Article pubs.acs.org/JAFC
Cite This: J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Chemiluminescent Determination of Oxamyl in Drinking Water and Tomato Using Online Postcolumn UV Irradiation in a Chromatographic System José A. Murillo Pulgarín,* Luisa F. García Bermejo, and Armando Carrasquero Durán Department of Analytical Chemistry and Foods Technology, University of Castilla-La Mancha, 13071 Ciudad Real, Spain ABSTRACT: High-performance liquid chromatography (HPLC) was used to separate oxamyl from other pesticides in drinking water and tomato paste. The eluate emerging from the column tail was mixed with an alkaline solution of Co2+ in EDTA and irradiated with UV light to induce photolysis of the carbamate in order to obtain free radicals and other reactive species that oxidize luminol and produce chemiluminescence (CL) as a result. The intensity of the CL signal was monitored in the form of chromatographic peaks. Under the optimum operating conditions for the HPLC-UV-CL system, the analyte concentration was linearly related to peak area. The limit of detection as determined in accordance with the IUPAC criterion was 0.17 mg L−1. Oxamyl was successfully extracted with recoveries of 88.7−103.1% from spiked tomato paste by using a simple QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) sample preparation approach. Similar recoveries were obtained from drinking water samples spiked with oxamyl concentrations above the LOD. The proposed method is a simple, fast, accurate choice for quantifying this pesticide. KEYWORDS: HPLC, photodecomposition, water, tomato, chemiluminescence, oxamyl
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water7 and contaminate water resources as a result. In addition, plants can absorb carbamates applied for insect control and facilitate their incorporation into the food chain.8 A growing need therefore exists for accurate, reproducible methods for the determination of pesticides in environmental and food samples. A number of chromatographic methods coupled with a variety of detectors including mass spectrometers have so far been used for this purpose. However, the reagents and equipment needed are often unaffordable by routine analytical laboratories. The luminol CL, light scattering, and colorimetry are some of the optical detection methods that have been coupled to a HPLC separation. These used gold nanoparticles as postcolumn reagents to determine low molecular aminothiols in complex matrices such as biological fluids.9,1011 These methods showed many advantages as for example very low detection limits, high specificity, and the use of postcolumn derivatization reactions that minimizes the pretreatment of samples prior to the HPLC separations. The CL of the luminol-functionalized silver nanoparticle (Lum-AgNP) was also used12 for the discrimination of organophosphate and carbamate pesticides. The CL sensor array was based on simultaneous utilization of the triple-channel properties and H2O2 CL system containing CL intensity, the time for CL emissions to appear, and the time to reach the CL peak value, which could be measured via a single experiment. The chemiluminescence (CL) produced by luminol and similar substances has been used to develop simple, inexpensive methods to analyze pesticides in a great variety of samples. For
INTRODUCTION Carbamates are a family of organic compounds deriving from carbamic acids and possessing insecticidal properties that were introduced into agricultural practices on the grounds of their low environmental persistence relative to organochlorine insecticides.1 The insecticidal action relies on their ability to inhibit acetylcholinesterase in the nervous system of insects. This enzyme breaks down and terminates the activity of acetylcholine by catalyzing the hydrolysis of the neurotransmitter to choline and acetic acid. As a result, acetylcholine accumulates at synapses and leads to uncontrolled movement, paralysis, convulsions, and eventual death.2 Particularly, oxamyl, (N,N-dimethylcarbamoyloxyimino-2(methylthio) acetamide) is used in a wide range of agricultural situations. It is systemic and active as an insecticide or a nematicide3 with a high solubility in water (280 g/L) and exhibits a very low soil sorption coefficient. It is used for the control of nematodes in vegetables, bananas, pineapple, peanut, cotton, Soya beans, tobacco, potatoes, sugar beet, and other crops. The toxicity of pesticides and their degradation products is making these chemical substances a potential hazard by contaminating our environment. Carbamic insecticides can be absorbed by the skin and from the gastrointestinal tract. Once absorbed, they are immediately distributed to internal tissues,4 where they can cause oxidative stress by producing free radicals, which play a central role in their toxicity.5 The presence of carbamates and many other pesticides in the environment has raised great concern owing to their deleterious effects on living organisms. The intensive use of insecticides, herbicides, and many other agrochemicals has led to their accumulation in soils, which have thus become natural reservoirs of hazardous pollutants. Soils can eventually release these toxic substances through leaching to surface6 subsurface © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
December 23, 2017 February 12, 2018 February 14, 2018 February 14, 2018 DOI: 10.1021/acs.jafc.7b06056 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
Figure 1. Mechanism process proposed.
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instance, Huertas-Pérez et al.13 determined the concentration of carbaryl in water from its boosting effect on the CL of the luminol−KMnO4 system. Tsogas et al.14 found carbaryl to emit CL upon oxidation by KMnO4 and used the effect to quantify the pesticide in water samples. Soto-Chinchilla et al.15 determined carbaryl in water with an LOD of 31 ng mL−1 by using another CL reaction involving the oxidation of bis(2,4,6-trichlorophenyl)oxalate by hydrogen peroxide in the presence of imidazole as catalyst; hydrolysis and derivatization of carbaryl yielded the CLemitting fluorophore. The chemiluminescence of luminol arises from its oxidation by free radicals and reactive oxygen species (ROS) formed by oxidants such as hydrogen peroxide in the presence of metal ions such as Cu2+, Co2+, or Fe3+ acting as catalysts. The reaction gives an aminophthalate as an electronically excited intermediate that relaxes to the ground state and releases excess energy as visible light.16 Therefore, any substance producing free radicals or ROS upon decomposition can in theory oxidize luminol and produce CL as a result. Irradiation of many pesticides with UV light has been found to cause their photodecomposition through promotion to excited singlet states that can produce triplet states by intersystem crossing. The excited states then undergo homolysis, heterolysis, or photoionization.17 According to Herweh and Hoyle,18 the UV photodegradation of n-aryl carbamates involves an excited singlet state that undergoes homolytic cleavage of the C−N bond to form a pair of free radicals. Thiocarbamate herbicides irradiated with UV light undergo C−S bond homolysis to formamide and disulfide as main products. The disulfide may result from the combination of two sulfur radicals.19 Climent and Miranda20 found the photolysis of various molecules of carbamates by UV irradiation to cause cleavage of C−S or C−N bonds and the formation of free radicals. Similarly, the photodecomposition of carbofuran involves cleavage of the C−O bond to give phenoxide anion and an acylium cation. In this work, UV irradiation of oxamyl after HPLC separation with acetonitrile/water as solvent was used to obtain the reactive species needed to produce luminol CL. Using the QuEChERS method to extract the insecticide enabled its quantification in drinking water and tomato paste.
MATERIALS AND METHODS
Chemicals and Reagents. All reagents used were analytical-grade, and all solvents were HPLC-grade. Ultrapure water from a Milli-Q Plus system (Millipore Bedford, MA, U.S.A.) was used throughout. Acetonitrile, methanol and luminol were supplied by Sigma−Aldrich (St. Louis, MO, U.S.A.); sodium hydroxide, EDTA disodium salt, and CoCl2·6H2O were purchased from Pancreac (Barcelona, Spain); and oxamyl was obtained from Riedel de Haën (Seelze, Germany). Drinking Water and Tomato Paste. Two samples of drinking water and tomato paste were obtained from a local market for analysis. The samples were previously analyzed by HPLC with UV−vis detection to confirm the absence of carbamates. Oxamyl Standards. Stock solutions of oxamyl were prepared by dissolving 25 mg of the carbamate in 98% methanol in 25 mL volumetric flasks. Then, 500 μL aliquots were transferred to 10 mL volumetric flasks and made to volume with further methanol in order to obtain solutions containing a 50 μg mL−1 concentration of oxamyl from which standard solutions spanning the range 0.1−3.0 ppm were prepared to construct a calibration curve. Hardware and Software. The HPLC system consisted of a Jasco PU-1585 quaternary pressure pump and a reverse-phase C18 Ultrabase AV-3053 column (particle size 5 μm, 150 mm × 4.6 mm). Samples were manually inserted into the chromatograph by using an injection valve with a 20 μ L sample loop. The CL intensity was measured with a Camspec CL-2 chemiluminescence detector equipped with a Hamamatsu 45773−20 photosensor module with a spectral response from 300 to 900 nm, and a spiral flow cell of 120 μL from Sawston (Cambridge, U.K.). The detector was interfaced to a computer through an analogue-to-digital converter. Data were acquired by using the software Clarity v. 2.4.1.77 from Data Apex (Prague, Czech Republic) to integrate chromatographic peaks in order to compute the peak area under the CL response signal. The CL postcolumn reagents and the Co2+/EDTA/NaOH mixture were delivered by a Gilson Minipuls 3 peristaltic pump. Eluates were UV-irradiated with a Cracker PSA 10.570 4.5. W low-pressure UV Hg lamp from PS Analytical (Orpington, U.K.) around which a Teflon tube (50 cm × 0.8 mm i.d. × 1.6 mm o.d.) was helically coiled. General Procedure. Separation was carried out in the C18 column, using an isocratic binary mobile phase consisting of (40:60) acetonitrile/water that was pumped at 1 mL min−1 at room temperature (25 ± 1 °C). The peristaltic pump was used to simultaneously pump the luminol/NaOH solution to the detector cell and the Co2+/EDTA/NaOH solution to a T-piece for mixing with the eluate emerging from the column tail. This mixture was passed through the Teflon tube coiled around the UV lamp for irradiation and B
DOI: 10.1021/acs.jafc.7b06056 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry the resulting stream sent to the detection cell for the reaction between luminol and the irradiation products to take place. The CL emission was measured in the form chromatographic peaks. Oxamyl was identified and quantified from its retention time and the increase in CL intensity in the form of the peak area was used to prepare calibration curves. Extraction of Oxamyl. A QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method was used to extract oxamyl from tomato paste. The procedure involved extraction with acetonitrile and partitioning with anhydrous magnesium sulfate.21 Homogenized tomato paste samples were spiked with oxamyl at concentrations from 0.1 to 1.9 mg kg−1. Then, 10 g aliquots of spiked paste were placed in 50 mL beakers and supplied with 10 mL of acetonitrile. The resulting slurries were magnetically stirred for 15 min and then loaded with 4 g of anhydrous MgSO4 and 1 g of NaCl, followed by further stirring for 5 min. At that point, the samples were transferred to centrifuge tubes and centrifuged at 3000 rpm for 15 min, the supernatants being transferred to other centrifuge tubes and cleaned up with 100 mg of activated alumina prior to shaking for 1 min and recentrifugation to obtain clear, colorless solutions. Validation of the Method. The results of the proposed method were validated by comparison with those provided by the HPLC/UV− vis system using the postcolumn detection/quantification principle and 230 nm for detection. Statistical Analysis. Regression analysis for calibration curves, testing of mean differences and parametric statistics were performed using the BM SPSS Statistics Version 25.
solution caused luminol CL to be detected as chromatographic peaks with a maximum CL of 46.0 ± 0.05. Dissolved transitionmetal ions boost photodegradation of pesticides by producing free radicals in photo-Fenton type reactions that facilitate redox processes.23 We chose to use Co2+ ion here because it increases luminol CL more markedly than other, similar cations.24 Dissolving the cobalt in 0.02 M NaOH required using the disodium salt of ethylenediaminetetraacetic acid (EDTA) to form a cobalt chelate. Both were used at a concentration of 0.1 or 0.5 mmol L−1. The results thus obtained confirmed that the presence of Co2+ increased CL and led to higher chromatographic peaks, reaching mean CL intensities values of 161.4 ± 0.5 and 159 ± 1.3, and these differences are not statistically significant using the analysis of variance. We altered the sequence of reagent mixing in order to determine whether the presence of the metal ion favored photodegradation of the pesticides or only influenced luminol CL. For this purpose, the eluate was directly sent to the UV lamp, whereas luminol was mixed with the Co2+ solution at the T-piece before entering the CL detection cell. The fact that no CL emission was observed under these conditions confirmed that Co2+ effectively boosted photodecomposition of the carbamate and that its degradation products reacted with luminol to form excited aminophthalates as is described in Figure 1. Raising the Co-EDTA concentration to 0.5 mmol L−1 diminished CL emission and led to lower peaks as a result. It was therefore necessary to find the ion concentration that maximized pesticide photodegradation. In this work, the concentration was 0.1 mmol L−1. On the other hand, no CL emission was observed in the absence of UV irradiation (i.e., with the UV lamp off) not even in the presence of the Co-EDTA chelate. Therefore, the energy of UV light was the agent effecting the formation of reactive species to oxidize luminol. The influence of the UV irradiation time was assessed by using different lengths of Teflon tubing to irradiate samples for 20, 30, 60, or 90 s. CL peaks increased with increasing irradiation time up to 60 s (viz., with a Teflon tube 50 cm long) and then decreased at the longest time used. Finally, the efficiency of the UV irradiation in the degradation of oxamyl was evaluated by connecting the eluate that emerges from the chromatographic column to an UV Visible detector setting at the conditions to detect the oxamyl. The chromatograms under these conditions showed small peaks that did not correspond to the oxamyl retention time, suggesting that the carbamate was transformed into other chemical species by the action of the UV irradiation Reagent Flow Rates. The CL intensity is strongly influenced by the rate of reagent mixing. This required optimizing the speed of the peristaltic pump and the flow-rate of the HPLC mobile phase. As can be seen from Figure 3, CL increased with an increase in both variables and peaked at 2.25 mL/min and 1.0 mL min−1, respectively, which were thus taken to be the optimum values for these variables. Luminol Concentration. The concentration of luminol was varied from 1.0 to 5.0 mmol L−1 affecting the CL emission intensity, which peaked at 3.5 mmol L−1. Then, this value was selected as optimum for the proposed study. Chromatographic Analysis. Under the optimum conditions for the HPLC-UV-CL system, the chromatograms exhibited a well-resolved peak for the analyte subject, no interference from other carbamic pesticides such as thiodicarb,
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RESULTS AND DISCUSSION Optimization of the Method. The proposed method was sequentially optimized in order to establish the greatest possible compatibility between chromatographic separation, postcolumn UV irradiation, and CL reaction. UV Irradiation. The first process to be optimized was UV irradiation of the carbamates emerging from the C18 column (Figure 1). Given the results of the Figure 2 (different letters at
Figure 2. Experimental conditions for UV irradiation. Oxamyl concentration = 0.9 mg L−1.
the top of the columns indicate significant differences between the mean values at P < 0.01), the direct irradiation failed to increase luminol CL with a signal equal to zero. This led us to insert a T-piece in the system in order to mix the eluates with an appropriate solution facilitating photodecomposition of the carbamates. It has been found that the rate of photodegradation of carbamates such as carbaryl and propoxur increases with increasing pH.22 Mixing our eluates with a 0.01 M NaOH C
DOI: 10.1021/acs.jafc.7b06056 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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Journal of Agricultural and Food Chemistry
Figure 3. Influence of the mobile phase and reagent flow-rates. Oxamyl concentration = 0.9 mg L−1.
kg1− after 10 days,26 which is an amount that can be easily detected by our method. Analysis of Drinking Water and Tomato Paste. Analyses of water samples spiked with oxamyl at concentrations above 0.20 mg L−1 provided recoveries from 86 to 101% (Table 1). Recovery was lowest for the samples containing analyte
bendiocarb, or carbaryl were obtained (Figure 4). The presence of the peak for oxamyl confirmed that UV irradiation caused
Table 1. Recovery of Oxamyl in Drinking Water and Tomato Paste drinking water concentration (mg L−1) spiked 0.43 0.86 0.64 1.29 1.07 0.54 0.30
Figure 4. CL emission curves from oxamyl at different concentrations.
tomato paste concentration (mg kg−1)
found
%R
spiked
± ± ± ± ± ± ±
91 101 98 92 89 86 94
0.21 0.44 0.64 0.86 0.50 0.21 0.44
0.39 0.87 0.63 1.19 0.96 0.46 0.28
0.03 0.03 0.03 0.04 0.03 0.02 0.02
found
%R
± ± ± ± ± ± ±
103 84 113 113 86 90 86
0.22 0.36 0.73 0.98 0.43 0.19 0.38
0.03 0.04 0.06 0.07 0.03 0.03 0.04
concentrations near the limit of detection. Also, the recoveries from tomato paste ranged from 84 to 113% and were thus similar to those from drinking water. Lehotay et al.27 previously obtained oxamyl recoveries above 90% from various types of food. In addition, Glauner28 achieved 103.3% recoveries of oxamyl from fruit samples in validating a QuEChERS method similar to that used in the present work. The effectiveness of this extraction procedure was also reported for the simultaneous analysis of carbamates in aromatic herbs, when the extraction was used in combination with a more sophisticated HPLC-MS29 and with the relatively low-sensitivity traditional detectors, such as UV, diode array, electron-capture, flame photometric, and nitrogen−phosphorus detectors.30 Validation of the Method. The proposed method for oxamyl was validated by using least-squares regression to compare its results with those of a chromatographic method using postcolumn UV−vis spectrophotometry for detection. A total of 7 samples containing oxamyl at levels within the application range of the proposed method were analyzed. The results of the two methods were subjected to least-squares paired analysis, which considers the effects of various types of error, the presence of random of errors in the test method causing points to scatter around the least-squares line, and the calculated slope and intercept to slightly depart from unity and
the carbamate to be converted into reactive substances that oxidized luminol and increased CL emission in proportion to the analyte concentration. Calibration Curve. An oxamyl calibration curve was constructed by using standard solutions spanning the concentration range 0.17−3.4 mg L−1. Each solution was injected in triplicate, and the calibration curve was constructed by plotting CL peak area against analyte concentration. The proposed method was then evaluated by statistical analysis. To this end, the experimental data were fitted to the overall leastsquares equation y = 105.9xC + 3.60. The standard deviation of the slope and intercept on the ordinate, sa, of the obtained regression line were 5.707 and 10.69, respectively. The high determination coefficient (r2 = 0.9857) obtained testifies to the good linearity of the standard curve throughout the usable concentration range and the negligible dispersion in the experimental points. The limits of detection in accordance with the IUPAC definition,25 which considers the standard deviation of the blank and the slope of the calibration graphs was 0.17 mg L−1. This detection limit can be adequate for several kinds of studies on the presence of this insecticide in vegetables. For instance, it has been found that the concentration of oxamyl after 25 mg kg1− foliar to tomato plants can be reduced to 1 mg D
DOI: 10.1021/acs.jafc.7b06056 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
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(2) Moser, V. C.; Phillips, P. M.; McDaniel, K. L. Assessment of biochemical and effects of carbaryl and methomyl in Brown-Norway rats from preweaning to senescence. Toxicology 2015, 331, 1−13. (3) Minnis, S. T.; Haydock, P. P. J.; Evans, K. Control of potato cyst nematodes and economic benefits of application of 1,3-dichloropropane and granular nematicides. Ann. Appl. Biol. 2004, 145, 145−156. (4) Banerjee, B.; Seth, V.; Bhattacharya, A.; Pasha, S. T.; Chakraborty, A. K. Biochemical Effects of Some Pesticides on Lipid Peroxidation and Free Radical Scavengers. Toxicol. Lett. 1999, 107, 33−47. (5) Krieger, R.; Doull, J.; Ecobichon, D.; Gammon, D.; Hodgson, E.; Reiter, L.; Ross, J. Handbook of Pesticide Toxicology Principles, 2nd ed.; Academic Press: San Diego, 2002; pp 1087−1108. (6) Struger, J.; Grabuski, J.; Cagampan, S.; Sverko, E.; Marvin, Ch Occurrence and Distribution of Carbamate Pesticides and Metalaxyl in Southern Ontario Surface Waters 2007−2010. Bull. Environ. Contam. Toxicol. 2016, 96, 423−431. (7) Hossain, M. S.; Fakhruddin, A. N. M.; Alamgir, Z. M. C.; Rahman, M. A.; Khorshed, A. M. Health risk assessment of selected pesticide residues in locally produced vegetables of Bangladesh. Int. Food Res. J. 2015, 22, 110−115. (8) Al-Antary, M. T.; Al-Dabbas, M. M.; Shaderma, A. M. Effect of UV-radiation on methomyl, oxamyl and carbosulfan residues in tomato juice. Fresen. Environ. Bull. 2014, 23, 924−928. (9) Xiao, Q.; Gao, H.; Yuan, Q.; Lu, C.; Lin, J. High-performance liquid chromatography assay of cysteine and homocysteine using fluorosurfactant-functionalized gold nanoparticles as postcolumn resonance light scattering reagents. J. Chromatogr. A 2013, 1274, 145−150. (10) Li, Q.; Shang, F.; Lu, C.; Zheng, Z.; Lin, J. (2011) Fluorosurfactant-prepared triangular gold nanoparticles as postcolumn chemiluminescence reagents for high-performed liquid chromatography assay of low molecular weight aminothiols in biological fluids. J. Chromatogr A 2011, 1218, 9064−9070. (11) Zhang, L.; Lu, B.; Lu, C.; Lin, J. (2014) Determination of cystein, homocystein, cystine and homocystin in biological fluids by HPLC using fluorosurfactant-capped gold nanoperticles as postcolumn colorimetric reagents. J. Sep. Sci. 2014, 37, 30−36. (12) He, Y.; Xu, B.; Li, W.; Yu, H. Silver Nanoparticle-Based Chemiluminescent Sensor Array for Pesticide Discrimination. J. Agric. Food Chem. 2015, 63, 2930−2934. (13) Huertas-Pérez, J. F.; García-Campaña, A. M.; Gámiz-Gracía, L.; González-Casado, A.; Iruela, M. d. O. Sensitive determination of carbaryl in vegetal food and natural waters by flor-injection analysis based on the luminol chemiluminescence reaction. Anal. Chim. Acta 2004, 524, 161−166. (14) Tsogas, G.; Giokas, D. L.; Nikolakopoulos, P. G.; Vlessidis, A. G.; Evmiridis, N. P. Determination of the pesticide carbaryl and its photodegradation kinetics in natural waters by flow injection-direct chemiluminescence detection. Anal. Chim. Acta 2006, 573−574, 354− 359. (15) Soto-Chinchilla, J. J.; Gámiz-Gracía, L.; García-Campaña, A. M.; Cuadros-Rodriguez, L. A new strategy for the chemiluminiscent screening analysis of total N-methylcarbamate content in water. Anal. Chim. Acta 2005, 541, 111−116. (16) Garcia-Campaña, A. M.; Baeyens, R. Chemiluminiscence in Analytical Chemistry, 1st ed.; Marcel Dekker: New York, 2001; p 621. (17) Burrows, H. D.; Canle L, M.; Santaballa, J. A.; Steenken, S. Invited Review Reaction pathways and mechanisms of photodegradation of pesticides. J. Photochem. Photobiol., B 2002, 67, 71−108. (18) Herweh, J.; Hoyle, C. Photodegradation of Some Alkyl narylcarbamates. J. Org. Chem. 1980, 45, 2195−2201. (19) DeMarco, A. C.; Hayes, E. R. Photodegradation of thiolcarbamate herbicides. Chemosphere 1979, 8, 321−326. (20) Climent, M.; Miranda, M. Gas chromatographic−mass spectrometry study of photodegradation of carbamate pesticides. J. Chromatogr. A 1996, 738, 225−231. (21) Anastassiades, M.; Lehotay, S.; Stajnbaher, D.; Schench, F. Fast and Easy Multi-residue Method Employing Acetonitrile Extraction/
zero, respectively, as a result. Random errors can be estimated from the standard deviation in the y-direction (also called “the standard deviation of the estimate of y on x”). A proportional systematic error causes a change in b, so the difference between b and unity provides an estimate of the error. A constant systematic error reflects in a nonzero value for the intercept. If both methods provide identical concentrations for the same samples, then the least-squares analysis should give a zero intercept and an unit slope. The results obtained demonstrated that the two methods compared were significantly correlated. Repeatability and Reproducibility. Samples of drinking water and tomato paste were spiked with a 1.0 mg L−1 and a 1.0 mg kg−1 of the analyte, respectively. Then, they were analyzed four times on the same day and by interday analyses. The resulting relative standard deviations ranged from 7.5 to 9.0%, in both cases. The proposed method provides a simple, fast, accurate, selective choice for the determination of oxamyl in drinking water and tomato paste with detection limits complying with international regulations on this insecticide. The QuEChERS method used affords extraction of the analyte with recoveries of 86−113% from samples spiked with oxamyl concentrations above the limit of detection (0.17 mg L−1). UV irradiation is commonly used to eliminate dangerous microorganism from drinking water, and this treatment can also reduce the concentration of several organic pollutants by decomposition reactions involving free radicals as occurs in the carbamates. The remaining concentrations of these pollutants in water after the irradiation can be easily quantified by the usual HPLC chromatographic systems coupled to UV−vis detectors. However, this system cannot be used to detect the presence of the free radicals remaining in the water, which are very dangerous to living cells when are consumed by humans or animals. The proposed detection based on the effect of the free radicals on luminol CL can be employed not only for oxamyl quantification but also for the detection of the free radicals produced during the carbamate decomposition. This work offers a new quantification procedure that can be used in future works to measure the mean life times of free radicals and the rates of their inactivation, among other factors, to ensure the good quality of drinking water.
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +34 926 295300. E-mail:
[email protected]. ORCID
Luisa F. García Bermejo: 0000-0003-3538-1811 Funding
The authors gratefully acknowledge financial support from the “Consejeriá de Educación, Cultura y Deportes” and “Fondo Europeo de Desarrollo Regional (FEDER)” Project no. PEII110351-7802. Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/acs.jafc.7b06056 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
