Publicação
Monitoring of pesticides in water media of Northeast Portugal
| Resumo: | In this work, an analytical methodology was developed for the monitoring of five emerging pollutants, namely, alachlor, metolachlor, heptachlor, dimethoate, and terbuthylazine. These compounds are among the most used pesticides in the northeast region of Portugal and Tunisia. A complete experimental methodology was optimized based on the simultaneous extraction and concentration of all five pesticides from aqueous matrices, by means of solid-phase micro-extraction (SPME) followed by detection and quantification using gas chromatography coupled to mass spectrometry (GC-MS). The optimization of the extraction step was performed using a polydimethylsiloxane–divinylbenzene (PDMS-DVB) coated SPME fiber by direct immersion (DI-SPME) in the aqueous sample. Experimental conditions, such as extraction temperature and time, pH value, salt concentration, and desorption time and temperature in the GC injector port were studied. The optimum value for each one of these parameters was selected based on the maximum total area value obtained in MS detector, using Full Scan Mode, for the mixture of the five pesticides. The extraction optimized conditions were achieved by immersion of a PDMS-DVB fiber in the sample mixture with 10% NaCl, a pH value of 2, at 60ºC for 80 min. Desorption of the compounds from the fiber is done in the GC port at 250ºC during 4 min. The GC-MS operating conditions were also studied and the main separation and detection parameters were selected. Samples were analyzed using the following oven temperature program: initial temperature of 120°C (held for 2 min), increased by 15°C min-1 to 190°C (held for 4 min) and, finally, increased by 10°C min-1 to 227°C held for 1min. The MS instrument operated in the Electron ionization mode (EI) was used for a full scan. The acquisition was performed in the range of 35–450 (m/z). The ion source temperature was 200 °C and the interface temperature was 270 °C. The identification and quantification were carried out using calibration curves obtained from the extraction of a standard mixture of the five selected pesticides for at least six concentrations levels, in the same experimental conditions used for the real samples. Detection limits ranged from 4.2 to 6.6 g/L. For pesticides with low values of KOW, like dimethoate, the use of a fiber of relatively non-polar nature would be favorable. The developed experimental methodology was implemented by the analysis of different samples collected from the surface water of three rivers from Bragança, namely, Fervença, Sabor and Onor. All three rivers showed different types and levels of contamination. |
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| Autores principais: | Hmida, Raed Ben |
| Assunto: | Emerging contaminants Pesticides Superficial waters micro-pollutants Solid hhase micro-extraction Gas chromatography – mass spectrometry |
| Ano: | 2020 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Instituto Politécnico de Bragança |
| Idioma: | inglês |
| Origem: | Biblioteca Digital do IPB |
| Resumo: | In this work, an analytical methodology was developed for the monitoring of five emerging pollutants, namely, alachlor, metolachlor, heptachlor, dimethoate, and terbuthylazine. These compounds are among the most used pesticides in the northeast region of Portugal and Tunisia. A complete experimental methodology was optimized based on the simultaneous extraction and concentration of all five pesticides from aqueous matrices, by means of solid-phase micro-extraction (SPME) followed by detection and quantification using gas chromatography coupled to mass spectrometry (GC-MS). The optimization of the extraction step was performed using a polydimethylsiloxane–divinylbenzene (PDMS-DVB) coated SPME fiber by direct immersion (DI-SPME) in the aqueous sample. Experimental conditions, such as extraction temperature and time, pH value, salt concentration, and desorption time and temperature in the GC injector port were studied. The optimum value for each one of these parameters was selected based on the maximum total area value obtained in MS detector, using Full Scan Mode, for the mixture of the five pesticides. The extraction optimized conditions were achieved by immersion of a PDMS-DVB fiber in the sample mixture with 10% NaCl, a pH value of 2, at 60ºC for 80 min. Desorption of the compounds from the fiber is done in the GC port at 250ºC during 4 min. The GC-MS operating conditions were also studied and the main separation and detection parameters were selected. Samples were analyzed using the following oven temperature program: initial temperature of 120°C (held for 2 min), increased by 15°C min-1 to 190°C (held for 4 min) and, finally, increased by 10°C min-1 to 227°C held for 1min. The MS instrument operated in the Electron ionization mode (EI) was used for a full scan. The acquisition was performed in the range of 35–450 (m/z). The ion source temperature was 200 °C and the interface temperature was 270 °C. The identification and quantification were carried out using calibration curves obtained from the extraction of a standard mixture of the five selected pesticides for at least six concentrations levels, in the same experimental conditions used for the real samples. Detection limits ranged from 4.2 to 6.6 g/L. For pesticides with low values of KOW, like dimethoate, the use of a fiber of relatively non-polar nature would be favorable. The developed experimental methodology was implemented by the analysis of different samples collected from the surface water of three rivers from Bragança, namely, Fervença, Sabor and Onor. All three rivers showed different types and levels of contamination. |
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