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Section 7. Achieving External EI
Specifications
If necessary, convert the MS to external mode as described in the Hardware
Manual. Purge the MS pneumatics as described in Section 2.1. Auto tune the
system as described in Section 4.2. Ensure the MS damping gas flow is set
appropriately and the Getter is at least 300 °C. The appropriate Damping Gas
flow rates can be found embedded in the names of the test data files from the
Test Files CD included with the system, and also in the Module Attributes section
of the Data File Information dialog of each external data file. Set the MS damping
gas flow rate to this value to ensure optimal system performance. Refer to
section 2.1 for help in programming the MS damping gas flow rate
The EI specifications for a 4000 GCMS system in External mode:
•
30:1 RMS signal-to-noise using the m/z 272 ion from a 1 µL injection of a
5 pg/µL OFN solution (03-931127-02). A 10:1 split ratio can be used to
reduce the amount of OFN from 5 pg to 500 fg. If necessary, a 10:1
dilution can be done using customer supplied glassware and 2,2,4-
trimethylpentane (isooctane) to reduce the amount of OFN from 5 pg to
500 fg. In addition, a background corrected spectrum should be library
searchable with any match > 500. If a Quick Switch Valve is used in the
GC oven the signal-to-noise spec is reduced from 30:1 to 15:1.
7.1 Methodology
NOTE: The 4000 GCMS system will arrive with a Test Files CD containing
factory test method and data files. These method files can be used to pass the
sensitivity tests associated with the installation. At the factory a diluted OFN
standard is injected using a pressure pulse and splitless injection technique. If a
diluted OFN standard is to be used at an installation the method from the Test
Files CD can be used with no editing. If a split style injection is to be used at an
installation, the Test Files CD method should be edited to remove the pressure
pulse and introduce a 10:1 split ratio. Retain the Test Files CD for your records.
Ensure the MS temperatures are set for this acquisition:
•
Trap: 150 °C
•
Manifold: 40 °C
•
Transfer Line: 230 °C
•
Source: 150 °C
If necessary, edit the Test Files CD external EI method and activate the method
in System Control.
Summary of Contents for 4000 GCMS
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