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Signal enhancement in laser diode thermal desorption-triple quadrupole mass spectrometry analysis using microwell surface coatings
摘要： Laser diode thermal desorption (LDTD) is an ionization source usually coupled to triple quadrupole mass spectrometry (QqQMS) and specifically designed for laboratories requiring high-throughput analysis. It has been observed that surface coatings on LDTD microwell plates can improve the sensitivity of the analysis of small polar molecules. The objective of the present study is to understand and quantify the effect of microwell surface coatings on signal intensity of small organic molecules of clinical, environmental and forensic interest. Experiments showed that the peak areas of diclofenac, chloramphenicol, salicylic acid and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol obtained by LDTD-QqQMS increased by up to 3 orders of magnitude when using microwells coated with ethylenediaminetetraacetic acid (EDTA). Tests with different chelating agents and polytetrafluoroethylene as microwell surface coatings showed that nitrilotriacetic acid gave significantly higher peak areas for five out of the nine compounds that showed signal enhancement using chelating agents as coatings. Scanning electron microscopy studies of EDTA-coated and uncoated microwells showed that analytes deposited in the former formed more uniform and thinner films than in the latter. The enhancement effect of surface coatings in LDTD-QqQMS was explained mainly by the formation of homogenous and thinner layers of nanocrystals of analytes that are easier to desorb thermally than the layers formed when the analytes dry in direct contact with the bare stainless steel surface. Chemisorption of some analytes to the stainless steel surface of the microwell plate appeared to be a minor factor. Surface coatings widen the number of compounds analyzable by LDTD-QqQMS and can also improve sensitivity and limits of detection.
关键词： pharmaceuticals,high-throughput,hormones,pesticides,x-ray photoelectron spectroscopy,scanning electron microscopy,stainless steel,small organic molecules,chelating agents
更新于2025-09-23 15:23:52
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Enhanced photocatalytic inactivation of E.coli by natural pyrite in presence of citrate and EDTA as effective chelating agents: Experimental evaluation and kinetic and ANN models
摘要： The effect of chelating agents (citrate and EDTA) on the visible light photocatalytic activity of natural pyrite for the inactivation of Escherichia coli ATCC 25922 (E.coli) was investigated. The influence of various parameters, such as chelating agent and H2O2 concentration, light intensity and aeration rate, was evaluated experimentally and through kinetic models. The presence of a chelating agent enhanced the photocatalytic activity of natural pyrite, and citrate was more effective than EDTA, considerably improving bacteria inactivation in natural pH and reducing the drawbacks of the photocatalytic inactivation system. For both citrate-pyrite and EDTA-pyrite, the inactivation rate went through a maximum for a concentration of the chelating agent of 0.5 mM. The increase of the light intensity (10–60 mW cm-2), H2O2 concentration (10-25 mg L-1) and aeration rate (2-8 L min-1) improved the radical generation, resulting in a high inactivation effect. The low effect of H2O2 on the catalytic activity of pyrite in the presence of EDTA was likely due to the inhibition of the hydrogen peroxide-to-hydroxyl radical conversion by EDTA. On the other hand, degradation of citrate at high aeration rate occurred, decreasing the catalytic activity of the citrate-pyrite system. Scavenging tests indicated that the bulk hydroxyl radicals are the most reactive radical species in the bacterial inactivation, closely followed by valence band holes, while conduction band electrons play a less important role. In addition, in order to generate predictions and to better understand the process, artificial neural networks were used as models for the considered process: the obtained performance indexes indicated a good correlation between experimental and predicted values.
关键词： Pyrite,Photo-Fenton,E.coli,Photocatalytic inactivation,Chelating agents
更新于2025-09-23 15:22:29
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Enhanced photovoltaic performance and stability of planar perovskite solar cells by introducing dithizone
摘要： In the two-step spin-coating method, the crystallization and morphology of PbI2 film are essential for producing highly efficient and stable planar heterojunction (PHJ) perovskite solar cells. In this work, the dithizone (DTZ) molecules were introduced into PbI2 precursor to improve the performance of perovskite films. We found that adding DTZ was an effective method to retard the crystallization of PbI2 film and consequently, produced a high-quality perovskite film with pinhole-free, smoother, and fewer defects surface. Most importantly, the presence of residual DTZ in wet PbI2 film also assisted DMSO to slow down the growth of perovskite grains. By tuning the concentration of DTZ, the power conversion efficiency of the best performed cell has increased to 20.66% with negligible photocurrent hysteresis. Meanwhile, the best DTZ device offer an excellent stability, which retained 97% of the initial PCE after storage in the dark for approximately 24 days. We expect this controlled crystallization method could be further explored and provides a useful strategy to improve the performance of perovskite solar cells.
关键词： Planar heterojunction,Dithizone,Perovskite solar cells,Two-step spin-coating method,Chelating agents
更新于2025-09-12 10:27:22