Axis BTA 2100D Instrukcja Operatora Pobierz pdf (Strona 194)

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mass range and scan time, more than one microscan may be obtained during

each scan. (The number of microscans per scan for each set of mass-

range/scan-time conditions selected is displayed on the data system monitor

after these conditions are specified.) If two or more microscans are obtained,

they are averaged by the SAP Board and then stored as one mass spectrum by

the data system. This averaging of microscans provides improved spectral

quality.

At the completion of the scanning period, the rf voltage is again set to near 0V,

and the electron multiplier put into STANDBY. The entire process (setup and

scanning) is repeated up to six times per microscan, once for each of the six

segments.

Basic Equation of the AGC Software

The AGC software sets the ionization time to maintain the optimum quantity of

ions for each of the segments according to the following equation:

pa SFx

TIC

xITIT 

where:

is the actual ionization time to be used for segment “a” in a six segment

microscan;

is the ionization time of the prescan (default value of 0.1 millisecond);

TIC

is the area in counts of the total ion AGC peak from the prescan

measurement;

TIC

is the tunable target TIC value used as a reference for the prescan

measurement calculations; and

is the scale factor for segment “a”. It is a percentage of the actual ionization

time (IT

) that permits individual adjustment of the response and resolution of

each segment.

Increasing the target TIC increases the ionization time for all the segments;

decreasing it will decrease the ionization time. The target TIC is used as a

general resolution adjustment for the entire mass range (all six segments

together).

From the equation above, it is apparent that when the measured TIC increases

because the ion trap is generating more ions (usually due to an increase in

sample or background pressure), then the AGC software will reduce the

ionization time automatically, and vice versa. Also, if the target TIC is increased,

the ionization time for any given pressure will increase. This causes the ion trap

to create more ions. Likewise, reducing the target TIC value will decrease the

number of ions in the trap.

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