4-16 Acquiring Data
2. Set z-focus to 40 and z-lens steering to 0.
3. Tune the instrument in EI with heptacosa or any other reference
compound.
4. In the Tuning Setup dialog box, set Data Format to Centroid.
See also: Tuning the instrument for EI on page 3-19.
5. Record the beam intensity as displayed on the MassLynx Tune window.
6. On the DRE tab, clear High Sensitivity.
Rationale: The instrument will operate in low sensitivity mode for the
z-focus and the z-lens steering.
7. Increase the value of z-focus until the beam intensity is approximately
1/40 of the size you noted in step 5.
Note: This would typically occur at a z-focus (V) value of 250, but varies
with source tuning.
8. In the DRE tab, select High Sensitivity.
9. Acquire centroid data for 1 minute between 1 and 800 Da (“high
intensity” data).
10. On the DRE tab, clear High Sensitivity.
11. Acquire centroid data for 1 minute between 1 and 800 Da (“low
intensity” data).
12. For each of the data files acquired in steps 9 and 11, sum the same
number of scans and examine the resulting spectra.
Requirements: The peaks must not be saturated in the high intensity
data, and there must be at least 1500 counts on each peak of interest in
the summed low intensity data.
Tip: A question mark displays above every saturated spectral peak when
a single spectrum is viewed.
See also: The MassLynx User’s Guide.
13. Use the following equation to calculate the magnification factor for each
of the masses shown in the Table titled “Mass values and example
magnification factor results for heptacosa in EI and CI positive ion
mode:” on page 4-17.
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