Automatic gain control

The maximum number of ions in a cylindrical QIT is limited to about 105 before space-charge effects seriously affect the performance, so the dynamic range is rather poor. The poor dynamic range can sometimes be compensated for by using automatic gain control. The linear QIT has a larger volume and can store more ions before space-charge affects the performance. 

Yost, R.A., McClennan, W. and Menzzelaar, H.L.C. Enhanced full scan sensitivity and dynamic range in Finnigan MAT ion trap detector with automatic gain control of software. Finnigan MAT IDT 22. 

Camp, C. Ion trap advancements. Higher sensitivity and greater dynamic range with automatic gain control software. Finnigan MAT IDT 23. 

If resolution is not important, scanning of QITs can be very fast, a property that can be employed to make a pre-scan. Then, the result of the pre-scan is used to adjust the number of ions inside the QIT close to the optimum for the subsequent analytical scan. Such an automatic gain control (AGC) [138,162] gives increased sensitivity at low sample flow and avoids overload of the QIT at high sample flow. 

Auditory scene analysis, 24, 26 Auditory system, 8, 10, 16 Auralization, 87 Automatic gain control, 255 Autoregressive (AR) model, 135, 142, 159, 164 Autoregressive (AR) model, Interpolation (See Restoration,Interpolation)... 

For MS work, the electron impact (El) mode with automatic gain control (AGC) was used. The electron multiplier voltage for MS/MS was 1450 V, AGC target was 10,000 counts, and filament emission current was 60 pA with the axial modulation amplitude at 4.0 V. The ion trap was held at 200°C and the transfer line at 250°C. The manifold temperature was set at 60°C and the mass spectral scan time across 50-450 m/z was 1.0 s (using 3 microscans). Nonresonant, collision-induced dissociation (CID) was used for MS/MS. The associated parameters for this method were optimized for each individual compound (Table 7.3). The method was divided into ten acquisition time segments so that different ion preparation files could be used to optimize the conditions for the TMS derivatives of the chemically distinct internal standard, phenolic acids, and DIMBOA. Standard samples of both p-coumaric and ferulic acids consisted of trans and cis isomers so that four segments were required to characterize these two acids. The first time segment was a 9 min solvent delay used to protect the electron multiplier from the solvent peak. 

Stafford, G.C. Jr. Taylor, D.M. Bradshaw, S.C. Syka, J.E.P. Uhrich, M. Enhanced sensitivity and dynamic range on an ion trap mass spectrometer with automatic gain control (AGC). Pmc. 3 ASMS Conference on Mass Spectrometry and Allied Topics, San Francisco, CA, June 5-10,1988. 

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