Upper m/z limit

Transmission (for ions separated in space) is defined as the ratio between the ion fluxes exiting and entering the mass analyzer. It decreases in the order time-of-flight quadrupole > sectors Upper m/z limit ... 

Analyze ppm window from center to upper m/z limit For O = (Z + 1) To NrRows... 

Every mass spectrometer has an upper mass limit for the m/z ratio it can measure. Thus the mass in Daltons corresponding to a particular tn/z will depend on the number of charges z that the ion carries. For example, with an upper m/z value of 2 000, the instrument can detect an ion of mass 80 000 Da if that ion has a charge of q = 40e. 

TOF mass spectrometers are very robust and usable with a wide variety of ion sources and inlet systems. Having only simple electrostatic and no magnetic fields, their construction, maintenance, and calibration are usually straightforward. There is no upper theoretical mass limitation all ions can be made to proceed from source to detector. In practice, there is a mass limitation in that it becomes increasingly difficult to discriminate between times of arrival at the detector as the m/z value becomes large. This effect, coupled with the spread in arrival times for any one m/z value, means that discrimination between unit masses becomes difficult at about m/z 3000. At m/z 50,000, overlap of 50 mass units is more typical i.e., mass accuracy is no better than about 50-100 mass... 

There is no theoretical upper limit on m/z that can be examined, and TOF mass spectrometry is useful for substances having very high molecular mass. In practice, the current upper limit is about 350,000. Unfortunately, ions even of the same m/z value do have a spread of velocities after acceleration, so the resolution achievable with TOF is not very high because bunches of ions of one m/z value overlap those at the next m/z value. 

Mass analyzer Resolving power (xlO3) Mass accuracy (ppm) m z range (upper limit) (xlO3) Acquisition speed (Hz) Linear dynamic range Price... 

The most intense peak of a mass spectrum is called base peak. In most representations of mass spectral data the intensity of the base peak is normalized to 100 % relative intensity. This largely helps to make mass spectra more easily comparable. The normalization can be done because the relative intensities are independent from the absolute ion abundances registered by the detector. However, there is an upper limit for the number of ions and neutrals per volume inside the ion source where the appearance of spectra will significantly change due to autoprotonation (Chap. 7). In the older literature, spectra were sometimes normalized relative to the sum of all intensities measured, e.g., denoted as % Lions, or the intensities were reported normalized to the sum of all intensities above a certain m/z, e.g., above m/z 40 (% L 4o)-... 

FAB is chiefly applied to analytes up to about m/z 3000, but significantly heavier ions are sometimes accessible. The upper limit surely has been demonstrated by the detection of [(CsI) Cs] cluster ions up to m/z 90,000. [42] In case of organic molecules, the detection of [Mh-H]", [Mh-2H] and [Mh-3H] ions of porcine... 

Example ESI selectively ionizes the basic compounds, i.e., only a small fraction of the entire chemical composition, in a sample of South American cmde oil. Nevertheless, the positive-ion ESI-FT-ICR mass spectrum exhibits more than 11,100 resolved peaks, of which >75 % may be assigned to a unique elemental composition (CcHhOoNnSJ. Such a separation in mass is possible because the average mass resolution in the m/z 225-1000 broadband spectrum is approximately 350,000 (Fig. 12.12). This demonstrates the current upper limit for the number of chemically distinct components resolved and identified in a single step. [86]... 

TOF analyzers have no theoretical upper limit on the m/z ratio which they can analyze. This is important because MALDI produces ions with high m/z values which cannot be measured by other types of mass analyzers. 

There is no theoretical upper limit on m/z that can be examined, and TOF mass spectrometry is useful for substances having very high molecular mass. In practice, the current upper limit is about 350,000. 

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