Comparison Between Three Chromatographic (GC-ECD, GC-PFPD and GC‑ITD‑MS) Methods and a UV-Vis Spectrophotometric Method for the Determination of Dithiocarbamates in Lettuce

Abstract

The purpose of this study was to compare the performance of gas chromatographic with electron capture detector, pulsed flame photometric detector and mass spectrometry (GC-ECD, GC-PFPD and GC-MS) and UV-Vis spectrophotometric methods, based on acidic hydrolysis with tin(II) chloride of dithiocarbamate and analysis of the evolved CS 2 . For the validation studies were assessed linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy and precision. Recovery experiments were performed at 0.05 and 0.4 (chromatographic method) and 0.4, 0.8 and 2.0 mg CS 2 kg -1 (UV-Vis spectrophotometric method). The analytical curves were linear from 0.08 to 2.0 µg CS 2 mL -1 (chromatographic method) and from 0.4 to 2.2 µg mL -1 and from 2.2 to 8.9 µg CS 2 mL -1 (both with r 2 > 0.995) (UV-Vis spectrophotometric method). Method LODs were 0.01 and 0.28 mg CS 2 kg -1 and LOQs were 0.02 and 0.4 mg CS 2 kg -1 for the chromatographic and spectrophotometric methods, respectively. Acceptable accuracy was obtained for both methods (RSDs < 15.9% and recoveries from 87.7-107.4%). There was no significant difference between the techniques and detectors employees.Keywords: dithiocarbamate, fungicide, lettuce, gas chromatography, UV-Vis spectrophotometry IntroductionDithiocarbamates (DTCs) are important fungicides and the most widely used group of pesticides in agriculture, due to their high efficiency for the control of fungal and bacterial pathogens, low production costs and relatively low mammalian acute toxicity.1-3 Furthermore, these compounds are also used as vulcanization accelerators and antioxidants in the rubber industry. Generally, DTCs are not considered to be highly toxic, but short-term exposure can cause eye, respiratory and skin irritation. 4 The toxicological significance of such fungicides in food is related to the metabolite or its degradation product ethylenethiourea (ETU), which is known to be carcinogenic, mutagenic and teratogenic. 23 Therefore, the purpose of this study was to compare critically and statically the performance of the gas chromatographic methods using three different detection systems (electron capture detection (ECD), pulsed flame photometric detection (PFPD) and mass spectrometry (MS)) with a UV-Vis spectrophotometric method for the determination of DTCs in lettuce. Experimental Chemicals and reagentsIso-octane, pesticide grade (Lab-scan Analytical Sciences, Dublin, Ireland), toluene, pesticide grade (Mallinckrodt, St. Louis, USA), solution of tin(II) chloride 1.5% in 4 mol L -1 hydrochloric acid (Boom, Meppel, The Netherlands), hydrochloric acid (Nuclear, São Paulo, Brazil), tin(II) chloride (Nuclear, São Paulo, Brazil), copper acetate (Vetec, Rio de Janeiro, Brazil), diethanolamine (Nuclear, São Paulo, Brazil), ethanol (Vetec, Rio de Janeiro, Brazil), sodium hydroxide (Merck, Darmstadt, Germany) and lead acetate (Vetec, Rio de Janeiro, Brazil) were used. Pesticide reference material of thiram (99% purity) and carbon disulfide (99.9%) were purchased from Dr. Ehrenstorfer (Augsburg, Ge...

Dithiocarbamate Residues in Fruits and Leaves of Passion Fruit (Passiflora edulis) from Different Brazilian Regions

“…The origin of CS 2 determined in the sample could not be identified, which is a limitation of the indirect methods to quantify dithiocarbamates, regardless of the detection method used. [11][12][13][14][15] Another limitation of the indirect methods is the possibility of false positive results in crops containing sulfur compounds, such as brassica (e.g., broccoli and cabbage), allium species (e.g., leek and onion) 27 and papaya, 13 a limitation that does not affect the analysis of passion fruit. Although there are specific methods for the determination of some dithiocarbamates in foods, mainly by high performance liquid cromatography (HPLC) using UV or mass spectrometric detectors, [28][29][30][31][32] none can discriminate all the dithiocarbamate compounds, including mancozeb from metiram.…”

“…from Different Brazilian Regions most organic solvents and low stability. 11 The classic method for the determination of dithiocarbamates quantifies the CS 2 generated by the acid degradation of the compound present in the sample, which can be spectrophotometrically determined after complexation, 7,[12][13][14] or by gas chromatography using different detectors. 11,[12][13][14][15] However, since all DTCs produce CS 2 , none of these methods allow the identification of the compound applied to the crop, and the results are expressed in mg kg -1 CS 2 .…”

A novel validated simple derivatization liquid chromatographic method with diode array detection for the simultaneous determination of mancozeb, azoxystrobin and difenoconazole in pesticide dosage form

“…However, most of these methods are applicable either to mancozeb, azoxystrobin or difenoconazole in various pesticide formulations for foods, fruits or water samples. For the determination of mancozeb by iodometry, 12 square-wave adsorptive stripping voltammetry (SWAdSV), 13,14 batch injection analysis (BIA) with pulsed amperometric detection (PAD) on boron-doped diamond (BDD) electrode, 15 UV-spectrophotometry, 16–20 flow injection (FI) spectrophotometry, 21,22 photoacoustic and Fourier transform infrared spectroscopy, 23,24 gas chromatography (GLC) with specific detectors such as an electron capture detector (ECD), flame atomic absorption spectroscopic detector (FAAS) and flame photometric detector (FPD), 25,26 high performance liquid chromatography (HPLC), 27–35 gas chromatography-mass spectrometry (GC-MS), 36–42 and liquid chromatography-mass spectrometry (LC-MS) 43–49 methods have been reported. Similarly, various analytical methods for the quantification of azoxystrobin using UV-spectrophotometry, 50 flow injection chemiluminescence (FI-CL), 51 gas chromatography (GLC), 52–58 high-performance liquid chromatography (HPLC), 59–68 gas chromatography-mass spectrometry (GC-MS) 69–71 and liquid chromatography-mass spectrometry (LC-MS) 72–74 for single and multipesticide formulations were reported in literature.…”

Clean-up Strategy for Dithiocarbamate Fungicide Determination in Soybean by GC-ITD-MS and GC-PFPD: Method Development and Validation

“…Even though traditional UV–vis spectrophotometric methods − are still being used, chromatographic methods ,,− are the most frequently applied techniques, providing acceptable and reproducible recoveries at low concentrations. Most methods have been developed for the analysis of fruit and vegetable matrices.…”