Trap-filled limit effect

Cold traps must be used if mercury is used in your system (such as manometers, diffusion pumps, bubblers, or McLeod gauges) and if your mechanical pump has cast aluminum parts. Mercury will amalgamate with aluminum and destroy a pump. Even if your mechanical pump does not have aluminum parts, the mercury may form a reservoir in the bottom of the mechanical pump, which may cause a noticeable decrease in pumping speed and effectiveness. Aside from a cold trap between the McLeod gauge and the system, place a film of low vapor pressure oil in the McLeod gauge storage bulb. This oil will limit the amount of mercury vapor entering the system that makes its way to the mechanical pump. In addition, an oil layer should be placed on the mercury surface in bubblers and other mercury-filled components. 

While the concept of duty cycle also applies to ion traps, if an attempt is made to produce a similar simple relationship the situation becomes immediately more complicated as a result of the need for such instruments to deal with the implications of space charge effects. For example, only a limited total number of ions (analyte plus matrix) can be accumulated in a trap at any one time, so the number of microscans (fill-scanout cycles. Section 6.4.5), which must be accumulated and averaged to provide adequate ion statistics for the analyte ions, is highly variable depending on the analyte matrix ratio. If selective ejection techniques (Section 6.4.5) are used to eliminate... 

Detection limits of analytes measured in ESI and MALDI using the mass analyzers covered in this chapter are quite noteworthy. Table 9.3 lists detection limits for various molecules analyzed by LC, CE, and EIA coupled to ESI QIT, LQIT, and the orbitrap or with the use of MALDI. The lowest limits of detection are measured when an isolation step is used to accumulate and/or isolate only the ion(s) of interest. For example, in Table 9.3, the detection limits for reserpine in SIM and SRM scan modes are better than in the full-scan mode. Although ion trap full MS scans have a higher duty cycle over QMF ion beam instruments, detection limits can be reduced in the full-scan MS mode due to matrix effects. In this latter case, at low analyte amounts, the QIT is filled up primarily with unwanted matrix ions, leaving little space to store the ions of interest. The advantage of the high-charge-capacity... 

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