5-18 Calibration
Calibrating the instrument in CI
The instrument can be calibrated in CI ion mode in a similar way as you
calibrate EI ion mode. In CI positive ion mode the calibration is performed
using a reference sample, such as heptacosa or tris (trifluoromethyl) triazine
without CI gas, to reproduce the EI spectrum. In CI positive you can only see
the molecular ion and not the lower mass fragments with tris
(trifluoromethyl) triazine.Heptacosa does produce some fragmentation when
the reagent gas is present.
See also: Calibrating the instrument in CI- mode on page 5-25.
Note: Check the resolution for deadtime correction, see Setting up resolution
for dead time correction manually on page B-48.
Calibrating the instrument in CI+ mode
To calibrate the instrument in CI+ mode:
1. In the MassLynx Tune window, click .
2. In the TDC Settings dialog box, set the Lock mass to 0.
3. Using a septum-piercing syringe, inject approximately 0.2 µL of tris
(trifluoromethyl) triazine into the reference inlet cap.
Tip: Heptacosa or FC70 can also be used.
See also: Introducing the reference sample on page 3-6.
4. Click , to switch the instrument into operate and obtain a beam.
See also: Obtaining a beam in positive CI mode on page 3-28.
Tris (trifluoromethyl) triazine predominantly yields the (M+H)
protonated molecular ion at 286. The resulting spectrum does not
contain enough ions to perform a multi point linear calibration.
Hence two options are available:
• Using tris (trifluoromethyl) triazine the CI gas must be partially or
totally removed to produce the classical EI spectrum of the reference
compound. You can then perform the calibration using the standard
EI calibration procedure.
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