Additional Peaks Of Unknown Origin (Mystery Peaks); Variable Sample Size - ABB PGC2000 Operation And Service Manual

Additional Peaks of Unknown Origin (Mystery Peaks)

Symptom: Chromatograph displays extra peaks or a noted difference in composite chromatograph
appearance from that of the calibration (see Figure 6-10).
NORMAL
Cause: If only present on calibration sample and not on process, verify that the correct calibration
and proto fuel samples are being analyzed. Possibly a new calibration blend has been installed that
contains a blending error. Perhaps the wrong calibration sample has been selected or incorrect
analysis is attached to it.
If mystery peaks are present on all process or calibration samples, the analyzer is experiencing a
sampling problem. The sample valve seals may be leaking. The sample valve may be double
sampling (see "Double Sampling"). The sample stem may be scratched or deformed. Peaks may
also be originating from a previous analysis cycle.
Check to ensure correct process stream is aligned with sample system.
Perform Test Procedure 19 (Double Sampling), and Test Procedure 36 (Residual Sample), as
applicable.

Variable Sample Size

Variable sample size can cause a nonrepeatability of peak concentrations if the peak area is varying
(see Figure 6-11).
ANALYSIS #1
Symptom: Chromatogram area or height appears to change with each consecutive injection.
Failure: The liquid sample volume is not consistent between consecutive injections. This can be
related to sample flow, defective sample valve hardware, leaks in column train, or sample bubbling.
Cause: Leaking sample valve seal can result in random bubbling of carrier into the sample chamber
causing the sample size to vary. If the sample chamber pressure is such that the temperature is
6-8
TIME
Figure 6-10. MYSTERY PEAKS
TIME
Figure 6-11. VARIABLE SAMPLE SIZE
Unknown
TIME
MYSTERY PEAKS
TIME
ANALYSIS #2
2000-OSM, F1