Mass spectrometers acquisition rate

During optimization of the procedure we have tested 100% methanol 70% methanol 30% water with 0.1% formic acid (FA) 100% methanol with 0.1% FA 100% acetonitrile 100% ethanol and 70% methanol 30% acetonitrile, as DESI solvents sprayed on the TLC plate surface. Finally, 100% methanol with a flow rate of 3 L min was used as an optimal solvent, providing best results. Other mass spectrometer acquisition settings were as follows mass spectra scan range 70-500 m/z ion accumulation time 200 ms heated capillary temperature 280°C voltage between capillaries 3200 V. Positively charged ion acquisition mode was applied. 

NaCl or KC1 (Peng et al., 2003 Ballif et al., 2004 Beausoleil et al., 2004 Wilmarth et al., 2004 DeSouza et al., 2005 Vitali et al., 2005) may be used for the SCX fractionation, in spite of the incompatibility of these salts with mass spectrometers. When using KC1, for example, the sample must be desalted off-line (Ballif et al., 2004 Beausoleil et al., 2004), on the RP column before MS/MS acquisition (DeSouza et al., 2005 Vitali et al., 2005), with a vented column (Peng et al., 2003), or with a RP-trap (Vollmer et al., 2004 Wilmarth et al., 2004). The configuration with a RP-trap is shown in Fig. 11.1, and in this case, a flow splitter is used to reduce the flow rate from hundreds of microliters per minute to hundreds of nanoliters per minute. However, HPLC pumps of lower flow rate are now available and could eliminate the need for a flow splitter. 

For non-simultaneously operating multi-sources it is necessary to check whether the data quality achieved is sufficient, especially for fast LC systems with very narrow peaks. A switching source splits the available acquisition time for the offered ionization types and therefore reduces the true acquisition rate of the mass spectrometer. However, simultaneously operating sources do not explicitly show which compound ionized with what technique. If this information is really necessary, two separate runs must be performed. 

Analysis was performed in a 96-well microtitre plate by ESI-MS on a Q-TOF mass spectrometer (Q-TOFmicro Micromass, Altrincham, UK) interfaced with a NanoMate M chip-based nanoESI source (Advion Biosciences, Ithaca, NY). Samples were infused at a flow rate 100 nL min . Calibration and sample acquisition were performed in positive ion mode in the range of m/z 500-5000. The ESI-MS screen identified noncovalent complexes of Bell and confirmed the preference of native Bell for certain... 

Theoretically, CCD s offered the most attractive features of the remaining choices, photodiodes and CCD s. However, at the time when the decision had to be made, CCD technology was, and still is, too much in flux, for their use in a mass spectrometer system and too higji in cost to be a reasonable choice. The cost factor would be amplified even further when one considers the increased requirements on the data acquisition system due to the 60-fold increase in data rate ( 860,00 vs 14,300 ) data points per spectrum. These and other considerations led to the decision to implement the second generation detector with a photodiode (Reticon) based camera. This system is now in operation producing excellent data and will be described in detail in the following section. 

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