2000-OSM, F1 6-9
above the bubble point of the sample, the sample will bubble in the sample chamber, causing an
inconsistent liquid fill of the sample loop. This results in a continuously variable sample size. A
defective sample valve stem or leaking seal(s) can also cause nonrepeatability.
Perform Test Procedure 20 (Variable Sample Size). If necessary, replace the sample valve seals
and stem (see "SAMPLE VALVE REPAIR" in Section 8).
Variable Retention Times
Variable retention times can result in nonrepeatability (see Figure 6-12).
TIME
TIME
TIME
t
34
t
27
t
30
t
0
t
0
t
0
Figure 6-12. VARIABLE RETENTION TIME
Symptom
: Retention times of calibration and individually gated process components change with
each consecutive cycle.
Parameters that affect retention times include the following:
1. Varying Carrier flow rate. Perform Test Procedure 2 (Carrier and Makeup Gas Flow
Adjustments).
2. Varying Isothermal Oven Temperature. Perform Test Procedure 30 (Checking Temperature
Table Values).
3. Defective flow controller. Perform Test Procedure 10 (Baseline Cyclic Flow Controller) and Test
Procedure 2 (Carrier and Makeup Gas Flow Adjustments), as applicable.
4. Leak(s) in column train. Perform Test Procedure 7 (Column Train Problems).
5. Variable back pressure on FID vent or TCD measurement vent. Perform Test Procedure 34
(Vent Back Pressure).
6. Sample valve malfunction. Perform Test Procedure 11 (Common Usage of Gases) and Test
Procedure 18 (Sample Valve Actuation Air), as applicable. See "SAMPLE VALVE REPAIR" in
Section 8.
7. Contaminated Carrier or Makeup Gas. Perform Test Procedure 11 (Common Usage of Gases),
Test Procedure 12 (Utility Gas Contamination Procedure), and Test Procedure 13 (Burner Air
Catalytic Cleanup Unit), as applicable.
Individual Peak Missing on Report
Symptom
: Chromatogram indicates all peaks are present; however, the data report shows the peak to
be nonexistent or unknown.
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