Check carefully to confirm whether the operation conditions are consistent with the analytical method requirements.
Compared with the standard chromatograms stored after analysis to see if there is a real problem.
Carefully observe the working state of instrument or equipment to see whether there is any peak failure caused by operational errors.
Analyze the following 3 kinds of abnormal peak shapes, find the possible causes and methods to eliminate them.
(1) TCD hot wire is corroded by elements such as halogen, oxygen and sulfur in the sample;
(2) sudden change of gas flow, such as sudden leakage of injection pad, obstruction of gas path, etc.
(3) record chromatographic peak device failure, such as the looseness of the bracing wire.
2. Negative peak:
(1) TCD use nitrogen (N2) as carrier gas. When the concentration of the component in nitrogen(N2) is different and the heat conduction value is nonlinear, the negative peak may appear, which sometimes can be overcome by changing the gas flow rate or the injection volume.
(2) When ECD is operated, the negative peak occurs due to the large injection volume. This is because that the sensitivity will be greatly reduced after the transformation of the working principle from electron capture to ionization detection.
(3) When FID is operated, solvents of low ionization efficiency, such as CS2, or impurities can reduce the output baseline with a relatively high primordial flow, ending up showing a negative peak.
(4)When FID is operated, the negative peak will occur if the sample is not polarized.
(5) When the NPD and FPD are operated, the solvent or some components will show a negative peak if the air flow ratio is not suitable.
3. "N" or "W" peak:
(1)When TCD is operated, with nitrogen used as carrier gas, the “N”or "W" peak will appear due to the non-linearity of thermal conductivity.
(2)When FID is operated, the ionization efficiency of the sample solvent is low, such as CS2, or the air flow ratio is not good enough .
(3) In ECD operation, the detector is polluted, the content of solvent peak or the components to be tested is higher, or pulse power supply is defective.