Sector field high-resolution

Figure 7.32 shows the identification of an oxidation product of Irganox 1330 by means of APCI-MS. LC-APCI-MS/MS (high-resolution sector field-ion trap hybrid) has also been used for the analysis (elemental composition and structure) of Irganox PS 802 [636]. 

Finally, the instrument can be operated in the peak-matching mode, which provides optimum mass resolving power and mass accuracy. Here the magnetic field strength is kept constant and the electric sector and acceleration voltages are scanned over a relatively small m/z range. This mode of operation is suitable when two ions that are very close in mass need to be separated or when the elemental composition of a molecule is to be determined at high resolution. 

Double-focusing mass spectrometers with high mass resolution are rather bulky and expensive instruments so that the development of single magnetic sector field mass spectrometers was of significance in the following years. 

As an alternative to commercial quadrupole based ICP-MS measurements at low mass resolution ( / 300), in 1996 Yiang and Douglas15 proposed a quadrupole ICP-MS system which allows a maximum mass resolution of 9000. At a mass resolution of 5000 the sensitivity was comparable to that of a commercial double-focusing sector field ICP-MS operated at the same mass resolution. Due to the very high continuum instrumental background of about lOOOcps no commercial high resolution quadrupole instrumentation with an inductively coupled plasma source exists and the development of high resolution quadrupole based ICP-MS has ceased. 

A sensitive high resolution ion microprobe (SHRIMP, with a maximum mass resolution of m/Am of 30 000) was designed on the basis of the double-focusing sector field Matsuda type instrument190 as discussed by Compston in 1996.191 The first SHRIMP and a modified version for precise isotope ratio measurements were constructed in the 1980s and later produced commercially.192 The main application of this instrument so far has been in situ U-Pb dating of zircon.192,193... 

However, nowadays some other different mass spectrometers are used for ICP-MS time-of-flight (TOP) systems for multielemental analysis of transient signals, ion trap analysers for ion storage, multicollector instruments for precise isotope ratio measurements and double-focusing sector field mass spectrometers for high mass resolution, but still the majority of instruments are equipped with quadrupole filters, which are simpler and cheaper. 

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