Axis BTA 2100D Instrukcja Operatora Pobierz pdf (Strona 195)

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Software Parameters

Segment Setpoints

Scan Time

The duration of each scan (in seconds). The scan time can be set to any value

from 0.100 to 5.000 seconds per scan. Below the scan time input box is

displayed the number of microscans per scan for the selected mass range and

scan time. The number of microscans per scan is computed automatically; it

cannot be set directly. It is displayed for information only. The minimum duration

for the scan time is determined by the selected mass range.

Multiplier Offset

To improve detection limits, the multiplier voltage may be increased or decreased

by 300 volts of the Electron Multiplier 10

gain. The same multiplier gain must be

used for determining the calibration curve and analyzing unknown samples.

Emission Current

The number of ions formed in the trap is a function of both the ionization time

and the intensity of the electron beam. In general, increasing the filament

emission current increases the quantity of ions produced. The relationship

between the filament emission current and the measured TIC (i.e., the number of

ions generated in the ion trap) is not a strictly linear one. In particular, the

emission current and the measured TIC do not vary linearly for emission current

values above 40 µA and at high sample concentration.

In certain cases, a high emission current can be used to increase the sensitivity.

One of these is EI/MS/MS where the MS/MS isolation step eliminates the higher

background that would normally arise from a high emission current. The

emission current may be set from 5 to 100 µA.

Count Threshold

The minimum number of intensity counts per sampling interval required before a

signal is recorded. (The maximum number of counts per sampling interval is

4095.) The peak threshold can be set to any value from 0 to 1000 counts; it is

typically set to 0 or 1 count.

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