TY - JOUR
AU - Li, Jian
AB - Abstract Magnetic molecularly imprinted polymers (MMIPs) were prepared with isoprocarb as template molecule and applied to extraction of carbamates pesticides in different water samples. This method based on magnetic solid-phase extraction (SPE) avoided the time-consuming column-passing process of loading large volume samples in conventional SPE. In the study, only 0.1 g MMIPs could be used to obtain satisfactory recoveries, due to the high-surface area and excellent adsorption capacity of these nano-magnetic adsorbents. Owing to the excellent selectivity of MMIPs, in high-performance liquid chromatography–mass spectrometry analysis, the matrix effects of this technique were obviously lower than the conventional SPE method. Under the optimal conditions, the detection limits of carbamates were in the range of 2.7–11.7 ng L−1. The relative standard deviations of intra-day and inter-day were 2.5–7.4% and 3.6–8.4%, respectively. At all the spiked level, the recoveries of four analyzed carbamates in environmental water samples were in the range of 74.2–94.2%. The significant positive results were achieved in the proposed method for the determination of four carbamates in water samples from different lakes and rivers. In the three samples we tested, the carbaryl was found in the lake water obtained from Yitong River, and the content was 2.4 ng L−1. Introduction Carbamates has broad biological activity, good curative effect, selectivity, low bioaccumulation potentials and other characteristics, so they are widely used in agricultural fields as insecticides, herbicides, fungicides, sprout inhibitors, etc. (1, 2). Their massive use in the last years has led to the residues of these pesticides accumulation in the environment, thus contaminating the water streams. Carbamates are inhibitors to acetylcholinesterase, which leads to accumulation of acetylcholine (3, 4). For these reasons, they are on the priority list issued by the United States Environmental Protection Agency (USEPA) (5). Hence, monitoring and determination of trace levels of carbamates in aqueous environmental samples have received particular attention. Up to present, several analytical methods to quantitative carbamates have been reported, including gas chromatography (GC) (6), enzyme-linked immunosorbent assays (7), micellar electrokinetic chromatography (8), GC with tandem mass spectrometry (MS/MS) (2, 9), biosensor (10) and high-performance liquid chromatography (HPLC) with diverse detectors (11–16). Due to carbamates were prone to decompose into corresponding phenols and amines in the injection port or chromatographic column when directly analyzed by GC, the carbamates were commonly derivatized to be thermally stable compound before determined by GC or GC–MS/MS (2, 12, 17). Consequently, the HPLC–MS/MS can be used as the more convenient and highly selective method for identifying and quantifying carbamate residues in water samples. Due to the relatively low concentration of most carbamates and the inherent complexity of environmental samples, pre-concentration and purification steps were usually one of the most crucial steps in the analytical procedure for complex samples. Currently, liquid–liquid extraction (LLE) and solid-phase extraction (SPE) are the most commonly used sample preparation techniques. However, LLE is a technology that takes a long time and requires a large amount of toxic organic solvents. Although SPE requires fewer amounts of organic solvent, SPE still has some obvious problems, including relatively expensive and complicated operation. As a promising sample pre-treatment technique, magnetic solid-phase extraction has received much attention because of its environment friendliness, rapid separation process, excellent adsorption efficiency and easily automated assay (18). Currently, the exploitation of various magnetic polymers for adsorption has been widely concerned. Therefore, various types of magnetic materials, such as magnetic polystyrene nanoparticles (19), magnetic strong cation-exchange resin (20), magnetic one-dimensional polyaniline (21), magnetic polypyrrole nanoparticles (22), magnetic poly (diethyl vinylphosphonate-co-ethylene glycol dimethacrylate) (23) and so on (24–28), have been prepared and applied. However, poor selectivity is the common drawback present in all these materials. Hence, magnetic molecularly imprinted polymers (MMIPs) have attracted increasing attention because of their superior selectivity, high adsorption capacity and reusability (29–33). Nowadays, many MMIPs have been developed, including magnetic surface-imprinting polymers (34), hydrophilic magnetic molecularly imprinted (35), quantum dots-doped MMIP (36) and magnetic multi-walled carbon nanotubes molecularly imprinted polymers (37). However, some problems such as complex preparation process and multi-step modification were presented and their applications were limited to some extent. Inspired by the above idea, herein, a new MMIPs has been synthesized in one step by one-pot synthesis based on the suspension polymerization, using iron oxide particles as magnetic cores, isoprocarb as template molecule, methacrylate (MAA) as functional monomer and ethylene glycol dimethacrylate (EGDMA) as cross linker. The schematic diagram of the preparation of MMIPs and the detection procedure are shown in Figure 1. Finally, the obtained MMIPs have been evaluated and applied for the extraction of carbamates from environmental water samples. Figure 1 Open in new tabDownload slide Schematic diagram of the preparation of MMIPs and their rapid detection of carbamate pesticides in environmental water samples. Figure 1 Open in new tabDownload slide Schematic diagram of the preparation of MMIPs and their rapid detection of carbamate pesticides in environmental water samples. Experimental Chemicals and materials The standards (purity >98%) of metolcarb, carbaryl, diuron and isoprocarb were obtained from the Dr Ehrenstorfer (Augsburg, Germany). Their chemical structures are shown in Figure 2. Chromatographic grade of acetonitrile (ACN) was obtained from Fisher (Pittsburgh, PA, USA). EGDMA, MAA, iron (II) chloride tetrahydrate (FeCl2·4H2O), iron (III) chloride hexahydrate (FeCl3·6H2O), oleic acid, polyvinylpyrrolidone (PVP) and azobisisbutyronitrile (AIBN) were obtained from Guangfu (Tianjin, China). Analytical grade of methanol, ethanol, acetic acid, sodium hydroxide (NaOH), hydrochloric acid (HCl) and trifluoroacetate acid (TFA), ACN were purchased from Beijing Chemical (Beijing, China), and toluene (analytical reagent ≥99.5%) used in this study was purchased from Guoyao Chemical Reagent Co. (Shanghai, China). The Milli-Q water was obtained from a Millipore purification system (Billerica, MA, USA) operating at a resistivity of 18.2 MΩ cm−1. Figure 2 Open in new tabDownload slide Chemical structures and homologues of the analytes. Figure 2 Open in new tabDownload slide Chemical structures and homologues of the analytes. Individual carbamate stock standard solutions (500 μg mL−1) were prepared in methanol and stored at −18°C. By diluting individual stock solutions with methanol, a mixed stock solution (20.0 μg mL−1) of four carbamates was prepared. The mixed solution should be stored in dark glass bottles at 4°C and replaced every 2 weeks. The working standard solutions were prepared daily by diluting the mix solution with deionized water. The lake water sample was collected from Nanhu (Changchun, China) and the river water sample was obtained from Yitong River (Changchun, China) and Songhua River (Changchun, China). All samples were collected randomly, filtrated and stored at 4°C. By adding a certain amount of cabamates standard solution to a fixed volume of the water samples, the spiked water samples were prepared. Before extraction, the pH of the water samples was adjusted to about 7.0 with 1.0 mol L−1 NaOH or 1.0 mol L−1 HCl. Preparation of the oleic acid-coated magnetite First, the Fe3O4 nanoparticles were prepared by a modified co-precipitation method. A complete precipitation of Fe3O4 was achieved by co-precipitating mixture solution containing Fe3+ and Fe2+ (a molar ratio of Fe2+ to Fe3+ is 1:2) in NaOH aqueous solution under inert environment (38). Then, oleic acid was coated on the Fe3O4 magnetite, thereby obtaining a hydrophobic shell that makes the Fe3O4 magnetite more thoroughly mixed with MAA and EGDMA. Fe3O4 magnetite (1.0 g) and oleic acid (2.0 mL) were added into a 100.0 mL beaker successively, and stirred thoroughly until magnetites were completely in contact with oleic acid. Hereafter, the magnetites of the grafted oleic acid were repeatedly washed with ethanol to remove the unreacted oleic acid. Preparation of MMIPs The MMIPs were prepared as follows: the isoprocarb (1.0 mmol) was dissolved in 10 mL toluene, and then MAA (4.0 mmol) was added into. The mixture was ultrasound for 10 min for preparation of pre-assembly solution. Then, the pre-assembly solution and EGDMA (20.0 mmol) were added into the mixture of Fe3O4 and oleic acid. This mixture was stirred for 30 min to prepare a pre-polymerization solution. The PVP (0.4 g) used as dispersant was dissolved into 100 mL of methanol in a three-necked flask. The pre-polymerization solution and 0.1 g of AIBN were added into the three-necked flask, separately. The mixture was stirred at 300 rpm and purged with nitrogen gas for 24 h while the temperature was maintained at 60°C. After the complete polymerization, the polymers were separated and washed with methanol and acetic acid (8:2, v/v) solution by soxhlet extraction until the template molecule could not be detected by liquid chromatography (LC)–MS. The polymers were washed with water several times, and then dried at 60°C and stored in a sealed brown flask. The preparation and processing of magnetic non-imprinted polymers (MNIPs) were the same as MMIPs, except that the template molecule isoprocarb was not added. The MMIPs and MNIPs were not ground or classified by size and can be used directly for extraction. Characterizations of the MMIPs The characterization of MMIPs was achieved by scanning electron microscopy (SEM; S-3400 N, Hitachi, Japan) and Fourier transform infrared spectrometer (FT-IR 360, Nicolet, Madison, WI, USA). The magnetic properties of the prepared Fe3O4 magnetite and MMIPs were prepared by vibrating sample magnetometry (JDM-13, Jilin University, Changchun, China). Binding experiment of the MMIPs The MMIPs (20 mg) or MNIPs (20 mg) were added to the aqueous solutions of isoprocarb (2 mL) at various concentrations (0.1–2.0 mmol L−1), respectively. The solution was incubated at room temperature for 24 h, and then the suspension was separated and analyzed by an Agilent 1100 HPLC system (Palo Alto, CA, USA) equipped with a XTerra MS C18 (250 mm × 4.6 mm i.d., 5 μm, Waters, Milford, MA, USA) and a ultraviolet detector (set at 205 nm). The eluent was ACN solution (40%, v/v) at the flow rate of 1.0 mL min−1. The column temperature was kept at 30°C and the injection volume was 20 μL. The isoprocarb standard solution would not be decomposed within 24 h at room temperature. The amount of isoprocarb not bound to the polymers was obtained. By subtracting the free concentration from the initial concentration of isoprocarb, the volume of isoprocarb combined with the polymers was obtained. The selectivity of the MMIPs The selectivity of the prepared MMIPs was assessed with template molecule (isoprocarb), the structural analogues (metolcarb, propoxur, carbofuran, diuron, carbaryl) and the reference compounds (phenthoate, enrofloxacin, sulfadiazine). A total of 20.0 mg of adsorbents (MMIPs or MNIPs) was added to the centrifuge tube, containing 2.0 mL of each standard solution with a concentration of 0.1 mmol L−1. After the mixture was shaken vigorously at 25°C for 24 h, the supernatant was separated and analyzed by HPLC. Extraction procedure The 100 mg MMIPs were conditioned with 3.0 mL methanol and 3.0 mL water in sequence. Then, the activated MMIPs were mixed with 500 mL water sample in a big beaker and the mixture was stirred for 15 min. And the adsorbents were readily separated from the solution by the action of an external magnetic field. After discarding the supernatant solution, 2 mL 20% methanol aqueous solution was used to wash the polymers with adsorbed carbamates. The target analytes adsorbed on the MMIPs were desorbed by 4 × 1.0 mL ACN solution containing 5% acetic acid with the aid of ultrasonic (60 s), and then the eluate was combined and dealt with a nitrogen drying step at 45°C. Finally, the residue was redissolved with 1.0 mL of mobile phase and used for further LC–MS/MS analysis. Conventional SPE method The conventional SPE procedure for the extraction of carbamates from water samples was implemented on the basis of the method described by Amelin et al. (39). Briefly, filtered water samples (500 mL) were acidified to pH 2 with a 1 M HCl solution. The Oasis® HLB 1 cc/30 mg cartridge was activated and regulated with 5 mL of methanol and 5 mL of water by passing them at a speed of 5 mL min−1. The sample of water was passed through the cartridge at a rate of 5 mL min−1, and then washed with 1 mL of water. After that the cartridge was eluted with 1 mL of methanol at a flow rate of 0.5 mL min−1. The eluate was evaporated to dryness under nitrogen gas at 40°C. The residue was reconstituted with 1.0 mL of 50% methanol aqueous solution and used for subsequent LC–MS/MS analysis. LC–MS/MS analysis The separation of carbamates was carried out on an Aglient 1100 HPLC system (Palo Alto, CA, USA) equipped with a XTerra MS C18 (250 mm × 4.6 mm i.d., 5 μm, Waters, Milford, MA, USA). The eluent was ACN–water (40:60, v/v) and the flow rate was 1.0 mL min−1. The eluate was split and introduced into the mass spectrometer (MS) detector at a flow rate of 0.2 mL min−1, and 20 μL was the total injection volume. The column temperature was kept at 30°C. The carbamates were detected on a Q-Trap mass spectrometer (Applied Biosystems/MDS Sciex, Concord, Canada) equipped with an electrospray ionization (ESI) source. MS data was utilizing multiple reaction monitoring mode. The setting of ESI–MS/MS was as follows: ionization mode, positive ion atmospheric pressure ionization; curtain gas, N2 (33 psi); collision gas, N2 (medium); gas 1, N2 (55 psi); gas 2, N2 (50 psi). The ion spray voltage was set to 4,500 V and the source temperature was 400°C. The precursor ion, product ion and corresponding declustering potential, entrance potential, collision energy, collision cell entrance potential and collision cell exit potential are set out in Table I. The Applied Biosystems Analyst software (version 1.4.2) was used for data processing. Table I Precursor Ion, Product Ion and Corresponding DP, EP, CEP, CE and CXP for the Carbamates Analytes . Precursor ion (m/z) . Product ion (m/z) . DP (V) . CE (eV) . EP (V) . CEP (V) . CXP (V) . RT (min) . Metolcarb 166.2 91.2 109.2a 40 40 25 23 7 7 20 20 4 4 6.22 Carbaryl 202.2 127.1 145.1a 45 45 40 25 9 8 20 20 5 5 9.19 Diuron 235.1 72.1a 160.1 45 45 30 40 9 8 20 20 4 5 10.44 Isoprocarb 194.2 77.2 95.2a 45 45 40 25 8 8 20 20 4 4 11.96 Analytes . Precursor ion (m/z) . Product ion (m/z) . DP (V) . CE (eV) . EP (V) . CEP (V) . CXP (V) . RT (min) . Metolcarb 166.2 91.2 109.2a 40 40 25 23 7 7 20 20 4 4 6.22 Carbaryl 202.2 127.1 145.1a 45 45 40 25 9 8 20 20 5 5 9.19 Diuron 235.1 72.1a 160.1 45 45 30 40 9 8 20 20 4 5 10.44 Isoprocarb 194.2 77.2 95.2a 45 45 40 25 8 8 20 20 4 4 11.96 CE, collision energy; CEP, collision cell entrance potential; CXP, collision cell exit potential; DP, declustering potential; EP, entrance potential. aThe product ion used for quantification. Open in new tab Table I Precursor Ion, Product Ion and Corresponding DP, EP, CEP, CE and CXP for the Carbamates Analytes . Precursor ion (m/z) . Product ion (m/z) . DP (V) . CE (eV) . EP (V) . CEP (V) . CXP (V) . RT (min) . Metolcarb 166.2 91.2 109.2a 40 40 25 23 7 7 20 20 4 4 6.22 Carbaryl 202.2 127.1 145.1a 45 45 40 25 9 8 20 20 5 5 9.19 Diuron 235.1 72.1a 160.1 45 45 30 40 9 8 20 20 4 5 10.44 Isoprocarb 194.2 77.2 95.2a 45 45 40 25 8 8 20 20 4 4 11.96 Analytes . Precursor ion (m/z) . Product ion (m/z) . DP (V) . CE (eV) . EP (V) . CEP (V) . CXP (V) . RT (min) . Metolcarb 166.2 91.2 109.2a 40 40 25 23 7 7 20 20 4 4 6.22 Carbaryl 202.2 127.1 145.1a 45 45 40 25 9 8 20 20 5 5 9.19 Diuron 235.1 72.1a 160.1 45 45 30 40 9 8 20 20 4 5 10.44 Isoprocarb 194.2 77.2 95.2a 45 45 40 25 8 8 20 20 4 4 11.96 CE, collision energy; CEP, collision cell entrance potential; CXP, collision cell exit potential; DP, declustering potential; EP, entrance potential. aThe product ion used for quantification. Open in new tab Results and Discussion Characterization of MMIPs The SEM image of the MMIPs is shown in Figure 3a, indicating that the polymers presented a loose and porous cross-linked state, and the diameter was between 5–25 μm. It is well known that the porous structure could not only enhance the adsorption capacity of polymers, but also improve the mass transfer rate of released and recombined analytes. The elemental analysis of the MMIPs (Figure 3b) showed the atomic ratio of Fe and C atoms was 58:39 by energy dispersive X-ray spectroscopy in the SEM, which suggests the Fe3O4 was filled into the polymers successfully. Figure 3 Open in new tabDownload slide Characterization of MMIPs, the SEM image (a) and elemental analysis (b) of the MMIPs; the magnetization curves of Fe3O4 magnetite (c) and MMIPs (d); the FT-IR spectrum of MMIPs (e); the evaluation of the MMIPs selectivity (f). Figure 3 Open in new tabDownload slide Characterization of MMIPs, the SEM image (a) and elemental analysis (b) of the MMIPs; the magnetization curves of Fe3O4 magnetite (c) and MMIPs (d); the FT-IR spectrum of MMIPs (e); the evaluation of the MMIPs selectivity (f). The magnetization curves showed the superparamagnetic property of Fe3O4 magnetite (Figure 3c) and MMIPs (Figure 3d). The magnetic saturation values were 58.5 and 14.7 emu g−1 for Fe3O4 magnetite and MMIPs, respectively. Owing to the superparamagnetic, the MMIPs could be rapidly isolated from the sample solution in a short time by placing a strong magnet in the separation step. The FT-IR spectrum of MMIPs is shown in Figure 3e. We can observe the typical bands such as O–H stretching at ~3,415 cm−1 and C=O stretching at ~1,733 and ~1,618 cm−1, which indicates the existence of carboxylic groups in the polymers. The peaks at ~482 and ~ 621 cm−1 are assigned to the stretch vibration mode and torsional vibration mode of Fe–O bond at the tetrahedral and the octahedral sites. Compared with the reference (40), these two infrared peaks in the prepared MMIPs were shifted to higher wave numbers, which may be caused by the effect of oleic acid, indicating that Fe3O4 had been successfully encapsulated into the polymers. The selectivity of the MMIPs As can be seen from Figure 3f, the amounts of isoprocarb and the structural analogues combined with the MMIPs were higher than the amount bound to the MNIPs. The results indicated that the MMIPs provided high selectivity for isoprocarb and its structural analogues. However, comparing MMIPs and MNIPs with respect to the adsorption capacity of phenthoate, enrofloxacin and sulfadiazine, it could be seen that there was no significant difference. Binding study The recognition ability of the imprinted magnetic nanoparticles toward the template isoprocarb was surveyed. From Figure 4a it can be concluded that, in equilibrium, the binding amount of isoprocarb with the MMIPs and MNIPs increased with the increase of the initial concentration of isoprocarb. At the same time, at all concentration ranges, the MMIPs had much higher recognition ability than the MNIPs. Figure 4 Open in new tabDownload slide Binding isotherms (a) and Scatchard plot analysis of the binding of isoprocarb to the MMIPs (b) and MNIPs (c). Figure 4 Open in new tabDownload slide Binding isotherms (a) and Scatchard plot analysis of the binding of isoprocarb to the MMIPs (b) and MNIPs (c). The Scatchard equation was used to further process the saturation binding data to estimate the binding characteristics of MMIP. The Scatchard equation was as follows: |$\frac{Q}{C_e}=\frac{Q_{\mathrm{max}}-Q}{K_d}$| where Q is the amount of isoprocarb bound to the MMIPs at equilibrium, Ce is the free isoprocarb concentration after adsorption equilibrium, Kd is the dissociation constant and the Qmax is the apparent saturated adsorption capacity. The values of Kd and the Qmax can be calculated from the slope and intercept of the linear line drawn with Q/Ce relative to Q. As can be seen from Figure 4b, the Scatchard plot of MMIPs was not a single linear curve and consisted of two linear parts with different slopes. The linear regression equation on the left part of the curve was Q/[ISO] = −14.055Q + 1.265. The Kd and Qmax of the dried polymer were calculated to be 71.2 μmol L−1 and 90.0 μmol g−1, respectively. The linear regression equation on the right part of the curve was Q/[ISO] = −1.286Q + 0.280. The Kd and Qmax of the dried polymer were calculated to be 777.6 μmol L−1 and 218.0 μmol g−1, respectively. The binding of isoprocarb to the MNIPs was also analyzed by Scatchard method (Figure 4c). It showed homogeneous binding sites with Kd and Qmax values of 1075 μmol L−1 and 72.7 μmol g−1, respectively. Reusability of the sorbent To make the sorbent economically competitive in food and environmental analysis, the potential reusability and stability of the MMIPs should be investigated. A series of adsorption/desorption experiments were carried out to evaluate the reusability of the prepared sorbent. After adsorption, the sorbent was treated with methanol:acetic acid (8:2, v/v) solution until the analytes could not be inspected by LC–MS/MS. After each desorption step, the acid-treated sorbent was regenerated using doubly distilled water followed by drying at 60°C. The result observed that the sorbent could be reused up to at least 15 times and had no significant effect on the recoveries for carbamates. Optimization of SPE conditions To obtain the best extraction recoveries, the influences of the MMIPs amount, extraction time, washing and desorption conditions and maximum extraction volume on the recoveries were investigated. Among them, when one parameter was changed, other factors need to be selected in their optimal values. All the optimization experiments were performed in triplicate by analyzing spiked river water samples (200 ng L−1). The amount of the MMIPs In Figure 5a, different magnetic adsorbents contents (30–150 mg) were evaluated to extract carbamates from spiked water samples (500 mL). The recoveries increased from 40.0–42.4% to 85.7–90.6% with the increasing of the polymers amount from 30 to 90 mg, further increasing the amount of the polymers did not significantly improve the recoveries. Based on the above results, 100 mg was selected as the final adsorption dose used in the following studies. Figure 5 Open in new tabDownload slide The amount of the MMIPs (a), stirring and magnetic separating time (b) and the eluting solvent volume (c). Figure 5 Open in new tabDownload slide The amount of the MMIPs (a), stirring and magnetic separating time (b) and the eluting solvent volume (c). Stirring and magnetic separating time In the process of SPE, it can be seen that the extraction time had a significant impact on the adsorption of target analytes. The effect of stirring and magnetic separation time on its adsorption effect is shown in Figure 5b. When the stirring time increased from 5 to 15 min, the recoveries of carbamates increased with the extraction time. After that, between 15 and 25 min, there was no significant difference in the recoveries. According to the obtained results, 15 min was chosen as the stirring time. In addition, due to its unique magnetic response, the separation of the adsorbent from the solution can be accelerated by the adscititious Nd–Fe–B magnet, and the separation of the adsorbent can be realized in only about 20 s. Therefore, compared with the traditional column-passing SPE, the analysis time is greatly reduced. Washing condition The wash step after extraction cannot be ignored, which can not only remove the interfering compounds from the sample matrix, but also not desorb the target analyte. In the experiment, 2.0 mL and 2× 2.0 mL water, methanol aqueous solution (10, 20 and 30%) and ACN aqueous solution (10, 20 and 30%) were evaluated as washing solvent. The satisfying recoveries of the carbamates (75.2–90.3%) were obtained using 2× 2.0 mL 20% methanol aqueous solution as the washing solution. Elution condition The highest recoveries of carbamates from a series of eluates, such as methanol, methanol–acetic acid (95:5, v/v), methanol–acetic acid (90:10, v/v), ACN–acetic acid (95:5, v/v) and ACN–TFA (95:5, v/v) were evaluated. The best recoveries (54.2–90.3%) were obtained when methanol–acetic acid (95:5, v/v) was used as eluent for detection. The eluting solvent volume of 1.0, 2 × 1.0, 3 × 1.0, 4 × 1.0, 5 × 1.0 and 6 × 1.0 mL was studied, and the results are shown in Figure 5c. The recoveries increased from 47.6–53.1% to 84.2–90.4% with the increase of the volume of eluting solution from 1.0 to 4.0 mL (1.0 mL each time, elution four times), further increase of the eluting solvent volume did not significantly improve the recoveries. Therefore, in the following study, 4 × 1.0 mL methanol–acetic acid (95:5, v/v) solution was used as the eluent. Furthermore, the MMIPs captured carbamates were ultrasonically treated for 40 s in each elution process to achieve complete elution. Maximum extraction volume To increase the sensitivity of this method, the maximum extraction volume was checked by pre-concentrating water samples of different volumes (200–1,000 mL) labeled with carbamate at a concentration of 200 ng L−1. Satisfactory recoveries of carbamates (73.3–90.3%) were acquired up to 500 mL. However, when the samples volume was >500 mL, the recoveries of the analyte decreased and insufficient recoveries occurred. The same results were obtained by Sun et al. (41) and Zhao et al. (34). Therefore, when 100 mg MMIP was used for extraction, 500 mL was considered as the maximum enrichment volume of the water samples. By enriching 500 mL of water samples, then, the 500 mL water samples were concentrated to 1.0 mL. So, the concentration factor of our method was 500. Table II Validation of the Method Analytes . Linear least square equations . Linearity ranges (ng L−1) . Determination coefficients (r2) . LOQ (ng L−1) . LOD (ng L−1) . Metolcarb Y = 414.0 + 61.1X 20–2,000 0.997 19.6 5.9 Carbaryl Y = 448.934 + 52.9X 20–2,000 0.996 18.6 5.6 Diuron Y = 81.9 + 20.0X 40–2,000 0.997 38.8 11.7 Isoprocarb Y = 2,910.1 + 142.5X 10–2,000 0.997 9.0 2.7 Analytes . Linear least square equations . Linearity ranges (ng L−1) . Determination coefficients (r2) . LOQ (ng L−1) . LOD (ng L−1) . Metolcarb Y = 414.0 + 61.1X 20–2,000 0.997 19.6 5.9 Carbaryl Y = 448.934 + 52.9X 20–2,000 0.996 18.6 5.6 Diuron Y = 81.9 + 20.0X 40–2,000 0.997 38.8 11.7 Isoprocarb Y = 2,910.1 + 142.5X 10–2,000 0.997 9.0 2.7 Y, the peak area of transitions used for quantification; X, the analyte concentration (ng L−1). Open in new tab Table II Validation of the Method Analytes . Linear least square equations . Linearity ranges (ng L−1) . Determination coefficients (r2) . LOQ (ng L−1) . LOD (ng L−1) . Metolcarb Y = 414.0 + 61.1X 20–2,000 0.997 19.6 5.9 Carbaryl Y = 448.934 + 52.9X 20–2,000 0.996 18.6 5.6 Diuron Y = 81.9 + 20.0X 40–2,000 0.997 38.8 11.7 Isoprocarb Y = 2,910.1 + 142.5X 10–2,000 0.997 9.0 2.7 Analytes . Linear least square equations . Linearity ranges (ng L−1) . Determination coefficients (r2) . LOQ (ng L−1) . LOD (ng L−1) . Metolcarb Y = 414.0 + 61.1X 20–2,000 0.997 19.6 5.9 Carbaryl Y = 448.934 + 52.9X 20–2,000 0.996 18.6 5.6 Diuron Y = 81.9 + 20.0X 40–2,000 0.997 38.8 11.7 Isoprocarb Y = 2,910.1 + 142.5X 10–2,000 0.997 9.0 2.7 Y, the peak area of transitions used for quantification; X, the analyte concentration (ng L−1). Open in new tab Figure 6 Open in new tabDownload slide LC–MS/MS extracted ion chromatograms obtained by the analysis of spiked river water sample (40 ng L−1). Figure 6 Open in new tabDownload slide LC–MS/MS extracted ion chromatograms obtained by the analysis of spiked river water sample (40 ng L−1). Evaluation of the method performance Matrix effect As we all know, the matrix effect (signal suppression or enhancement) is a noteworthy problem, owing to it greatly affects the accuracy of LC–MS/MS. The co-extractives of complex samples may seriously influence the analyte signals or enhance background noise, which may damage the quantification of the analytes at trace levels. Large differences in matrix effect were also observed between sample preparation techniques. The experimental results showed that the matrix effect could be decreased dramatically when the selective extraction method was used (42). In order to evaluate the matrix effects of this proposed method, the calibration curves of solvent and blank environmental water extract in the concentration range of 40–1000 ng L−1 were compared. The matrix effects were evaluated by the following equation: Matrix effect (%) =|$\Big[\frac{Am+s- Am}{A0}-1\Big]\times 100$| where Am + s is the peak area of the analyte in the spiked sample, Am is the peak area of the analyte in the unspiked sample and A0 is the peak area of the analyte in highly pure water. In this equation, positive values mean signal enhancement due to different sample matrices, whereas negative values mean signal suppression. In the results, we could see that the matrix of the proposed method had signal enhancement for the carbaryl, and the signals of metolcarb, diuron and isoprocarb were suppressed in the sample matrix. The values of the enhancement of carbaryl were 1.1%, and the values of the suppression of metolcarb, diuron and isoprocarb were 13.9, 1.3 and 3.0%, respectively. However, the signal suppression of the SPE method based on commercial Oasis HLB cartridges is in the range of 8.9–28.3%. The matrix suppression effects of carbamates in water samples obtained by direct injection were about 5.0–42.0% (43). From here we can see that, the matrix effects of the proposed method not only lower than the matrix effect of the direct injection method but also the matrix effects of the conventional SPE method. At the same time, no marked differences of the matrix effects were discovered between different environmental water samples, which signified that the matrix effect between different water samples could be ignored. Linearity and limit of detection The calibration curves and the linearity range of this method researched by analyzing spiked water samples are listed in Table II. The determination coefficients (r2) of all the analytes ranging from 0.996 to 0.997 were obtained. Limit of detection (LOD) and limit of quantification (LOQ) are considered as the analyte minimum concentrations that can be identified and quantified by the method, respectively. The LOD and LOQ calculated according to the signal/noise ratio generated by the analyte concentration of 3:1 and 10:1 were ranging from 2.7 to 11.7 ng L−1 and from 9.0 to 38.8 ng L−1, respectively, which were lower than that given by the USEPA method (EPA method 531.1). The ion chromatograms of LC–MS/MS extracted by analyzing the spiked river water sample (40 ng L−1) are illustrated in Figure 6. Precision and recovery Precision was evaluated by measuring intra- and inter-day relative standard deviations (RSDs). The intra-day precision was determined by analyzing six times of spiked water samples in a day at three different fortified concentrations of 40, 100 and 200 ng L−1. And by analyzing spiked water samples at three different fortified concentrations of 40, 100 and 200 ng L−1, the inter-day precision was achieved within 6 days. The average intra-day and inter-day precisions expressed as %RSD are shown in Table III. The RSDs of intra- and inter-day tests ranging from 2.5 to 7.4% and from 3.6 to 8.4% were obtained. The recoveries of the four kinds of carbamates are in the range of 74.2–94.2% at all three strengthening levels. Table III The Intra- and Inter-day Precisions and Recoveries of the Assay (n = 6) Analytes . Intra-day precision . Inter-day precision . . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Metolcarb 82.1 6.2 84.4 4.2 90.8 3.9 78.4 4.9 87.0 7.7 87.4 5.0 Carbaryl 84.5 4.3 87.4 4.2 86.9 2.5 84.8 8.2 91.3 5.4 94.2 4.7 Diuron 83.2 7.4 92.8 4.0 87.4 4.4 81.0 7.0 84.2 8.2 93.0 3.6 Isoprocarb 80.2 5.9 83.0 5.2 82.7 6.4 74.2 8.4 82.9 6.4 88.1 4.0 Analytes . Intra-day precision . Inter-day precision . . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Metolcarb 82.1 6.2 84.4 4.2 90.8 3.9 78.4 4.9 87.0 7.7 87.4 5.0 Carbaryl 84.5 4.3 87.4 4.2 86.9 2.5 84.8 8.2 91.3 5.4 94.2 4.7 Diuron 83.2 7.4 92.8 4.0 87.4 4.4 81.0 7.0 84.2 8.2 93.0 3.6 Isoprocarb 80.2 5.9 83.0 5.2 82.7 6.4 74.2 8.4 82.9 6.4 88.1 4.0 Open in new tab Table III The Intra- and Inter-day Precisions and Recoveries of the Assay (n = 6) Analytes . Intra-day precision . Inter-day precision . . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Metolcarb 82.1 6.2 84.4 4.2 90.8 3.9 78.4 4.9 87.0 7.7 87.4 5.0 Carbaryl 84.5 4.3 87.4 4.2 86.9 2.5 84.8 8.2 91.3 5.4 94.2 4.7 Diuron 83.2 7.4 92.8 4.0 87.4 4.4 81.0 7.0 84.2 8.2 93.0 3.6 Isoprocarb 80.2 5.9 83.0 5.2 82.7 6.4 74.2 8.4 82.9 6.4 88.1 4.0 Analytes . Intra-day precision . Inter-day precision . . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . 40 ng L−1 . 100 ng L−1 . 200 ng L−1 . Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Recovery (%) RSD (%) Metolcarb 82.1 6.2 84.4 4.2 90.8 3.9 78.4 4.9 87.0 7.7 87.4 5.0 Carbaryl 84.5 4.3 87.4 4.2 86.9 2.5 84.8 8.2 91.3 5.4 94.2 4.7 Diuron 83.2 7.4 92.8 4.0 87.4 4.4 81.0 7.0 84.2 8.2 93.0 3.6 Isoprocarb 80.2 5.9 83.0 5.2 82.7 6.4 74.2 8.4 82.9 6.4 88.1 4.0 Open in new tab Table IV Comparison of Present Method with Reported Methods for the Detection of Carbamates in Water Samples Adsorben . Method . Linearity ranges (ng L−1) . LOD (ng L−1) . RSD (%) . Reference . μ-SPE with graphene-modified TiO2 nanotube arrays HPLC 5,000–150,000 2,260–2,880 1.8–8.3 (46) SBSE with ZnS–AC–NPs-coated stir bar HPLC 2,000–30,000,000 300–500 3.3–4.5 (47) Fused-core columns (C18) for on-line SPE Poly (EGDMA–MATrp) microbeads HPLC 10,000–800,000 950–2,850 2.15–2.52 (45) LDS–USAEME with on-column derivatization GC–MS 50–100,000 10–100 3.7–9.2 (17) Direct derivatization of xanthydrol in water GC–MS 200–20,000 2.0–9.0 — (48) SPME with TpPn–CMPS-coated fibers UPLC–MS/MS 5–100,000 0.6–17 1.1–8.1 (49) MSPE with MMIPs HPLC–MS/MS 10–2,000 2.7–11.7 2.5–8.4 This work Adsorben . Method . Linearity ranges (ng L−1) . LOD (ng L−1) . RSD (%) . Reference . μ-SPE with graphene-modified TiO2 nanotube arrays HPLC 5,000–150,000 2,260–2,880 1.8–8.3 (46) SBSE with ZnS–AC–NPs-coated stir bar HPLC 2,000–30,000,000 300–500 3.3–4.5 (47) Fused-core columns (C18) for on-line SPE Poly (EGDMA–MATrp) microbeads HPLC 10,000–800,000 950–2,850 2.15–2.52 (45) LDS–USAEME with on-column derivatization GC–MS 50–100,000 10–100 3.7–9.2 (17) Direct derivatization of xanthydrol in water GC–MS 200–20,000 2.0–9.0 — (48) SPME with TpPn–CMPS-coated fibers UPLC–MS/MS 5–100,000 0.6–17 1.1–8.1 (49) MSPE with MMIPs HPLC–MS/MS 10–2,000 2.7–11.7 2.5–8.4 This work Open in new tab Table IV Comparison of Present Method with Reported Methods for the Detection of Carbamates in Water Samples Adsorben . Method . Linearity ranges (ng L−1) . LOD (ng L−1) . RSD (%) . Reference . μ-SPE with graphene-modified TiO2 nanotube arrays HPLC 5,000–150,000 2,260–2,880 1.8–8.3 (46) SBSE with ZnS–AC–NPs-coated stir bar HPLC 2,000–30,000,000 300–500 3.3–4.5 (47) Fused-core columns (C18) for on-line SPE Poly (EGDMA–MATrp) microbeads HPLC 10,000–800,000 950–2,850 2.15–2.52 (45) LDS–USAEME with on-column derivatization GC–MS 50–100,000 10–100 3.7–9.2 (17) Direct derivatization of xanthydrol in water GC–MS 200–20,000 2.0–9.0 — (48) SPME with TpPn–CMPS-coated fibers UPLC–MS/MS 5–100,000 0.6–17 1.1–8.1 (49) MSPE with MMIPs HPLC–MS/MS 10–2,000 2.7–11.7 2.5–8.4 This work Adsorben . Method . Linearity ranges (ng L−1) . LOD (ng L−1) . RSD (%) . Reference . μ-SPE with graphene-modified TiO2 nanotube arrays HPLC 5,000–150,000 2,260–2,880 1.8–8.3 (46) SBSE with ZnS–AC–NPs-coated stir bar HPLC 2,000–30,000,000 300–500 3.3–4.5 (47) Fused-core columns (C18) for on-line SPE Poly (EGDMA–MATrp) microbeads HPLC 10,000–800,000 950–2,850 2.15–2.52 (45) LDS–USAEME with on-column derivatization GC–MS 50–100,000 10–100 3.7–9.2 (17) Direct derivatization of xanthydrol in water GC–MS 200–20,000 2.0–9.0 — (48) SPME with TpPn–CMPS-coated fibers UPLC–MS/MS 5–100,000 0.6–17 1.1–8.1 (49) MSPE with MMIPs HPLC–MS/MS 10–2,000 2.7–11.7 2.5–8.4 This work Open in new tab Comparison of methods The proposed method was compared with other reporting methods and the results are summarized in Table IV. A good linear range was obtained for carbamates by the proposed method and LODs was lower than the maximum allowable concentration (0.1 μg L−1) of each pesticide in drinking water specified in the European Union Directive (44). Hence, good extraction performance was presented in the proposed method. Besides, the LODs of the proposed method were lower than that of other methods, such as SPE–HPLC (45, 46), stirring bar–HPLC (47) and dispersive liquid–liquid microextraction–GC–MS (17, 48). The lower LODs confirmed the high sensitivity of the method. Compared with other detection methods (49), the extraction and clean-up procedures in the proposed method can be completed in a single step by using external magnetic field. Therefore, our method was an efficient and sensitive method for determination of carbamates in environmental water samples. Environmental water sample analysis In this study, three different types of water samples were collected and each sample was measured three times. The results were analyzed to confirm the applicability and feasibility of the method. Among them, carbamates were not detected in the lake water obtained from Nanhu Park and the river water obtained from Songhua River. Carbaryl was detected in the samples extracted from the water of the Yitong River, and the detected content was 32.4ng L−1. In order to further evaluate the accuracy of the method, the conventional SPE method was also used to analyze the real samples. Through comparison, we could know that there is no significant difference between the results obtained by the two methods. However, the proposed method has the advantages of simplifying the operation procedures, shortening the analysis time and reducing the matrix effect in comparison with the conventional SPE methods. This method shows enormous analytical potential in the treatment of complex samples. Table V Recoveries of Carbamates in Environmental Water Samples (%, mean ± SD, n = 3) Analytes . Added (ng L−1) . Nanhu Park . Yitong River . Songhua River . . . The proposed method . The traditional method . The proposed method . The traditional method . The proposed method . The traditional method . . . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Metolcarb 0 — — — — — — — — — — — — 40 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 34.0 ± 1.6 85.0 ± 4.0 24.0 ± 2.8 60.0 ± 7.0 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 Carbaryl 0 — — — — 32.4 ± 0.8 — 32.7 ± 1.1 — — — — — 40 33.2 ± 1.6 83.0 ± 4.0 33.6 ± 2.4 84.0 ± 6.0 66.8 ± 1.2 86.0 ± 3.0 66.7 ± 2.0 85.0 ± 5.0 35.6 ± 1.6 89.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 Diuron 0 — — — — — — — — — — — — 40 35.6 ± 2.0 89.0 ± 5.0 34.4 ± 3.2 86.0 ± 11.0 36.4 ± 1.6 91.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 36.4 ± 2.0 91.0 ± 5.0 34.4 ± 4.4 86.0 ± 11.0 Isoprocarb 0 — — — — — — — — — — — — 40 36.4 ± 1.6 91.0 ± 4.0 36.0 ± 2.8 90.0 ± 7.0 34.0 ± 1.2 85.0 ± 3.0 34.8 ± 2.4 87.0 ± 6.0 36.4 ± 2.0 91.0 ± 4.0 36.4 ± 2.8 91.0 ± 7.0 Analytes . Added (ng L−1) . Nanhu Park . Yitong River . Songhua River . . . The proposed method . The traditional method . The proposed method . The traditional method . The proposed method . The traditional method . . . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Metolcarb 0 — — — — — — — — — — — — 40 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 34.0 ± 1.6 85.0 ± 4.0 24.0 ± 2.8 60.0 ± 7.0 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 Carbaryl 0 — — — — 32.4 ± 0.8 — 32.7 ± 1.1 — — — — — 40 33.2 ± 1.6 83.0 ± 4.0 33.6 ± 2.4 84.0 ± 6.0 66.8 ± 1.2 86.0 ± 3.0 66.7 ± 2.0 85.0 ± 5.0 35.6 ± 1.6 89.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 Diuron 0 — — — — — — — — — — — — 40 35.6 ± 2.0 89.0 ± 5.0 34.4 ± 3.2 86.0 ± 11.0 36.4 ± 1.6 91.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 36.4 ± 2.0 91.0 ± 5.0 34.4 ± 4.4 86.0 ± 11.0 Isoprocarb 0 — — — — — — — — — — — — 40 36.4 ± 1.6 91.0 ± 4.0 36.0 ± 2.8 90.0 ± 7.0 34.0 ± 1.2 85.0 ± 3.0 34.8 ± 2.4 87.0 ± 6.0 36.4 ± 2.0 91.0 ± 4.0 36.4 ± 2.8 91.0 ± 7.0 Open in new tab Table V Recoveries of Carbamates in Environmental Water Samples (%, mean ± SD, n = 3) Analytes . Added (ng L−1) . Nanhu Park . Yitong River . Songhua River . . . The proposed method . The traditional method . The proposed method . The traditional method . The proposed method . The traditional method . . . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Metolcarb 0 — — — — — — — — — — — — 40 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 34.0 ± 1.6 85.0 ± 4.0 24.0 ± 2.8 60.0 ± 7.0 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 Carbaryl 0 — — — — 32.4 ± 0.8 — 32.7 ± 1.1 — — — — — 40 33.2 ± 1.6 83.0 ± 4.0 33.6 ± 2.4 84.0 ± 6.0 66.8 ± 1.2 86.0 ± 3.0 66.7 ± 2.0 85.0 ± 5.0 35.6 ± 1.6 89.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 Diuron 0 — — — — — — — — — — — — 40 35.6 ± 2.0 89.0 ± 5.0 34.4 ± 3.2 86.0 ± 11.0 36.4 ± 1.6 91.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 36.4 ± 2.0 91.0 ± 5.0 34.4 ± 4.4 86.0 ± 11.0 Isoprocarb 0 — — — — — — — — — — — — 40 36.4 ± 1.6 91.0 ± 4.0 36.0 ± 2.8 90.0 ± 7.0 34.0 ± 1.2 85.0 ± 3.0 34.8 ± 2.4 87.0 ± 6.0 36.4 ± 2.0 91.0 ± 4.0 36.4 ± 2.8 91.0 ± 7.0 Analytes . Added (ng L−1) . Nanhu Park . Yitong River . Songhua River . . . The proposed method . The traditional method . The proposed method . The traditional method . The proposed method . The traditional method . . . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Found (ng L−1) . Recovery (%) . Metolcarb 0 — — — — — — — — — — — — 40 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 34.0 ± 1.6 85.0 ± 4.0 24.0 ± 2.8 60.0 ± 7.0 34.4 ± 1.6 86.0 ± 4.0 25.2 ± 2.4 63.0 ± 6.0 Carbaryl 0 — — — — 32.4 ± 0.8 — 32.7 ± 1.1 — — — — — 40 33.2 ± 1.6 83.0 ± 4.0 33.6 ± 2.4 84.0 ± 6.0 66.8 ± 1.2 86.0 ± 3.0 66.7 ± 2.0 85.0 ± 5.0 35.6 ± 1.6 89.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 Diuron 0 — — — — — — — — — — — — 40 35.6 ± 2.0 89.0 ± 5.0 34.4 ± 3.2 86.0 ± 11.0 36.4 ± 1.6 91.0 ± 4.0 33.2 ± 2.4 83.0 ± 6.0 36.4 ± 2.0 91.0 ± 5.0 34.4 ± 4.4 86.0 ± 11.0 Isoprocarb 0 — — — — — — — — — — — — 40 36.4 ± 1.6 91.0 ± 4.0 36.0 ± 2.8 90.0 ± 7.0 34.0 ± 1.2 85.0 ± 3.0 34.8 ± 2.4 87.0 ± 6.0 36.4 ± 2.0 91.0 ± 4.0 36.4 ± 2.8 91.0 ± 7.0 Open in new tab The recoveries of carbamates were studied by adding carbamates to the water samples at a concentration of 40 ng L−1. Among them, four carbamates including metolcarb, carbaryl, diuron and isoprocarb were quantitatively analyzed, and the results are shown in Table V. At the spiked level, the recoveries of the four quantitatively analyzed carbamates in environmental water samples ranged from 83.0 ± 4.0% to 91.0 ± 5.0%. The results showed that the recoveries of the carbamates were satisfied. Thus, the proposed methodology was suitable for the determination of carbamates in water samples from different environments. After an exhaustive search of existing similar literature (50, 51) by comparison, we found that our method have the advantage of cheap equipment, mild experimental conditions and simple extraction steps. Conclusion In this study, magnetic MIPs were synthesized and successful application to the separation of carbamates pesticides from water samples, and then analyzed by LC–MS/MS. The polymers have strong magnetic responsiveness and could be reused 15 times without significant loss of the recoveries for the analytes. When using this method to extract a 500 mL water sample, the concentration factor of 500 was accomplished. 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TI - Fast Determination of Carbamates in Environmental Water Based on Magnetic Molecularly Imprinted Polymers as Adsorbent
JO - Journal of Chromatographic Science
DO - 10.1093/chromsci/bmab008
DA - 2021-03-03
UR - https://www.deepdyve.com/lp/oxford-university-press/fast-determination-of-carbamates-in-environmental-water-based-on-d4BOVg0n0F
SP - 1
EP - 1
VL - Advance Article
IS - 
DP - DeepDyve
ER -