Detection of carbofuran and metabolites directly or as their heptafluorobutyryl derivatives using gas-liquid or high-pressure liquid chromatography with different detectors

Highly Selective Electrochemical Sensor Based on Gadolinium Sulfide Rod-Embedded RGO for the Sensing of Carbofuran

Nowadays, a lot of pesticides have been used in the agriculture field due to the global demand for food production. Carbofuran (CF) is the most commonly used carbamate compound that is responsible for the highest toxicity to humans compared to any other pesticide used in agricultural settings. Thus, rapid, portable, and low-cost sensors are needed for the detection of CF in the environment and food samples. Herein, we have successfully developed an electrochemical sensor using a glassy carbon electrode (GCE) modified with gadolinium sulfide (Gd₂S₃) and reduced graphene oxide (RGO) composite for the detection of carbofuran (CF). A novel Gd₂S₃/RGO composite was prepared by the facile hydrothermal route and confirmed by morphological and structural analyses such as field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX), powder X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and also the formation mechanism of Gd₂S₃/RGO composite was discussed. The desired electrical conductivity of Gd₂S₃ was enhanced by the RGO, which was estimated from the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Electrochemical studies demonstrated that the developed Gd₂S₃/RGO sensor was highly sensitive and selective to CF. In addition, the Gd₂S₃/RGO sensor exhibits a low detection limit (LOD) and the linear ranges were 0.0128 and 0.001-1381 μM, respectively, for CF detection under optimized experimental conditions. Moreover, we also investigated the practical applicability of the sensor for CF detection in the environment and food samples.

A fluorescence detection scheme for capillary electrophoresis of N-methylcarbamates with on-column thermal decomposition and derivatization

This paper describes a fluorescence detection method for N-methylcarbamate (NMC) pesticides in micellar electrokinetic chromatography (MEKC) separation. Fulfillment of the fluorescence detection hinged on the discovery that quaternary ammonium surfactants (particularly cetyltrimethylammonium bromide, CTAB), besides serving as hydrophobic pseudophases in MEKC, are also capable of catalyzing the thermal decomposition of NMCs to liberate methylamine. Thus, a multifunctional MEKC medium consisting of borate buffer, CTAB, and derivatizing components (o-phthaldialdehyde/2-mercaptoethanol) was formulated, which allowed first normal MEKC separation, subsequent thermal decomposition, and finally in situ derivatization of NMCs. With careful optimization of the operation conditions, fluorescence detection of 10 NMC compounds was achieved, with column efficiencies typically higher than 50,000 and detection limits better than 0.5 ppm. The present work represents an unprecedented effort in capillary electrophoresis (CE), in which an intact capillary was consecutively utilized as chambers for separation, decomposition, derivatization, and detection, without involving any interfacing features. The success in the implementation of such a detection system resulted in strikingly simple instrumentation as compared with the traditional postcolumn fluorescence determination of NMCs by reversed-phase HPLC. Similar protocols should be workable in the determination of a wide range of pesticides and pharmaceuticals in CE formats.

Gas-liquid chromatography of triazine herbicides as heptafluorobutyryl derivatives and some applications to analysis in foods

The heptafluorobutyryl (HFB) derivatives of ten triazine herbicides were prepared by reacting the pesticides with heptafluorobutyric anhydride in benzene, in the presence of trimethylamine or pyridine as catalyst. The reactions produced mainly the mono-HFB products while some of the herbicides had small quantities of the di-HFB derivatives present. The derivatives were 300 fold to several thousand fold more sensitive to electron-capture detection than the underivatized triazines. They also were 5-10 fold more sensitive than the parents by electrolytic conductivity detection in the halogen mode while they were of similar sensitivity with the same detector in the nitrogen mode. The derivatives eluted in the same general order as the parent triazines on stationary phases of OV-1, OV-101, OV-101/QF-1, and OV-210. This method was successfully applied to the analysis of potatoes, peas and tomatoes spiked with various triazines at levels of 0.13-0.86 ppm.