Detection

The standard detector in IMS instruments is a simple Faraday plate. The vast majority of IMS instruments have an aperture grid placed c. 2 mm forward of the detector. While removal of this feature increases the total signal, it also causes broadening of the peaks, typically from c. 0.3 ms to c. 3 ms, and thus a loss of resolution. The aperture grid prevents incoming ions from inducing a current in the detector plate. Sensitivity may also be increased by increasing the electric field between the aperture grid and detector to a value significantly higher than that of the standard drift field.

The development of new methods and applications for IMS is greatly eased with the use of a mass spectrometer coupled to the drift cell. IMS-MS has been in routine use in research laboratories since the inception of the technique almost 30 years ago. The instruments are interfaced by using a pinhole aperture to the MS vacuum chamber in the Faraday plate of the ion mobility spectrometer. Such a system can be operated in several modes:

• Total ion monitoring yields the full IMS spectrum.

• Opening the shutters provides a full atmospheric pressure chemical ionization mass spectrometric characterization of the ions in the reaction region.

• Selective ion monitoring enables the contribution of specific species to the mobility spectra to be observed.

An exciting and important development has been the introduction of IMS to ion storage mass spectro-metry (Figure 5). This combination of instruments has the potential to isolate selectively trace levels of volatile and nonvolatile materials from a wide range of matrices, identify and quantitate them in a time-scale of milliseconds to seconds. The separation speeds reported so far are of the order of greater than 106 theoretical plates per minute. Although the approach is still very much in its early stages of development, the potential for vastly increasing the speed of many analyses is considered by many in this field to be a very important factor in the future development of IMS.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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