Page 31 - Volume 3, Issue 2, July 2010
Basic HTML Version
© Benaki Phytopathological Institute
GC multiresidue method of multiclass pesticides
61
numbers of the tested analytes were at least
20% percent of the total number of each
chemical pesticide class, covering the whole
range of selected physicochemical proper-
ties (polarity, solubility in water, vapor pres-
sure). In addition, in the representative ana-
lytes those for which the worst performance
was expected were also included (4, 6).
The selected analytes belong to different
chemical classes: 17 organophosphorous, 3
organochlorines, 3 amides, 6 triazoles, 4 tri-
azines, 1 strobilurins, 2 dinitroanilines and 8
pyrethroids.
Pesticides may be base- or acid-sensi-
tive (correspondingly captan and pymetro-
zine), high volatile (dichlorvos), very polar
(acephate, omethoate) or unstable in the
chromatographic system (metribuzin, car-
baryl). For example, dichlorvos high volatil-
ity resulted in increased uncertainty during
the evaporation phase and all the polar or-
ganophosphorus pesticides demonstrated
low recoveries (10). So it is expected that, in
a multiresidue method, pesticides with sim-
ilar physicochemical properties yield similar
results. This similar behavior is used during
validation of a method by choosing repre-
sentative analytes covering physicochemi-
cal properties of choice.
The pesticide active ingredients used in
this study were obtained from Dr Ehrenstor-
fer Laboratories (GmbH Germany).
(c) GC–ECD/NPD system
The pesticides were separated and de-
termined in a Agilent 6890
gas chromato-
graph, with two splitless injectors,
a DB-5-
MS column (30 m, 0.32 mm i.d. and 0.25 μm
film thickness) connected to the ECD and a
DB-17 MS column (30 m, 0.3 mm i.d. and 0.25
μm film thickness) connected to the NPD.
The oven temperature programme started
from 60
o
C for 1.5 min, increased to 220
o
C
at a rate 14
o
C/min, held for 4 min, then in-
creased to 280
o
C at 20
o
C /min and held for
20 min. The helium carrier gas flow rate was
1.5 ml/min for both columns.
Injectors’ tem-
perature was set at 230
o
C and splitless in-
Table 1 (continued)
Analyte
K
OW
, logP
Vapor Pressure (mPa)
Solubility (mg/l)
cyfluthrin
6.0 (20
o
C)
5.9 (20
o
C)
6.0 (20
o
C)
5.9 (20
o
C)
9.6x10
-4
(20
o
C)
1.4x10
-5
(20
o
C)
2.1x10
-5
(20
o
C)
8.5x10
-5
(20
o
C)
(I) 9.6x10
-4
; (II) 1.4x10
-5
; (III)
2.1x10
-5
; (IV) 8.5x10
-5
(all in, 20°C)
deltamethrin
(I,II) 4.6 (25
o
C)
1.2x10
-5
(25
o
C)
< 0.2 μg/l
esfenvalerate
6.22 (25°C)
2x10
-4
(25°C)
0.002 (25°C)
fenpropathrin
2.9 (pH 7, 25
o
C)
17 (25
o
C)
530 g/m
3
(pH 7, 25
o
C)
flucythrinate
4.7 (25°C)
0.0012 (25°C)
0.5 (21°C)
permethrin
6.1 (20°C)
cis- 0.0025 ; trans- 0.0015
(both 20°C) (12)
6x10
-3
(pH 7, 20°C)
Triazines
atrazine
2.5 (25°C)
3.85x10
-2
(25°C) (OECD 104)
33 (pH 7, 22°C)
prometryn
3.1 (25 °C,
unionised)
0.165 (25°C) (OECD 104)
33 (25°C)
simazine
2.1 (25°C,
unionised)
2.94x10
-3
(25°C) (OECD 104)
6.2 (pH 7, 20°C)
terbuthylazine
3.21 (unionised)
0.15 (25°C)
8.5 (pH 7, 20°C).
Strobilurins
kresoxim-methyl
3.4
2.3x10
-3
2
Dinitroanilines
pendimethalin
5.18
4.0 (25°C)
0.3 mg/l (20°C)
trifluralin
4.83 (20°C) (EECAS)
6.1 (25°C) (EECA4)
0.184 (pH 5), 0.221 (pH 7),
0.189 (pH 9)
