An electrochemical fentanyl sensor based on modified screen-printed carbon electrode by Zn(ii)-MOF.

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A simultaneous derivatization/air-assisted liquid-liquid microextraction technique has been developed for the sample pretreatment of some parabens in aqueous samples. The analytes were derivatized and extracted simultaneously by a fast reaction/extraction with butylchloroformate (derivatization agent/extraction solvent) from the aqueous samples and then analyzed by GC with flame ionization detection. The effect of catalyst type and volume, derivatization agent/extraction solvent volume, ionic strength of aqueous solution, pH, numbers of extraction, aqueous sample volume, etc. on the method efficiency was investigated. Calibration graphs were linear in the range of 2-5000 μg/L with squared correlation coefficients >0.990. Enhancement factors and enrichment factors ranged from 1535 to 1941 and 268 to 343, respectively. Detection limits were obtained in the range of 0.41-0.62 μg/L. The RSDs for the extraction and determination of 250 μg/L of each paraben were <4.9% (n = 6). In this method, the derivatization agent and extraction solvent were the same and there is no need for a dispersive solvent, which is common in a traditional dispersive liquid-liquid microextraction technique. Furthermore, the sample preparation time is very short.

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A green biocomposite of sunflower stalks and graphitic carbon nitride nanosheets has been applied as a solid-phase extraction adsorbent for sample preparation of five polycyclic aromatic hydrocarbons in different solutions using high-performance liquid chromatography with ultraviolet detection. Before the modification, sunflower stalks exhibited relatively low adsorption to the polycyclic aromatic hydrocarbons extraction. The modified sunflower stalks showed increased adsorption to the analytes extraction due to the increase in surface and existence of a π-π interaction between the analytes and graphitic carbon nitride nanosheets on the surface. Under the optimal conditions, the limits of detection and quantification for five polycyclic aromatic hydrocarbons compounds could reach 0.4-32 and 1.2-95 ng/L, respectively. The method accuracy was evaluated using recovery measurements in spiked real samples and good recoveries from 71 to 115% with relative standard deviations of <10% have been achieved. The developed method was successfully applied for polycyclic aromatic hydrocarbons determination in various samples-well water, tap water, soil, vegetable, and barbequed meat (kebab)-with analytes contents ranging from 0.065 to 13.3 μg/L. The prepared green composite as a new sorbent has some advantages including ease of preparation, low cost, and good reusability.

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