Axis BTA 2100D Manual do Operador descarregar pdf (Página 218)

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High Edge Offset: The integer value step to optimize the ejection of the mass

just above the parent ion mass. The High Edge Offset range is -20 to 20 steps.

The default value is 2.

High Edge Offset affects the isolation window on the high mass side of the

parent ion. Increasing the offset (from 4 to 5 steps) increases the window;

decreasing the offset (from 4 to 3 steps) decreases the window. The offset

should be adjusted to minimize the amplitude of adjacent masses above the

parent ion.

High Edge Amplitude: Amplitude of broadband waveform use to eject masses

above the isolated parent ion. Default is 30 volts.

Isolation Time: The dwell time during which the rf field is held constant in the

high mass ejection step.

The isolation time range is 1 to 10 msec. The default time is 5 msec.

A decrease in the Isolation Time may be required to isolate unstable ions. This

depends on the amount of parent ion intensity that is lost when adjusting the high

offset. Adjustment of the isolation time reflects a compromise between the

requirements of long times to efficiently eject the next highest mass during

isolation, and minimization of CID-based parent ion losses during isolation.

Unstable ions can often be recognized by asymmetric tailing of the mass peak

towards the low side of the spectrum during normal mass scanning. In the case

of the mass at m/z = 219 from the calibration gas PFTBA, the parent ion intensity

is frequently reduced to the CID intensity of the parent ion by the broadband

waveform used to eject the high mass ions above the parent ion.

Some of the frequency components in the waveform will fall close to the resonant

frequency of the parent ion and may couple energy into the ion motion. Unstable

ions can undergo CID at very low energies. By decreasing the isolation time, the

parent ion spends less time in the trap with the waveform present. Stable ions

from PFTBA that can be used to adjust the isolation parameters are m/z = 69,

131, 264, 464, 502, and 614. Column bleed from polysiloxane phases produces

stable clusters of ions starting at m/z = 181, 207, 281, and 429.

1 2 ... 213 214 215 216 217 218 219 220 221 222 223 ... 596 597

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