The Double Focusing Magnetic Sector Mass Spectrometer

The double focusing magnetic sector mass spectrometer differs from those discussed so far in that the mass analyser comprises two distinct components, an electromagnet and an electrostatic analyser. The magnet acts as a momentum analyser and affects mass separation, while the addition of an electrostatic analyser corrects for some variations in the kinetic energy of ions of the same m/z value and allows them to be brought to focus on the detector at the same time. Hence the use of a double focusing arrangement as a mass analyser allows very high resolution to be achieved. In mass spectrometry resolution is defined as the ability of the mass spectrometer to separate ions of very similar m/z value.

Resolution is important in mass spectrometry since it may be used to introduce specificity into an experiment. An important application of high resolution arises in the determination of polychlorinated diben-zodioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) by GC-MS. These compounds are found ubiquitously in the environment and their determination is important owing to concern about their toxicity, mutagenicity and carcinogenicity. The only method that has been found to offer the appropriate degree of sensitivity and specificity for this analysis is GC followed by high resolution MS detection. High resolution is required since matrices which accumulate PCDDs and PCDFs are also likely to accumulate other polychlorinated aromatic hydrocarbons, e.g. polychlorinated biphenyls. These compounds, which may co-elute with the PCDDs and PCDFs of interest, contain fragment ions in their EI mass spectra which have the same integer m/z value as the molecular ions of PCDDs and PCDFs. However, by monitoring the accurate mass value of the PCDD and PCDF molecular ions (i.e. the exact mass value of their elemental composition), at an adequate resolution to separate them from likely interfering ions, specificity is introduced. GC-MS is used extensively in environmental analysis for a range of ap plications including dioxin analysis. For further details the interested reader is referred to Bruner (1993).

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.

Get My Free Ebook


Post a comment