© Benaki Phytopathological Institute
LC-MS/MS multiresidue method in peaches
87
more accurate results than multi-level cali-
bration if the detector response is variable
with time (5). When single-level calibration
is employed, the sample response should
be within ±50% of the calibration standard
response. Matrix-matched calibration stan-
dards in blank extract from previously anal-
ysed organically produced stone fruit were
used (5).
In the cases of positive samples, a blank
extract spiked at a concentration level near
the concentration found in the samples was
analysed in order to assure the correct ex-
ecution of the whole procedure. Recovery
rates between 60 and 140% were expect-
ed for the spiked sample for the analysis to
be considered accurate. Figure 1 shows the
chromatogram of a commercial cherry sam-
ple that contained carbendazim at 0.191
mg/kg.
Conclusions
The 56 selected pesticides were of different
physicochemical characteristics and chem-
Table 5.
Results from the 14 stone fruit samples analysed, the multiresidue methods (MRMs)
used for confirmation/quantification, the retention times and relative MRM intensities of the
samples and the matrix matched standards, the reported results with the measurement un-
certainty and the MRLs.
Sample No
Commodity Analyte
Retention time
(min)
Relative intensity
(m/z)
C
1
(mg/kg)
Uncertainty
4
MRL
sample standard sample standard
1 apricots
-
2 apricots
carbaryl
7.65 7.63 10.0% 12.6% LOQ
5
< C
1
<LOD
6
0.05
2
3 apricots carbendazim 4.50 4.60 7.0% 7.4% 0.1458 ± 0.073 0.2
3
4 apricots
indoxacarb 13.63 13.48 23.4% 18.6% 0.0756 ± 0.038 no MRLs
5 cherries
-
6 cherries
-
7 cherries
-
8 cherries
-
9
cherries imidacloprid 3.40 3.34 75.4% 67.5% LOQ
5
< C
1
<LOD
6
0.5
3
cherries thiamethoxam 2.22 2.17 29.2% 31.1% 0.0223 ± 0.011 no MRLs
10
cherries
thiacloprid 5.19 5.19 9.8% 7.3% 0.0345 ± 0.017 0.3
3
cherries carbendazim 4.56 4.53 9.6% 7.1% 0.1910 ± 0.096 0.5
3
11 cherries
-
12 peaches
-
13 peaches
-
14 plums
-
1
Concentration
2
According to Commission Directive 2006/59/EC
3
According to Commission Directive 2008/17/EC
4
Measurement of uncertainty is a quantitative indicator of the confidence in the analytical data and describes
the range around a reported or experimental result within which the true value can be expected to lie within
a defined probability. Considering the results obtained to date from EU proficiency tests, a default expanded
uncertainty figure of 50% (corresponding to a 95% confidence level), in general covers the inter-laboratory
variability between the European laboratories and is recommended to be used by regulatory authorities in cases
of enforcement decisions (MRL-exceedances) (5).
5
Limit of quantification
6
Limit of detection
1...,31,32,33,34,35,36,37,38,39,40 42,43,44,45,46,47,48,49,50,51,...65