Xu Li-hua
Carlos VargasThis Information Applies To: All Agilent 5977 GC/MSD systems working in EI mode
Issue:
You can evaluate the 5977 MSD tune performance by reviewing the autotune report. Follow the steps in this article to review MSD tune performance.
Steps to follow:
1. Obtain the hardcopy tune report or open the PDF tune report file in the path X/MassHunter/GCMS/1/5977/PDF (see Figure 1).
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Figure 1. PDF tune file in X/MassHuner/GCMS/1/5977/PDF
2. The mass peak profiles for the tune masses (m/z 69, 219 and 502) are shown in Figure 2.
The mass peak profiles should be smooth, symmetrical and even in width, the mass peak profiles should not have visible noise, splits, or precursors visible. Figure 2 shows a normal example.
Figure 2. Main peak profiles in the autotune report
3. The table in Figure 3 displays the Mass Assignment (Actual m/z), Mass Abundance (Abund), Mass Relative Abundance (Rel Abund), and Mass Peak Width at 50% Height (PW50) for each of the three tune mass profiles.
The Actual m/z (mass assignments) for the tune masses should be within +/- 0.2 m/z of the actual mass at m/z 69.0, 219.0, and 502.0.
The Abund (Mass Abundance) for the highest abundance mass (m/z 69) should be between 450,000 and 550,000 counts if the target value is 500,000 counts. The abundances will change based on the target values.
The Rel Abund (Relative Mass Abundance to the Base Peak) should be >40% for m/z 219 and >2% for m/z 502.
The PW50 (Mass Peak Width at 50% Height) of all three tune masses should be 0.60 +/- 0.05 m/z if the target width is set to 0.60.
Figure 3. Actual m/z and PW50 in the autotune report
4. The MS Parameters table (see Figure 4) shows the parameter values set by the tune. These parameters are automatically saved in the tune file when the tuning is complete.
Figure 4. MS parameter table in the autotune report
5. The temperatures and pressures shown in the report are the actual values of the Mass Spectrometer during the tune. This example is for a Turbo Pump 5977 with a High Vacuum Gauge accessory(see Figure 5).
Figure 5. The temperatures and pressures during the tune
6. The table in Figure 6 displays the spectrum scan data:
Target Mass Assignment (Target m/z).
Measured Mass Assignment (Actual m/z ) - should be within +/- 0.1 m/z of 69.0, 219.0, and 502.0.
Mass Abundance (Abund) – m/z 69 will have the highest abundance and should be between 450,000 and 550,000 counts if the target value is 500,000 counts. The abundances will change based on the target values.
Relative Mass Abundance (Rel Abund) - should be >40% for m/z 219 and >2% for m/z 502.
Isotope Measured Mass (Iso m/z ) - should be within +/- 0.1 m/z of 70.0, 220.0, and 503.0.
Isotope Abundance (Iso Abund) – should all be > 1000 counts.
Isotope Ratio (Iso Ratio) – should be close to the theoretical values (m/z 70 at 1.08%, m/z 220 at 4.32% and m/z 503 at 10.09%). As a quick check +/- 20% of the theoretical value is a good estimate, but the exact limits are shown in the tune evaluation report (See Figure 10)
Figure 6. Spectrum scan result
7. Figure 7 displays the Air/Water (background of H2O, N2, O2, and CO2).
Values are Relative % abundance to m/z 69 abundance .
Acceptable values for tune evaluation are:
H2O: < 20%, N2: < 10%
For systems that have been under vacuum and at default operating temperature for at least 2 hours (Ion Source at 230℃ and Quadrupole at 150℃), typical values are:
H2O: < 20%, N2: < 5%, O2:< 1.5% (values may be different depending on the specific instrument conditions).
For systems that have been under vacuum and at default operating temperature for > 24 hours (Ion Source at 230℃ and Quadrupole at 150℃) there should be lower levels of H2O, typically < 5%.
The Air/Water Check is performed as part of the Tune Report after the MSD tuning processes.
If you need to quickly check for air leaks without having to run a full autotune, select Tune > Air and Water Check from the Tune and Vacuum Control View.
Note: If the MS hasn’t had the Calibration Valve opened from previous tuning or air/water check within the last hour, there may be a higher than normal air background. If unsure, repeat the air/water check several times until obtaining consistent values. The Air / Water check in the autotune report is performed at the end of the tuning process and the calibration valve will have typically been open for at least 3 minutes.
8. Figure 8 displays the Gain Factor result from the current autotune. The Gain Factor is a calculation of the current sensitivity of the MS. Typically with a clean ion source, with new filaments, at normal operating temperatures for more than 12 hours, the Gain Factor will be between 0.3 and 0.5. As the ion source becomes contaminated and the filament ages with use, the Gain Factor will progressively increase. Once the Gain Factor has increased by two to three times the value of the clean ion source with a new filament, you should consider performing ion source maintenance. e.g., Post Maintenance Gain Factor = 0.4 increases over time to 0.8 to 1.2
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Note: A sudden stepwise increase in the Gain Factor may be an indication of other possible issues (e.g. PFTBA calibrant has run out, vacuum pressure too high, air leak, too high column flow, aged / used filament). It will typically be associated with a sudden stepwise increase in the EM volts. Review several previous Autotune Reports (atune.u) to determine if the Gain Factor has been progressively increasing or has had a sudden stepwise increase. |
Figure 8. Autotune Report Gain Factor
9. To help interpret the current tune report results, you can perform a Tune Evaluation for the current tune file from the Tune and Vacuum Control view (see Figure 9, View > Tune and Vacuum Control > Tune > Tune Evaluation).
Figure 9. Tune evaluation option
10. The Tune Evaluation generates a System Verification report with results against the preset limits shown. In this example, the Tune Evaluation does not have any out-of-limits results and states “Tune portion of System Verification passed” (see Figure 10).
Figure 10. The tune evaluation report
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