Mass scanning speed

These authors also analysed marine diesel fuel with GC X GC, connected to a quadrupole mass spectrometer for identification purposes, although the scan speed of the spectrometer was not quite suited for the fast second-dimension peaks... 

The molecular mass of the protein was redetermined by infusing a 5-10 pmolp.l solution of the protein in 50% aqueous acetonitrile containing 0.2% formic acid at a flow rate of 6 p,lmin into an electrospray source. The scan rate employed on the mass spectrometer was from m/z 60 to m/z 1800 in 12 s. This is a relatively slow scan speed which will lead to a more precise molecular weight determination. Scan speeds of this order may be, and indeed should be, utilized for infusion experiments if sufficient sample is available but it is unlikely to be feasible when chromatographic separations, particularly those involving capillary columns, are employed because of the restriction imposed by the chromatographic peak width (see Section 3.5.2.1 above). 

Different options are available for LC-MS instruments. The vacuum system of a mass spectrometer typically will accept liquid flows in the range of 10-20 p,L min-1. For higher flow-rates it is necessary to modify the vacuum system (TSP interface), to remove the solvent before entry into the ion source (MB interface) or to split the effluent of the column (DLI interface). In the latter case only a small fraction (10-20 iLrnin ) of the total effluent is introduced into the ion source, where the mobile phase provides for chemical ionisation of the sample. The currently available commercial LC-MS systems (Table 7.48) differ widely in characteristics mass spectrometer (QMS, QQQ, QITMS, ToF-MS, B, B-QITMS, QToF-MS), mass range m/z 25000), resolution (up to 5000), mass accuracy (at best <5ppm), scan speed (up to 13000Das-1), interface (usually ESP/ISP and APCI, nanospray, PB, CF-FAB). There is no single LC-MS interface and ionisation mode that is readily suitable for all compounds... 

The choice of an analyzer depends on the kind of studies and applications that will be carried out m/z range, resolution, mass accuracy, scan speed, number of mass separations, are some of the parameters that have to be considered. 

The speed of the analyzer highly depends on the mode of operation. The scan speed affects both the resolution and the mass accuracy, so if high quality data is needed, a... 

Figure 5.8. Shape and area of a chromatographic peak depending on the scan speed, (a) Analog signal (b) 13 mass spectra are recorded during the elution of the analyte (c) 7 mass spectra are recorded during the elution of the analyte (d) 3 mass spectra are recorded during the elution of the analyte.

To further improve the performance of a sector instrument in terms of scan speed, resolution, transmission, and mass range, the construction, in particular that of the magnet, needs some additional refining. 

TOF High resolution and mass accuracy when operated in reflectron mode or in Q-TOF systems, elemental composition can be obtained Tandem MS available for generation of sub-structure information or quantitative analysis High sensitivity Very fast scan speed Unlimited mass range Initial energy and spatial distribution must be corrected for ions High-performance electronics needed... 

In terms of overall sensitivity (one molecule detection), mass resolution (in excess of 10 ), mass accuracy (<2ppm), scan speed, and MS capabilities, PT-ICR analyzers remain a very promising technique for the on-line coupling with CE. However, its technical demands, in terms of vacuum technology, and its high price currently limits its use mostly to fundamental studies. 

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