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