Method of operating a mass filter in mass spectrometry

1. A method of mass spectrometry comprising:

transmitting ions from an ion source through a mass filter;

providing a discontinuous ion optical device downstream of the mass filter for processing ions received from the mass filter wherein the processing comprises discontinuously transmitting ions;

operating the mass filter for a plurality of periods in a mass/charge ratio (m/z) filtering mode to transmit ions in one or more selected ranges of m/z to the discontinuous ion optical device; and

analysing ions in a mass analyser downstream of the discontinuous ion optical device that have been processed by the discontinuous ion optical device, wherein a duration of processing ions with the discontinuous ion optical device is exceeded by a duration of analysing ions in a downstream mass analyser, wherein a plurality of idle times are defined between periods in which the discontinuous ion optical device is processing ions; and

operating the mass filter in a broad mass range mode transmitting ions of a mass range substantially wider than any mass range transmitted in the m/z filtering mode during the idle times, whereby during the idle times ion deposition on surfaces of the mass filter is reduced compared to during the periods when the mass filter is operated in the mass/charge ratio (m/z) filtering mode.

2. A method as claimed in claim 1 , wherein the broad mass range mode is a substantially non-m/z filtering mode.

3. A method as claimed in claim 1 , comprising switching the mass filter at least once between transmitting different m/z ranges wherein, in order to reduce charging of one or more surfaces of the mass filter, the switching includes a time interval during which the mass filter is operated in the substantially non-filtering mode.

4. A method as claimed in claim 3 , comprising switching the mass filter a plurality of times between transmitting different m/z ranges wherein, in order to reduce charging of one or more surfaces of the mass filter, each switching includes a time interval during which the mass filter is operated in the substantially non-filtering mode.

5. A method as claimed in claim 1 , wherein in substantially all idle times the mass filter is operated in the broad mass range mode.

6. A method as claimed in claim 1 , wherein the broad mass range mode is a substantially RF-only mode wherein electrodes of the mass filter are supplied with substantially only RF voltage.

7. A method as claimed in claim 6 , wherein a DC/RF voltage ratio is not greater than 0.06.

8. A method as claimed in claim 1 , wherein the duration of the periods of operating in the broad mass range mode on average exceed at least 1% of the duration of the periods operating in the filtering mode.

9. A method as claimed in claim 1 , wherein the mass filter is a multipole mass filter, preferably a quadrupole a mass filter.

10. A method as claimed in claim 1 , wherein the transmission of ions though the mass filter is continuous.

11. A method as claimed in claim 1 , wherein the discontinuous ion optical device is a pulsed ion optical device.

12. A method as claimed in claim 1 , wherein the discontinuous ion optical device is an ion trap, or ion deflector, or an orthogonal accelerator.

13. A method as claimed in claim 12 , wherein the discontinuous ion optical device is a linear ion trap, preferably a curved linear ion trap (C-trap).

14. A method as claimed in claim 1 , wherein the mass analyser is one of: a Fourier Transform (FTMS) mass analyser, an FT-ICR mass analyser, an electrostatic orbital trap mass analyser, a TOF mass analyser, an ion trap mass analyser and a dynamically operating quadrupolar mass analyser.

15. A mass spectrometer comprising:

an ion source for producing ions;

a mass filter for transmitting ions from the ion source;

a discontinuous ion optical device downstream of the mass filter for processing ions received from the mass filter, wherein the processing comprises discontinuously transmitting ions;

a mass analyser downstream of the discontinuous ion optical device for mass analysing ions that have been processed by the discontinuous ion optical device, wherein a duration of processing ions with the discontinuous ion optical device is exceeded by a duration of analysing ions in the mass analyser, wherein a plurality of idle times are defined between periods in which the discontinuous ion optical device is processing ions; and,

a controller arranged to operate the mass filter for a plurality of periods in a mass/charge ratio (m/z) filtering mode to transmit ions in one or more selected ranges of m/z to the discontinuous ion optical device and to operate the mass filter in a broad mass range mode transmitting ions of a mass range substantially wider than any mass range transmitted in the m/z filtering mode during the idle times, whereby during idle times ion deposition on surfaces of the mass filter is reduced compared to during periods when the mass filter is operated in the mass/charge ratio (m/z) filtering mode.

16. A method of mass spectrometry comprising:

transmitting ions from an ion source through a first mass filter and subsequently through a second mass filter;

providing a discontinuous ion optical device downstream of the second mass filter for processing ions received from the second mass filter;

operating at least one of the mass filters for a plurality of periods in a mass/charge ratio (m/z) filtering mode to transmit ions in one or more selected ranges of m/z to the discontinuous ion optical device;

analysing ions in a mass analyser downstream of the discontinuous ion optical device that have been processed by the discontinuous ion optical device, wherein a duration of processing ions with the discontinuous ion optical device is exceeded by a duration of analysing ions in the downstream mass analyser, wherein a plurality of idle times are defined between periods in which the discontinuous ion optical device is processing ions; and,

operating the mass filter in a broad mass range mode transmitting ions of a mass range substantially wider than any mass range transmitted in the m/z filtering mode during the idle times, whereby during the idle times ion deposition on surfaces of the mass filter is reduced compared to during the periods when the mass filter is operated in the mass/charge ratio (m/z) filtering mode.

17. A method of mass spectrometry comprising:

transmitting ions from an ion source through a mass filter;

providing a mass analyzer downstream of the mass filter for processing ions received from the mass filter;

operating the mass filter for a plurality of periods in a mass/charge ratio (m/z) filtering mode to transmit ions in one or more selected ranges of m/z to the mass analyzer;

analysing ions in the mass analyser downstream of the discontinuous ion optical device that have been processed by the discontinuous ion optical device, wherein a duration of processing ions with the discontinuous ion optical device is exceeded by a duration of analysing ions in the downstream mass analyser, wherein a plurality of idle times are defined between periods in which the discontinuous ion optical device is processing ions; and

operating the mass filter in a broad mass range mode transmitting ions of a mass range substantially wider than any mass range transmitted in the m/z filtering mode during the idle times, whereby during the idle times ion deposition on surfaces of the mass filter is reduced compared to during the periods when the mass filter is operated in the mass/charge ratio (m/z) filtering mode.