C l O - SecurEau · SPE method using LC-18 column yielded better results regarding recovery...
1
Raquel Sousa, José Luís Moreira, Luís Miguel Madeira, Arminda Alves * LEPAE, Chemical Engineering Department, Faculty of Engineering, University of Porto Rua Dr. Roberto Frias, 4200-465 Porto, Portugal * Corresponding author: Tel. +351 22 508 1883. E-mail: [email protected] Pesticides are types of well-known environmental contaminants. The use of pesticides provides benefits for increasing agricultural production. However, because of their highly persistent properties, their residues may appear in fruits and vegetables and can be distributed in aqueous environments by leaching and run-off from soil into ground and surface water. Owing to the toxicity of pesticides, the European Directive 98/83/EC about the quality of water intended for human consumption establishes maximum concentrations of 0.1 μg L -1 for individual pesticides and 0.5 μg L -1 for the sum of all pesticides. Two pesticides from different families were selected in this work – carbofuran (carbamate) and chlorfenvinphos (organophosphorus), in order to act as models to extend to other compounds of the same families. The main objective was to develop an analytical methodology capable of detecting these pesticides at the legislated levels of concentration, but also suitable to be applied to cases in which there is a limitation of sample volume (e.g. from studies of pesticides degradation by advanced oxidation processes). Three types of SPE sorbents were tested, using different extraction methods accordingly to the sorbent nature: LC-18 (non-polar silica based); HR-P (polymeric polystyrene-divinylbenzene resin based); OASIS HLB (copolymeric reversed-phase) Sorbent: LC-18; HR-P, Oasis HLB Conditioning: 5 mL methanol 5 mL water Sorption: 15 mL water sample Elution: 5 mL methanol Drying column Evaporate to dryness with N 2 Re-dissolve in 0.5 mL methanol and 1 mL water Temperatures: Injector: 290 °C; MS Transfer Line: 250 °C Temperature Program: 130 °C for 2 min, 20 °C min -1 to 275 °C, and held for 1 min Injection Volume: 1 μL (splitless injection) Detection: SIM mode Identification Ions: Carbofuran – 164, 149, 131 Chlorfenvinphos – 267, 269, 323 Extraction: 10 mL water sample 500 μL acetonitrile – dispersive solvent 100 μL chlorobenzene – extraction solvent This study showed that SPE and DLLME are both suitable extraction methods for the pesticides studied. In comparison, DLLME is more simple and requires lower sample and solvent volumes. SPE method using LC-18 column yielded better results regarding recovery percentage, but LODs were higher than DLLME for similar sample volume. DLLME showed lower detection limits (0.01 μg.L -1 ), simplicity and proved more suitable if sample volume is a limitation. However SPE cannot be excluded as a suitable analytical method even for extremely low concentrations, but in that case higher sample volume (up to 1 L) has to be used. a S/N=3; b CV – coefficient of variation from 3 independent extractions; c %R – recovery percentage of 3 independent extractions. Sorbent : LC-18; HR-P Conditioning: 5 mL methanol 5 mL water Sorption: 15 mL water sample Elution: 5 mL methanol Drying column Evaporate to dryness with N 2 Re-dissolve in 1 mL ethyl acetate Sorbent : Oasis HLB Conditioning: 5 mL ethyl acetate 5 mL methanol 5 mL water Sorption: 15 mL water sample Elution: 2x4 mL ethyl acetate Drying column Evaporate to dryness with N 2 Re-dissolve in 1 mL ethyl acetate Carbofuran (CBF) Carbamate Pesticide O O HN O Chlorfenvinphos (CVFP) Organophosphorus Pesticide Cl Cl O Cl P O O O Figure 1. Comparative performance of 3 different sorbents used to extract a 1 mg.L -1 standard mixture, using Method 1. Figure 2. Comparative performance of 3 different sorbents used to extract a 10 μg.L -1 standard mixture, using Methods 2 and 3. Lower LOD would be achievable using larger sample volume Figure 4. Calibration curve for extracted standards of (A) carbofuran, (B) chlorfenvinphos. Table 2. Calibration curve for extracted standards of carbofuran and chlorfenvinphos. Figure 3. Comparative performance of 3 extraction solvents used in the extraction of a 1 mg.L -1 standard mixture of the selected pesticides. 0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 Carbofuran Chlorfenvinphos A (counts) Chlorobenzene Carbon tetrachloride Tetrachloroethylene Chlorobenzene was the chosen extraction solvent Preliminary assays showed that acetonitrile was the best dispersive solvent Analyte Carbofuran Chlorfenvinphos Linearity Range (μg.L -1 ) 0.05 – 10 0.05 – 10 LOD a (μg.L -1 ) 0.01 0.01 1 μg.L -1 10 μg.L -1 1 μg.L -1 10 μg.L -1 Precision (% CV) b 14.5 7.9 28.1 6.5 % R c 69.5 74.3 74.2 80.2 A = 55194 C - 1269.7 R² = 0.9999 0 100000 200000 300000 400000 500000 600000 0 2 4 6 8 10 12 A (counts) C (μg/L) (A) A = 51689 C + 2488.5 R² = 0.998 0 100000 200000 300000 400000 500000 600000 0 2 4 6 8 10 12 A (counts) C (μg/L) (B) GC-MS: Varian 4000 GC-MS, equipped with an ion trap mass detector Column: DB-5MS (30 m x 0.25 mm i.d. x 0.25 μm film thickness column) Method 1 (same extraction procedure) LC-18 column showed the best results (Method 1) Quantification problems (by GC/MS) occurred due to the solvents used (methanol/water) Methods 2 and 3 (different extraction procedures) Analyte Carbofuran Chlorfenvinphos Extraction column LC-18 HR-P Oasis LC-18 HR-P Oasis Linearity Range (μg.L -1 ) 2 – 60 2 – 60 LOD estimated a (μg.L -1 ) 0.9 0.9 0.7 1.7 1.7 1.5 % R b 124 128 175 109 107 118 Table 1. Validation data for SPE (Methods 2 and 3). a Limit of detection; b %R – recovery percentage of 2 independent extractions. 0 200000 400000 600000 800000 1000000 1200000 Carbofuran Chlorfenvinphos A (counts) LC-18 HR-P Oasis HLB 0 10000 20000 30000 40000 50000 Carbofuran Chlorfenvinphos A (counts) LC-18 (method 2) HR-P (method 2) Oasis HLB (method 3)
Transcript of C l O - SecurEau · SPE method using LC-18 column yielded better results regarding recovery...
Raquel Sousa, José Luís Moreira, Luís Miguel Madeira, Arminda Alves*
LEPAE, Chemical Engineering Department, Faculty of Engineering, University of Porto
Rua Dr. Roberto Frias, 4200-465 Porto, Portugal*Corresponding author: Tel. +351 22 508 1883. E-mail: [email protected]
Pesticides are types of well-known environmental contaminants. The use of pesticides provides benefits for increasing agricultural production. However,
because of their highly persistent properties, their residues may appear in fruits and vegetables and can be distributed in aqueous environments by leaching
and run-off from soil into ground and surface water.
Owing to the toxicity of pesticides, the European Directive 98/83/EC about the quality of water intended for human consumption establishes maximum
concentrations of 0.1 µg L-1 for individual pesticides and 0.5 µg L-1 for the sum of all pesticides.
Two pesticides from different families were selected in this work – carbofuran (carbamate) and chlorfenvinphos (organophosphorus), in order to act as
models to extend to other compounds of the same families.
The main objective was to develop an analytical methodology capable of detecting these pesticides at the legislated levels of concentration, but also suitable
to be applied to cases in which there is a limitation of sample volume (e.g. from studies of pesticides degradation by advanced oxidation processes).
Three types of SPE sorbents were tested, using different extraction methods accordingly to the sorbent nature:LC-18 (non-polar silica based); HR-P (polymeric polystyrene-divinylbenzene resin based); OASIS HLB (copolymeric reversed-phase)
Sorbent: LC-18; HR-P, Oasis HLB
Conditioning:5 mL methanol5 mL water
Sorption:15 mL water sample
Elution:5 mL methanol
Drying column
Evaporate to dryness with N2
Re-dissolve in 0.5 mL methanoland 1 mL water
Temperatures: Injector: 290 °C; MS Transfer Line: 250 °C
Temperature Program: 130 °C for 2 min, 20 °C min-1 to 275 °C,
and held for 1 min
Injection Volume: 1 µL (splitless injection)
Detection: SIM mode
Identification Ions: Carbofuran – 164, 149, 131
Chlorfenvinphos – 267, 269, 323
Extraction:
10 mL water sample
500 µL acetonitrile – dispersive solvent
100 µL chlorobenzene – extraction solvent
This study showed that SPE and DLLME are both suitable extraction methods for the pesticides studied.
In comparison, DLLME is more simple and requires lower sample and solvent volumes. SPE method using LC-18 column yielded better results regarding recovery percentage, but LODs were higher than DLLME for similar sample volume.
DLLME showed lower detection limits (0.01 µg.L-1), simplicity and proved more suitable if sample volume is a limitation. However SPE cannot be excluded as a suitable analytical method even for extremely low concentrations, but in that case
higher sample volume (up to 1 L) has to be used.
a S/N=3; b CV – coefficient of variation from 3 independent extractions;c % R – recovery percentage of 3 independent extractions.
Sorbent : LC-18; HR-P
Conditioning:5 mL methanol5 mL water
Sorption:15 mL water sample
Elution:5 mL methanol
Drying column
Evaporate to dryness with N2
Re-dissolve in 1 mL ethyl acetate
Sorbent : Oasis HLB
Conditioning:5 mL ethyl acetate5 mL methanol5 mL water
Sorption:15 mL water sample
Elution:2x4 mL ethyl acetate
Drying column
Evaporate to dryness with N2
Re-dissolve in 1 mL ethyl acetate
Carbofuran (CBF)Carbamate Pesticide
O
O
HN
O
Chlorfenvinphos (CVFP)Organophosphorus Pesticide
Cl
Cl
O
Cl P
O
O
O
Figure 1. Comparative performance of 3 different sorbents used toextract a 1 mg.L-1 standard mixture, using Method 1.
Figure 2. Comparative performance of 3 different sorbents used to extract a10 µg.L-1 standard mixture, using Methods 2 and 3.
Lower LOD would be achievable using larger sample volume
Figure 4. Calibration curve for extracted standards of (A) carbofuran, (B) chlorfenvinphos.
Table 2. Calibration curve for extracted standards of carbofuran and chlorfenvinphos.
Figure 3. Comparative performance of 3 extractionsolvents used in the extraction of a 1 mg.L-1 standardmixture of the selected pesticides.
0
1000000
2000000
3000000
4000000
5000000
6000000
7000000
CarbofuranChlorfenvinphos
A (c
ou
nts
)
Chlorobenzene
Carbon tetrachloride
Tetrachloroethylene
Chlorobenzene was the chosen extraction
solvent
Preliminary assays showed that acetonitrile
was the best dispersive solvent
Analyte Carbofuran Chlorfenvinphos
Linearity Range (μg.L-1) 0.05 – 10 0.05 – 10
LOD a (μg.L-1) 0.01 0.01
1 µg.L-1 10 µg.L-1 1 µg.L-1 10 µg.L-1
Precision (% CV) b 14.5 7.9 28.1 6.5
% R c 69.5 74.3 74.2 80.2
A = 55194 C - 1269.7R² = 0.9999
0
100000
200000
300000
400000
500000
600000
0 2 4 6 8 10 12
A (c
ou
nts
)
C (µg/L)
(A)
A = 51689 C + 2488.5R² = 0.998
0
100000
200000
300000
400000
500000
600000
0 2 4 6 8 10 12
A (c
ou
nts
)
C (µg/L)
(B)
GC-MS: Varian 4000 GC-MS,
equipped with an ion trap mass
detector
Column: DB-5MS (30 m x 0.25 mm
i.d. x 0.25 μm film thickness
column)
Method 1 (same extraction procedure)
LC-18 column showed the best results
(Method 1)
Quantification problems (by GC/MS)
occurred due to the solvents used
(methanol/water)
Methods 2 and 3 (different extraction procedures)
Analyte Carbofuran Chlorfenvinphos
Extraction column LC-18 HR-P Oasis LC-18 HR-P Oasis
Linearity Range (μg.L-1) 2 – 60 2 – 60
LOD estimated a (μg.L-1) 0.9 0.9 0.7 1.7 1.7 1.5
% R b 124 128 175 109 107 118
Table 1. Validation data for SPE (Methods 2 and 3).
a Limit of detection; b % R – recovery percentage of 2 independent extractions.
0
200000
400000
600000
800000
1000000
1200000
CarbofuranChlorfenvinphos
A (c
ou
nts
)
LC-18
HR-P
Oasis HLB
0
10000
20000
30000
40000
50000
CarbofuranChlorfenvinphos
A (c
ou
nts
)
LC-18 (method 2)
HR-P (method 2)
Oasis HLB (method 3)
![Preconcentration of Silver using Solidification of ... · microextraction (DLLME), was recently introduced by Assadi and co-workers [2] based on the formation ... recovery of 1-undeconol](https://static.fdocuments.net/doc/165x107/5e783081d4987046df7acc2c/preconcentration-of-silver-using-solidification-of-microextraction-dllme.jpg)
