6-10
2000-OSM, F1
Cause: The gating in the method needs to be modified to ensure gating of the missing peak in the
report. This can be done by modifying the gate ON/OFF time in the method table. See "PEAK
DETECTION" in Section 4 for detailed instructions.
Peak Inversion
Symptom: The peaks on the strip chart recorder are reversed or negative (see Figure
6-13).
NORMAL
OFFSET
Baseline offset
adjusted up scale
Figure 6-13. PEAK INVERSION
Cause: Negative peaks on the strip chart recorder could be due to reversed recorder wiring at the
analyzer or at the recorder. Some recorders are equipped with polarity reversal. Ensure correct
polarity setting on recorder. Other possible causes include reversal of sense and reference tubing
connections or filament wiring if a TCD is used, or a grounded jet or missing jet voltage if a FID is
used.
1. Check for reversed sense and reference filament wires.
2. Check for reversed sense and reference tubing connections to the detector.
3. Make necessary corrections.
4. Perform
Test Procedure 28
(FID Polarizing Voltage Test).
Chromatogram Oversized or Off Scale
Symptom: The chromatogram or peak areas are excessively large. The condition may be severe
enough that all peaks are off scale on the highest attenuation (see Figure 6-14). Chromatogram may
go off scale at approximately the time of distillation on and not return to scale until time of distillation
off.
NORMAL
PEAK OFFSCALE
Figure 6-14. CHROMATOGRAM OFF SCALE
Cause: The attenuation could be set too low, making the chromatogram or peaks appear large (loss
of polarizing voltage on FID). Another possible cause is the wrong carrier gas is being used (e.g.
nitrogen used instead of helium).
