Adsorption studies of trifluralin on chitosan and its voltammetric determination on a modified chitosan glassy carbon electrode

Abstract

Os estudos sobre adsorção do herbicida trifluralina (TRF) em quitosana foram realizados em batelada, usando temperaturas entre 298 e 313 K. Os resultados de adsorção ajustaram-se perfeitamente ao modelo de adsorção de Langmuir. O valor de entalpia obtido −10,2 ± 0,8 kJ mol -1 confirma que a interação TRF-quitosana é exotérmica e que o processo de adsorção é relativo à interação eletrostática entre o grupo amônio da quitosana e o dipolo negativo dos grupos substituintes de TRF, sendo dependente da força iônica. Estudos voltamétricos mostraram que TRF apresentou dois picos de redução em eletrodo de CV, ambos de natureza difusional e irreversível, referentes à redução dos grupos nitroaromáticos. A corrente do primeiro pico de redução intensificou-se no eletrodo de carbono vítreo modificado com quitosana, em comparação com o eletrodo não modificado. Isto foi atribuído à adsorção/acumulação de TRF em quitosana. A corrente de redução em voltametria de pulso diferencial foi proporcional à concentração de TRF na faixa de 2,49 × 10 −7 a 5,79 × 10 −6 mol L -1 , com limite de detecção de 7,45 × 10 -8 mol L -1 .The studies about adsorption of the herbicide trifluralin (TRF), on chitosan, were carried out by batch methods using temperatures from 298 up to 313 K. The adsorption results were well fitted to Langmuir adsorption model. The obtained enthalpic value of −10.2 ± 0.8 kJ mol -1 confirms that the TRF-chitosan interaction is exothermic and that the adsorption process is relative to electrostatic interaction between the ammonium group of chitosan and the negative dipole of the substituent groups of TRF, being dependent on ionic strength. Voltammetric studies showed that TRF exhibited two irreversible, diffusional reduction waves related to the reduction of the nitroaromatic groups. The current of the first reduction peak intensified on the chitosan-modified glassy carbon electrode in comparison with the unmodified one. This was attributed to the adsorption/accumulation of TRF on chitosan. The reduction current, using Differential Pulse Voltammetry, was proportional to the concentration of TRF in the range of 2.49 ×10 −7 to 5.79 ×10 −6 mol L -1 , with a detection limit of 7.45 × 10 -8 mol L -1 . Keywords: adsorption, trifluralin, electroanalytical, chitosan IntroductionWater pollution by pesticides from routine agricultural practices is a common and growing problem in the major agricultural areas of the world. Herbicide contamination of water systems has been of major concern in recent years. Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) aniline, CAS 1582-09-8] is a dinitroaniline pre-emergence herbicide used for the control of broadleaf weeds in a wide variety of crops including cotton, brassica, soybeans and ornamentals, among others. 1 TRF is a relatively immobile herbicide in soils so there is little hazard for groundwater contamination, however it has a tendency to volatilize, 2 with vapor pressure 1.5 × 10 -2 Pa 3 and Henry Constant H = 16.8 Pa m 3 mol -1 at 25 o C, hence it can relatively easily enter ...

RETRACTED: Lab-on-fruit skin and lab-on-leaf towards recognition of trifluralin using Ag-citrate/GQDs nanocomposite stabilized on the flexible substrate: A new platform for the electroanalysis of herbicides using direct writing of nano-inks and pen-on paper technology

“…Also, the results obtained from the more sensitive DPV and SWV techniques confirm the conductivity of the sensor provided and its ability to detection of analyte. The interaction mechanism of trifluralin on the prepared Ag-citrate/GQDs nano-ink/leaf electrode was based on electrostatic interactions, probably, between the dipole nitro group of trifluralin with negative charge and protonated amine group (R–NH 3 + ) of chitosan which was diluted in acetic acid and also Ag + group of Ag-citrate in the conductive nano-ink [ 23 ]. Trifluralin experiences three types of chemical transformation (oxidation mechanism), including: I) Addition of OH to the aromatic ring, II) abstraction of H by OH radicals of two alkyl chains, and III) dealkylation possibly because of photolysis [ 34 ].…”

“…There are various methods for detection of trifluralin, including; liquid chromatography [ 15 ], gas chromatography (GC) [ 16 ], HPLC-mass spectrometry (MS) [ 17 ], UV spectrometry [ 18 ], solution-state nuclear magnetic resonance spectroscopy [ 19 ], capillary electrophoresis [ 20 ] and electrochemical methods [ 21 , 22 , 23 ].…”

Electrochemical behavior of metribuzin on a glassy carbon electrode in an aqueous medium including quantitative studies by anodic stripping voltammetry

“…Pesticides have been used extensively as a strategy to improve agricultural productivity, but their use poses environmental and toxicological risks and groundwater contamination by herbicides has been a major concern in recent years. 1,2 Metribuzin (4-amino-6-tert-butyl-3methylthio-1,2,4-triazin-6(4H)-one (MTZ) belongs to the class of triazines that are widely used for weed control. 3 It is a selective triazinone that inhibits photosynthesis and is used for the pre-and post-emergence control of many grasses and broad-leaved weeds in soybeans, potatoes, tomatoes, sugarcane, alfalfa, asparagus, maize and cereals at 0.07-1.05 kg active ingredient (a.i.)/ha.…”

Stripping voltammetric methods for determination of the antiparasitic drug nitazoxanide in bulk form, pharmaceutical formulation and human serum

“…-4 mol L -1 nitazoxanide recorded at the HMDE in the B-R universal buffer of various pH values (2 to 11) containing 20% (v/v) ethanol displayed a well-defined single 4-electron irreversible cathodic peak, Figure 1, which was attributed to reduction of its NO 2 group to the hydroxylamine stage [15][16][17] as confirmed from controlled-potential coulometry measurements. The peak potential (E p ) shifted to more negative values upon the increase of pH of the medium indicating the involvement of protons in the electrode reaction and that the proton-transfer reaction precedes the electron transfer.…”