Article pubs.acs.org/JAFC
Automated Multiplug Filtration Cleanup for Pesticide Residue Analyses in Kiwi Fruit (Actinidia chinensis) and Kiwi Juice by Gas Chromatography−Mass Spectrometry Yuhong Qin,† Jingru Zhang,† Yining He,† Yongtao Han,† Nan Zou,† Yanjie Li,† Ronghua Chen,§ Xuesheng Li,§ and Canping Pan*,† †
Beijing Advanced Innovation Center for Food Nutrition and Human Health, Department of Applied Chemistry, College of Science, China Agricultural University, Beijing 100193, China § Institute of Pesticide and Environmental Toxicology, Guangxi University, Nanning 530005, China ABSTRACT: To reduce labor-consuming manual operation workload in the cleanup steps, an automated multiplug filtration cleanup (m-PFC) method for QuEChERS (quick, easy, cheap, effective, rugged, and safe) extracts was developed. It could control the volume and speed of pulling and pushing cycles accurately. In this study, m-PFC was based on multiwalled carbon nanotubes (MWCNTs) mixed with primary−secondary amines (PSA) and anhydrous magnesium sulfate (MgSO4) in a packed column for analysis of pesticide residues followed by gas chromatography−mass spectrometry (GC-MS) detection. It was validated by analyzing 33 pesticides in kiwi fruit and kiwi juice matrices spiked at two concentration levels of 10 and 100 μg/kg. Salts, sorbents, m-PFC procedure, 4 mL of automated pulling and pushing volume, 6 mL/min automated pulling speed, and 8 mL/min pushing speed were optimized for each matrix. After optimization, spike recoveries were within 71−120% and 0.99 between concentration levels of 10 and 1000 μg/kg. The developed method was successfully applied to the determination of pesticide residues in market samples. KEYWORDS: m-PFC, automated, MWCNTs, kiwi fruit and kiwi juice, pesticide multiresidue analysis
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INTRODUCTION Kiwi fruit (Actinidia chinensis) or Chinese gooseberry (also known as kiwi) is the edible berry of a woody vine in the genus Actinidia.1,2 It can be considered a highly nutritious product containing a high level of vitamin C and possessing a strong antioxidant capacity due to a wide number of phytonutrients including carotenoids, lutein, phenolics, flavonoids, and chlorophyll.3,4 Because of the high nutrition content in kiwi fruit, it may be eaten raw, made into juices, used in baked goods, prepared with meat, or used as a garnish. Papers have been published reporting a regular kiwi fruit intake decreasing the risk of prostate cancer or cardiovascular diseases.5,6 The long-term selection process imposed to improve kiwi fruit productivity and quality has made kiwi fruit crops less resistant to diseases, pests, and adverse environmental conditions.7,8 To maintain a high kiwi fruit production yield, the use of pesticides is necessary. However, excessive pesticide use can pose a threat to human health and the environment.9,10 Maximum residue limits (MRLs) have been established for kiwi by various international organizations and countries (as well as for other cultivars)11 (http://www.mrldatabase.com). Therefore, pesticide residue determination in kiwi fruit and kiwi fruit products is a very demanding task in public health food safety and trade. Pesticide residue analysis is advancing rapidly, which is required by the market monitoring of various countries in domestic and international trade, risk assessment of dietary intakes, or environmental research and so on.12,13 The critical procedure of this technique is cleanup of sample extracts to © XXXX American Chemical Society
avoid interferences from complicated matrices. The most common extraction technique is solid-phase extraction (SPE).14 However, conventional SPE is time-consuming and not selective enough to develop a comprehensive method for multiresidue analysis. Recently, the QuEChERS method is the preferred method in pesticide multiresidue analysis by governments and research laboratories, especially in vegetables and fruits.15,16 It involves a miniaturized extraction with acetonitrile, a liquid−liquid partition by salting out with sodium chloride and magnesium sulfate, and a cleanup step, which is carried out by mixing the acetonitrile extract with loose sorbents before GC or LC injection. The cleanup step is based on reversed-dispersive solid phase extraction (r-DSPE) to adsorb the interference substances in the matrices, rather than the analytes. In most cases, primary−secondary amine (PSA) was used as the r-DSPE sorbent to remove the interference substances in the matrices such as fatty acid compounds, pigments, sterols, and other nonpolar interfering substances. MWCNTs are a carbon-based nanomaterial, which was first reported by Iijiama in 1991.17,18 In our previous study, MWCNTs were used as an alternative r-DSPE material in Special Issue: 52nd North American Chemical Residue Workshop Received: December 20, 2015 Revised: January 19, 2016 Accepted: January 25, 2016
A
DOI: 10.1021/acs.jafc.5b06027 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry Table 1. GC-MS Conditions for the Identification and Quantitation of the 33 Pesticides monitor ions, m/z (%, relative abundance) group
pesticide
retention time (min)
A A A A A A A B B B B C C C C C C C D D D D D D D D E E E E E E E E E E F F F F F F
phorate atrazine simazine propyzamide diazinon acetochlor vinclozolin malathion fenthion chlorpyrifos triadimefon chlorfenvinphos procymidone methidathion paclobutrazol flutriafol napropamide uniconazole oxyfluorfen RH-5849 triazophos propiconazole-1 propiconazole-2 tebuconazole diclofop-methyl epoxiconazole bifenthrin fenpropathrin d-phenothrin-1 d-phenothrin-2 pyriproxyfen λ-cyhalothrin-1 λ-cyhalothrin-2 λ-cyhalothrin-3 λ-cyhalothrin-4 pyridaben cypermethrin-1 cypermethrin-2 cypermethrin-3 cypermethrin-4 deltamethrin-1 deltamethrin-2
10.5 11.64 12.47 12.48 13.04 14.99 15.13 17.2 17.5 17.64 17.81 19.88 20.25 20.61 20.89 21.57 21.89 22.58 23.51 25.34 25.54 26.02 27 26.49 26.71 27.06 27.86 27.85 28.55 30.22 28.77 29.25 28.52 28.99 29.3 30.19 31.39 31.77 32.28 33.95 33.28 32.97
quantitation 121 200 173 173 179 146 198 173 278 197 208 267 96 145 236 123 128 234 252 105 161 259 259 125 253 192 181 181 183 183 136 181 181 181 181 147 163 163 163 163 253 253
multiresidue analysis with the QuEChERS method.19,20 A more practical way to perform the r-DSPE method is to use an multiplug filtration cleanup (m-PFC) column packed with sorbents to adsorb the sample matrix compounds in the acetonitrile extraction. The m-PFC process can be done in tens of seconds with no additional concentration or solvent exchange steps.21 In the work presented here, an automated m-PFC cleanup method for kiwi fruit product extracts was developed, followed by GC-MS analysis. The objective of this study was to develop and validate an efficient and labor-saving automated cleanup method for the detection and quantification of multiresidues in kiwi fruit products. Thirty-three pesticides with different Log P values (2.1−7) and different chemical structural catalogs were selected to validate the method. These pesticides were registered for use on kiwi fruit in China (http://www.
(100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100) (100)
identification 1 260 215 186 255 304 162 212 125 169 199 210 323 283 85 125 164 72 70 361 240 162 261 261 250 281 183 165 125 123 123 78 197 197 197 197 309 181 181 181 181 181 181
(74) (61) (89) (45) (62) (92) (51) (58) (40) (98) (36) (150) (46) (18) (73) (55) (53) (26) (38) (66) (72) (70) (72) (71) (73) (34) (29) (69) (65) (61) (38) (45) (48) (46) (46) (9) (68) (57) (62) (51) (100) (83)
identification 2 231 58 201 240 137 223 185 93 153 314 181 269 285 302 167 219 271 236 172 77 172 263 263 70 342 138 166 265 184 184 96 141 141 141 141 364 165 165 165 165 209 209
(52) (40) (112) (31) (60) (81) (66) (79) (34) (89) (38) (94) (32) (27) (46) (50) (42) (38) (59) (38) (39) (20) (23) (79) (67) (35) (30) (49) (21) (14) (15) (52) (58) (63) (50) (12) (77) (85) (76) (70) (269) (300)
chinapesticide.gov.cn). Moreover, several international organizations and countries had established the MRLs for the 33 pesticides on kiwi fruit products22 (http://www.mrldatabase. com).
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MATERIALS AND METHODS
Standards, Reagents, and Materials. Analytical standards of the pesticides in the study were provided by the Institute of the Control of Agrochemicals, Ministry of Agriculture, Peoples’ Republic of China. The purities of the standard pesticides were from 95 to 99%. Stock solutions of 10 mg/L for mixture pesticides were prepared in acetonitrile and stored at −20 °C. The working solutions were prepared daily. HPLC grade acetonitrile was obtained from Fisher Chemicals (Fair Lawn, NJ, USA). Analytical reagent grade anhydrous sodium chloride (NaCl) and magnesium sulfate (MgSO4) were obtained from Sinopharm Chemical Reagent (Beijing, China). PSA was provided by Tianjin Agela Co. Ltd. Co. (China). MWCNTs with B
DOI: 10.1021/acs.jafc.5b06027 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry
Figure 1. Automated m-PFC equipment: (a) schematic diagram of equipment; (b) components of automated m-PFC equipment.
Figure 2. GC-SIM chromatograms for (a) typical blank kiwi fruit sample and (b) blank kiwi fruit spiked with 100 μg/kg of the target analytes. average external diameters of 10−20 nm were provided by Tianjin Agela Co. Ltd. Co. m-PFC tips were packed with 5 mg of MWCNTs, 25 mg of PSA, and 150 mg of MgSO4 (for kiwi fruit samples) or with 25 mg of PSA and 150 mg of MgSO4 (for kiwi juice samples) with assistance from Tianjin Bonna-Agela Technologies. Dispensable 10 mL syringes were supplied by Zhiyu Technologies (Shanghai, China). Automated m-PFC equipment (AGELA FFP001) was developed by Tianjin Bonna-Agela Technologies. Centrifugation was performed in two different instruments: an Anke TDL-40B centrifuge equipped with a bucket rotor (8 × 100 mL) (Shanghai, China) and a Sigma 3K15 microcentrifuge equipped with an angular rotor (24 × 2.0 mL) (BMH Instruments Co., Ltd., China); a TARGIN VX-III multitube vortexer was used for preparing the samples. GC-MS Analytical Conditions. Determinations were performed using a Thermo Scientific TSQ Quantum XLS quadrupole mass spectrometer interfaced to a Thermo Trace 1300 GC. An Agilent Technologies capillary column HP-5 MS analytical column (30 m × 250 μm × 0.25 μm film thickness) was used for GC separation, with helium (99.9999%) as carrier gas at a constant flow rate of 1.0 mL/ min. The column temperature was initially at 80 °C (held 1 min), increased at 30 °C/min to 150 °C, then at 3 °C/min to 210 °C, and finally at 10 °C/min to 290 °C, and held for 9 min. The temperature of the injector port was 280 °C, and a volume of 1 μL was injected in splitless mode. The total running time was 40.33 min. Mass spectrum signal was not acquired before 8 min or after 35 min. The mass spectrometer was operated in electron ionization mode (70 eV). The setting of collision gas flow of Ar at 1 mTorr was used. The temperature of electron impact ion source and AUX transfer line was 250 and 290 °C, respectively. A full autotune of the mass spectrometer using the default parameters of the instrument was
performed before each sequence. Thermo Xcalibur software was used for instrument control and data acquisition/processing. The electron multiplier voltage was set at 1635 V when selected ion monitoring was performed, and solvent delay was set to 8.0 min. For the final MS acquisition method, three ion transitions were monitored for each analyte. To obtain better separation efficiency, the 33 compounds were divided into 6 groups: groups A−F consisted of two to seven compounds, respectively. Table 1 summarizes the MS conditions for the individual analytes and their typical retention times in different groups. Sample Preparation. Organic kiwi fruit and kiwi juice samples were taken from local supermarkets of Beijing. Kiwi fruit (pulp) samples were homogenized with a blender for 2 min at room temperature. The samples were stored at −20 °C until analysis. Blank samples were used for validation studies and matrix-matched standard calibrations. Samples for recovery studies were spiked with a known amount of the fortification standard and left for 30 min before the extraction was begun. In this study, a modified QuEChERS method was used, an amount (10.0 ± 0.1 g) of kiwi fruit or kiwi juice samples was weighed into a 50 mL centrifuge tube, and 10 mL of acetonitrile was added. The resulting solution was shaken by the vortex for 1 min. One gram of NaCl and 4 g of anhydrous MgSO4 were added for kiwi fruit extracts. The tube was cooled in an ice−water bath immediately. Three grams of NaCl was added for kiwi juice extracts. The centrifuge tube was shaken vigorously for an additional 1 min. The extract was then centrifuged at 3800 rpm for 5 min. The supernatant was used for further m-PFC procedures. Automated m-PFC Procedures. After a 10 mL syringe was connected to an m-PFC tip, the unit was fixed on the automated mC
DOI: 10.1021/acs.jafc.5b06027 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry
Figure 3. Optimization of m-PFC sorbents: pesticide recoveries at a spike level of 100 μg/kg on (a) a kiwi fruit sample and (b) a kiwi juice sample. PFC equipment. At the same time, 2 mL microcentrifuge tubes were placed on the frame (Figure 1a). Optimum method parameters were listed as follows: 4 mL m-PFC volumes; pulling and pushing cycles were three times; automated pulling speed was 6 mL/min; automated pushing speed was 8 mL/min. As shown in Figure 1b, the piston was driven by automated m-PFC equipment to let extracts through the sorbents. When the method was finished, the syringe needle was removed and the acetonitrile layer was filtered through a 0.22 μm filter membrane. At the same time, the extract was placed into an LC vial for the chromatographic analysis. Method Performances. The validation was carried out for kiwi fruit and kiwi juice. Linearity, limit of quantification (LOQ), limit of detection (LOD), accuracy and precision, and matrix effects were established to determine the accuracy and precision of the method following the SANCO guideline on analytical quality control and validation procedures.23 Linearity was evaluated by assessing the signal responses of the target analytes from matrix-matched calibration solutions prepared by spiking blank extracts at five concentration levels, from 10 to 1000 μg/kg. The LODs were determined as the concentration of analyte giving a signal-to-noise ratio (S/N) of 3 for the target ion (the less intense transition); LOQs were determined as the concentration of analytes giving a signal-to-noise ratio (S/N) of 10 for the target ion (the less intense transition).24,25 The recovery and reproducibility experiments were carried out in five replicates at two fortification levels (10 and 100 μg/kg). For the assessment of matrix effects, standard calibration curves prepared in kiwi fruit and kiwi juice extracts between 10 and 500 μg/kg were compared. Furthermore, matrix-matched calibration curves were used for quantitative determinations to minimize any ion suppression/enhancement effects, a consequence of the presence of sample matrix components.26
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Figure 4. Optimization of pushing speed on the kiwi fruit and kiwi juice samples spiked with the pesticides at 100 μg/kg.
Figure 5. Comparison of color at different pushing speeds on the kiwi fruit sample spiked with the pesticides at 100 μg/kg: (a) 4 mL/min; (b) 6 mL/min; (c) 8 mL/min.
RESULTS AND DISCUSSION
Optimization of GC-MS Conditions. The analysis was determined by GC-MS-SIM using one quantitation and at least two identification ions, in addition to their relative abundances, the retention time, and the assistance of the National Institute of Standards and Technology’s (NIST) pesticide library.27 All pairs of the transitions were used for confirmation analysis, which can meet the EU Decision,28 and the most sensitive transitions were selected for quantification. Table 1 summarizes the chosen ions along with the relative abundances and the typical retention time. According to their polarities and volatilities to increase the sensitivity, the 33 compounds were divided into 6 groups: groups A, C, and D consisted of seven compounds; group B consisted of four compounds; group E consisted of six compounds; and group F consisted of 2 compounds. Therefore, the 33 pesticides can be detected in one GC-MS analysis. The condition of gas chromatography for the two
groups was the same, but the MS conditions were different due to the various pesticides. Figure 2 shows the GC-SIM chromatography for a blank and a kiwi fruit sample spiked at 100 μg/kg of the target analytes. Optimization of Sample Preparation Procedure. Optimization of Salts. In the original QuEChERS study, the amounts of anhydrous MgSO4 and NaCl were 4 and 1 g per 10 mL of the sample, respectively.29 However, MgSO4 dissipated heat after adsorbing water, which may have influenced pesticides’ recoveries.30 Thus, the different amounts of MgSO4 (0, 4 g) and NaCl (1, 2, and 3 g) were performed and analyzed in triplicate at one calibration point (100 μg/kg) in this study. The results showed that when 4 g of MgSO4 and 1 g of NaCl were used as salts, the recoveries of kiwi fruit were higher than that of NaCl (1, 2, and 3 g). When 3 g of anhydrous NaCl was used, the recoveries of analytes in kiwi D
DOI: 10.1021/acs.jafc.5b06027 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry
Table 2. Matrix Effect, R2, LODs (S/N Ratio of 3), and LOQs (S/N Ratio of 10) for 33 Pesticides in Kiwi Fruit and Kiwi Juice kiwi fruit
a
kiwi juice
pesticide
MEa
R2
LOD (μg/kg)
LOQ (μg/kg)
MEa
R2
LOD (μg/kg)
LOQ (μg/kg)
phorate atrazine simazine propyzamide diazinon acetochlor vinclozolin malathion fenthion chlorpyrifos triadimefon chlorfenvinphos procymidone methidathion paclobutrazol flutriafol napropamide uniconazole oxyfluorfen RH-5849 triazophos propiconazole-1 propiconazole-2 tebuconazole diclofop-methyl epoxiconazole bifenthrin fenpropathrin d-phenothrin-1 d-phenothrin-2 pyriproxyfen λ-cyhalothrin-1 λ-cyhalothrin-2 λ-cyhalothrin-3 λ-cyhalothrin-4 pyridaben cypermethrin-1 cypermethrin-2 cypermethrin-3 cypermethrin-4 deltamethrin-1 deltamethrin-2
1.03 1.06 0.79 1.08 0.93 0.86 0.90 0.74 0.94 0.66 1.10 0.54 1.02 0.84 0.93 0.88 0.64 0.99 1.02 1.10 0.92 0.88 0.96 0.79 0.90 0.67 0.89 0.91 0.69 0.84 0.70 0.72 0.68 0.75 0.56 0.83 0.77 0.73 0.64 0.72 0.84 0.67
0.995 0.997 0.999 0.998 0.997 0.996 0.999 0.999 0.998 1.000 0.998 0.998 0.999 0.999 0.998 0.997 0.998 0.998 0.998 0.999 1.000 0.999 0.996 0.999 0.997 0.998 0.998 0.999 0.998 0.996 0.999 0.998 0.996 0.996 0.997 0.999 0.998 0.998 0.996 0.997 0.998 0.998
3 4 3 3 3 3 4 1 1 3 3 4 3 3 3 3 3 3 4 2 3 3 3 3 3 3 3 3 3 3 3 3 3 4 3 2 3 3 4 3 3 3
10 10 10 10 10 10 10 3 3 10 10 10 10 10 10 10 10 10 10 5 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 5 10 10 10 10 10 10
0.93 0.71 0.85 0.96 0.89 0.51 0.89 0.62 0.76 0.82 0.71 0.53 1.05 0.74 1.08 0.76 0.99 0.63 1.00 1.03 0.83 0.90 0.78 0.81 0.90 0.79 0.90 0.93 0.61 0.78 0.74 0.66 0.72 0.79 0.52 0.82 0.65 0.72 0.64 0.70 0.82 0.64
0.998 0.998 0.999 0.998 0.997 0.998 0.999 0.999 0.998 0.999 1.000 0.998 0.999 0.997 0.998 0.997 0.998 0.996 0.998 0.999 1.000 0.999 0.998 0.999 0.997 0.998 0.998 0.997 0.998 0.999 0.999 0.998 0.996 0.998 0.997 0.999 0.998 0.998 0.999 0.997 0.998 0.998
1 3 3 3 3 3 3 3 1 3 4 3 3 3 3 3 3 3 3 2 1 3 3 3 3 3 3 3 3 3 3 3 3 4 3 2 3 1 3 3 3 3
3 10 10 10 10 10 10 10 3 10 10 10 10 10 10 10 10 10 10 5 3 10 10 10 10 10 10 10 10 10 10 10 10 10 10 5 10 3 10 10 10 10
Matrix effect.
kg (n = 3). The spiked extracts were purified using different amounts of the tested sorbent with constant amounts of the rest of sorbents. The impurities in kiwi fruit were mostly organic acids and sugars;32 different amounts of MWCNTs (i.e., 3, 5, and 10 mg) mixed with 25 mg of PSA and 150 mg of MgSO4 were used. In the original QuEChERS method, 25 mg of PSA was used and the amounts of PSA for fruits were tested in our previous work.33 As the amount of MWCNTs increased, the recoveries of most analytes were at the acceptable range (from 70 to 120%).34 However, when the amounts of MWCNTs were increased to 10 mg, the recoveries of some analytes were decreased to 31−57% (Figure 3a). Consequently, 5 mg (1 mL extract) of MWCNTs mixed with 25 mg of PSA and 150 mg of MgSO4 was used as sorbents packed in m-PFC tips.
juice samples were notably higher in comparison with the other salt combinations. Optimization of m-PFC Sorbents. After analytes were extracted by 10 mL of acetonitrile followed by partitioning of the analyte molecules in organic solvent in the presences of the salting-out agent, the acetonitrile phase was further cleaned up and dried by mixing with the sorbents and anhydrous MgSO4. The cleanup step was designed to retain matrix components and allow the analytes of interest to dissolve in the acetonitrile phase. During the process of sample preparation, it was reported that different amounts of dispersive sorbents had significant influences on the purification and recoveries of the pesticide extracts.31 To evaluate cleanup efficiency, pesticide recoveries were studied with two matrices spiked with the pesticides at 100 μg/ E
DOI: 10.1021/acs.jafc.5b06027 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry
Recoveries were accepted with one or two times of pulling and pushing, but the cleanup performance was not as good as with three times, and there were more chromatography interferences when pulling and pushing one or two times. In addition, four or more times were also tested, but there was no significant difference in the cleanup performance between three and four times. As a result, three times of pulling and pushing was chosen as the optimized m-PFC procedure. Optimization of Automated m-PFC Volume. Any volume of automated m-PFC method influenced the cleanup efficiency. In this study, the automated m-PFC volume was investigated in four levels of 2, 4, 6, and 8 mL on the equipment. When the volume was 0.99. As recommended in the European Union (EU) guidelines, in our study validation experiments were calculated using matrix-matched calibration standards for the more accurate results, excluding any influence produced by matrix effects.36 As LODs and LOQs are matrix dependent, the proposed method was tested for extraction and determination of multiresidues in different kinds of matrices (kiwi fruit and kiwi juice); LODs and LOQs were obtained on the basis of signal-to-noise ratios of S/N = 3 and S/N = 10, respectively. As shown in Table 2, LODs were found to be 1−4 μg/kg, whereas LOQs were in the range of 3−10 μg/kg. Comparison of the results with those obtained using a cleanup step with SPE and
Table 3. Average Recoveries and RSDs at Two Spiked Levels in Kiwi Fruit and Kiwi Juice av recovery, % (RSD, %) (n = 5) kiwi fruit pesticide phorate atrazine simazine propyzamide diazinon acetochlor vinclozolin malathion fenthion chlorpyrifos triadimefon chlorfenvinphos procymidone methidathion paclobutrazol flutriafol napropamide uniconazole oxyfluorfen RH-5849 triazophos propiconazole-1 propiconazole-2 tebuconazole diclofop-methyl epoxiconazole bifenthrin fenpropathrin d-phenothrin-1 d-phenothrin-2 pyriproxyfen λ-cyhalothrin-1 λ-cyhalothrin-2 λ-cyhalothrin-3 λ-cyhalothrin-4 pyridaben cypermethrin-1 cypermethrin-2 cypermethrin-3 cypermethrin-4 deltamethrin-1 deltamethrin-2
kiwi juice
10 μg/kg
100 μg/kg
10 μg/kg
100 μg/kg
101 105 89 89 91 114 102 86 102 87 101 81 111 103 104 83 71 84 96 98 84 98 114 109 110 95 92 105 110 113 107 86 112 98 87 79 84 74 75 76 108 98
112 84 82 100 99 108 86 101 102 106 106 114 97 106 101 96 114 110 100 84 112 101 87 107 108 106 98 84 108 100 102 92 99 100 76 100 87 73 101 77 105 102
78 84 90 88 76 114 88 107 104 87 104 107 92 91 105 76 104 84 103 90 101 85 76 120 97 93 109 106 110 113 92 116 117 88 75 89 108 112 75 103 112 104
110 100 86 100 74 108 104 99 102 106 106 93 82 115 101 95 117 120 99 88 110 101 108 114 98 102 113 83 108 112 102 87 107 81 87 113 109 107 101 94 102 98
(7) (14) (16) (8) (9) (11) (9) (16) (9) (6) (5) (9) (14) (7) (16) (8) (10) (5) (6) (7) (8) (5) (11) (6) (12) (8) (20) (8) (6) (20) (14) (8) (13) (15) (6) (6) (12) (9) (8) (9) (13) (7)
(6) (15) (9) (13) (7) (8) (14) (10) (5) (5) (6) (8) (20) (5) (15) (13) (9) (14) (8) (9) (4) (2) (12) (13) (7) (10) (7) (13) (8) (7) (9) (6) (2) (5) (3) (5) (5) (12) (8) (14) (8) (15)
(7) (2) (6) (8) (7) (11) (13) (12) (8) (5) (7) (4) (5) (3) (8) (12) (4) (9) (6) (9) (3) (12) (7) (5) (4) (6) (2) (11) (6) (6) (10) (3) (2) (7) (6) (7) (10) (10) (8) (7) (7) (12)
(2) (7) (9) (3) (10) (8) (6) (3) (5) (6) (5) (2) (3) (5) (7) (6) (8) (7) (8) (7) (9) (9) (5) (8) (7) (2) (8) (7) (2) (11) (9) (4) (3) (12) (8) (5) (9) (7) (2) (6) (3) (10)
For kiwi juice, different amounts of MWCNTs (i.e., 3, 5, and 10 mg) mixed with 25 mg of PSA and 150 mg of MgSO4 were optimized. The results showed that PSA without MWCNTs could remove most matrix interferences and meet the requirement of recoveries (76−108%). However, adding MWCNTs decreased the recoveries of some pesticides to
