Calibration curves were established through the range of
0.01–0.5g/mL with correlation coefficients from 0.9950
to 0.9999. For real samples such as tomato, credible determination
of the pesticide studied were achieved due to the
lack of interfering peaks and the low background noise as
shown in blank sample (Fig. 1(A)). Chromatograms obtained
from LC–MS analysis tomato spiked with 0.05 mg/kg and
0.05g/mL standard solution are, respectively, illustrated in
Fig. 1(B and C). Compared with the two chromatograms, it is
easy to observe an obvious trend that pirimiphos-methyl and
etrimfos were separated completely in tomato sample, while
only partial separation was achieved by injection of the standard
solution. It is thought that pirimiphos-methyl was protonated
in the acid tomato matrix which resulted in decreasing the
retention on the column. For other types of samples matrices,
there is some concern that target pesticides co-eluted with
other components at about the same retention time originating
from the matrix itself. As a result, with the aid of selection ion chromatogram, co-chromatography of each pesticide enabled
the selective and positive identification of peaks of interest. No
interfering peaks from endogenous compounds of matrices were
found