Method and a mass spectrometer and uses thereof for detecting ions or subsequently-ionised neutral particles from samples

Abstract

A method is used in a time-of-flight mass spectrometer for analysis of a first pulsed ion beam, the ions of which are disposed along the pulse direction, separated with respect to their ion masses. The ions of at least one individual predetermined ion mass or of at least one predetermined range of ion masses can be decoupled from the first pulsed ion beam, as at least one decoupled ion beam, and the first ion beam and the at least one decoupled ion beam are analyzed.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a divisional of U.S. patent application Ser. No. 13 / 811,455, filed Jan. 22, 2013 (now U.S. Pat. No. 8,785,844, issued Jul. 22, 2014). This application claims priority of International Patent Application No. PCT / EP2011 / 003803, filed Jul. 28, 2011, which is a §371 application of German Application No. 10 2010 032 823.5, filed Jul. 30, 2010, both of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]The present invention relates to a method and to a mass spectrometer and uses thereof for detecting ions or subsequently-ionised neutral particles from samples.[0003]Methods and mass spectrometers of this type are required in particular for determining the chemical composition of solid, liquid and / or gaseous samples.[0004]Mass spectrometers have a wide application in determining the chemical composition of solid, liquid and gaseous samples. Both chemical elements and compounds and also mixtures of eleme...

AI Technical Summary

Benefits of technology

[0023]In order to alleviate or remedy the problems described in prior art, it is the object of the present invention to make available a method for operating a time-of-flight mass spectrometer and also a time-of-flight mass spectrometer and uses thereof, with which the dynamic range of the measurement can be improved in the case of very high accuracy, in particular in the case of temporally varying intensities, for detecting traces in the ppm or ppb range, in the measurement of distribution maps. The method according to the invention and the mass spectrometer according to the invention are intended furthermore to have a high time resolution, in particular when recording with TDC in the single particle counting technique. Furthermore, the life span of the ion detectors which are used is intended to be improved, the loading thereof with high intensities reduced and in total the technical complexity and the costs of the method according to the invention or of the mass spectrometer are intended to be reduced or kept low.

[0038]It is possible by means of the present invention to avoid saturation of the detectors in a high dynamic range of intensities of a pulsed ion beam, either by using different detectors of different sensitivity and / or by reducing / attenuating the intensity of the ions in those mass ranges or those masses in which a single particle counting technique would no longer be possible without attenuation.

[0040]The method according to the invention enables high accuracy and linearity of the measurement with simultaneously high time resolution and low technical complexity. In particular, a single particle counting technique with TDC recording can be applied.

[0042]The invention can be structured such that additional trajectories with different attenuation factors are used. Thus for example the beam switch can undertake a deflection in two different directions and, in the case of the two resulting trajectories, filters with two different attenuation factors can be used. By means of the deflection direction, a suitable attenuation factor can then be chosen for each mass line with an intensity above the single particle counting limit. The dynamic range can hence be increased even further. Thus extremely intensive masses with e.g. 1,000 ions per cycle could be detected still by an attenuation by the factor 1,000 in the single particle counting technique and, with the second filter unit, average intensities could be reduced by a factor √1,000≈32. By using these two different filters, intensity measurements can be implemented with great accuracy over a large dynamic range.

[0044]Beyond extending the dynamic range with high linearity and time resolution, the invention also increases the lifespan of the detector. Due to the attenuation of the intensive mass lines to single ions, the loading and wear and tear on the detector is comparable to normal operation in the single particle counting technique.

[0045]Furthermore, the invention reduces the technical complexity of the recording in comparison with solutions with ADC or a plurality of ADCs or arrangements with a plurality of detectors in the single particle counting technique. The economical, conventional solution with TDC in the single particle counting technique can be used furthermore. Merely the pulsed beam switch is required in addition.

Problems solved by technology

In the case of too high signals, the intensity is not measured correctly (saturation limit) as a result of saturation effects of the detector or of the recording.

This leads to significantly falsified relative peak in densities.

Higher counting rates than approx. one ion per mass and cycle can generally not be measured with sufficient accuracy in the single particle counting technique, even when using the Poisson correction.

The technical complexity hence increases significantly with the number of detectors so that typically only a small number of detectors is used in parallel.

However, high accuracy of the intensity measurement can be achieved only with great difficulty with such an arrangement.

The measurement of large intensity ratios with an accuracy of better than 1% is hence impossible.

Since these high intensities can however result in saturation effects in the MCPs, the accuracy of the intensity measurement when using fast MCP detectors is not very high.

The output current of the MCPs, in the case of sufficiently high amplification, is no longer sufficiently proportional to the input current.

A further disadvantage of the ADC solution resides in the reduced time resolution of detector and ADC in comparison with conventional TDC recording.

The technical complexity with these recording systems is therefore very high.

A similar problem is shown also in the detection of traces in the ppm or ppb range.

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