Duty cycle, typical

MS/MS Duty Cycle Typical MS/MS analysis is a serial process, relying on the selection of precursors (peptides) in MS mode, followed by high-energy fragmentation in MS/MS. This process is termed data dependent acquisition (DDA). The duty cycle for the completion of MS and MS/MS cycles (the time necessary for MS/MS spectrum acquisition) is of primary importance. When the separation performance is viewed from the mass spectrometry perspective, the peak capacity can be characterized by the number of MS/MS scans, yielding successful... 

Differential flow modulation employs a multiport diaphragm valve with sample loop located in the chromatographic oven, or separate thermostatted oven box, to couple the two separation columns [227-229]. The effluent from the first column is collected in the sample loop and then transferred to the second column. During the transfer process, the effluent from the first column is vented to waste. Thus, sample transfer from the first to the second column is periodic, but not quantitative, and is described by a duty cycle. Typically, the valve is in the collect position for about 80-90% of the time and the switching frequency is about 1 Hz. These conditions allow, for example, filling of the sample loop for 0.9 s with a 0.1 s flush of the loop onto the second column. 

Every current-mode control application that exceeds 50 percent duty cycle must have slope compensation on the current ramp waveform. Otherwise an instability will occur whenever the duty cycle exceeds 50 percent. This is typically done by summing into the current waveform some of the oscillator ramp waveform. This will increase the slope of the current waveform and therefore trip the current sense comparator earlier. A common problem is the inadvertent loading of the oscillator, so I will use a PNP emitter-follower to buffer the oscillator. The circuit configuration can be seen in Figure 3-74. 

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. 

The maximum LC-MS peak capacity calculated fora DDA duty cycle of 1 s is shown in Table 12.3. The number of MS/MS scans exceeds 100,000 for lOh long 1D/2DLC experiment, but the number of identified peptides is typically lower. When considering the 25% success rate of a database search and the limited 2DLC orthogonality, the number of identified peptides is not more than 4500 in a 10 h experiment. 

Typical quadrupoles transmit ions with mass-to-charge ratios ranging from 1-300 or greater with a mass-dependent resolution of twice the mass. More sophisticated instmments can achieve m/z of 4000 with comparable resolution. The suitability of a quadrupole mass analyzer depends in large part on the duty cycle... 

Describe the duty cycle of a typical Van de Graaff accelerator, a linac, and a synchrotron. 

The combustion system requires cleaning of the boiler tubes after every 30 days of operation. A typical incinerator run is 7 to 17 days. This type of duty cycle is suitable for solid waste disposal at the tire plants, although it would be unacceptable for steady production of electric power. 

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... 

In order to select the most economical drive for an Injection molding machine, the duty cycle must be calculated (3). This calculation must be made for each specific application to determine the applicable motor rating. A typical duty cycle Is shown In Figure 3. The motor rating Is defined In terms of 1) Nameplate horsepower and service factor (SF) and 2) Breakdown torque In terms of full load. One first calculates the RMS HP via Equation (1). ... 

Table 1 summarizes these calculations for the typical duty cycle shown In Figure 3. The required motor horsepower Is given In Equation (2). 

Figure 3. Typical injection molding duty cycle (3)...

We will see later that the characteristics of vacuum triodes are replicated in npn junction transistors, albeit by a very different mechanism. One can operate very well with vacuum tubes, but they are more costly and difficult to manufacture and are prone to relatively early failure, mainly due to the tube becoming "gassy" with the evaporation of W from the filament or from vacuum breakdown, due to the prolonged heating of the vacuum tube. The typical vacuum tube duty cycles (a few thousand hours) are much inferior to the duty cycles of transistors. 

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