Charging plate for enhancing multiply charged ions by laser desorption

Abstract

A sample plate for an ion source is disclosed comprising a plurality of ionization regions, each ionization region comprising a first electrode and a second separate electrode separated by an insulator.

Claims

1. A sample plate comprising: one or more ionisation regions, each ionisation region comprising a first electrode and a second separate electrode; and a voltage device for applying a voltage between said first and second electrodes in order to maintain an electric field between said first and second electrodes; wherein said sample plate is arranged and adapted so that, in use, one or more droplets are deposited in an ionisation region so as to extend between said first electrode and said second electrode so that an electrical pathway is provided between said first electrode and said second electrode via said one or more droplets.

2. A sample plate as claimed in claim 1, wherein said first electrode and said second electrode are substantially co-planar.

3. A sample plate as claimed in claim 1, wherein each said first electrode is separated from said second electrode by an insulator.

4. A sample plate as claimed in claim 3, wherein said first electrode, said second electrode and said insulator are substantially co-planar.

5. A sample plate as claimed in claim 1, wherein said sample plate comprises an array of ionisation regions.

6. A sample plate as claimed in claim 1, wherein said voltage device is arranged and adapted to apply a DC voltage between said first and second electrodes.

7. A sample plate as claimed in claim 1, wherein said voltage device is arranged and adapted to apply an AC voltage between said first and second electrodes.

8. A sample plate as claimed in claim 1, wherein at least some of said first electrodes or said second electrodes comprise a needle or other projection.

9. A sample plate as claimed in claim 8, wherein said needle or other projection is arranged and adapted to secure, in use, a biological or other sample to said sample plate.

10. An ion source comprising: a sample plate including: one or more ionisation regions, each ionisation region comprising a first electrode and a second separate electrode; and a voltage device for applying a voltage between said first and second electrodes in order to maintain an electric field between said first and second electrodes, wherein said sample plate is arranged and adapted so that, in use, one or more droplets are deposited in an ionisation region so as to extend between said first electrode and said second electrode so that an electrical pathway is provided between said first electrode and said second electrode via said one or more droplets.

11. An ion source as claimed in claim 10, further comprising a laser for ionising or desorbing analyte deposited upon said sample plate.

12. An ion source as claimed in claim 10, wherein said ion source comprises a Matrix Assisted Laser Desorption Ionisation (“MALDI”) ion source.

13. An ion source as claimed in claim 10, wherein said ion source comprises a Desorption Electrospray Ionisation (“DESI”) ion source.

14. An ion source as claimed in claim 10, wherein said ion source comprises a Laser Ablation Electrospray Ionisation (“LAESI”) ion source.

15. An ion source as claimed in claim 10, wherein said ion source comprises a Solvent Assisted Inlet Ionisation (“SAII”) ion source.

16. An ion source as claimed in claim 10, wherein said ion source comprises a Matrix Assisted Inlet Ionisation (“MAII”) ion source.

17. An ion source as claimed in claim 10, wherein said ion source comprises a Laserspray Ionisation (“LSI”) ion source.

18. An ion source as claimed in claim 10, further comprising a sonic, electrical, spark or mechanical device for ionising or desorbing analyte deposited upon said sample plate.

19. A mass spectrometer comprising: an ion source including: a sample plate having, one or more ionisation regions, each ionisation region comprising a first electrode and a second separate electrode; and a voltage device for applying a voltage between said first and second electrodes in order to maintain an electric field between said first and second electrodes, wherein said sample plate is arranged and adapted so that, in use, one or more droplets are deposited in an ionisation region so as to extend between said first electrode and said second electrode so that an electrical pathway is provided between said first electrode and said second electrode via said one or more droplets.

20. A mass spectrometer as claimed in claim 19, further comprising: an ion inlet orifice; and a device for maintaining an electric field between said sample plate and said ion inlet orifice.

21. A mass spectrometer as claimed in claim 20, further comprising an energy imparting device arranged between said sample plate and said ion inlet orifice.

22. A mass spectrometer as claimed in claim 21, wherein said energy imparting device comprises a heated inlet transfer tube or other heated device for increasing the generation of multiply charged ions.

23. A method of ionising a sample comprising: providing a sample plate comprising one or more ionisation regions, each ionisation region comprising a first electrode and a second separate electrode; applying a voltage between said first and second electrodes in order to maintain an electric field between said first and second electrodes; and depositing one or more droplets in an ionisation region so as to extend between said first electrode and said second electrode so that an electrical pathway is provided between said first electrode and said second electrode via said one or more droplets.

24. A method of mass spectrometry comprising a method as claimed in claim 23.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 shows an electro-MALDI sample plate according to an embodiment of the present invention; and

(3) FIG. 2 shows a preferred sample plate for utilisation in MS imaging comprising needle shaped electrodes which assist in securing a sample to the sample plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) According to a preferred embodiment of the present invention an electro-MALDI sample plate 1 is provided for enhancing the generation of multiply charged ions. A sample plate 1 according to a preferred embodiment is shown in FIG. 1. Droplets of liquid matrix 3 are preferably provided on a target plate 2. Two electrodes 4 per droplet are preferably arranged so as to apply an electric field to or maintain an electric field within the liquid droplet 3. The electrodes 4 are preferably separated by an insulator 4a. The electrodes 4 and the insulator 4a are preferably co-planar. The electric field preferably charges the analyte and electrolytes in the matrix solution 3 prior to laser desorption by a laser beam from a laser 5.

(5) The liquid matrix 3 may or may not contain conventional MALDI matrices.

(6) Upon desorption, droplets of charged liquid retain or attain a high charge imbalance. The droplets are preferably directed towards an inlet of a mass spectrometer 7 and preferably collide with an energy imparting device such as a heated vacuum inlet transfer tube 6 prior to analysis in the mass spectrometer 7. The inlet 6 is preferably arranged to cause shearing of the desorbed droplets in a similar manner to Laserspray and Sonicspray. The evaporation/shearing and desolvation of droplets within the transfer tube 6 significantly increases the number of multiply charged analyte ions which are observed.

(7) According to an alternative embodiment the pre-charging sample plate 2 may be utilised in conjunction with other surface ambient ionisation techniques using liquids such as Desorption Electrospray Ionisation (“DESI”) and Laser Ablation Electrospray ionisation (“LAESI”).

(8) According to an alternative embodiment the droplet desorption may be caused by means other than a laser e.g. by using sonic, electrical, spark or mechanical energy.

(9) The target plate 2 does not necessarily need to be maintained at atmospheric pressure and according to less preferred embodiments the target plate 2 may be maintained at an intermediate pressure or in a low pressure regime.

(10) According to an embodiment a supplemental electric field may be provided between the target plate 2 and the inlet of the mass spectrometer 7 in order to help transfer ions and enhance ionisation.

(11) According to another embodiment elongated channel structure electrodes instead of circular droplets of liquid may be used in order to provide on surface electrophoresis.

(12) The present invention may also be applied to the field of MS imaging (“MSI”). The target plate 2 may comprise an array of needle electrodes 8 that hold, pin or otherwise secure a tissue surface or biological sample 9 on to the surface of the sample or target plate 2. A liquid matrix 3 is then preferably applied on top of the tissue 9 as shown in FIG. 2. The liquid matrix 3 may include chemicals which draw out analytes from the tissue 9 into the liquid matrix solution ready for ionisation. Such an arrangement is particularly advantageous since current imaging methods are more effective when analyte species are close to the surface of the tissue 9.

(13) According to an embodiment an additional burst of high voltage may be applied to the electrodes 8 in a timed sequence so as to Electrospray each liquid droplet towards the inlet of the mass spectrometer 7 for predetermined sample positions.

(14) Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.