Instrument duty cycle

The electrical jumps of the acceleration voltage are very fast, and provide an excellent instrument duty cycle. Any outside influences from incidental background ions, long-term drift or minute electronics fluctuations are taken care of and do not influence the result. 

Over the years, MS/MS duty cycle of modern MS instruments has constantly been improving, but for simplicity we assume it is equal to 1 s. Considering this it is possible to identify up to 60 peptides per minute and up to 3600 peptides in a LC-MS/MS analysis of 1 h. It is important to mention that only a small percentage of MS/MS scans typically yield a spectrum of sufficient quality that can be matched against a protein database and can result in peptide identification. 

Quadrupole mass spectrometers has been used mainly in CE—MS because they can be obtained at relatively low cost, possess small dimensions, and are easy to operate. As previously mentioned, the scanning process is relatively slow and allows operation of only a small fraction of the available ions, which is not suitable with very narrow CE peaks. The use of selected ion monitoring (SIM) mode greatly improves sensitivity and duty cycle, but it is not always appropriate for the detection of complex mixtures. This kind of analyzer is currently used as a low-resolution instrument and for quantitative determination. 

Verify a True Peak measurement instrument by first establishing an initial calibration nsing a sine wave. Then verify the pulse response of the instrument nsing a nonsymmetrical duty cycle pulse and compare the results to the sine wave calibration. Follow these steps ... 

The particularity of the LIT-orbitrap instrument is the independent operation of the orbitrap and the LIT. Because high resolution requires longer transient time, further data can already be collected in the LIT at the same time. As an example accurate mass measurements of the precursor ion can be performed in the orbitrap while MS and MS spectra are recorded with the linear ion trap. The LIT-orbitrap has less resolution than a FT-ICR instrument with similar duty cycle, but its maintenance costs are far lower than for the FT-ICR. Both instruments will have a major impact in mainly qualitative analysis of low molecular weight compounds and macromolecules. 

One critical feature of mass spectrometry when combined with chromatographic or electrophoretic separation techniques remains the duty cycle of the mass analyzer. A conventional LC chromatographic peak lasts about 10 s, which is sufficient to perform various MS and MS/MS experiments on various types of instruments. In the case of fast LC, the peak width can be in the range 1-2 s which is too fast for most mass analyzers except for TOF mass spectrometers. 

Sampling with fiber optic sensors can be continuous if needed otherwise they can be operated discontinuously, with a lower duty cycle. These sensors could be used for laboratory-based or in situ applications. The cost of instrumentation for fiber optic systems should be 25,000 to 50,000. Sensors would need to be replaced periodically (several weeks to many months), depending upon their design. Sensors using fiber optic probes will be available within 5 years for some applications and within 10 years for some others. Sensors for pH, C02, and 02 are in development now new sensors should be capable of measuring from high concentrations down to 1 part per million for ions and organic materials. Basic research is still required for specific applications. 

Finally one must also recognize that the duty cycle efficiencies of the two types of instrument are also different. The duty cycle efficiency, , is defined as the ratio of the time... 

Several scan modes are unique to the triple-quadrupole instrument, and most of these modes are superior in duty cycle versus an ion trap, Fourier transform (FT), or time-of-flight (TOF) mass spectrometers. Different elements of the triple-quadrupole perform different operations for each scan mode. These scan modes, each of which will be described in detail, are single-reaction monitoring (SRM) or multiple-reaction monitoring (MRM), precursor ion scanning (PIS), and constant-neutral-loss scanning (NLS). These scan modes and applications for structural elucidation have been described in detail (Yost and Enke, 1978, 1979). 

The quadrupoles in an MS instrument serve as selective mass filters to isolate ions with m/z-values specific for the analytes of interest. The triple quadrupole MS/MS instrument is typically operated by a pneumatically assisted electrospray source with an additional heated auxiliary gas flow for higher flow rates. There is a trade-off between resolution (favored by lower flow) and sensitivity (favored by higher flow) of the quadrupole analyzers. The biological molecules can be proto-nated or deprotonated at multiple sites to produce ions of n charged states [M nH]n . The MRM-MS/MS scan mode has a high duty cycle for the detection... 

The novel approaches in LC-MS-based lipidomics, such as ultra-high performance LC (UHPLC), combined with high-resolution MS methodologies allow fast and reliable analysis of various classes of lipids (33). The modem instruments, with fast duty cycles, allow acquisition of high and low collision energy data simultaneously to provide both data on precursor ions and fragmentation data for all detectable molecular ions (34). 

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