Article pubs.acs.org/JAFC
Transfer Rates of 19 Typical Pesticides and the Relationship with Their Physicochemical Property Hongping Chen,†,‡,§ Meiling Pan,‡ Rong Pan,† Minglu Zhang,† Xin Liu,*,†,‡,§ and Chengyin Lu*,†,‡,§ †
Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310008, China Ministry of Agriculture, Tea Quality and Supervision Testing Center, Hangzhou 310008, China § CAAS Key Laboratory of Tea Quality and Safety & Risk Assessment, Hangzhou 310008, China ‡
S Supporting Information *
ABSTRACT: Determining the transfer rate of pesticides during tea brewing is important to identify the potential exposure risks from pesticide residues in tea. In this study, the transfer rates of 19 typical pesticides from tea to brewing were investigated using gas chromatography tandem mass and ultraperformance liquid chromatography tandem mass. The leaching rates of five pesticides (isocarbophos, triazophos, fenvalerate, buprofezin, and pyridaben) during tea brewing were first reported. The pesticides exhibited different transfer rates; however, this result was not related to residual concentrations and tea types. Pesticides with low octanol−water partition coefficients (Logkow) and high water solubility demonstrated high transfer rates. The transfer rates of pesticides with water solubility > 29 mg L−1 (or 25% (or 2.48) were >65% (or > > > > > > > > > >
CE (eV)
258 111 136 162 141 152 152
ion transitions (m/z) 314 250 230 161 181 209 181
286 139 212 134 153 181 127
10 20 5 10 20 10 25
163 > 127
5
181 > 152
25
167 > 125
10
125 > 89
20
326 > 228 UPLC-MS/MS
8
26 > 233
10
DP (V)
CE (V)
36 11 31 34 41 41 61 25 35 62 52
23 14 18 22 25 29 34 20 20 34 48
160.1 88.1 211.2 209.1 56.1 150.0 251.1 201.0 231.0 147.2 152.1
> > > > > > >
CE (eV)
15 10 10 14 20 25 25
ion transitions (m/z)
> > > > > > >
ion transitions (m/z) 192.1 163.1 292.1 256.1 223.1 528.0 406.1 306.2 368.1 365.2 326.9
> > > > > > > > > > >
132.1 88.1 181.2 175.1 126.1 218.0 337.2 116.1 175.1 309.2 168.1
DP (V)
CE (V)
36 18 32 36 42 41 58 25 35 59 52
42 12 29 22 27 31 24 20 20 17 52
prepared with acetone for 9 pesticides analyzed by GC-MS/MS and methanol for 10 pesticides analyzed by UPLC-MS/MS. IS TPP at 1000 mg L−1 was prepared with acetone. Intermediate mixed standard solutions at 40 mg L−1 and IS TPP solution at 20 mg L−1 were prepared by dilution of stock standard solutions with acetone (for GCMS/MS) and methanol (for UPLC-MS/MS). All stock solutions and intermediate solutions were stored in the dark at −18 °C. Matrix-matched standard solutions were prepared for quantification of 19 pesticides. A 5 mL amount of liquids obtained from blank sample (made tea, tea infusion, and spent tea) with the proposed treatment was evaporated to dryness. Afterward, 5 mL of solvent standard solutions (containing IS TPP at 50 μg L−1) with concentrations ranging from 1 to 1000 μg L−1 for the pesticides analyzed by UPLCMS/MS and 2 to 2000 μg L−1 for the pesticides analyzed by GC-MS/ MS were added to produce solutions with final concentrations corresponding to the levels of matrix-matched calibration standards. GC-MS/MS Analysis. Volatile and thermally stable pesticides, such as bifenthrin, chlorpyrifos, cyhalothrin, cypermethrin, dicofol (expressed as dichlorobenzophenone), fenpropathin, fenvalerate, isocarbophos, and triazophos, were analyzed by GC-MS/MS using a Bruker 450 GC coupled with a 300 MS. Separation was performed on a VF-5 MS column (30 m × 0.25 mm × 0.25 μm; Agilent, USA). The column temperature was maintained at 80 °C for 1.0 min and then ramped at 15 °C min−1 up to 180 °C, held for 2 min, and then at 5 °C min−1 up to 280 °C, held for 10 min. The injection volume was 1.0 μL, and splitless mode was adopted. Helium (99.99%) at a flow rate of 1.0 mL min−1 was used as the carrier gas and argon (99.99%) as the collision gas. The MSD transfer line, ion source, and manifold temperatures were 280, 230, and 40 °C, respectively. The triplequadrupole mass spectrometer was operated in electron impact ionization mode. Two mass transitions were acquired for each
min. The supernatant (5 mL) was added in the GCB/PSA SPE column (SPE column was conditioned with 5 mL of MeCN/toluene 3:1 (v/v) prior to sample). Target pesticides were eluted from the SPE column with 25 mL of MeCN/toluene 3:1 (v/v). The elutes were evaporated into dryness and dissolved in 5 mL of acetone. Approximately 2 mL was filtered through a 0.22 μm membrane into an autosampler vial for GC-MS/MS analysis. Exactly 2 mL of the rest was solvent changed with 2 mL of methanol for UPLC-MS/MS analysis. Tea Infusion. NaCl (10 g) was added into 100 mL of infusion and then transferred into a 250 mL separating funnel. IS TPP (50 μL) was added to achieve a concentration of 10 μg L−1 prior to extraction. DCM (100 mL) was used to extract the target pesticides from infusion by liquid−liquid extraction. The lower liquid (DCM phase) was filtered into a 150 mL heart-shaped bottle through a filter paper, which was filled with 15−20 g of Na2SO4. The infusion was re-extracted with 100 mL of DCM by LLE. Approximately 50 mL of DCM was used to wash Na2SO4 and then collected. The combined extractions (DCM phase from two LLE extraction) were evaporated into dryness at 40 °C and then dissolved with 5 mL of acetone. Approximately 2 mL of acetone solution was filtered through a 0.22 μm membrane into an autosampler vial for GC-MS/MS analysis. Exactly 2 mL of the rest was solvent changed with 2 mL of methanol for UPLC-MS/MS analysis. Tea Spent. The tea spent (means all the solid residues of made tea after brewing twice) was cut into small pieces and then transferred into a 50 mL centrifuge tube. IS TPP (50 μL) was added to achieve a concentration of 25 μg kg−1 prior to extraction. Then, 15 mL of MeCN was added into the samples and then homogenized at 12 000 rpm for 2 min. The following steps were the same as the made tea in Made Tea section. Preparation of Standard Solutions. Individual pesticide stock solutions at 1000 mg L−1 (200 mg L−1 for carbendazim) were 725
DOI: 10.1021/jf506103d J. Agric. Food Chem. 2015, 63, 723−730
Journal of Agricultural and Food Chemistry
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Table 2. Transfer Rates of 19 Pesticides from Made Tea into Infusion during Tea Brewing mean transfer rate ± SD (%) pesticides by UPLC-MS/MS analysis methomyl imidacloprid carbendazim acetamiprid difenoconazole propargite pyridaben buprofezin thiamethoxam indoxacarb
tea sample (numbers)
concentration in made tea (μg kg−1)
green tea (3) oolong tea (4) green tea (8) oolong tea (10) green tea (7) oolong tea (7) green tea (10) oolong tea (10) green tea (3) oolong tea (3) green tea (3) oolong tea (4) green tea (4) oolong tea (3) green tea (6) oolong tea (8) green tea (4) oolong tea (5) green tea (1) oolong tea (0)
68−453 54−310 12−1030 30−1330 49−1470 39−1211 43−1520 20−2780 29−371 22−288 27−795 25−638 219−1974 337−1550 227−2550 316−6017 47−675 39−515 28
mean residual rate in tea spent ± SD (%)
first soup
second soup
total soup
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
75.1 ± 7.9 73.7 ± 5.9 62.6 ± 8.2 64.5 ± 9.9 63.2 ± 10.2 64.5 ± 13.7 53.8 ± 11.5 50.9 ± 9.7 4.1 ± 2.6 5.2 ± 3.4 0 0 0.8 ± 0.7 0.8 ± 0.6 2.4 ± 0.9 2.3 ± 1.2 72.1 ± 10.4 70.6 ± 14.4 0
13.5 ± 4.6 13.1 ± 6.2 12.6 ± 5.4 12.9 ± 6.7 17.6 ± 7.4 16.1 ± 6.9 14.5 ± 7.2 16.7 ± 7.7 4.7 ± 3.1 3.4 ± 2.1 0 0 0.8 ± 0.6 0.8 ± 0.8 2.3 ± 1.1 2.4 ± 0.7 14.5 ± 6.5 17.8 ± 4.4 0
91.3 ± 14.2 89.5 ± 15.1 76.5 ± 8.5 77.3 ± 10.6 79.6 ± 11.4 81.2 ± 13.3 68.3 ± 9.7 67.8 ± 11.5 8.4 ± 3.3 8.2 ± 2.5 0 0 1.1 ± 0.7 0.9 ± 0.8 4.5 ± 1.3 4.2 ± 0.9 90.6 ± 10.2 90.4 ± 11.7 0
7.6 6.4 11.2 10.1 8.9 11.6 22.5 24.0 92.7 90.4 91.7 93.3 95.9 96.3 85.2 83.5 4.1 3.5 7.1
5.7 5.3 3.2 4.7 4.0 5.2 8.4 9.3 6.7 7.6 9.3 11.2 8.1 5.6 4.4 6.1 2.1 1.0 2.6
mean transfer rate ± SD (%)
tea spent pesticides by GC-MS/MS analysis chlorpyrifos isocarbophos triazophos dicofol bifenthrin fenpropathrin cyhalothrin cypermethrin fenvalerate
tea sample (numbers)
concentration in made tea, (mg kg−1)
green tea (7) oolong tea (6) green tea (3) oolong tea (4) green tea (3) oolong tea (3) green tea (6) oolong tea (8) green tea (12) oolong tea (12) green tea (8) oolong tea (6) green tea (5) oolong tea (5) green tea (4) oolong tea (6) green tea (2) oolong tea (2)
218−1935 37−849 17−886 36−1705 19−906 15−838 11−2117 11−4139 334−3515 437−7495 15−1527 34−995 27−525 32−2165 309−1094 211−3465 11−72 46−1020
mean residual rate ± SD (%)
first soup
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.4 ± 0.3 0.3 ± 0.2 26.1 ± 9.5 26.9 ± 8.2 23.1 ± 4.6 21.9 ± 5.2 2.2 ± 1.7 2.9 ± 1.4 0 0.5 ± 0.5 0 0 0 0 0 0 0 0
89.1 93.6 49.7 54.0 49.8 56.0 91.4 93.4 94.9 92.4 98.3 97.1 98.3 97.6 93.8 89.4 90.2 88.5
11.5 11.5 22.8 29.3 28.4 29.7 8.4 9.5 7.6 8.5 1.3 1.9 1.2 1.7 5.5 10.1 9.3 9.9
second soup 0.5 0.5 4.7 5.4 6.7 5.7 3.4 4.0 0 0.5 0 0 0 0 0 0 0 0
± ± ± ± ± ± ± ±
0.3 0.4 2.9 3.2 3.1 6.9 0.7 2.1
± 0.5
total soup 0.8 ± 0.5 0.7 ± 0.6 31.4 ± 8.5 32.2 ± 9.2 29.6 ± 8.9 27.1 ± 10.2 5.4 ± 1.3 5.6 ± 1.7 0 0.9 ± 0.8 0 0 0 0 0 0 0 0
Calculating the Transfer Rate of Pesticides. The transfer rate was calculated by two models. In one model, the rates of the first and second brewing are added (eq 1), whereas the other model involves indirect calculation of the residual rate of pesticides in tea spent (eq 2)
compound, the higher sensitivity of which was used for quantification. The GC-MS/MS parameters for nine pesticides are shown in Table 1. UPLC-MS/MS Analysis. UPLC-MS/MS was used to analyze 10 pesticides (acetamiprid, buprofezin, carbendazim, difenoconazole, imidacloprid, indoxacarb, methomyl, propargite, pyridaben, and thiamethoxam). A Waters Acquity UPLC system equipped with an applied Biosystems 3200 QTRAP system (ABI, USA) and controlled Analyst 1.5 software was used. Chromatography was performed on an Acquity UPLC HSS T3 column (100 mm × 2.1 mm i.d., 1.8 μm particle size, Waters, USA). The mobile phase consisted of water (A) and methanol (B) containing 0.1% formic acid (v/v). Gradient elution was performed as follows: 90% A initially, 5% A for 1−10 min (held for 2 min), and then 90% A for 12−13 min (held for 1 min). The flow rate, autosampler temperature, and injection volume were 0.25 mL min−1, 4 °C, and 3 μL, respectively. Analysis was performed in electron spray ionization mode, and analytes were detected by selective reaction monitoring. The UPLC-MS/MS parameters of the 10 pesticides are shown in Table 1.
R in = C in × Vin/C × M × 100%
(1)
Respent = Cspent /C × 100%
(2)
where Rin is the transfer rate (%), Cin is the concentration of pesticides in tea infusion (ng mL−1), Vin is the volume of tea infusion (mL), C is the concentration of pesticides in made tea (μg kg−1), M is the mass of made tea (g), Respent(%) is the residual rate calculated by spent tea, and Cspent is the concentration of pesticides in tea spent (μg kg−1).
■
RESULTS AND DISCUSSION Method Validation. Method validation was evaluated with selectivity, linearity, accuracy, precision, and limits of
726
DOI: 10.1021/jf506103d J. Agric. Food Chem. 2015, 63, 723−730
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Figure 2. Typical UPLC-MS/MS chromatograms of 9 pesticides in made tea (1), tea spent (2), first soup (3), and second soup (4).
quantification (LOQs) (Table S-2, Supporting Information). Matrix-matched calibration solutions were used for quantification. No interfering peaks were observed for UPLC-MS/MS and GC-MS/MS because of the high selectivity of tandem mass
(Figures 1 and 2, Supporting Information). The linearity obtained with r2 > 0.995 for 10 pesticides analyzed by UPLCMS/MS ranged from 1 to 1000 μg L−1 (except for methomyl, 8−2000 ug L−1), whereas that obtained with r2 > 0.991 for 9 727
DOI: 10.1021/jf506103d J. Agric. Food Chem. 2015, 63, 723−730
Journal of Agricultural and Food Chemistry
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Figure 3. Typical GC-MS/MS chromatograms of 9 pesticides in made tea (1), tea spent (2), first soup (3), and second soup (4).
pesticides analyzed by GC-MS/MS was 2−2000 μg L−1 (except for cypermethrin, 4−2000 ug L−1). The accuracy of the method was verified by measuring the recovery from blank samples of made tea, tea spent, and infusion spiked with the analytes at two concentrations of 80 and 400 μg kg−1 for both made tea and tea spent but 8 and 40 μg L−1 for tea infusion. For all matrices, satisfactory accuracy was achieved with a recovery of 80.4−119.3% for 10 pesticides analyzed by UPLC-MS/MS and 83.4−113.4% for 9 pesticides analyzed by GC-MS/MS. Method precision was determined five times (n = 5) at the two spiked levels. Good precision was obtained with relative standard deviations (RSDs) < 10% for all pesticides with two spiked levels. LOQs were defined when the signal-to-noise ratio was 10 times above the blank signal. The LOQs of 19 pesticides were 1−20 μg kg−1 in made tea and tea spent and 0.005−0.150 ng L−1 in tea soup. Transfer Rate of Pesticides during Tea Brewing. The transfer rates of 19 pesticides are summarized in Table 2. The typical UPLC-MS/MS or GC-MS/MS chromatograms for 19 pesticides in made tea, spent, and infusion are shown in Figures 2 and 3, respectively. Compared with the pesticides analyzed by GC-MS/MS, those analyzed by UPLC-MS/MS were easier to
leach into the infusion during tea brewing. The transfer rates of thiamethoxam, methomyl, carbendazim, imidacloprid, and acetamiprid were 90.4−90.6%, 89.5−91.3%, 79.6−81.2%, 76.5−77.3%, and 67.8−68.3%, respectively, which were much higher than those of the other 14 pesticides. These results were in accordance with previous studies by Hou et al.8 and Wang et al.9 but higher than the results from Gupta et al., where the transfer rates of acetamiprid and imidacloprid were lower than 50%.24−26 This study is the first to report the transfer rates of pyridaben and buprofezin, which were all lower than 15%. Similar with the results from Cho et al.27 the transfer rate of difenoconazole was found with nearly 8%. The lowest transfer rate of pesticides analyzed by UPLC-MS/MS was nearly 0% for propargite and indoxacart. Nearly no residues in tea infusion were observed for the pesticides (chlorpyrifos, dicofol, bifenthrin, fenpropathrin, cyhalothrin, cypermethrin, and fenvelerate) analyzed by GC-MS/MS. The results were in accordance with previous studies by Manikandan et al.,10 Jaggi et al.,11 and Tewary et al.28 The transfer rates of isocarbophos (31.4−32.2%) and triazophos (27.1−29.6%) were also first reported in this study. 728
DOI: 10.1021/jf506103d J. Agric. Food Chem. 2015, 63, 723−730
Journal of Agricultural and Food Chemistry
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Figure 4. Relationship between water solubility and transfer rates of pesticides during tea brewing.
Figure 5. Relationship between octanol−water partition coefficient (Logkow) and transfer rates of pesticides during tea brewing.
transfer rates of pesticides from made tea to infusion because water is the most important carryover of pesticides during tea brewing. The relationship between transfer rate and water solubility of 19 pesticides is shown in Figure 4. The transfer rates increased as the water solubility of the pesticides increased. Low transfer rates of
