Non-fluorescent Substances Research Articles

Hydrothermal temperature-dependent compositions and copper complexing behaviors of hydrochar-derived dissolved organic matter: Insights from FT-ICR MS and multi-spectroscopic analysis

The copper complexing of dissolved organic matter released from hydrochar (HDOM) affects the former's environmental behavior. In this study, how hydrothermal temperatures (180, 220 and 260 °C) influence the molecular-level constitutions and Cu(II) binding features of HDOM were elucidated via fourier transform ion cyclotron resonance mass spectrometry and multi-spectroscopic analysis. The findings demonstrated that the almost HDOM molecules had the traits of lower polarity and higher hydrophobicity. As the hydrothermal temperature increased, the molecules with particularly high relative strength gradually disappeared, average molecular weight, percentages of CHON and aliphatic compounds of HDOM reduced while the percentages of CHO and aromatic compounds increased. In general, the fluorescence quenching of Cu(II) weakened as hydrothermal temperature rose and the Cu(II) binding stability constants of fluorophores in HDOM were 4.50–5.31. In addition, the Cu(II) binding order of fluorophores in HDOM showed temperature heterogeneities, and polysaccharides or aromatic rings of non-fluorescent substances had the fastest responses to Cu(II) binding. Generally, fluorescent components tend to bind Cu(II) at relatively trace concentrations (0–40 µmol/L), whereas non-fluorescent substances tend to the bind Cu(II) at relatively higher concentrations (50–100 µmol/L). This study contributed to the prediction of the potential environmental behaviors and risks of Cu(II) at the molecular level after hydrochar application.

Molecular imprinting-based indirect fluorescence detection strategy implemented on paper chip for non-fluorescent microcystin

Fluorescence analysis is a fast and sensitive method, and has great potential application in trace detection of environmental toxins. However, many important environmental toxins are non-fluorescent substances, and it is still a challenge to construct a fluorescence detection method for non-fluorescent substances. Here, by means of charge transfer effect and smart molecular imprinting technology, we report a sensitive indirect fluorescent sensing mechanism (IFSM) and microcystin (MC-RR) is selected as a model target. A molecular imprinted thin film is immobilized on the surface of zinc ferrite nanoparticles (ZnFe2O4 NPs) by using arginine, a dummy fragment of MC-RR. By implementation of IFSM on the paper-based microfluidic chip, a versatile platform for the quantitative assay of MC-RR is developed at trace level (the limit of detection of 0.43 μg/L and time of 20 min) in real water samples without any pretreatment. Importantly, the proposed IFSM can be easily modified and extended for the wide variety of species which lack direct interaction with the fluorescent substrate. This work offers the potential possibility to meet the requirements for the on-site analysis and may explore potential applications of molecularly imprinted fluorescent sensors.

The degradation of municipal solid waste incineration leachate by UV/persulfate and UV/H2O2 processes: The different selectivity of SO4•- and •OH

In this work, the different selectivity of SO4•- and •OH towards municipal solid waste incineration leachates (MSWILs) was studied by a comparative study of UV/persulfate (PS) and UV/H2O2. Results showed SO4•- preferentially mineralized carbon atoms of higher average oxidation state, while •OH showed a two-stage mechanism of partial oxidation and mineralization successively. Electron spin resonance (ESR) analysis showed SO4•- had superior selectivity towards MSWILs than •OH, and Fe(II) would significantly affect the selectivity via forming Fe-MSWILs complex. As the consequence, Fe(II) showed slightly negative effect on UV/PS, but greatly enhanced the performance of UV/H2O2/Fe(II). High concentration of Cl- affected the degradation of non-fluorescent substances by UV/PS, while SO42- and NO3- showed no effect. In contrast, anions showed no effect on UV/H2O2. In addition, •OH preferentially attacked large molecules, but SO4•- showed no selectivity. This study further revealed the selectivity of SO4•- and •OH in the treatment of hypersaline wastewater, and provided theoretical support for the development of targeted technology.

A Fast and Easy Probe Based on CMC/Eu (Ⅲ) Nanocomposites to Detect Acrylamide in Different Food Simulants Migrating from Food-Contacting Paper Materials.

The residual acrylamide in food paper packaging can be transferred into water and food, which will cause harmful effects on human beings. In this paper, a rapid and easily available fluorescent probe based on carboxymethyl cellulose (CMC)/Eu (Ⅲ) nanocomposites was designed to detect the residue acrylamide with high sensibility. The probe could respond in 1 min. The concentration of acrylamide was linearly correlated to the fluorescence intensity of the probe at the emission wavelength of 615 nm in the concentration range of 0.1–100 μmol/L. The limit of detection (LOD) of the probe was 0.085 μg/L, which is lower than the guideline value of the European Union, the U.S. EPA, and the WHO. An experiment was performed to simulate the acrylamide migrating from food-contacting paper materials to different foods, including waterborne food, alcohol beverage, acidic food, and greasy food. The recoveries and RSDs of acrylamide in all samples indicated that the CMC/Eu (Ⅲ) fluorescent probe was efficient for acrylamide detection. The possible mechanism of the probe for acrylamide detection involved both dynamically quenching and static quenching by forming of non-fluorescent substances.

Reciprocal interferences of heavy metal and dissolved organic matter on their immobilizations by modulating the interfacial interactions with nanoscale zero-valent iron

With the increasing application of nanoscale zero-valent iron (nZVI) in environmental remediation, exploring the reciprocal effects of heavy metals (HMs) and dissolved organic matter (DOM) on their immobilizations by nZVI is crucial for predicting carbon dynamics and contaminant behavior in the environment. By using manifold analyses, the reciprocal effects of HMs (Cr(VI) and Cd(II)) and humic acid (HA) on their immobilizations by modulating the interfacial interactions with nZVI were systematically investigated. It was found that the previous interaction of HA especially its contained nonfluorescent substances (i.e., lipids, polysaccharides, and lignin) with nZVI improved the immobilization of HMs on nZVI; the previous interaction of Cd(II) with HA or nZVI promoted the sequestration of organic carbon (up to 1.8-fold) especially the aromatic carbon and humic-like fluorophores of HA by nZVI, but Cr(VI) had no such effect. The oxidized iron complexes on nZVI dominated the ultimate immobilizations of HA and HMs. The increased immobilizations of unsaturated hydrocarbons and quinone ketones by the formed nZVI-HM complexes decreased the reduction capability but enhanced the photochemical stability of the residual aqueous HA. These findings are of significance to understanding nZVI interactions with DOM and HMs and the effects on the carbon cycle and HM immobilization in the environment.

MIP-coated Eu(BTC) for the fluorometric determination of lincomycin in eggs

This study provides a new perspective for the determination of weak ultraviolet absorption or non-fluorescent substances.

UV Absorption Spectral Characteristics of Dissolved Organic Matter in Fen River of Taiyuan in China

UV absorption is one of the important properties of chromophoric dissolved organic matter (CDOM). The UV absorption spectral characteristics of dissolved organic matter (DOM) were analyzed to infer the main components in Taiyuan urban section. Based on the UV absorption spectral characteristics of the CDOM, and relationship between DOC concentration and UV absorbance, conclusions were drawn: (1) Content of DOM in the treated section was at a low degree and constituent.The anthropogenic pollution accounted for a major role. (2)DOM constituents in Taiyuan section in May, July and November were relatively simple. The molecular structure of mainly CDOM was simple with mostly two or three species among the hydroxyl, carboxyl and phenyl. However, DOM constituent in September was more complicated, there were more non-fluorescent substances besides CDOM.

Further insights into metal-DOM interaction: consideration of both fluorescent and non-fluorescent substances.

Information on metal binding with fluorescent substances has been widely studied. By contrast, information on metal binding with non-fluorescent substances remains lacking despite the dominance of these substances in aquatic systems. In this study, the metal binding properties of both fluorescent and non-fluorescent substances were investigated by using metal titration combined with two-dimensional correlation spectroscopy (2D–COS) analysis. The organic matters in the eutrophic algae-rich lake, including natural organic matters (NOM) and algae-induced extracellular polymeric substances (EPS), both contained fluorescent and non-fluorescent substances. The peaks in the one-dimensional spectra strongly overlapped, while 2D–COS can decompose the overlapped peaks and thus enhanced the spectral resolution. Moreover, 2D FTIR COS demonstrated that the binding susceptibility of organic ligands in both NOM and algal EPS matrices followed the order: 3400>1380>1650 cm−1, indicative the significant contribution of non-fluorescent ligands in metal binding. The modified Stern-Volmer equation also revealed a substantial metal binding potential for the non-fluorescent substances (logKM: 3.57∼4.92). As for the effects of organic ligands on metal binding, EPS was characterized with higher binding ability than NOM for both fluorescent and non-fluorescent ligands. Algae-induced EPS and the non-fluorescent substances in eutrophic algae-rich lakes should not be overlooked because of their high metal binding potential.

In vivo methods for the analysis of the penetration of topically applied substances in and through the skin barrier

The efficacy of a drug is characterized by its action mechanism and its ability to pass the skin barrier. In this article, different methods are discussed, which permit this penetration process to be analysed non-invasively. Providing qualitative and quantitative information, tape stripping is one of the oldest procedures for penetration studies. Although single cell layers of corneocytes are removed from the skin surface, this procedure is considered as non-invasive and is applicable exclusively to the stratum corneum. Recently, optical and spectroscopic methods have been used to investigate the penetration process. Fluorescence-labelled drugs can be easily detected in the skin by laser scanning microscopy. This method has the disadvantage that the dye labelling changes the molecular structures of the drug and consequently might influence the penetration properties. The penetration process of non-fluorescent substances can be analysed by Raman spectroscopy, electron paramagnetic resonance, CARS and multiphoton microscopic measurements. Using these methods, the concentration of the topically applied formulations in different depths of the stratum corneum can be detected by moving the laser focus from the skin surface deeper into the stratum corneum. The advantages and disadvantages of these methods will be discussed in this article.

Binding of Organic Ligands with Al(III) in Dissolved Organic Matter from Soil: Implications for Soil Organic Carbon Storage

The binding characteristics of organic ligands with Al(III) in soil dissolved organic matter (DOM) is essential to understand soil organic carbon (SOC) storage. In this study, two-dimensional (2D) FTIR correlation spectroscopy was developed as a novel tool to explore the binding of organic ligands with Al(III) in DOM present in soils as part of a long-term (21-year) fertilization experiment. The results showed that while it is a popular method for characterizing the binding of organic ligands and metals, fluorescence excitation-emission matrix-parallel factor analysis can only characterize the binding characteristics of fluorescent substances (i.e., protein-, humic-, and fulvic-like substances) with Al(III). However, 2D FTIR correlation spectroscopy can characterize the binding characteristics of both fluorescent and nonfluorescent (i.e., polysaccharides, lipids, and lignin) substances with Al(III). Meanwhile, 2D FTIR correlation spectroscopy demonstrated that the sequencing/ordering of organics binding with Al(III) could be modified by the use of long-term fertilization strategies. Furthermore, 2D FTIR correlation spectroscopy revealed that the high SOC content in the chemical plus manure (NPKM) treatment in the long term fertilization experiment can be attributed to the formation of noncrystalline microparticles (i.e., allophane and imogolite). In summary, 2D FTIR correlation spectroscopy is a promising approach for the characterization of metal-organic complexes.

Liquid Chromatography with Fluorescence Detection in the Analysis of Biological Fluids

ABSTRACT Liquid chromatography with fluorescence detection is well suited to the analysis of biological fluids, as it combines both selectivity and sensitivity. The determinations are not limited to fluorescent compounds, as non-fluorescent substances can be converted to fluorescent derivatives by appropriate reactions. As a consequence of progress in methodology and of the development of new reagents, a great number of biological substances and drugs can now be successfully analyzed by this technique. Reliable automated procedures using pre-column derivatization are available, in particular for the analysis of amino acids and amines. In addition, systems using short columns, reduced particle size of the stationary phase and ultramicro detector cells represent a promising approach to the analysis of very small volumes of sample.

An improved lidar method for monitoring surface waters: Experiments in the laboratory

Lidar monitoring of surface waters is usually applied to fluorescent substances like phytoplankton, yellow substances and oil. A lidar method is introduced which allows the measuring of the total attenuation coefficient at the laser wavelength considering also nonfluorescent substances besides fluorescent ones. Two signals are measured: first the total fluorescence lidar signal L, which is characterized by long path-lengths of the laser radiation in the water column, and second, the fluorescence F, which originates from the first layers immediately below the water surface. A simple experiment in the laboratory was performed using a nitrogen laser. Water samples containing algae and varying amounts of humic and ligninesulfonic acids were investigated. Synchronously the attenuation coefficients were measured. The F/L ratio yielded the total attenuation at the laser wavelength. Good correlations between the conventional and the lidar-derived attenuation coefficients were achieved described by squared correlation coefficients of R2 > 0.95. The F/L ratio seems to be a good tool in lidar monitoring of waters.

A portable absorption-fluorometer for detection of organic substances in fluids

Using the method of multipath-saturation fluorescence, which considers both fluorescent as well as nonfluorescent substances, the total absorption coefficient can be determined with high sensitivity. This new fluorescence method is appropriate, e.g. for in-situ applications. Thus a portable absorption-fluorometer has been constructed. The main part of the device is a multireflection cell based on a design of Herriott with a 1 cm quartz-cuvette. Two pairs of spherical dielectric mirrors are used to realize the multireflection of the excitation radiation in the UV and blue spectral range. The combination of a cylindrical and a convace mirror leads to a long pathway of the excitation radiation and, thus, to a full absorption by the fluid. A first experiment has been performed with drinking water samples defined polluted by non-fluorescent p-nitrophenol and 2-nitroaniline. Based on the method of multipath-saturation fluorescence a good correlation to the substance concentration was achieved, whereas the conventional absorption failed.

A new fluorescence technique to measure the total absorption coefficient in fluids

Conventional fluorescence methods are usually applied for the detection of fluorescent substances. A simple technique taking into account nonfluorescent substances has been introduced applying two different signals: (i) the linear or conventional fluorescence (CF) occurring at relatively short path-lengths of the exciting radiation in the fluids, and (ii) the multi-path saturation fluorescence (MPSF) originating at long path-lengths, as in multi-path reflection cells, where the radiation is fully absorbed by the fluid. A relation between the fluorescence signals and the absorption coefficients of fluorescent and nonfluorescent substances has been theoretically derived. An experiment has been performed with drinking water polluted by aromatic substances. The fluorescence ratio between CF and MPSF obtained has yielded the total absorption. Thus, it has been influenced by both fluorescent and nonfluorescent substances. In comparison to the conventional absorption technique, CF/MPSF has been characterized by high correlations to substance concentrations and has shown a much higher sensitivity. The method of CF/MPSF combines the advantage of fluorescence being very sensitive and of absorption spectrometry measuring the total absorption coefficient.

Changes in hot water soil extracts brought about by nitrogen immobilization and mineralization processes during incubation of amended soils

During incubation of an acid cambisol and an alkaline fluvisol, amended with glucose and nitrate, hot water soil extracts were analysed for N content, ultraviolet absorption, and fluorescence. Humic substances in the hot water extracts and in a neutral sodium pyrophosphate extract were fractionated on polyvinylpyrrolidone and measured spectroscopically. Changes in the hot water and pyrophosphate extract compositions were related to changes in microbial biomass, as estimated by substrate-induced respiration, and the hexosamine content of soil hydrolysates. During the incubation, the microbial population in each type of soil developed quite differently, according to the soil pH. Microbial growth and death in the alkaline soil sample induced a maximum of hot-water-extractable ultraviolet-absorptive non-fluorescent substances. The fluorescence of the hot water soil extract increased steadily with incubation time even after the microbial activity was reduced. A similar increase in fluorescence, in accord with the ultraviolet absorption, was found during incubation of the acid soil samples. After 95 days of incubation, the hot-water-extractable fluorescent and ultraviolet-absorptive substances were reduced. N immobilization induced an increase, and N mineralization a decrease, in dissolved organic N. The relative increase in humic substances in the hot water soil extract was much higher than in the pyrophosphate extract. Therefore, humic material, produced by microbial growth and death, is obviously extractable with hot water.

Optical methods for the detection and quantification of caries.

The commonly used clinical methods are inadequate for reliable diagnosis of caries lesions until demineralization is established. By the time a reliable diagnosis can be made, the damage is often irreversible, and restorative methods may be necessary to prevent further progress of the lesions. Early detection of the caries lesion would enable the dentist, by using effective prophylactic measures, to provide remineralization and conservation of the tooth substance rather than restoration of the dentition. Attempts to improve traditional methods or to develop new methods of detecting caries lesions have been numerous. Most of the presently used diagnostic methods require visual observation of an optical signal. Reflected light is used tc detect changes in color, texture, and translucency of the tooth substance. The tools required are a bright light source and a mouth mirror. With special methods utilizing drying, magnification, and photography, the sensitivity of the method can be increased. Various optical methods for the detection and quantification of caries will be discussed - for example, fiber optic transillumination, ultraviolet illumination, the use of various dyes, and fluorescent or non-fluorescent substances to enhance the contrast between the carious and the sound enamel. This presentation will focus on the following two methods: (1) a method that uses visible laser light within the blue-green region as the light source to improve signal-to-noise ratio and increase sensitivity for detection of early caries lesions, and (2) a recently developed quantitative method based on the scattering of light by enamel crystals in relation to their surrounding environment. The possibilities and limitations of the different methods will be critically evaluated. In the near future, optical methods for the detection and quantification of early caries lesions will provide efficient tools for reliable evaluation of caries-preventive measures.