Axis BTA 2100D Manual do Operador descarregar pdf (Página 165)

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Choice of Liquid CI Reagents

Many liquids may be used as CI reagents. The general requirements are a

moderate vapor pressure and fairly low molecular weight. If the molecular weight

is too high, you may have problems seeing low molecular weight analytes

because they will be excluded as the reagent ions are ejected. If the vapor

pressure is too low, not enough reagent will enter the Saturn GC/MS for effective

CI operation. This may be remedied by passing a stream of helium through the

reagent vial. This strategy has been used successfully with water as the reagent.

The following have been used as liquid CI reagents on a Saturn GC/MS:

 Methanol

 Dimethyl ether

 Dimethylamine

 Acetonitrile

 Diethyl ether

 Carbon disulfide

 Water (with a helium stream)

Setting CI Parameters for Liquid Reagents

Set the CI Storage level sufficiently low to store the CI reagent ions.

Set the CI background mass to a level sufficiently high that reagent ions do not

appear in the CI spectrum.

Set the Reagent ion eject amplitude to a value between 7.4 and 12.5 volts. As a

starting point, use these values:

Mass Eject Amplitude

<20 7.5

21-50 9

>50 12.5

Adjust the value up or down as necessary to eject ions above the highest

reagent ion while not ejecting the ions from the reagent.

Suggested CI Parameters for Liquid CI Reagents

Reagent Liquid Acetonitrile d3-Acetonitrile Methanol

CI Storage Level (m/z) 19 19 19

Ejection Amplitude (v) 15 15 15

Background Mass (m/z) 65 65 55

Target TIC 5000 5000 5000

Maximum Ionization Time

(µsec)

2000 2000 2000

Maximum Reaction Time

(msec)

40 20 40

Prescan Ion Time (sec)

100 100 100

1 2 ... 160 161 162 163 164 165 166 167 168 169 170 ... 596 597

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Axis BTA 2100D Manual do Operador Página 165

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