Axis BTA 2100D Manual do Operador descarregar pdf (Página 81)

100

101

In CI, as in EI, the Saturn GC/MS is tuned to achieve the best combination of

maximum peak height (sensitivity), optimum resolution of peaks, and smooth

peak shape. And in CI, as in EI, the key to proper tuning is to optimize the

number of ions in the ion trap: Too few ions, sensitivity suffers; too many ions,

resolution and peak shape suffer.

In CI, the two main factors that affect the number of ions in the ion trap are the

ionization time and the reaction time. (Once again, the emission current is an

important third factor.)

The CI ionization time is the time that energetic electrons, emitted from the

filament, are allowed to interact with reagent gas to form reagent ions. The

reaction time is the time that reagent gas ions are allowed to react with sample

molecules to form ions.

To a first approximation, the number of reagent ions formed is directly

proportional to the ionization time, and the number of sample ions formed is

directly proportional to the reaction time.

Once you have selected methane as the CI reagent gas it is time to adjust the

flow rate of the gas into the mass spectrometer. Make sure that the gas tank is

open and connected to the back of the instrument. Select the adjust button. This

will open the CI valves, turn on the filament and multiplier. You will see the

screen below. This is an example of the CI gas spectrum for methane, when the

CI gas pressure is too low and needs to be increased. Notice the resolution and

relative ratio between masses 10 and 30.

See the Chemical Ionization

section in the Hardware Manual for setup and CI gas adjustment.

1 2 ... 76 77 78 79 80 81 82 83 84 85 86 ... 596 597

Comentários a estes Manuais

Sem comentários

Axis BTA 2100D Manual do Operador Página 81

Comentários a estes Manuais

Manuais e produtos relacionados com Software Axis BTA 2100D