangement 110 according to the invention which includes the mass analysis chamber 114, the first orthogonal time-of-flight mass analyser 111 and the second orthogonal time-of-flight mass analyser 112.

[0113] The mass analyser arrangement 110 of FIG. 2 includes a chamber housing 115 surrounding the mass analysis chamber 114 and an intake 113 for inserting the positively charged ions and the negatively charged ions into the mass analysis chamber 114 where the positively charged ions are transferred to the first orthogonal time-of-flight mass analyser 111 for mass analysing the positively charged ions with the first orthogonal time-of-flight mass analyser 111 and where the negatively charged ions are transferred to the second orthogonal time-of-flight mass analyser 112 for mass analysing the negatively charged ions with the second orthogonal time-of-flight mass analyser 112. With this mass analyser arrangement 110, the method according to the invention for mass analysing positively charged ions and negatively charged ions can be employed. Thereby, the mass analyser arrangement 110 can be part of an apparatus 101 for mass analysing a sample with a method for mass analysing the sample as described above in the context of FIG. 1. Of course, the mass analyser 110 can include one or more of the further elements described in the context of FIG. 1. For example, the mass analyser arrangement 110 includes the switchable ion gate arranged in front of the intake 113 and the ion trap even though they are not shown in FIG. 2. Similarly, the apparatus 101 can include one or more of the further elements like the one or more than one ion source for ionising the sample to positively charged ions and negatively charged ions.

[0114] The first orthogonal time-of-flight mass analyser 111 of the mass analyser arrangement 110 of FIG. 2 provides a first extraction section 131 for accelerating the positively charged ions into a first mass separation section 133 of the first time-of-flight mass analyser 111. Furthermore, the second orthogonal time-of-flight mass analyser 112 of the mass analyser arrangement 110 of FIG. 2 provides a second extraction section 132 for accelerating the negatively charged ions into a second mass separation section 134 of the second time-of-flight mass analyser 112.

[0115] Between the first extraction section 131 and the second extraction section 132, the mass analyser arrangement 110 of FIG. 2 provides a common filling region 120 for the first orthogonal time-of-flight mass analyser 111 and the second orthogonal time-of-flight mass analyser 112. This common filling region 120 is located in the mass analysis chamber 114, wherein the first extraction section 131 is arranged from the common filling region 120 in a first direction towards the first mass separation section 133, while the second extraction section 132 is arranged from the common filling region 120 in a second direction towards the second mass separation section 134. Thereby, the first direction is oriented opposite to the second direction.

[0116] When the positively charged ions and the negatively charged ions are inserted via the intake 113 into the mass analysis chamber 114, they enter the common filling region 120 as an ion beam. Thereby, the ion beam entering the common filling region 120 may comprise a homogeneous mixture of the positively charged ions and the negatively charged ions, may comprise sections with positively charged ions and sections with negatively charged ions or may comprise one section of positively charged ions or one section of negatively charged ions. In either case, the common filling region 120 has essentially an elongated cylindrical shape, wherein the longitudinal axis of the cylindrical shape is oriented along the ion beam. Thus, the ions are inserted into the common filling region 120 along the longitudinal axis of the cylindrical shape of the common filling region 120.

[0117] In case the switchable ion gate is adapted for being switched between a positive ions insertion mode where the positively charged ions are allowed to pass through the intake 113 into the mass analysis chamber 114 while the negatively charged ions are prevented from passing through the intake 113 into the mass analysis chamber 114, and a negative ions insertion mode where the negatively charged ions are allowed to pass through the intake 113 into the mass analysis chamber 114 while the positively charged ions are prevented from passing through the intake 113 into the mass analysis chamber 114, the ion beam inserted via the intake 113 into the mass analysis chamber 114 comprises along its length sections with positively charged ions and sections with negatively charged ions. As a consequence, depending on how fast the switchable ion gate is switched between the positive ions insertion mode and the negative ions insertion mode, the common filling region 120 is filled with several sections of positively charged ions and several sections of negatively charged ions or is only filled with one section or a part of a section of positively charge ions or is only filled with one section or a part of a section of negatively charged ions.

[0118] On the other hand, in case the switchable ion gate is adapted for allowing positively charged ions and negatively charged ions pass at the same time through the intake 113 into the mass analysis chamber 114, the ion beam inserted via the intake 113 into the mass analysis chamber 114 comprises a homogeneous mixture of the positively charged ions and the negatively charged ions.

[0119] Once the common filling region 120 is filled with the positively charged ions and the negatively charged ions, only the positively charged ions or only the negatively charged ions, the ions are extracted from the common filling region 120 towards the respective one of the first orthogonal time-of-flight mass analyser 111 and the second orthogonal time-of-flight mass analyser 112. In order to achieve this extraction, the mass analyser arrangement 110 includes two extraction electrodes 116.1, 116.2 for generating electric field pulses for accelerating the positively charged ions in the first extraction section 131 and the negatively charged ions in the second extraction section 132. Thereby, the first extraction section 131, the common filling region 120 and the second extraction section 132 are arranged between the two extraction electrodes 116.1, 116.2.

[0120] More precisely, a first one of the two extraction electrodes 116.1 is arranged on the side of the first orthogonal time-of-flight mass analyser 111, while the second one of the two extraction electrodes 116.2 is arranged on the side of the second orthogonal time-of-flight mass analyser 112 of the first extraction section 131, the common filling region 120 and the second extraction section 132. The two extraction electrodes 116.1, 116.2 are both made from a grid providing openings for letting pass the accelerated positively charged ions and the accelerated negatively charged ions through the openings of the respective one of the two extraction electrodes 116.1, 116.2 into the first mass separation section 133 and the second mass separation section 134, respectively. Thus, the mass analyser arrangement 110 includes two extraction electrodes 116.1, 116.2 for generating electric field pulses for both accelerating the positively charged ions in the first extraction section 131 and accelerating the negatively charged ions in the second extraction section 132. As a result of this geometry, the positively charged ions and the negatively charged ions can be accelerated starting from one and the same common filling region 120 towards the first mass separation section 133 and towards the second mass separation section 134, respectively.

[0121] In order to generate the electric field pulses for extracting the positively charged ions from the common filling region 120 and accelerating the positively charged ions in the first extraction region 131 and for extracting the negatively charged ions from the common filing region 120 and accelerating the negatively charged ions in the second extraction region 132, the mass analyser arrangement 110 includes a voltage pulse generation arrangement 137 for applying voltage pulses to the two extraction electrodes 116.1, 116.2 for generating the electric field pulses. For this reason, the voltage pulse generation arrangement 137 is connected to the two extraction electrodes 116.1, 116.2 in order to apply voltage pulses having opposite signs to the two extraction electrodes 116.1, 116.2. More precisely, for generating one extraction pulse, a negative voltage pulse is applied to the first extraction electrode 116.1 while at the same time, a positive voltage pulse having the same strength as the negative voltage pulse is applied to the second extraction electrode 116.2, such that the positively charged ions are accelerated to the first extraction electrode 116.1 while the negatively charged ions are accelerated to the second extraction electrode 116.2.

[0122] Due to this functionality of the two extraction electrodes 116.1, 116.2, the two extraction electrodes 116.1, 116.2 are transfer electrodes for generating an electric field, in particular an electrostatic field, for transferring the positively charged ions inside the mass analysis chamber 114 from the intake 113 to the first orthogonal time-of-flight mass analyser 111 for being mass analysed with the first orthogonal time-of-flight mass analyser 111 and for transferring the negatively charged ions inside the mass analysis chamber 114 from the intake 113 to the second orthogonal time-of-flight mass analyser 112 for being mass analysed with the second orthogonal time-of-flight mass analyser 112.

[0123] The first orthogonal time-of-flight mass analyser 111 includes a first ion detector 135 for detecting the positively charged ions after they have passed the first mass separation section 133, while the second orthogonal time-of-flight mass analyser 112 includes a second ion detector 136 for detecting the negatively charged ions after they have passed the second mass separation section 134. In order to measure the time-of-flight the positively charged ions require to reach the first ion detector 135 after an electric field pulse generated by the two extraction electrodes 116.1, 116.2 and in order to measure the time-of-flight the negatively charged ions require to reach the second ion detector 136 after an electric field pulse generated by the two extraction electrodes 116.1, 116.2, the mass analyser arrangement 110 includes a time-of-flight determination arrangement 138 providing two channels. A first channel of these two channels is for determining the time-of-flight the positively charged ions require to reach the first ion detector 135 after an electric field pulse and a second channel of these two channels is for determining the time-of-flight the negatively charged ions require to reach the second ion detector 136 after an electric field pulse. Thereby, the time-of-flight determination arrangement 138 is connected to the first ion detector 135 for receiving a first detector signal from the first ion detector 135 and connected to the second ion detector 136 for receiving a second detector signal from the second ion detector 136.

[0124] The time-of-flight determination arrangement 138 provides a clock 139 and a clock starting module 140 for starting the clock 139 when an electric field pulse is generated by the two extraction electrodes 116.1, 116.2 for measuring the time-of-flight the positively charged ions require to reach the first ion detector 135 after the respective electric field pulse and for measuring the time-of-flight the negatively charged ions require to reach the second ion detector 136 after the respective electric field pulse. In order to enable these time-of-flight measurements, the time-of-flight determination arrangement 138 provides a start signal input for receiving a start signal from the voltage pulse generation arrangement 137 indicating when a voltage pulse is applied to the two extraction electrodes 116.1, 116.2 and thus when an electric field pulse is generated by the two extraction electrodes 116.1, 116.2. Upon receipt of this start signal, the clock starting module 140 starts the clock 139 such that the time-of-flight the positively charged ions require to reach the first ion detector 135 after the respective electric field pulse and the time-of-flight the negatively charged ions require to reach the second ion detector 136 after the respective electric field pulse can be determined with the time-of-flight determination arrangement 138 based on the first detector signal received from the first ion detector 135 and the second detector signal received from the second ion detector 136 indicating the moments when ions arrive at the respective one of the first ion detector 135 and the second ion detector 136.

[0125] In the embodiment shown in FIG. 2, the time-of-flight determination arrangement 138 is an analog-to-digital converter (ADC) having two channels. It is adapted to convert in the first channel a continuous-time signal of the clock 139 and the first detector signal being a continuous-amplitude analog signal of the first ion detector 135 to a discrete-time discrete-amplitude signal of the first channel and to convert in the second channel the continuous-time signal of the clock 139 and the second detector signal being a continuous-amplitude analog signal of the second ion detector 136 to a discrete-time discrete-amplitude signal of the second channel.

[0126] The invention is not limited to the embodiments described in the context of FIG. 1. Other embodiments, variants and variations are readily available to the person skilled in the art.

[0127] In summary, it is to be noted that a method and a mass analyser arrangement pertaining to the technical field initially mentioned are created, that provide more freedom to the ionisation method used for generating the positively charged ions and the negatively charged ions.