The atom is ionised by knocking one or more electrons off to give a positive ion. This is true even for things which you would normally expect to form negative ions (chlorine, for example) or never form ions at all (argon, for example). Mass spectrometers always work with positive ions. Ionization Ionization method refers to the mechanism of ionization while the ionization source is the mechanical device that allows ionization to occur. The different ionization methods, summarised here, work by either ionizing a neutral molecule through electron ejection, electron capture, protonation, cationization, or deprotonation, or by transferring a charged molecule from a condensed phase to the gas phase.
The different methods are summarised here: http://masspec.scripps.edu/mshistory/whatisms_details.php#ionization (b) accelerated The positive ions are repelled away from the very positive ionization chamber and pass through three slits, the final one of which is at 0 volts. The middle slit carries some intermediate voltage. All the ions are accelerated into a finely focused beam.
Accuracy This is the ability with which the analyzer can accurately provide m/z information and is largely a function of an instrument’s stability and resolution. For example, an instrument with
0.01% accuracy can provide information on a 1000 Da peptide to ±0.1 Da or a 10,000 Da protein to ±1.0 Da. The accuracy varies dramatically from analyzer to analyzer depending on the analyzer type and resolution. An alternative means of describing accuracy is using part per million (ppm) terminology, where 1000 Da peptide to ±0.1 Da could also be described as
1000.00 Da peptide to ± 100 ppm.
Resolution (Resolving Power) Resolution is the ability of a mass spectrometer to distinguish between ions of different masstocharge ratios. Therefore, greater resolution corresponds directly to the increased ability to differentiate ions. The most common definition of resolution is given by the following equation: Resolution = M/ΔM Equation 2.1 where M corresponds to m/z and ΔM represents the full width at half maximum (FWHM). An example of resolution measurement is shown in Figure 2.2 where the peak has an m/z of 500 and a FWHM of 1. The resulting resolution is M/ΔM = 500/1 = 500. (d) separated The separation of ions in the mass spectrometer takes place with the mass analyser(s). There are many different types of mass analysers which function based on different physical principles but these devices separate ions with different