11.2.2 Triple Quadrupole MS Settings
Mass spectrometric detection was carried out using the
TSQ 8000 triple-quadrupole mass spectrometer in
timed-SRM mode. All method and SRM settings were
taken from the Thermo Scientific TSQ 8000 Pesticide
Analyzer system method.
6
Ion ratio values were revised
and adapted for each investigated matrices.
The settings were as follows:
Scan type:
timed-SRM (details in Table 2)
Ionization:
EI +
MS transfer line temp:
250 °C
Ion source temp:
300 °C
Cycle time:
0.3 s
Minimum baseline peak width: 3 s
Desired scans per peak:
10
Minimum dwell time:
0.001 s
Q1 resolution:
normal (0.7 Da)
11.3 Calculation of Results
Internal standardization was applied for quantification
of target pesticides. The relevant response factors (R
f
)
were defined by the equation below. Calculation of final
result was performed using the following equations.
11.3.1 Equations
Calculation of the response factor:
R
f
– the response factor
A
St
– the area of the pesticide peak in the calibration standard
A
[IS]
– the area of the internal standard peak of the calibration standard
c
St
– pesticide concentration of the calibration standard solution
c
[IS]
– the internal standard concentration of the calibration
standard solution
Calculations of sample amount in each sample (the
absolute amount of pesticide extracted from the sample):
X
analyte
– the absolute amount of pesticide that was extracted from
the sample
A
analyte
– the area of pesticide peak in the sample
A
[IS]
– the area of the internal standard peak in the sample
X
[IS]
– the absolute amount of internal standard added to the sample
Calculations of sample amount in each sample (the
absolute amount of pesticide extracted from the sample):
m – the weight of sample [g]
X
analyte
– absolute analyte amount [ng]
12. Method Performance Characteristics
In-house validation of the method was carried out on all
matrices and target pesticides. European guidelines for
single laboratory validation and pesticide residue
analysis were used for establishing method performance
criteria.
1, 2
All method performance parameters were
compared to the relevant legislative requirements and
maximum residue limit (MRLs).
2-4, 7
For compounds
containing more isoforms, only one performance criteria
was established.
12.1 Selectivity
Method (SRM) selectivity was assessed based on the
presence of specific ion transitions (quantifier ion and
two transitions for compound confirmation) at the
corresponding retention time (Table 2), as well as the
observed ion ratio values corresponding to those of the
standards. Acceptance criteria for retention time and ion
ratios were set according to current quality control
criteria.
1, 3
Matrix blank samples were also inspected for
the presence of interfering peaks in close vicinity of the
target retention times for which (according to SANCO
guidline definitions) <30% of LOQ acceptance criteria
was applied.
3
Additional peaks in close vicinity of target
peaks in blank samples were observed for chlorpropham
(LK), demethon-s-methyl (SB), fenhexamide (WF, LK),
fenitrothion (WF, LK), procymidon (WF), phosphalone
(SB), permethrin (WF, LK), fenpropathrin (LK),
o-phenylphenol (WF) and carbofuran (SB, WF).
However, they were all clearly resolved by retention time
from the target peaks (Rs>1.5) except carbofuran in SB
and WF and propargite in WF and LK matrices.
5
f
IS
IS
analyte
analyte
R A
X
A
X =
+
+
m
X
C
analyte
=
St
f
[IS]
[IS]
St
c A
c A
+
+
R =
