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Analogue detection for TOF MS

Generally speaking, at a given time resolution, ion counting systems are more cost effective than analogue systems, if they can be used. However, counting systems are limited by their inability to measure multiple ions in a single TOF cycle and in a single mass peak. This is because the time focussing of a good TOF MS means it is highly likely that two ions of the same mass will arrive so close together that the pulses in the early stages of the electronics overlap each other. A counting system will therefore record them as a single ion and the associated spectral peak will saturate. If this is a problem, then an analogue system, or transient recorder, must be considered.

Possibly the simplest analogue system is just a digital oscilloscope with sufficient time resolution. This would certainly be good for one cycle of the TOF. An example where this might be sufficient is in Laser Microprobe TOF MS, where a single laser pulse creates a small crater in the sample, in the process creating enough ions for a complete spectrum.

In other applications the nature of the experiment requires many TOF cycles to be added together to improve the signal to noise level. The choice of transient recorder then depends on the TOF cycle repetition rate. For example, this might be limited by the rate at which an ionising laser can be pulsed. In other cases, for example where kinetic studies are being made, it may be necessary to not only perform some averaging, but also record a sequence of spectra at closely spaced time intervals.

There are a range of transient recorder products available with various time resolutions, averaging schemes and readout options. The corresponding costs vary over a wide range! Kore has experience in designing a variety of TOF MS experiments and is therefore in a good position to devise a suitable detection scheme given details of the desired measurement. Please contact us by emailing info@kore.co.uk, by using the web form, or by telephoning, being prepared to describe the purpose of your experiment in some detail.


Last updated: 14 September 2005 20:54

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