After a period of sample injection in the GC, the system is covered by non-volatile impurities, which will affect the peaks of some organophosphorus pesticides with strong polarity
As shown in Figure 2-19, the standard peaks of acephate and omethoate are normal.
After a period of time, the standard peaks of acephate and omethoate become weaker and smaller (Figure 2-20)
This is a typical analysis of organophosphorus pesticide residues when the active sites adsorb the pesticides.
The formation of active sites is caused by the continuous pollution of the system by non-volatile impurities after multiple injections
When this happens, the system should be cleaned or replaced for maintenance
Figure 2-19 The normal peaks of acephate and omethoate standard GC
Figure 2-20 The standard of acephate and omethoate becomes weaker and smaller
In addition, there is another situation where the matrix effect causes the retention time of the peak to change.
If the matrix matching standard is not used and the pesticide in the standard and the sample peak at the same position, it will cause missed detection, as shown in Figure 2-21
Figure 2-21 The retention time of the phoxim standard in the sample has shifted
Related Links: Chromatogram Analysis of Gas Chromatography Detection