液质样品前处理方法汇总(英)

Note: GCB strongly retains planar analytes
Recovery
Pesticide recoveries vs. fat content
120%
100%
80%
60%
40% orange lettuce
20%
0% 0%
milk
eggs
5%
10%
Fat content
120%
No Buffering
100% 80% 60% 40% 20%
pH = 2 PH = 3.25 pH = 4.5 pH = 5.75 pH = 7
Buffering
0% 120%Acephate* 100%
80% 60% 40% 20%
0%
Carbaryl*
* Carbendazim
Chlorothalonil
centrifuge for 1 min at 3450 rcf
dispecrsleivaen-SuPpE
1 mL of the upper layer
+ 50 mg PSA + 150 mg MgSO4 mix for 20 s
centrifuge for 1 min at 3450 rcf
2)
1)
9 Consistently high recoveries (mostly 90-110%
with RSDs < 5%) of a wide range of GC- and LCamenable pesticides are achieved from many matrices.
Recoveries in the QuEChERS method
pH of QuEChERS Extract
pH of the water and MeCN layers
Original QuEChERS procedure
7
No buffering
6 water phase
5
4 MeCN phase
3
2
1
3
5
7
Original pH of Sample
5
pH of the water and MeCN layers
6
pH of the MeCN extract
before and after dispersive-SPE clean-up with PSA
pH of MeCN Extract
8
Effect of buffering
7
6
without buffering (after clean-up)
5
with buffering (before clean-up)
N
N
N
O
N NH
pymetrozine
Pymetrozine:
- imine (Schiff base) - hydrolysis in acidic conditions
- recovery:
lettuce > 80% oranges ≈ 25%
- insecticide registered for application on citrus fruits
add internal standard
add 6 g MgSO4 + 1.5 g NaAc shake vigorously for 1 min
centrifuge for 1 min at 3450 rcf
dispecrsleivaen-SuPpE
1 mL of the upper layer
100 ng/g Lettuce 40%
30%
20%
10%
0% <20 20-49 50-69 70-79 80-89 90-110 111-120 >120
%Recovery
3
Effect of pH
fruits and vegetables: pH 2.5 - 6.5
potential problems = lower recoveries of certain analytes in certain matrices caused by:
consistent results independent of matrix pH increased recoveries and improved stability of acid- and base-sensitive pesticides
Applicability of the buffered QuEChERS to low fatty foods - C18 needed for additional clean-up - lower recoveries obtained for the most lipophilic pesticides (e.g. HCB, DDE) as lipid content increased
Base-sensitive pesticides
- degrade even in certain lots of MeCN - addition of 0.1% acetic acid improves their stability
O
Cl
NS
Cl
Cl
O captan
O Cl
Cl Cl
Cl
OH
NS
Outline
¾ Original QuEChERS method for analysis of pesticide residues in produce
¾ Effect of pH and buffered QuEChERS method ¾ Analysis of pesticide residues in fatty food
229 pesticides analyzed by GC-MS and LC-MS-MS
Percentage of Pesticides
90%
80%
10 ng/g Orange
25 ng/g Orange
70%
100 ng/g Orange
60%
10 ng/g Lettuce
50%
50 ng/g Lettuce
Conclusions
Buffered QuEChERS method = the use of 1% HAc in MeCN for extraction in combination with NaAc for liquid-liquid partitioning - buffered extracts:
QuEChERS steps 3)
4)
2
QuEChERS Advantages
9 A batch of 6-12 extracts can be prepared in 30-
40 min by a single analyst with $1 of disposable materials per sample in the lab or field and generate no hazardous waste and only a single reusable item (FEP tube) for cleaning.
120%
100%
80%
60%
40%
chlordane DDE
20%
HCB
lettuce/orange avocado
0%
1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06
Pesticide Solubility in Water (mg/L)
+ 50 mg PSA + 150 mg MgSO4 mix for 20 s
centrifuge for 1 min at 3450 rcf
7
Collaborative study
¾ inter-laboratory validation of the buffered QuEChERS method ¾ 15 laboratories in 7 countries (Canada, Denmark, Germany, the Netherlands, Spain, UK, and USA) ¾ 21 fortified (at 10 - 1,000 ng/g) and 6 incurred pesticides in 3 commodities (grape, lettuce, and orange) ¾ analysis by (LVI-)GC-MS and LC-MS-MS
Pesticide analysis in fatty foods
Food samples Nonfatty Low fatty High fatty
Fat content (%) <2
2 - 20 > 20
QuEChERS method
Low fatty matrices (milk, eggs, avocado etc.) - addition of C18 for dispersive-SPE clean-up
Dichlofluanid*
Imazalile*thamidophos M
Propoxur Pymetrozine*Thiabendazole*
Tolyfluanid*
Tolyfluanid Thiabendazole Pymetrozine Propoxur Methamidophos Imazalil Dichlofluanid Chlorothalonil Carbendazim Carbaryl Acephate
Cl
Cl Cl
O folpet
Cl
dicofol
OO
S
S
F
N
N
Cl Cl
OO
S
S
F
N
N
Cl Cl
dichlofluanid
tolylfluanid
Cl
Cl
Cl
N
N
Cl
chlorothalonil
4
Acid-sensitive pesticide
- pesticides generally more stable at lower pH
8
Dispersive-SPE clean-up of egg extracts
Co-Extractives
0.25%
0.20% 0.15%
final conditions
Байду номын сангаас
0.10%
0.05%
0.00%
no cleanup
MgSO4 only
+PSA
+PSA+C18 +PSA+GC+PBSA+C18+GCB
1 mL 1% HAc in MeCN and 0.1 g NaAc per 1 g sample
7
Buffering
6
water phase
pH of Buffered Extract
5
4
MeCN phase
3
1
3
5
7
Original pH of Sample
Effect of buffering on pesticide recoveries
New Developments in the QuEChERS Method for
Pesticide Residues in Food
Katerina Mastovska and Steven J. Lehotay
Eastern Regional Research Center Wyndmoor, PA, USA
4
3
without buffering (before clean-up)
2
1
3
5
with buffering (after clean-up)
7
Original pH of Sample
Buffered QuEChERS method
extraction
15 g sample + 15 mL 1% HAc in MeCN (v/v)
matrices using the buffered QuEChERS method
1
Original QuEChERS method
extraction
10 g sample + 10 mL MeCN
add internal standard
add 4 g MgSO4 + 1 g NaCl shake vigorously for 1 min
penconazole chlorpyrifos-methyl lindane heptachlor epoxide permethrin chlordane DDE hexachlorobenzene
avocado
15%
9
Pesticide recoveries vs. fat content
Pesticide Recovery
¾ ionization - mainly protonization of basic pesticides in acidic conditions = reduced partition into organic layer
¾ degradation
- base-sensitive pesticides in higher pH samples - acid-sensitive pesticides in lower pH samples