Determination of chlorfenapyr in leek grown under greenhouse conditions with GC-μECD and confirmation by mass spectrometry

Article (PDF Available)inBiomedical Chromatography 26(2):172-7 · February 2012with123 Reads
DOI: 10.1002/bmc.1643 · Source: PubMed
Abstract
A simple analytical method was developed for the determination of chlorfenapyr residues in leeks grown under greenhouse conditions. Residues were extracted by salting out, analyzed by gas chromatography with microelectron-capture detection, and confirmed via gas chromatography-mass spectrometry. The calibration curves were found to be linear with correlation coefficients (r(2) ) in excess of 0.998. The limits of detection and quantification were 0.0015 and 0.005 mg kg(-1) , respectively. For validation purposes, recovery studies were carried out at low and high levels. Yield recovery rates were 87.27-89.64% with a relative standard deviation <6%. A maximum of 0.32 mg kg(-1) of chlorfenapyr residue was detected in leek sample sprayed three times at 7 day intervals until 7 days prior to harvest. The results of this study suggest that chlorfenapyr is acceptable for application in/on leeks under the recommended dosage regimen.
Determination of chlorfenapyr in leek grown
under greenhouse conditions with GCμECD
and conrmation by mass spectrometry
Md. Musqur Rahman
a
, JeongHeui Choi
a
, A. M. Abd ElAty
b
*,
Jong Hyouk Park
a
,JiYeon Park
a
, GeonJae Im
c
and JaeHan Shim
a
*
ABSTRACT: A simple analytical method was developed for the determination of chlorfenapyr residues in leeks grown under
greenhouse conditions. Residues were extracted by salting out, analyzed by gas chromatography with microelectroncapture
detection, and conrmed via gas chromatographymass spectrometry. The calibration curves were found to be linear with
correlation coefcients (r
2
) in excess of 0.998. The limits of detection and quantication were 0.0015 and 0.005 mg kg
1
,
respectively. For validation purposes, recovery studies were carried out at low and high levels. Yield recovery rates were
87.2789.64% with a relative standard deviation <6%. A maximum of 0.32 mg kg
1
of chlorfenapyr residue was detected in
leek sample sprayed three times at 7 day intervals until 7 days prior to harvest. The results of this study suggest that
chlorfenapyr is acceptable for application in/on leeks under the recommended dosage regimen. Copyright © 2011 John
Wiley & Sons, Ltd.
Keywords: chlorfenapyr; gas chromatography; leek; greenhouse
Introduction
Pesticides, including organochlorine pesticides (OCPs), organo-
phosphates (OPs) and nitrogencontaining herbicides are well
known types of environmental contami nants. The use of
pesticides provides benets for increasing agricultural produc-
tion; however, residues may remain in foods in amounts in
excess of maximum residue limits (MRLs). Bioaccumulation
through the food chain can eventually become a risk to both
animals and humans (Ahmadi et al., 2006). Chlorfenapyr, 4
brom o 2(4chlorophenyl)1ethoxymethyl5triuoro methyl-
pyrrole3carbonitrile, is a novel broadspectrum insecticide/
acaricide used for the control of various species of insects and
mites, including those resistant to carbamate, organophosphate
andpyrethroidinsecticides,andalsoaschitinsynthesis
inhibitors against pests in cotton, vegetables, citrus and soy
beans (Tomlin, 2000). Various research has been carried out to
identify and estimate its efcacy against insects (Guglielmone
et al., 2000; Kaufman et al., 2001; McLeod et al., 2002; Ahmad
et al., 2003; Rand, 2004).
Chlorfenapyr is a proinsecticide that is converted to an active
metabolite in the midgut of insects and mites. Once the formed
metabolite has inhibited oxidative phosphorylation by disrupt-
ing the proton gradient across mitochondrial membranes, the
ability of cells to produce ATP from ADP is affected, ultimately
resulting in cell death and death of the organism (Treacy et al.,
1994; Rand, 2004). This specic acaricide/insecticide generally
has no effect on benecial insects, including predaceous mites,
which is desirable for the development of new strategies
involving integrated pest management in vegetables (Cao et al.,
2005).
Application of pesticides is carried out once or several times
during cultivation. The average residue level of any pesticide in
fruit and vegetables depends primarily on the application rate of
its active ingredient (Sadlo, 2000). Determination of a pesticides
fate on crops is very important for good agricultural practice,
and will greatly affect the effectiveness of sprayed pesticides on
plants, the preharvest interval (PHI) and the amounts of residue
on crops at time of harvest (Metwally et al., 1997). However, the
fate of pesticides under normal environmental conditions is
controlled mainly by temperature, humidity and light intensity
(Mabey and Mill, 1978). Therefore, it is not possible to predict
their fate under environmental conditions.
* Correspondence to: JaeHan Shim, Natural Products Chemistry Labora-
tory, Division of Applied Bioscience and Biotechnology, College o f
Agriculture and Life Science, Chonnam National University, 300
Yongbongdong, Bukgu, Gwangju 500757, Republic o f Korea. Email:
jhshim@chonnam.ac.kr
A. M. Abd ElAty, Department of Pharmacology, Faculty of Veterinary Medicine,
Cairo University, 12211Giza, Egypt. E-mail: abdelaty44@hotmail.com
a
Natural Products Chemistry Laboratory, Division of Applied Bioscience and
Biotechnology, College of Agriculture and Life Science, Chonnam National
University, 300 Yongbongdong, Bukgu, Gwangju 500757, Republic of
Korea
b
Department of Pharmacology, Faculty of Veterinar y Medicine, Cairo
University, 12211Giza, Egypt
c
Pesticide Safety division, National Institute of Agriculture Science and
Technology, Rural Development Administration, Suwon, 441707, Republic
of Korea
Abbreviations used: MRLs, maximum residue limit s; OCPs, organochlorine
pesticides; OPs, organophosphates; PHI, preharvest interval; WP, wettable
powder.
Biomed. Chromatogr. 2012; 26: 172177 Copyright © 2011 John Wiley & Sons, Ltd.
Research article
Received 21 March 2011, Accepted 4 April 2011 Published online in Wiley Online Library: 24 May 2011
(wileyonlinelibrary.com) DOI 10.1002/bmc.1643
172
On the other hand, cultivation under greenhouse conditions
can eliminate the actions of rain and partially sun on the
reduction of treated pesticides. Thus, it is possible to obtain
accurate information about the persistence of these residues in a
greenhouse. Hence, p esticide residues on crops grown in
greenhouses should be determined to ensure the quality of
products and to prevent public health problems (Kurz et al., 2008).
Several analy tical methods have been described for
chlorfenapyr in different matrices. Multiresidue analysis for
monitoring chlorfenapyr in hops has been published in which a
gas chromatog raphy mass spectrometry method involved
several steps including derivatization (Hengel and Shibamoto,
2002). In order to omit the timeconsuming derivatization step
in GC analysis, Cao et al. (2005) developed an analytical method
for analysis of chlorfenapyr in cabbage and soil using high
performance liquid chromatography coupled with an ultraviolet
detector. However, chlorfenapyr is probably detected in a gas
chromatographyelectron capture detector owing to its physi-
cochemical properties, including halogen components (F, Cl, Br)
and low vapor pressure (9.81 × 10
3
mPa, 25°C; IUPAC).
Ditya et al. (2010) reported a gas chromatography with
electroncapture detection (GCECD) method without derivati-
zation for the determination of chlorfenapyr in chili, cabbage
and soil, and the method demonstrated very high recovery
results of 8997%. However, the GCECD method for chlorfenapyr
using liquidliquid extraction and a conventional preparative
column for cleanup is very timeconsuming. In order to
overcome this problem, we developed a simple and timesaving
analytical method using salting out, solidphase extraction
(SPE) cleanup, and more sensitive gas chromatography with
microelectroncapture detection (GCμECD) detection to measure
chlorfenapyr in leeks grown under greenhouse conditions. The
treatment parameters, including the PHI, were evaluated to assess
eldincurred residues.
Experimental
Chemicals
Standard chlorfenapyr (purity 98.0%) was obtained from Dr Ehrenstorfer
(Augsburg, Germany). Acetone, nhexane, acetoni trile and sodium
chloride of analytical grade were obtained from Merck (Darmstadt,
Germany). Chlorfenapyr stock standard solutions were prepared in
acetone, and working standard solutions were prepared by serial
dilution of the stock solution using the same solvent. All standard
solutions were stored at 5°C.
GCμECD analysis
Analysis was performed on an Agilent GC model 7890A (CA, USA)
equipped with an Agilent 7683B autosampler and a μECD (
63
Ni), and
chromatographic separation was performed on an HPUltra 2 capillary
column (50 m × 0.32 mm i.d., 0.17 µm lm thickness, Agilent Technologies,
CA, USA), owing at 2 mL min
1
with nitrogen gas. A standard split/
splitless injector was used for the split injection mode at a ratio of 30:1 at
270°C with an injection volume of 1 μL. The detector was maintained at
300°C with the makeup gas (N
2
) owing at 30 mL min
1
. The oven
temperature was set to 150°C for 2 min, increased to 210°C at 10°C min
1
,
held for 1 min, then increased to 300°C at 15°C min
1
and held for 5 min.
Under these conditions, chlorfenapyr presented an average retention
time of 11.6 min. An Agilent Chemstation was used for data acquisition.
GCMS conrmation
An Agilent 6890 GC was used to conrm the identity of chlorfenapyr. It
was tted with a massselective detector Agilent 5973N and was
equipped with an Agilent 7683B autosampler and a split/splitless
injector with an electronic pressure controller. Chlorfenapyr was
separated on a HP5MS capillary column (30 m × 0.25 mm, 0.25 µm lm
thickness, Agilent Technologies, CA, USA). The column oven temperature
was held at 90°C for 1 min, then increased to 270°C at 10°C min
1
, and
held for 5 min. Helium was used as a carrier gas at a ow rate of 1.0 mL
min
1
. The temperatures of the ion source and quadruple were set at
230 and 150°C, respectively. The temperature of the injector was set to
250°C, and a 2 μL portion of the sample was injected in splitless mode.
The mass spectrometer was operated in electron impact ionization
mode (EI, 70 eV), and analysis was carried out in selected ion monitoring
(SIM) mode in which two characteristic ions (m/z = 59 and 247) for
chlorfenapyr were monitored.
Field trial design in a greenhouse
Experiments were conducted in a greenhouse at the experimental elds of
Chonnam National University, Gwangju, Republic of Korea. The experi-
mental area comprised 15 plots, in which a random block scheme was
established with three replicates. In addition, control samples were
cultivated in a separate plot without receiving any treatment with
insecticides. Chlorfenapyr 5% wettable powder (WP; Kyung Nong Co.,
Seoul, Republic of Korea) was diluted 1000 times and sprayed at a.i
0.0125 kg 10a
1
, which was recommended by the manufacturer. Plants
were sprayed in August and September 2009. The rst and second plots
were treated once at 7 or 14 days; the third plot was treated twice at 14 and
7 days; the fourth plot was treated twice at 21 and 14 days; and the fth
plot was treated three times at 21, 14, and 7 days prior to harvest (Table 1).
As soon as they were picked, the samples were transferred to the
laboratory where they were chopped and blended. Subsamples weighing
approximately 50 g each were stored in a freezer pending analysis.
Sample extraction and cleanup
A 20 g leek sample was weighed in a 250 mL Erlenmeyer ask, after
which 100 mL acetonitrile was added. Subsequently, the mixture was
shaken for 1 h on a shaker at 250 rpm and ltered through Whatman no.
1 lter paper. The ltrate was transferred to a separatory funnel
containing 15 g of NaCl, shaken in a mechanical shaker for 5 min, and
Table 1. Spraying schedule of chlorfenapyr 5% wettable powder onto leeks
Treatment frequency Interval prior to harvest (days) Final spraying date Harvest date
0 ——10 September 2009
1 7 3 September 2009
1 14 27 August 2009
2 147 3 September 2009
2 2114 27 August 2009
3 21147 3 September 2009
Chlorfenapyr residues in leek
Biomed. Chromatogr. 2012; 26: 172177 Copyright © 2011 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/bmc
173
allowed to stand for 20 min. A 50 mL portion of the upper layer was
transferred to a roundbottomed ask, evaporated under 40°C in vacuo,
and then dissolved in 10 mL of 2% acetone in nhexane. The
reconstituted sample was loaded into an SPE Florisil cartridge (2 g,
12 mL, Phenomenex, CA, USA), which was conditioned with 10 mL of
nhexane in advance and then eluted with 10 mL of 2% acetone in
nhexane. The eluate was evapo rated under 40°C in vacuo and
reconstituted in 2 mL of 2% acetone in nhexane.
Validation of the analytical method
Validation was tested to dete rmine specicity, analytical curves
linearity, limit of detection (LOD) and limit of quantication (LOQ),
and to decide whether or not the method provides adequate precision
and accuracy, associated with recovery. Specicity was assessed by
analyzing the standards of the analyte, blank sample and fortied
sample. The fortied leek sample was prepared at 0.25 mg kg
1
and
min
0
5 10 15
Hz
10000
20000
30000
40000
50000
60000
Chlorfenapyr
(d)
min0 5 10 15
Hz
10000
20000
30000
40000
50000
60000
Chlorfenapyr
(c)
min
0 5
10
15
Hz
10000
20000
30000
40000
50000
60000
Chlorfenapyr
(b)
min0
5 10 15
Hz
10000
20000
30000
40000
50000
60000
Chlorfenapyr
(a)
Figure 1. (a) Standard chlorfenapyr at 2 mg L
1
; (b) untreated leek sample; (c) fortied leek sample at 0.25 mg kg
1
; and (d) eld sample treated
thrice (21147).
Md. Musqur Rahman et al.
Biomed. Chromatogr. 2012; 26: 172177Copyright © 2011 John Wiley & Sons, Ltd.wileyonlinelibrary.com/journal/bmc
174
extracted by the method described above. The lowest concentrations of
the working standard solution injected to show signaltonoise ratios of
3 and 10, corresponding to the LOD and LOQ, respectively, were
observed (Ribani et al., 2004, 2007). The analytical curve was constructed
by injecting different concentrations (0.025, 0.05, 0.1, 0.2, 0.5, 1 and
2mg L
1
) of standard solutions prepared in pure solvent. The recovery
study was performed by fortifying standard solutions into blank leeks at
two fortication levels of 0.05 and 0.25 mg kg
1
. The fortied samples
were placed to gasify solvent and then extracted as described above
and analyzed by GCμECD. Recoveries were assessed in three replicates
for each level. The precision of the method was evaluated considering
the relative standard deviations (RSD) of the recovery assay.
Results and discussion
Validation of the developed method
Specicity. The endogenous compounds interfering with the
analyte were assessed by comparing the chromatograms of the
standard, blank sample and fortied sample (Fig. 1). There were
no interference peaks at the retention time of chlorfenapyr. The
developed method consisted of saltingout extraction and
GCμECD detection and was very selective in enabling analysis
of the analyte in the enormous matrix components.
Linearity
For most chromatographic analyses, a linear relation was
observed between the area ( y) and concentration (x)ofthe
analyte. This can be expressed as a linear regression equation
(y = a + bx), and the corresponding calibration curve of
chlorfenapyr was y = 75710 980x in the range of 0.0252mg
L
1
. The linearity was excellent with a correlation coefcient of
r
2
= 0 .9986. The residual concentrations of chlorfenapyr in the
treated samples were determined via the calibration curve
developed herein.
Recovery and precision
The extraction efciency of the analytical procedure was
evaluated via recovery experiments conducted in triplicate using
the fortied blank leek samples at two different fortication
levels (0.05 and 0.25 mg kg
1
). The precision reects the variation
in results when repetitive analyses were carried out under the
same conditions. The numerical value used for precision was the
RSD. Recoveries were measured by comparing peak areas of
the spiked samples with external standards in acetone. The mean
recoveries were 89.64 and 87.27% with RSD less than 6%
(Table 2). Although the recovery rates acquired through the
developed method were slightly lower than those of Ditya et al.
(2010) (8997%), the current method was accurate and precise
enough to produce at least 87.27% recovery and 4.46% RSD.
Fieldincurred residues and preharvest intervals
of chlorfenapyr
The developed method was applied to the treated leek samples.
The leek samples were analyzed according to the methodology
described above. The highest residual concentrations were
found in the samples treated three times and was decreased
with treatment twice (14 and 7 days and 21 and 14 days) and
treatment once (7 and 14 days). The chlorfenapyr residues after
application 14 and 7 days preharvest (PHI, the time between
the last pesticide application and harvest of the treated crops)
to the leeks are given in Table 3, and were less than the MRLs
[3 mg kg
1
, KFDA (2008); 1 mg kg
1
, EPA (2003)]. Chlorfenapyr
residues below their MRLs were successfully determined
through the developed method.
Conrmation of the positive treated sample
In order to avoid a falsepositive result, the existence of
chlorfenapyr in the eldtreated sample was veried via mass
Table 2. Validation of the analytical method for chlorfenapyr in leeks
Compound Spiked level
(mg kg
1
)
Recovery (%) Mean (RSD%) LOD (mg kg
1
) LOQ (mg kg
1
)
1 23
Chlorfenapyr 0.05 93.61 90.76 84.19 89.64 (5.55) 0.0015 0.005
0.25 83.61 92.24 85.97 87.27 (5.11)
Table 3. Residues of chlorfenapyr in leeks
Spray frequency Interval before
harvest
Chlorfenapyr residues (mg kg
1
) MRL (mg kg
1
)
1 2 3 Mean (RSD %)
Control ND ND ND
1 7 0.100 0.098 0.096 0.098 (2.04)
14 0.057 0.069 0.071 0.066 (10.6) 3
2 147 0.314 0.299 0.295 0.303 (3.3) (KFDA)
2114 0.083 0.101 0.096 0.093 (9.67) 1
3 21147 0.322 0.309 0.308 0.313 (2.24) (EPA)
ND, Not detected. KFDA, Korea Food and Drug Administration (2008). EPA, United States Environmental Protection Agency (2003).
Chlorfenapyr residues in leek
Biomed. Chromatogr. 2012; 26: 172177 Copyright © 2011 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/bmc
175
spectrometry. For optimization of the MS parameters, the
standard chlorfenapyr was monitored in fullscan mode in the
range m/z 50450. Although the range of m/z should be
reduced to the smallest appropriate scope so as to increase the
sensitivity of the full scan, the range of m/z was set based on its
molecular mass ([M
·+
] = 407) and the main fragmented ion (m/z
59). It is better to test three or four ions for the target compound
in the matrix and then choose two ions that are more sensitive
and show less interference in the nal SIM mode. Therefore, in
the mass spectrum of chlorfenapyr shown in Fig. 2, m/z 59, m/z
137, m/z 247 and m/z 328 were tested, with m/z 59 and 247
nally chosen, and the positive treated leek samples were
conrmed in SIM mode.
Conclusion
In this study, a fast, easy and effective method was described for
the analysis of chlorfenapyr in leek using GCμECD in combina-
6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
22.00
500000
1000000
1500000
2000000
2500000
3000000
3500000
Time-->
Abundance
Chlorfenapyr
(c)
6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
22.00
500000
1000000
1500000
2000000
2500000
3000000
3500000
Time-->
Abundance
Chlorfenapyr
(a)
Figure 2. Selected ion monitoring mass chromatogram obtained using a HP5MS fused silica capillary column for (a) standard chlorfenapyr (10 ppm),
(b) EI mass spectrum of chlorfenapyr from mass library and (c) mass chromatogram of treated leek sample.
Md. Musqur Rahman et al.
Biomed. Chromatogr. 2012; 26: 172177Copyright © 2011 John Wiley & Sons, Ltd.wileyonlinelibrary.com/journal/bmc
176
tion with GCMS. Salting out method for extraction and SPE
cartridge using solvent of optimum polarity fraction for cleanup
with GCμECD analysis gave this experiment good repeatability
(RSD) and accuracy (recovery) within a short time. Thus, the
proposed methodology was rapid and selective with a simple
sample preparation procedure, and could be used for the
convenient and effective determination of chlorfenapyr in leek
samples. Therefore, application of chlorfenapyr at the recom-
mended level to leek is safe from crop protection and
environmental contamination points of view.
References
Ahmad M, Iqbal Arif M and Ahmad Z. Susceptibility of Helicoverpa
armigera (Lepidoptera: Noctuidae) to new chemistries in Pakistan.
Crop Protection 2003; 22: 539544.
Ahmadi F, Assadi Y, Milani Hosseini SMR and Rezaee M. Determination of
organophosphorus pesticides in water samples by single drop
microextraction and gas chromatographyame photometric detec-
tor. Journal of Chromatography A 2006; 1101: 307.
Cao Y, Chen J, Wang Y, Liang J, Chen L and Lu Y. HPLC/UV analysis of
chlorfenapyr residues in cabbage and soil to study the dynamics of
different formulations. Science of the Total Environment 2005; 350:3846.
Ditya P, Das SP, Sarkar PK and Bhattacharyya A. Degradation dynamics of
chlorfenapyr residue in chili, cabbage and soil. Bulletin of Environ-
mental Contamination and Toxicology 2010; 84: 602605.
EPA. Federal Register 2003; 68(187): 55519.
Guglielmone A, Volpogni MM, Scherling N, Cobeñas MM, Mangold AJ,
Anziani OS, Ioppolo M and Doscher M. Chlorfenapyr ear tags to
control Haematobia irritans (L.) (Diptera: Muscidae) on cattle.
Veterinary Parasitology 2000; 93:7782.
Hengel MJ and Shibamoto T. Method development and fate determination
of pesticidetreated hops and their subsequent usage in the production
of beer. Journal of Agricultural and Food Chemistry 2002; 50: 34123418.
Kaufman PE, Rutz DA, Doscher ME and Albright R. Efcacy of chlorfenapyr
(AC 303630) experimental pouron and CyLence formulations against
naturally acquired louse infestations on cattle in New York. Veterinary
Parasitology 2001; 97: 123129.
KFDA. MRLs for Pesticides in Food . Korea Food and Drug Administration:
Republic of Korea, 2008; 93.
Kurz MHS, Gonçalves FF, Adaime MB, da Costa IFD, Primel EG and
Zanella R. A gas chromatographic method for the determination of
the fungicide chlorothalonil in tomatoes and cucumbers and its
application to dissipation studies in experimental greenhouses.
Journal of the Brazilian Chemical Society 2008; 19: 11291135.
Mabey W and Mill T. Critical review of hydrolysis of organic compounds
in water under environmental conditions. Journal of Physical and
Chemical Reference Data 1978; 7: 383407.
McLeod P, Diaz FJ and Johnson DT. Toxicity, persistence, and ef
cacy of
spinosad, chlorfenapyr, and thiamethoxam on eggplant when
applied against the eggplant ea beetle (Coleoptera: Chrysomeli-
dae). Journal of Economic Entomology 2002; 95: 331335.
Metwally M, Osman MS and AlRushaid R. A highperformance liquid
chromatographic method for the determination of cypermethrin in
vegetables and its application to kinetic studies after greenhouse
treatment. Food Chemistry 1997; 59: 283.
Rand GM. Fate and effects of the insecticidemiticide chlorfenapyr in
outdoor aquatic microcosms. Ecotoxicology and Environmental Safety
2004; 58: 50.
Ribani M, Bottoli CBG, Collins CH, Jardim ICSF and Melo LFC. Validação
em métodos cromatográcos e el etroforét icos ( Validation for
chromatographic and electrophoretic methods). Quimica Nova 2004;
27: 771780.
Ribani M, Collins CH and Bottoli CBG. Validation of chromatographic
methods: Evaluation of detection and quantication limits in the
determination of impurities in omeprazole. Journal of Chromato-
graphy A 2007; 1156: 201.
Sadlo S. Quantitative relationship of application rate and pesticide
residues in green house tomatoes. Journal of AOAC International
2000; 83: 214219.
Tomlin CDS (ed.). The Pesticide Manual: A World Compendium, 12th edn.
British Crop Protection Council: Surrey, 2000; 154.
Treacy M, Miller T, Black B, Gard I, Hunt D and Hollingworth RM.
Uncoupling activity and pesticidal properties of pyrroles. Biochemical
Society Transaction 1994; 22: 244247.
Chlorfenapyr residues in leek
Biomed. Chromatogr. 2012; 26: 172177 Copyright © 2011 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/bmc
177
    • "Samples were prepared according to our previous study with major modifications (Rahman et al. 2012). A 25 g homogenized perilla leaf sample was weighed in a 250 mL Erlenmeyer flask to which 100 mL acetonitrile was added. "
    [Show abstract] [Hide abstract] ABSTRACT: Perilla leaves contain many interfering substances; thus, it is difficult to protect the analytes during identification and integration. Furthermore, increasing the amount of sample to lower the detection limit worsens the situation. To overcome this problem, we established a new method using a combination of solid-phase extraction (SPE) and dispersive solid-phase (d-SPE) extraction to analyze pyraclostrobin in perilla leaves by liquid chromatography with ultraviolet absorbance detection. The target compound was quantitated by external calibration with a good determination coefficient (R(2) = 0.997). The method was validated (in triplicate) with three fortification levels, and 79.06- 89.10% of the target compound was recovered with a relative standard deviation < 4. The limits of detection and quantification were 0.0033 and 0.01 mg/kg, respectively. The method was successfully applied to field samples collected from two different areas at Gwangju and Muan. The decline in the resiudue concentrations was best ascribed to a first-order kinetic model with half-lives of 5.7 and 4.6 days. The variation between the patterns was attributed to humidity. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Full-text · Article · May 2015
  • [Show abstract] [Hide abstract] ABSTRACT: A modified quick, easy, cheap, effective, rugged and safe (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as a reversed-dispersive solid-phase extraction (r-DSPE) material combined with gas chromatography-mass spectrometry was developed for the determination of 14 pesticides in complex matrices. Four vegetables (leek, onion, ginger and garlic) were selected as the complex matrices for validating this new method. This technique involved the acetonitrile-based sample preparation and MWCNTs were used as the r-DSPE material in the cleanup step. Two important parameters influencing the MWCNTs efficiency, the external diameters and the amount of MWCNTs used, were investigated. Under the optimized conditions, recoveries of 78-110% were obtained for the target analytes in the complex matrices at two concentration levels of 0.02 and 0.2 mg/kg. In addition, the RSD values ranged from 1 to 13%. LOQs and LODs for 14 pesticides ranged from 2 to 20 μg/kg and from 1 to 6 μg/kg, respectively.
    Article · Jan 2012
  • [Show abstract] [Hide abstract] ABSTRACT: A simple and rapid method based on high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for the simultaneous determination of imidacloprid and chlorfenapyr residues in chieh-qua. Field trials were designed to investigate the dissipation and terminal residue behavior of the mixed formulation of imidacloprid and chlorfenapyr in chieh-qua in Guangzhou and Nanning areas. Risk assessment was performed by calculating the risk quotient (RQ) values. The developed analytical method exhibited recoveries of 89.9–110.3 % with relative standard deviations (RSDs) of 2.8–12.5 % at the spiked levels of 0.01, 0.10, and 1.00 mg/kg. The limit of detection (LOD) was 0.003 mg/kg, and the limit of quantification (LOQ) was 0.01 mg/kg for both imidacloprid and chlorfenapyr. It was found that the half-lives of imidacloprid in chieh-qua under field conditions were 3.3 and 3.5 days in Guangzhou and Nanning at a dose of 180 g ai/ha, while the half-lives of chlorfenapyr were 3.3 and 2.6 days, respectively. The terminal residues of imidacloprid and chlorfenapyr were from 0.01 to 0.21 mg/kg and from 0.01 to 0.46 mg/kg, respectively. Results of dietary exposure assessment showed that the RQ values were much lower than 1, indicating that the risk of imidacloprid and chlorfenapyr applied in chieh-qua was negligible to human health under recommended dosage and good agricultural practices. The proposed study would provide guidance for safe and reasonable use of imidacloprid and chlorfenapyr in chieh-qua cultivation in China.
    Article · Oct 2015
Show more