Acidic pesticdes using QuEChERS methodquechers.cvua-stuttgart.de/pdf/acidicpesticides.pdf · Acidic...
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Acidic pesticdes using QuEChERS method
Transcript of Acidic pesticdes using QuEChERS methodquechers.cvua-stuttgart.de/pdf/acidicpesticides.pdf · Acidic...
Acidic pesticdesusing QuEChERS method
Acidic pesticidespH-issue: Ionization of pesticides at low or high pH-values
� Acids: HX � H+ + X-
� Bases: B + H+ � BH+
� Ionic form prefers to stay in the water phase
pH-range of agricultural samples: ~2.5 – 7
Acidic pesticides –influence of pH on recovery
pH 6
pH 5
pH 4pH 3
MC
PB
2,4-
DB
Bro
mac
il
Flu
azifo
p
Bro
mox
ynil
Ben
tazo
n
Ioxy
nil
Pro
pyza
mid
2,4-
DP
2,4,
5-T
P
Tric
lopy
r
Mec
opro
p
2,4,
5-T
Flu
oxyp
yr
Nap
hthy
lace
tic a
cid
Imaz
aqui
n
2,4-
D
MC
PA
Dic
amba
Imaz
etha
pyr
4-C
PA
Ben
azol
in
Pic
lora
m
Clo
pyra
lidIm
azap
yr
0
20
40
60
80
100
120
Recovery %
���������������� ������ ����
max. pH 5.5
lower pKa � general trend � higher pKa
Acidic pesticides – cleanup issue
Example: Extract of red currant
�Losses of acidic components after cleanup
�Acidic compounds interact with PSA
Citrate-BufferedSample pH 5.1
2,4
1,00,5
pH=3.5
pH=7.8pH=8.3
0
2
4
6
8
10
12
Raw Extract PSA 25mg/mL
PSA 50mg/mL
mg/mL
0
1
2
3
4
5
6
7
8
9pH
mg co-extractives/mL Extract
pH
QuEChERS has to be modified,
to include acidic pesticides
�� Avoid special cleanup with PSA Avoid special cleanup with PSA
�� Special conditions during chromatographySpecial conditions during chromatography
Compound pKa-value Chemical Class acidic structure2,4,5-T 2,852,4,5-TP 2,842,4-D 2,732,4-DB 4,82,4-DP 3,674-CPA 3,56 Fenoxaprop-P 3,2Fluazifop 3,2Fluazifop-P-Butyl 3,1Haloxyfop 2,9MCPA 3,07MCPB 4,84MCPP 3,78Fluroxypyr 2,94Triclopyr 3,97Naphthoxyacetic acid, 2- naphthoxyacetic herbicideBromoxynil 3,86Ioxynil 3,96Clopyralid 2 pyridine herbicideDicamba 1,97 benzoic acidImazapyr 1,9Imazaquin 3,8Imazethapyr 2,1Quinmerac 4,32 quinolinecarboxylic acidPicloram 2,3 pyridine herbicideBentazone 3,3 unclassifiedFomesafen 2,83 amide herbicideImazosulfuron 4 pyrimidinylsulfonylurea herbicidesThifensulfuron-Methyl 4Metsulfuron-Methyl 3,3Metosulam 4,8 sulfonanilide herbicideCycloxydim 4,17 cyclohexene oxime herbicide special caseFludioxonil no acid
triazinylsulfonylurea herbicides
phenoxyalcanoic acid
pyridine herbicide
phenolic herbicide
imidazolinone herbicide
Acidic pesticides – pesticide list
Acidic pesticides – pesticide list
Cycloxydim�� Three mesomeric structuresThree mesomeric structures
�� Difficult chromatogramic behaviourDifficult chromatogramic behaviour
Acidic pesticides - findings
Pes
ticid
e
CIT
RU
S &
PO
ME
F
RU
IT
LEA
FY
VE
GE
T.
FR
UIT
ING
V
EG
ET
.
CE
RE
ALS
LEG
UM
ES
RO
OT
& T
UB
ER
ALL
CO
MM
OD
.
Ann
ex I
91/4
14
Fludioxonil 45 297 651 7 10 3283 PendingFluazifop 1 125 47 9 85 421 Out2,4-D 98 17 7 1 1 314 InHaloxyfop 1 44 5 2 6 146 OutBentazone 72 1 94 InMCPA 6 1 81 InClopyralid 30 1 49 InDicamba 8 4 31 Pending2,4-DP 14 2 25 InMCPP 2 2 24 Pending4-CPA 18 18 PendingNaphthoxyacetic acid, 2- 1 16 18 pendingBromoxynil 10 16 InTriclopyr 2 9Imazaquin 7 Pending2,4,5-T 1 6 InQuinmerac 1 3Fluroxypyr 1 2 InIoxynil 2 2 In2,4-DB 1 InCycloxydim 1 PendingMetosulam 1 1 Pending2,4,5-TP InFenoxaprop-P PendingFormesafenImazapyr OutImazethapyr OutImazosulfuron InMCPB OutMetsulfuron-MethylPicloram OutThifensulfuron-Methyl In
2004 - 2007
N° of samples with positive findings
Relatively often found:
� Fluazifop� 2,4-D
Interlaboratory Method Validation Study
Modified QuEChERS (without PSA-cleanup)
August 2006:
�� 1919 Labs expressed interest from 99 Countries(Germany, Latvia, Spain, Czech Republic, Switzerland, Finland, Austria, The Netherlands and Great Britain)
� 4 Commodities(Raisins, Cucumber, Lemon, Wheat Flour)
� 32 Pesticides (LC-MS/MS, ESI pos and neg) with 2 Levels (0.1 and 0.01 mg/kg)
0
20
40
60
80
100
120
140
2,4,
5-T
2,4,
5-TP
2,4-
D2,
4-DB
2,4-
DP4-
CPABen
tazo
neBro
mox
ynil
Clopy
ralid
Cyclo
xydim
Dicam
ba
Fenox
apro
p-P
Fluaz
ifop
Fluaz
ifop-
P-But
ylFlu
dioxo
nil
Fluro
xypy
rFom
esaf
enHal
oxyf
opIm
azap
yrIm
azaq
uinIm
azet
hapy
r
Imaz
osul
furo
nIo
xynil
MCPA
MCPB
MCPP
Met
osul
am
Mets
ulfur
on-M
ethy
l
Napht
hoxy
acet
ic ac
id, 2
-Picl
oram
Quin
mer
ac
Thifen
sulfu
ron-
Met
hyl
Triclo
pyr
mea
n re
cove
ry in
%
Spiking Level 0.1 mg/kg Spiking Level 0.01 mg/kg
ILMV 2006 Acids –Results (Example Cucumber)
QuEChERS – alkaline hydrolysis
Acids are often covalently bound to matrix components and Acids are often covalently bound to matrix components and thus their concentration underestimated!thus their concentration underestimated!
Example 2,4-D
�� Selective systemic herbicideSelective systemic herbicide
�� Control of broad leaved weedControl of broad leaved weed
�� Plant growth regulator used to prevent premature fruit dropPlant growth regulator used to prevent premature fruit drop
�� Formulations include free acid, salts, estersFormulations include free acid, salts, esters
�� May form conjugatesMay form conjugates
�� Method designed to convert all possible residues to free acidMethod designed to convert all possible residues to free acid
Citrate-Buffered QuEChERS
Weigh 10 g of Frozen Sample
Shake
Shake and Centrifuge
Add ISTD-Solution
Analysis of acidic pesticides by LC-MS/MS
Add 10 mL Acetonitrile
Add 4 g MgSO 4 / 1 g NaCl / Citrate Buffer(pH 5-5.5)
optionally: Freeze-out of extracted
fat over night
QuEChERS – schematic description with AH
optionally: Add NaOH to adjust pH
alkaline hydrolysis: Add NaOH and store for
30 min at RT,then neutralize
Shake
���������������������������������������������� �
Alkaline Hydrolysis for the release of phenoxy-acid pesticideswheat sample
606 619715
336 275135 100
0
200
400
600
800
1000
1200
1400
pH 1
2/30
min
pH 1
0/30
min
pH 1
2/30
min
pH 1
0/60
min
pH 1
0/30
min
pH 9
/30
min
QuE
ChERS w
/o h
ydro
l.
Rel
ativ
con
cent
ratio
n
At 70 °C At Room Temperature
pH 1230 min
pH 1060 min
pH 1030 min
pH 930 min
!��������"��#�������"��� ����� "��
Alkaline Hydrolysis –Level of MCPA in berries
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Alkaline Hydrolysis –Level of 2,4-D in different citrus samples
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