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(2) Optimization of retrieval parameters
The screening parameters include mass deviation window, retention time window, and ionization form
.
Appropriate parameter settings can avoid false positive and false negative results and improve the accuracy of screening methods
The accurate mass deviation refers to the difference between the actual measured accurate mass and the theoretical accurate mass of the instrument
.
The deviation of accurate mass is an important basis for compound qualitative, so the deviation range of accurate mass data needs to be limited
Figure 22-40 The quality deviation distribution of 40 veterinary drugs at three levels (n=6)
The retention time limit parameters are evaluated in the honey matrix, and the retention time limits are 0.
1min, 0.
25min, 0.
5min, 1min and no retention time limit respectively
.
Experimental results show that a too wide or too narrow retention limit will cause search errors and false positive or false negative results
Figure 22-41 Proportion of false results under different time limit windows
In addition, the experiment investigated the stability of retention time through the repeatability (n=6) and reproducibility (n=6) of the retention time of the target compound.
The experimental results showed that the maximum standard deviation of the retention time within the day was less than 0.
14 min.
, The maximum standard deviation of the daytime retention time is less than 0.
24min
.
Therefore, the retention time limit parameter is set to 0.
Ionization form: Since LC-MS has a variety of ionization forms ([M+H] + , [M+NH 4 ] + and [M+Na] + ), the choice of ionization form must be investigated
.
For the 40 veterinary drugs in this study, the ionized form with the highest response is the [M+H] + form
