Mass analyser resolution

There are a number of different mass separation devices - analysers - used in mass spectrometry and each has its own advantages and disadvantages. Those most likely to be encountered by users of LC-MS are described briefly below, while more detailed descriptions may be found elsewhere [2-4]. One property that is important in defining the analytical capabihties of a mass analyser is the resolution which it may achieve. 

In this instrnment, the final stage of the triple quadrnpole is replaced by an orthogonal time-of-fiight (ToF) mass analyser, as shown in Fignre 3.10. The con-fignration is typical of the latest generation of ToF instrnments in which a nnmber of reflectrons, in this case two, are used to increase the flight path of the ions and thns increase the resolution that may be achieved. 

Double-focusing mass spectrometer A mass spectrometer consisting of electrostatic and magnetic sector analysers capable of achieving high-mass spectral resolution. 

Electrostatic analyser (ESA) An energy-focusing device used in a double-focusing mass spectrometer to increase mass specnal resolution. 

Magnetic sector A low-resolution mass analyser in which the variation of a magnetic field is used to bring ions of different m/z ratios to a detector. 

The resolution obtainable with a UTI-100C quadrupole mass analyser is m/Am 2m (Jjt)). These three peaks are also separated to baseline resolution In Figure 7a however, they appear as one peak due to the wide mass range which is displayed. 

The main function of the mass analyser is to separate (resolve) the ions formed in the ionisation source on the basis of their mass to charge ratios (m/z). The resolving power of a mass spectrometer is a measure of its ability to separate two ions of any defined mass difference. More precisely, the resolution (R) of a mass analyser is defined as its ability to separate the ion envelopes of two peaks of equal intensity, i.e. the ratio of the mass of a peak (M ) to the difference in mass between this peak and an adjacent higher mass peak (Af2), i.e. ... 

ToFs can also be used in combination with other mass analysers. Both hybrid sector and quadrupole systems are available. oaToF-MS has been interfaced to a quadrupole mass filter and hexapole gas collision cell, such as to allow recording of mass spectra and product ion spectra with good mass resolution (ca. 10000), high sensitivity, high mass range (ca. 10 000 Da) and high mass accuracy (<5ppm) [177,178]. QqToFMS may be fitted with API sources with flow-rates from nL... 

Mass resolution generally increases for instruments in the listed order. Hybrid variants utilising various composites of mass analysers are likewise available and have become commonplace (e.g. quadrupole-ToF). 

Reflectron An ion lens used in the time-of-flight mass analyser to increase the distance travelled by an ion and thereby increase the resolution of the instrument. 

Quadrupole mass filters, Qs, which are still widely used for flavonoid analysis, isolate ions of a selected miz ratio. They are mainly able to perform low-resolution mass analyses,... 

Static secondary ion mass spectroscopy (SSIMS) is another surface selective technique for surface characterisation [262, 263, 264]. The information obtained from SSIMS is complementary to XPS because SSIMS can differentiate those polymers that give very similar XPS spectra. Moreover, it offers more surface selectivity than XPS. The typical sampling depth of SSIMS is approximately 1 nm. This method has sensitivity, sufficient to detect amounts less than a monomolecular layer, particularly when a high resolution time-of-flight (ToF) mass analyser is used [265]. 

With respect to MS equipment significant performance improvements are promised by the use of most modem mass analysers (e.g. Orbitrap, FT-ICR, TOF-TOF) that provide highest resolution and mass accuracy important for, e.g. in-depth elucidation of biotransformation. 

Low Voltage Mass Spectrometry of Macrocyclic Extractables. Nominal parent mass analyses of the macrocyclic extractables, obtained from typical polymerization products of cyclooctene and 1,5-cyclooctadiene, were performed on a Model MS-9 double focusing mass spectrometer (Associated Electrical Industries, England) at a resolution of 1/1000 and an emission of 7.0 e.v. Samples were introduced directly into the source chamber by the direct-probe technique. The temperature range during the experiment was 125°-200°C., and the source pressure was maintained in the 0.1-3 X 10-6 torr range. In addition, a high resolution measurement was carried out on the mass number 220 to identify the two components present at that mass number. 

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