On-line extraction and determination of two herbicides: comparison between two modes of three-phase hollow fiber microextraction.

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Journal of Separation Science

On-line extraction and determination of two herbicides: Comparison between two

modes of three-phase hollow fiber microextraction Mohammad Tajikᵃ, Yadollah Yaminiᵃ*, Ali Esrafiliᵇ, Behnam Ebrahimpourᵃ

ᵃ Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P. O. Box: 14115-175, Tehran,

Iran

ᵇ Department of Environmental Health Engineering, School of Public Health,

Iran University of Medical Sciences, Tehran, Iran

Received: 01-Oct-2014; Revised: 19-Nov-2014; Accepted: 19-Nov-2014 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/jssc.201401075. This article is protected by copyright. All rights reserved.

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Abbreviations: BEN, bensulfuron-methyl; CCD, central composite design; DSPE, dispersive solid-phase extraction; HF-LLLME, hollow fiber liquid phase microextraction; LIN, linuron; Two different modes of three-phase hollow fiber liquid-phase microextraction were studied for the extraction of two herbicides, bensulfuron-methyl and linuron. In these two modes, the acceptor phases in the lumen of the hollow fiber were aqueous and organic solvents. The extraction and determination were performed using an automated hollow fiber microextraction instrument followed by high-performance liquid chromatography. For both three-phase hollow fiber liquid-phase microextraction modes, the effect of main parameters on the extraction efficiency were investigated and optimized by central composite design. Under optimal conditions, both modes showed good linearity and repeatability, but the threephase hollow fiber liquid-phase microextraction based on two immiscible organic solvents has better extraction efficiency and figures of merit. The calibration curves for three-phase hollow fiber liquid-phase microextraction with an organic acceptor phase were linear in the range of 0.3–200 and 0.1–150 μg/L and the limits of detection were 0.1 and 0.06 μg/L for bensulfuron-methyl and linuron, respectively. For the conventional three-phase hollow fiber liquid-phase microextraction, the calibration curves were linear in the range of 3.0–250 and 15–400 μg/L and LODs were 1.0 and 5.0 μg/L for bensulfuron-methyl and linuron, respectively. The real sample analysis was carried out by three-phase hollow fiber liquid phase microextraction based on two immiscible organic solvents because of its more favorable characteristics.

Keywords: Automated instruments; Herbicides; High-performance liquid chromatography ;Hollow fibers; Liquid-phase microextraction;

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1 Introduction Herbicides are important toxins used considerably in agriculture worldwide and can improve the yield by affecting the undesirable herbs and weeds. However, because of the solubility of these materials in water, they have long been considered as omnipresent environmental substances. Phenylureas and sulfonylureas are two types of powerful herbicides for crop protection [1-3]. Considering the extensive use of these herbicides and their high toxicity potential, determination of these materials in water resources and soil is of great importance in environmental analysis. Since the analytical instruments are not sensitive enough to determine the low levels of desired analytes, sample preparation techniques have been introduced in the recent decades [4]. Traditionally, LLE and SPE were applied for preconcentration of analytes. However, LLE has the limitation of being solvent consuming and not being environment friendly. SPE is basically a difficult method to run with its expensive sorbents and several time-consuming steps [5]. However, microextraction techniques are introduced to tackle these limitations. LPME and SPME are miniaturized models of LLE and SPE, which only use small amounts of liquid and solid extraction phases, respectively [6-9]. Several sample preparation techniques were applied for preconcentration and determination of phenylureas and sulfonylureas compounds; including Ionic-liquidfunctionalized magnetic particles solid-phase microextraction (SPE) [1], dispersive solidphase extraction (DSPE) followed by dispersive liquid–liquid microextraction (DLLLME) [10], and salting-out assisted liquid–liquid extraction [11, 12]. The analysis and detection of phenylureas and sulfonylureas compounds with GC is difficult because they usually have polar functional groups in their structure and a derivatization step is necessary before their analysis. This process also make the time of sample preparation longer [13, 14]. Therefore, LC is preferred as a separation and detection step. Hollow-fiber-based LPME is a novel


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microextraction technique introduced by Pedersen-Bjergaard et al. in 1999 [15]. They used a porous hollow fiber membrane containing an organic-supported liquid membrane (SLM) and aqueous acceptor phase in the pores and into the lumen of the hollow fiber, respectively. The extraction of desired analytes will occur by adjustment of pH of the donor and acceptor phases or using an appropriate carrier. In another alternative of hollow-fiber-based LPME, an organic acceptor phase is applied instead of an aqueous acceptor phase, which must be immiscible with the SLM solvent [16]. In the current study, two modes of three-phase hollow fiber (HF) LPME for the extraction and determination of linuron (LIN), a phenylurea herbicide, and bensulfuron-methyl (BEN), a sulfonylurea herbicide, were applied and the related results were compared. Fig.1 shows the structure of the analytes and their ionic and hydrophilic properties. The two modes of threephase HF-LPME were performed with an automated HF-LPME instrument, which was introduced by Esrafili et al., followed by HPLC–UV for quantitative analysis of the analytes [17].

2 Materials and methods 2.1 Standards and materials LIN and BEN were purchased from Sigma–Aldrich (Milwaukee, WI, USA). HPLC-grade acetonitrile was obtained from Daejung Chemicals and Metals (Siheung-city, South Korea). The Q3/2 Accurel polypropylene hollow fiber was bought from Membrana (Wuppertal, Germany) with the inner diameter of 600 μm, wall thickness of 200 μm, and the pore size of 0.2 μm. n-Dodecane, 1-octanol, and dihexyl ether of analytical grades were bought from Merck (Darmstadt, Germany). Sodium hydroxide, sodium perchlorate, and hydrochloric acid were of analytical grades and purchased from Merck (Darmstadt, Germany). Both of the analytes were dissolved in acetonitrile to prepare the individual stock solutions with concentration of 1000 mg/L. Mixed standard solution of the analytes were prepared with


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different concentrations by adding appropriate volumes of the stock solution into ultra-pure water. Water samples were collected from Abali (Tehran, Iran) and the soil was collected from an agriculture field in Damavand (Tehran, Iran) five days after spraying of the herbicides. All the water samples were diluted at a 1:1 with ultra-pure water to reduce the matrix effect. The soil sample was dried in the room temperature and then was passed through a 1 mm sieve. 2.2 Apparatus The microextraction procedure was performed via an automated hollow fiber microextraction instrument with a programmable design, which was introduced by Esrafili et al. [17]. The chromatographic instrument was a Varian 9012 (Mulgrave Victoria, Australia) with a Varian 9050 variable wavelength UV-vis detector. An ODS-3 column (250 × 4.0 mm, with 5 μm particle size) was prepared from MZ-Analysentechnik (Mainz, Germany) for the separation. Water was purified on an AquaMax ultra-pure water purification system from Younglin (Seoul, Korea). The microextraction instrument was successfully coupled with HPLC–UV instrument and the preconcentration and separation steps were carried out automatically. The mobile phase consists of NaClO4 (0.05 M) and acetonitrile (45:55) and elution of the analytes was performed under isocratic elution condition at the flow rate of 1 mL min-1. The injection volume was 20 μL and detection of the analytes was performed at the wavelength of 240 nm. 2.3 Automated HF-LLLME procedure The microextraction procedure was held in a sample vial containing 25 mL of the sample solution and all the microextraction steps carried out via an automated hollow fiber microextraction instrument followed by HPLC–UV, which was designed by Esrafili et al. [17]. This instrument has the ability to support all modes of the hollow fiber microextraction technique, containing two- or three-phase hollow fiber LPME. At the beginning of the experiment, the hollow fiber membrane was manually cut and located in the respective place.


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The appropriate vials containing required solvents were located in the position of solvents. Injection of the required solvents into the hollow fiber membrane was carried out by a syringe pump. After importing the mode and time of microextraction, the procedure started and the sample vial was stirred via a stirrer. After a given time, the acceptor phase was injected into the HPLC column automatically by substituting a six-port injection valve instead of the main injection valve of the HPLC instrument. As it is noted, the microextraction, separation, and analysis of the analytes were fast, simple, and automated with this instrument. The two modes of three-phase HF-LPME were performed and optimized with this automated instrument.

3 Results and discussion 3.1 Optimization of the procedure To optimize the effective parameters on the two modes of three-phase HF-LPME, the experimental design was used. Before this step, a set of investigations were carried out for the two modes of three-phase HF-LPME to shorten the optimization process by experimental design. To this end, the effect of hollow fiber length and stirring rate on the extraction efficiency of the analytes were investigated by one variable at a time method. The hollow fiber length must be long enough to contain appropriate volume of the acceptor phase according to the injection volume of the HPLC system. However, it must not be very large as it will lead to the dilution effect. Stirring rate is another initial parameter that can affect the extraction kinetics and efficiencies by increasing the mass transfer. By doing some experiments, hollow fiber length of 7 cm and stirring rate of 1000 rpm were selected for this goal. Among several statistical protocols for optimizing the analytical procedures, central composite design (CCD) has been widely used, as it is based on reducing the required experimental runs to reach the optimal conditions [18-20]. The two modes of three-phase HFThis article is protected by copyright. All rights reserved.

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LPME were optimized by orthogonal central composite design. It was carried out by the Design Expert Analysis software for Windows, version 7, which contains a collection of mathematical, statistical, and graphical information. For the three-phase HF-LPME based on two immiscible organic solvents, five parameters remained including the type of organic acceptor phase, extraction time, pH of the donor phase, composition of SLM, and salt addition. Based on our previous experiments, the organic acceptor phase could be methanol or acetonitrile. By carrying out several experiments, acetonitrile was chosen as the organic acceptor phase. The other four parameters were optimized by the CCD. A four-factor, fivelevel orthogonal CCD was chosen for this goal. Table 1 shows the actual variables and their corresponding coded variables for the two modes of three-phase HF-LPME, which were selected in the CCD. By this protocol, 27 experiments were introduced by the CCD for the three-phase HF-LPME based on immiscible organic solvent. The results of each experiment were entered to the software by converting the related responses to normalized peak area. The results obtained were evaluated by the analysis of variance (ANOVA) at 95% confidence level. To determine the effect of each factor, in the ANOVA table, a Fisher’s statistical test (F-test) was used. The following equation shows the normalized peak area obtained by the CCD: Sqrt (normalized peak area) = 3.50 + 0.090A – 0.83B + 0.61C + 0.087D – 0.057AB + 0.052AC – 0.13AD – 0.30BC – 0.076BD + 0.17CD – 0.076 A2 – 0.064 B2 – 0.52 C2 + 0.001992 D2 According to this equation and the respective coefficient of each parameter, the pH of the donor phase (B) has the most significant effect on the extraction efficiency. The flux of the analytes is increased when they are in the neutral forms. Thus, pH value must be in an appropriate level, at which the desired analytes are in the neutral forms. By increasing the pH of the donor phase, the analytes will give partial negative charges and the extraction


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efficiencies will decreased. The extraction time (C) is the next most important parameter. In the three-phase HF-LPME, the extraction time must be longer enough till the suitable amounts of the analytes pass through the SLM and enter in to the acceptor phase. Salt addition (A) is another parameter that has a positive effect on the extraction efficiencies, because of the salting out effect. The last parameter is the SLM composition. Considering the presence of polar functional groups on the analytes, the analytes can pass through n-dodecane (SLM) containing some polar additives [21]. This parameter was adjusted by dissolving trioctylphosphine oxide (TOPO) into the SLM. Due to the respective coefficient of this parameter, it has a positive effect on the extraction efficiency. Interactions and quadratic terms are also significant according to their coefficients in equation (1). Fig. 2 illustrates the relationship between the response variables for three-phase HF-LPME based on two immiscible organic solvents with a three-dimensional representation. To this end, 12% w/v, 4.00, 40 min, and 8.00% w/v were selected as the optimal conditions for the salt addition, pH of the donor phase, extraction time, and the composition of SLM, respectively. In the next step, the experimental parameters of conventional three-phase HF-LPME were investigated and optimized using the CCD. The effective parameters were pH of the donor and acceptor phases, extraction time, salt addition, and type of the SLM. Dihexyl ether and 1octanol could be selected as the SLM. According to results obtained from some preliminary experiments, dihexyl ether was selected as the SLM because of its more desirable behavior against 1-octanol. Among the parameters remained, pH of the donor phase has similar effect on the extraction efficiencies in both modes of three-phase HF-LPME. Considering this, the optimal value obtained for the donor pH in three-phase HF-LPME based on two immiscible organic solvents was selected as the optimal value in this mode, too. The other three parameters were investigated and optimized by the CCD. Altogether, 17 experiments were


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carried out by the automated HF-LPME instrument followed by HPLC–UV. The model was described for this three-phase HF-LPME mode by the following equation: Normalized peak area = 46.46 + 38.07A + 23.59B + 11.02C +18.00AB +8.67AC + 7.08BC + 2.19A2 – 9.23B2 – 5.89C2 (2) This equation shows that pH of the acceptor phase (A) has the largest effect on the extraction efficiencies according to its coefficient. For successful extraction of the analytes in this mode, they must be in the ionized form. Thus, by increasing the acceptor phase pH, the extraction efficiencies increased dramatically. The extraction time (B) has the second noticeable effect on the extraction efficiencies. As usual, in three-phase HF-LPME procedures, the extraction time must be high enough; so that the analytes pass through the SLM. The next parameter is the salt addition (C). As it is mentioned, the extraction efficiencies increased by increasing the salt concentration according to the salting-out effect. The optimal conditions for this three-phase HF-LPME mode are 13.00 for the pH of the acceptor phase, 40.00 min for the extraction time, and 15% w/v for the ionic strength. 3.2 Method validation To test the figures of merit of the two three-phase HF-LPME modes, the calibration curves of the analytes were plotted under the optimal conditions in ultra-pure water. The calculated figures of merit for the two analytes by applying two modes of three-phase HF-LPME are summarized in Table 2. The LODs were calculated based on the S/N of 3. The calibration curves were linear in the range of 3.0–400 μg/L for the conventional three-phase HF-LPME (r2 > 0.9909) and 0.1–250 μg/L for the three-phase HF-LPME based on two immiscible organic solvents (r2 > 0.9956). Inter-day and intra-day precision for the analytes in both modes of three-phase HF-LPME was calculated by five consecutive replicates and expressed as RSDs at the concentration of 25 μg/L. For the three-phase HF-LPME based on two immiscible organic solvents, the inter-day and intra-day precision was in the ranges of 3.74–


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4.21 and 3.61–4.11%, respectively. For the conventional three-phase HF-LPME, the inter-day and intra-day precision was in the ranges of 3.21–3.84 and 4.22–3.76%, respectively. The preconcentration factors (PFs) were calculated by the following equation: PF =

(3)

in this equation, Cacceptor, final is the final concentration of the analyte in the organic or aqueous acceptor phase and Cdonor, initial is the initial concentration of the analyte in the donor phase [21]. The PFs in the ranges of 98–128 and 629–653 were obtained for conventional and threephase HF-LPME based on two immiscible organic solvents respectively. The following equation was applied to calculate the extraction efficiency (EE%): EE% = PF ×

× 100 (4)

where Va is the acceptor phase volume and Vs is the sample solution volume [22]. EE values as much as 81.7 were obtained for HF-LPME based on two immiscible organic solvents. According to the results from Table 2, the figures of merit for the three-phase HF-LPME based on two immiscible organic solvents are considerably more desirable than the conventional three-phase HF-LPME and this mode was selected for analysis of real samples. In the conventional three-phase HF-LPME, the LOD for LIN was 5 µg/L, because this molecule is not considerably ionizable under the optimal pH value. Unlikely, in the threephase HF-LPME based on two immiscible organic solvents, the analyte must be neutralized to pass through the organic SLM. Under the optimal pH value, LIN is completely neutral and this is the main reason for the low value of the LOD for this analyte (0.06 µg/L) in the threephase HF-LPME based on two immiscible organic solvents.


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3.3 Analysis of real samples Analysis of real samples was performed by the three-phase HF-LPME based on two immiscible organic solvents. To evaluate the applicability and accuracy of this mode of threephase HF-LPME, different water samples and a sprayed soil sample were analyzed under the optimal conditions by the automated HF-LPME instrument followed by HPLC–UV system. The results obtained confirmed that all the water samples were free of the desired herbicides. For extraction of the herbicides from the soil sample, ultrasound-assisted extraction was performed [23]. This step was performed according to the following procedure: 2 g of the soil sample was weighed accurately and placed in a centrifuge tube. Two mL of methanol was added to the soil and sonicated for 5 min. After centrifugation at 3800 rpm for 3 min, the supernatant was filtered via a PTFE syringe filter (13 mm and 0.22 μm pore size) and transferred into the sample vial and the total volume was adjusted to 25 mL by ultra-pure water. The effect of the two mentioned parameters (volume of methanol and sonication time) on extraction procedure were investigated and optimized separately. The volume of methanol was changed in the range of 1.5, 2, 2.5, 3, and 3.5 mL and the sonication time was changed in the range of 1, 2, 3, 4, and 5 min. The results indicated that 2 mL of methanol was suitable for the ultrasound-assisted extraction of the herbicides. On the other hand further experiments showed the presence of 2 mL methanol in 25 mL of sample solution cannot considerably decrease the extraction efficiency of the analytes from aqueous solution. Also, 3 min was selected as the sonication time. The relative recovery (RR%) was calculated by the following equation: RR% =

× 100 (5)

where Cfound, Creal, and Cadded are concentration of the analyte after addition of an exact amount of the standard into the real sample, concentration of the analyte in the real sample, and concentration of the standard spiked into the real sample, respectively [22, 24]. The


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obtained relative recoveries (94.0–11.5%) indicate the major role of hollow fiber membrane to achieve excellent clean-up and accuracy in different matrices. Table 3 shows the performance of the three-phase HF-LPME based on two immiscible organic solvents in analysis of three water samples and a soil sample. Fig. 3 shows the chromatogram obtained after extraction of the analytes from a river water sample spiked with 10 and 25 μg/L of the two herbicides. Fig. 4 shows the chromatogram obtained for extraction of the herbicides from the soil sample before and after spiking 0.5 mg/kg of the analytes.

4 Conclusions In the present study, two different modes of three-phase HF-LPME were tested for preconcentration and determination of two herbicides via an automated HF-LPME instrument. The data represents the supreme power of the three-phase HF-LPME based on two immiscible organic solvents in comparison with the conventional three-phase HF-LPME using an aqueous acceptor phase. Along with the high sensitivity and accuracy of this mode, the applicability of using GC instrument as a separation and detection system is possible, because the acceptor phase in this mode is an organic solvent. In addition, because of using an automated HF-LPME instrument, the repeatability was acceptable according to the RSDs. At last, the main advantage of using membrane protected solvent microextraction techniques is their potential as a clean-up and sample preparation step in very complicated matrices.


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References [1] He, Z., Liu, D., Zhou, Z., Wang, P., J. Sep. Sci. 2013, 36, 3226–3233. [2] Asiabi, H., Yamini, Y., Moradi, M., J. Supercrit. Fluids 2013, 84, 20–28. [3] Carabias-Martínez, R., Rodríguez-Gonzalo, E., Herrero-Hernández, E., Díaz-García, M. E., J. Sep. Sci. 2005, 28, 453–461. [4] Wu, H.-F., Yen, J.-H., Chin, C.-C., Anal. Chem. 2006, 78, 1707–1712. [5] Kokosa, J. M., TrAC, Trends Anal. Chem. 2013, 43, 2–13. [6] Boyd-Boland, A. A., Chai, M., Luo, Y. Z., Zhang, Z., Yang, M.J.; Pawliszyn, J B.; Gorecki, T.Environ. Sci. Tech. 1994, 28, 569A-574A.

[7] Boyd-Boland, A. A., Pawliszyn, J. B., Anal. Chem. 1996, 68, 1521–1529. [8] Jeannot, M. A., Cantwell, F. F., Anal. Chem. 1996, 68, 2236–2240. [9] Jeannot, M. A., Cantwell, F. F., Anal. Chem. 1997, 69, 2935–2940. [10] Chou, T.-Y., Lin, S.-L., Fuh, M.-R., Talanta 2009, 80, 493–498. [11] Trujillo-Rodríguez, M. J., Rocío-Bautista, P., Pino, V., Afonso, A. M., TrAC Trends Anal. Chem. 2013, 51, 87–106. [12] Gure, A., Lara, F. J., Moreno-González, D., Megersa, N., del Olmo-Iruela, M., GarcíaCampaña, A. M., Talanta 2014, 127, 51–58. [13] Mughari, A. R., Vázquez, P. P., Galera, M. M., Anal. Chim. Acta 2007, 593, 157–163. [14] Berrada, H., Font, G., Moltó, J. C., J. Chromatogr. A 2000, 890, 303–312. [15] Pedersen-Bjergaard, S., Rasmussen, K. E., Anal. Chem. 1999, 71, 2650–2656. [16] Ghambarian, M., Yamini, Y., Esrafili, A., Yazdanfar, N., Moradi, M., J. Chromatogr. A 2010, 1217, 5652–5658. [17] Esrafili, A., Yamini, Y., Ghambarian, M., Ebrahimpour, B., J. Chromatogr. A 2012, 1262, 27–33.


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[18] Asadollahzadeh, M., Tavakoli, H., Torab-Mostaedi, M., Hosseini, G., Hemmati, A., Talanta 2014, 123, 25–31. [19] Ghambarian, M., Yamini, Y., Esrafili, A., J. Chromatogr. A 2012, 1222, 5–12. [20] Ara, K. M., Akhoondpouramiri, Z., Raofie, F., J. Chromatogr. B 2013, 931, 148–156. [21] Yamini, Y., Ghambarian, M., Esrafili, A., Microchim. Acta, 2012, 177, 271–294. [22] Seidi, S., Yamini, Y., Rezazadeh, M., Esrafili, A., J. Chromatogr. A 2012, 1243, 6–13. [23] Tahmasebi, E., Yamini, Y., Anal. Chim. Acta 2012, 756, 13–22. [24] Ebrahimpour, B., Yamini, Y., Esrafili, A., J. Sep. Sci. 2013, 36, 1493–1499


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Figure 1. The structures of the analytes and their ionic and hydrophilic properties.


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Figure 2. Three-dimensional representation of interactions between effective parameters in the three-phase HF-LPME based on two immiscible organic solvents.


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Figure 3. Chromatograms of non-spiked (a), 20 μg/L (b), and 50 μg/L (c) spiked river water.


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Figure 4.Chromatograms of non-spiked (a) and 0.50 mg/kg (c) spiked soil samples.


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Table 1. Actual variables and their corresponded coded variables for the two modes of threephase HF-LPME in the central composite design. Factor

Name

Levels -α

-1

0

+1

+α

A

Salt addition (w/v)

2.3

5.0

10.0

15.0

17.7

B

Donor pH

2.9

4.0

6.0

8.0

9.1

C

Extraction time (min)

2.5

20.0

30.0

40.0

45.5

D

SLM composition (w/v)

14.5

2.0

5.0

8.0

9.6

Actual variables and their corresponded coded variables for the conventional HF-LLLME A

Acceptor pH

8.3

9.0

11.0

13.0

14.0

B

Extraction time (min)

20.0

20.0

30.0

40.0

45.0

C

Salt addition (w/v)

2.5

2.5

8.75

15.0

18.0


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Table 2. Performance of the three-phase HF-LPME based on two immiscible organic solvents (Org) and the conventional three-phase HF-LPME with and aqueous acceptor phase (Aqua).

Org

Analytes

Linear range (μg/L)

LOD (μg/L)

r2

RSD%a (n = 5) PFb EEc (%)

BEN

0.30–200

0.1

0.9938

3.92

629

78.8

LIN

0.18–200

0.06

0.9956

3.94

653

81.7

BEN

3.0–250

1.0

0.9909

3.52

128

17.2

LIN

15–400

5.0

0.9926

3.14

98

12.4

Aqua

a

RSD

b

Preconcentration factor c Extraction efficiency


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Table 3. Analytical performance characteristics of the fully automated HF-LLLME based on two immiscible organic solvents. Samples Tap Water

Analyte

Cinitial

Cadded

Cfound

RSD% (n=3)

RR (%)

Bensulfuronmethyl

0 µg/L

10 µg/L

9.4 µg/L

3.8

94.0

25 µg/L

24.6 µg/L

2.9

98.4

10 µg/L

10.3 µg/L

3.6

103.0

25 µg/L

25.8 µg/L

4.1

103.2

10.0 µg/L

10.7 µg/L

3.3

107.3

25.0 µg/L

27.9 µg/L

3.6

111.5

10.0 µg/L

10.9 µg/L

3.6

109.3

25.0 µg/L

26.7 µg/L

3.9

106.7

10.0 µg/L

10.4 µg/L

4.0

104.2

25.0 µg/L

24.8 µg/L

3.8

99.3

10.0 µg/L

10.2 µg/L

3.9

102.3

25.0 µg/L

25.9 µg/L

3.2

103.9

Linuron

Mineral spring

River water

Sprayed soil

0 µg/L

Bensulfuronmethyl

0 µg/L

Linuron

0 µg/L

Bensulfuronmethyl

0 µg/L

Linuron

0 µg/L

Bensulfuronmethyl

0 mg/Kg

0.50 mg/Kg

0.48 mg/Kg

3.3

96.0

Linuron

0.44 mg/Kg

0.50 mg/Kg

0.96 mg/Kg

3.7

104.1


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