Excitation-emission Matrix Fluorescence Spectroscopy Research Articles

Fast and efficient processes for oxidation and monitoring of polycyclic aromatic hydrocarbons in environmental matrices

This study proposes a new approach for the efficient photodegradation of polycyclic aromatic hydrocarbons (PAH) and derivatives. PAH removal was achieved in just a few minutes using a microwave photochemical reactor capable of producing a high concentration of •OH (2.3 mmol L−1 h−1). Fluorescence excitation-emission matrix (EEM) spectroscopy coupled to parallel factor analysis (PARAFAC) was used for quantifying two PAH and one alkylated PAH at low concentrations (μg L−1). These results highlight the high potential of the photochemical degradation system coupled to EEM-PARAFAC as an alternative fast, inexpensive, and efficient approach for environmental remediation studies of PAH.

Classification of water by bacterial presence using chemometrics associated with excitation-emission matrix fluorescence spectroscopy

Bacterial presence in water is an important indicator of water quality and, when found in high concentrations, may risk human health. The detection of total coliforms, thermotolerant coliforms, and Escherichia coli (E. coli) in water through standard methods involves time-consuming and expensive laboratory tests, which may not always provide timely and accurate results. An alternative approach is excitation-emission matrix fluorescence spectroscopy (EEMFS), which offers fast detection of bacteria in water by analyzing fluorescent compounds. Chemometrics methods can be used to process EEMF spectrum, extract the relevant information, and differentiate water samples based on the presence of bacteria using classification models. In this study, various classification algorithms were applied to EEMFS datasets, including k-nearest neighbors (k-NN), partial least squares discriminant analysis (PLS-DA), multiway-PLS (NPLS-DA), principal component analysis with discriminant analysis (PCA-DA), support vector machines (SVM), and random forest (RF). Models were developed after the unfold multiway and parallel factor analysis (PARAFAC) to classify groundwater, freshwater, saltwater, and treated water samples according to the presence of E. coli, thermotolerant coliforms, and total coliforms. Among these models, PLS-DA, SVM, and RF demonstrated superior performance in discriminating the samples in most cases. In the test sets, the accuracy of the best models for total coliforms varied from 85.2% to 100% for groundwater, 71.4% to 98.2% for freshwater, 64.6% to 81.3% for treated water, and 65.8% to 71.1% for saltwater. Accuracy for E. coli and thermotolerant coliforms ranged from 89.3% to 100% in groundwater and from 64.7% to 87.5% for treated water. Results for thermotolerant coliforms in freshwater were 64.8% to 95.2%, and 63.3% to 76.7% for saltwater. For E. coli, accuracy ranged from 73.8% to 78.6% for freshwater and 65.0% to 80.0% for saltwater.

Solid-phase fluorescence: Reproducibility and comparison with the solution states

Solid-phase fluorescence excitation-emission matrix (SPF-EEM) spectroscopy has potential for non-extractive, non-destructive, and non-contact analytical measurements of powder and solid-state samples, as well as front-face EEM spectroscopy for suspensions of high optical density. However, as there is no unified measurement method for SPF spectroscopy, comparing samples measured in different research fields is difficult. Therefore, this study designs a cell that can be created by a 3D printer and examines reproducibility on measuring fluorescent powders. The developed cell is applied to proteins (ovalbumin, BSA, gliadin, gluten, powdered collagen, casein), amino acids (tryptophan, tyrosine, and phenylalanine), soybean ingredients (daidzein, and genistein), and fluorescent chemicals (rhodamine B, fluorescein sodium salt, pyrene, and quinine sulfate dihydrate) and their spectra are compared with those in the solution states. When samples are refilled into the cell three times, the cell exhibits high reproducibility in terms of fluorescence peak wavelength and intensity. The solid proteins exhibit peaks attributed to the fluorescent amino acid residues, and broad peaks which are not detected for the proteins in the solution states. Powdered rhodamine B and fluorescein sodium salt do not exhibit fluorescence, possibly due to the inner-filter effect (IFE). Some non-colored molecules also exhibit loss of fluorescence or a remarkable difference between the solid and solution states, possibly due to the interaction of the fluorescent structure with the surrounding local environment, similar to the solvent effect, which is possibly affected by the molecular proximity, three-dimensional structure, and moisture absorption capacity.

Humification levels of dissolved organic matter in the eastern plain lakes of China based on long-term satellite observations

Under the influence of intensive human activities and global climate change, the sources and compositions of dissolved organic matter (DOM) in the eastern plain lake (EPL) region in China have fluctuated sharply. It has been successfully proven that the humification index (HIX), which can be derived from three-dimensional excitation-emission matrix fluorescence spectroscopy, can be an effective proxy for the sources and compositions of DOM. Therefore, combined with remote sensing technology, the sources and compositions of DOM can be tracked on a large scale by associating the HIX with optically active components. Here, we proposed a novel HIX remote sensing retrieval (IRHIX) model suitable for Landsat series sensors based on the comprehensive analysis of the covariation mechanism between HIX and optically active components in different water types. The validation results showed that the model runs well on the independent validation dataset and the satellite-ground synchronous sampling dataset, with an uncertainty ranging from 30.85 % to 36.92 % (average ± standard deviation = 33.6 % ± 3.07 %). The image-derived HIX revealed substantial spatiotemporal variations in the sources and compositions of DOM in 474 lakes in the EPL during 1986–2021. Subsequently, we obtained three long-term change modes of the HIX trend, namely, significant decline, gentle change, and significant rise, accounting for 74.68 %, 17.09 %, and 8.23 % of the lake number, respectively. The driving factor analysis showed that human activities had the most extensive influence on the DOM humification level. In addition, we also found that the HIX increased slightly with increasing lake area (R2 = 0.07, P < 0.05) or significantly with decreasing trophic state (R2 = 0.83, P < 0.05). Our results provide a new exploration for the effective acquisition of long-term dynamic information about the sources and compositions of DOM in inland lakes and provide important support for lake water quality management and restoration.

Effect of experimental warming on dissolved organic matter and bacterial diversity in a forest swamp soil

Forest swamp ecosystems play an important role in the global carbon cycle, yet they are often overlooked. With global climate warming, it is inevitable that it will impact the relationship between soil microorganisms and organic matter. Dissolved organic matter (DOM) in the soil environment is extremely sensitive to environmental changes. Understanding the effects of climate change on DOM and microorganisms is crucial for assessing the stability of carbon (C) in forest swamp soils. Therefore, we conducted a 142-day laboratory warming incubation experiment (control: 10 °C, and warming: 20 °C) to investigate the response of forest swamp soil microbial and DOM properties to warming. Excitation-emission matrix (EEM) fluorescence spectroscopy was used to explore the changes in different material compositions of DOM over time at different incubation temperatures, and high-throughput sequencing was used to investigate the changes in soil bacteria. The DOM content (dissolved organic C, DOC) and the degree of humification index (HIX) increased with an increase in incubation time under warming conditions (p < 0.05). In contrast, microbial humic substances (C3) decreased with increasing time. Long-term warming has separated bacterial communities and gradually tightened the degree of connectivity between bacterial networks. The degree of soil humification (Mantel test r = 0.58, p < 0.01) and DOC (r = 0.21, p < 0.05) were the most critical indicators that changed the diversity of the bacterial community. Our findings suggest a degree of interaction between changes in forest swamp soil microbial communities and DOM under warming conditions. The results of this study contribute to our understanding of changes in DOM fluorescence indices in forest swamp soils under the influence of climate change and their associated microbial mechanisms.

Extracellular proteins enhance Cupriavidus pauculus nickel tolerance and cell aggregate formation

Heavy metal-resistant bacteria secrete extracellular proteins (e-PNs). However, the role of e-PNs in heavy metal resistance remains elusive. Here Fourier Transform Infrared Spectroscopy implied that N-H, C = O and NH2-R played a crucial role in the adsorption and resistance of Ni2+ in the model organism Cuprividus pauculus 1490 (C. pauculus). Proteinase K treatment reduced Ni2+ resistance of C. pauculus underlining the essential role of e-PNs. Further three-dimension excitation-emission matrix fluorescence spectroscopy analysis demonstrated that tryptophan proteins as part of the e-PNs increased significantly with Ni2+ treatment. Proteomic and quantitative real-time polymerase chain reaction data indicated that major changes were induced in the metabolism of C. pauculus in response to Ni2+. Among those lipopolysaccharide biosynthesis, general secretion pathways, Ni2+-affiliated transporters and multidrug efflux play an essential role in Ni2+ resistance. Altogether the results provide a conceptual model for comprehending how e-PNs contribute to bacterial resistance and adsorption of Ni2+.

Characterization of the dynamic aging and leached dissolved organic carbon from biodegradable and conventional plastics under photooxidation

Biodegradable plastics have been regarded as promising candidates in the struggle against plastic pollution. However, the aging and dynamic leaching process of biodegradable and conventional plastics under photooxidation is still unclear. Herein, three types of non-biodegradable plastics (polypropylene, polyethylene, and polyethylene terephthalate), and two types of biodegradable plastics (polylactic acid and cornstarch-based plastics) were treated with 21 days of photooxidation followed by 13 days of dark conditions. Scanning electron microscopy was applied to display the morphological changes. Also, the carbonyl index, oxygen-to-carbon ratio, and contact angle were utilized to characterize the aging degree of the plastic surface. Unexpectedly, biodegradable plastics did not always display a greater aging degree than non-biodegradable plastics. Moreover, the dissolved organic carbon during the leaching process was identified using excitation-emission matrix fluorescence spectroscopy. The findings suggested that biodegradable plastics showed the potential to release more dissolved organic carbon. Particularly, the polylactic acid plastic displayed higher concentrations and more types of dissolved organic carbon release than that of conventional plastics in our experiment. This research highlights the necessity for monitoring the aging process of both biodegradable and non-biodegradable plastics and the non-negligible ecological risk of leached organic pollutants due to plastic degradation.

Interactions of humic acid with pristine poly (lactic acid) microplastics in aqueous solution

Microplastics and natural organic matter are present in the aquatic environment and their reciprocal interaction plays important roles in the transport and behavior of nutrients and contaminants. Nevertheless, we lack mechanistic understanding on these interactions, especially in the case of biodegradable plastics. Here we investigate the adsorption of a commercial humic acid onto poly (lactic acid) (PLA) microplastics in aqueous solution. While the pseudo-second order kinetic model provided a more accurate representation of the adsorption kinetics, the Elovich model also produced a good fit, suggesting that chemisorption may be the rate-limiting step. The equilibrium data was better fit by the Langmuir model, that provided a maximum adsorption capacity of 0.118 ± 0.006 mg·g−1. The obtained values for the separation factor (RL) and free energy (E) suggest that adsorption of humic acid onto PLA is controlled by physisorption. We studied the effects of pH, ionic strength, and PLA concentration on the adsorption of humic acid onto PLA and demonstrated that electrostatic interactions and aggregation are important. The humic acid was characterized by Fourier-transform infrared (FTIR) spectroscopy, excitation-emission matrix (EEM) fluorescence spectroscopy, and parallel factor analysis (PARAFAC), before and after interacting with PLA. This set of analyses demonstrated that PLA caused alterations in the molecular structure of humic acid, primarily attributed to modifications in hydrogen bonding and hydrophobic interactions. Therefore, we hypothesize that the carboxylic groups of humic acid formed dimers in contact with PLA. This study provides new insights into the interactions between organic matter and a biodegradable microplastic in aqueous systems.

Responses of partial denitrification process to long-term perfluorooctane sulfonic acid stress: Performance, microbial community and functional genes

This study investigated the changes in reactor performances, microbial communities and functional genes in partial denitrification (PD) process under elevated perfluorooctane sulfonic acid (PFOS) stress. The results showed that PFOS significantly (P ≤ 0.001) decreased NO-2-N accumulation rate from 71.15 ± 1.83 % to 65.96 ± 3.97 % and increased total nitrogen removal efficiency from 25.49 ± 1.67 % to 30.90 ± 4.97 %, which indicated that PFOS addition hindered the PD process but promoted the total nitrogen removal. Excitation emission matrix fluorescence spectroscopy and fourier transform infrared spectroscopy suggested significant changes in fluorescence characteristics and functional groups of extracellular polymeric substances, especially, PFOS induced the considerable synthesis of protein-like substances. In addition, high-throughput sequencing revealed that the abundance of genus Thauera, which is responsible for the NO-2-N accumulation, was significantly decreased from 35.98 % to 26.00 % under PFOS stress. While the abundances of common denitrifying bacteria, such as genus Denitratisoma, SM1A02 and OLB8, increased after PFOS exposure, which was consistent with the changes of nitrogen transition. Moreover, PICRUSt showed that the abundance of NO-3-N reductase genes (napA) significantly (P ≤ 0.001) downregulated from 0.02 % to 0.01 %, while NO-2-N reductase genes (nirK) significantly (P ≤ 0.001) upregulated by 1.97 folds after PFOS addition. These results showed that PFOS stress had a profound influence on microbial structure and the functional genes. Overall, this study demonstrated the response mechanism of PD system to long-term PFOS stress and made some contributions to the improvement in the control strategy of wastewater treatment plants (WWTPs).

3D excitation-emission matrix fluorescence spectroscopy of Biluochun before and after Tomb-Sweeping Day

&lt;p class="Abstract"&gt;Tea is an important public drink and its value is in accordance with the time of picking, for example, tea picked before Tomb-Sweeping Day is more expensive than that after Tomb-Sweeping Day. To avoid buying shoddy tea, it is necessary to identify the picking time of the tea. Considering the fact that the chemical components are related to the picking time, in this work, fluorescence spectroscopy is proposed to find the difference between these two kinds of Biluochun. The intensity of the excitation and emission wavelengths for the Biluochun was measured at the same to obtain 3D fluorescence spectra. The contour maps of Biluochun picked before and after Tomb-Sweeping Day were drawn and compared. The results shown that fluorescent intensity at the region from 660 nm to 680 nm, which is corresponding to chlorophyll, is obviously different for both kinds. The different fluorescent intensity demonstrated that the chlorophyll contained in Biluochun after Tomb-Sweeping Day was higher than that before Tomb-Sweeping Day, which can be used to classify these two kinds.&lt;/p&gt;

Geographical origin traceability and authenticity detection of Chinese red wines based on excitation-emission matrix fluorescence spectroscopy and chemometric methods

Excitation–emission matrix fluorescence (EEMF) spectroscopy combined with chemometrics was developed for the geographical origin traceability and authenticity detection of Chinese red wines. Parallel factor analysis coupled with partial least squares-discriminant analysis (PARAFAC-PLS-DA), N-way partial least squares-discriminant analysis (N-PLS-DA) and unfolded partial least squares-discriminant analysis (U-PLS-DA) were used to identify the geographical origins and adulteration of red wines. Accuracy, sensitivity, specificity and precision were used to evaluate the performances of the discriminant models. The accuracy of PARAFAC-PLS-DA for training samples and prediction samples from different origins was 0.88 and 0.83, respectively. N-PLS-DA and U-PLS-DA, which used full EEMF data as model inputs, had the same excellent performance and both provided an accuracy of 1. With regard to the identification of adulterated samples, the accuracy of PARAFAC-PLS-DA for training samples and prediction samples was 0.71 and 0.83, respectively. By comparison, in both N-PLS-DA and U-PLS-DA models, only one prediction sample with the lowest adulteration level was misclassified. N-way partial least squares regression (N-PLSR) was successfully used to quantify adulteration levels for the first time, with Rc2 > 0.98, both RMSEC and RMSEP < 6%. This study showed that EEMF combined with chemometrics is an effective method for the geographical origin traceability and authenticity detection of Chinese red wines.

Unveiling the molecular responses of dissolved organic matter in landfill leachate to activated carbon adsorption

Powdered activated carbon (PAC) is an effective method for removing dissolved organic matter (DOM) in membrane bioreactor effluent of landfill leachate (MBR effluent). Among commercially available PACs, wood-based PAC (WoAC) and coal-based PAC (CoAC) are two most common ones. However, the interactions between two PACs and DOM in MBR effluent at the molecular level as well as the effect of PACs properties on the adsorption of DOM compounds are not fully understood. To address the gap, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy and other spectroscopic techniques were employed to study the change of DOM in MBR effluent when adsorbed by WoAC and CoAC. The results showed that CoAC had a better removal performance of DOM (89.2% for UV254 and 78.4% for DOC) than WoAC (80.9% for UV254 and 70.8% for DOC), which was likely due to the Fe component in CoAC playing an important role in the DOM adsorption process. Both WoAC and CoAC exhibited preferential adsorption for compounds with high unsaturation or poor oxygen. Moreover, the Fe component in CoAC may bind with some functional groups (e.g., carboxyl groups) in unsaturated compounds, which may enhance the adsorption of unsaturated compounds. These findings deepen our understanding of PAC-DOM interactions at the molecular level and provide guidance for designing cost-effective PACs for landfill leachate treatment.

Identification and Quantification of the Main Psychoactive Ingredients of Cannabis in Urine Using Excitation-Eemission Matrix Fluorescence Coupled with Parallel Factor Analysis.

Cannabis is the most prevalent abused substance after alcohol, and its consumption severely harms human health and thus adversely impacts society. The identification and quantification of cannabis in urine play important roles in practical forensics. Excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis was developed to identify and quantify the four main ingredients of cannabis in urine samples. The main ingredients of cannabis including Δ-9-tetrahydrocannabinol (THC), cannabidiol, cannabinol, and tetrahydrocannabinolic acid (THC-COOH) exhibited diverse fluorescence characteristics, and the concentrations of these compounds depicted a positive linear relationship with the fluorescence intensity at the ng/mL level. The EEM/PARAFAC method adequately characterized and discriminated the four ingredients in calibration and prediction samples with a low root-mean-square error of prediction (RMSEP; 0.03-0.07 μg/mL) and limit of quantitation (LOQ; 0.26-0.71 μg/mL). The prediction results of the EEM/PARAFAC method well correlated with that of GC-MS with a low RMSEP range (0.01-0.05 μg/mL) and LOQ range (0.07-0.44 μg/mL) in urine samples. The EEM spectroscopic investigation coupled with the PARAFAC algorithm results in an organic, solvent-less, fast, reliable tool to perform accurate and rapid screening of cannabis abusers.

Compositional and spectroscopic analysis of dissolved organic matter samples from Everglades periphyton and water.

Periphyton is a ubiquitous niche in aquatic environments and can be a significant source of dissolved organic matter (DOM) production and leaching, especially in such environment as the Everglades, a slow-water flow wetland in Florida, USA. We employed an array of methods, including compositional analysis, 3-dimensional excitation emission matrix (3-D EEM) fluorescence spectroscopy, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, to perform quantitative and qualitative analyses on the DOM produced by periphyton and DOM in surrounding surface water and periphyton overlying water for comparison purposes. Higher dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) contents in periphyton pore water than surface water and periphyton overlying water indicated the remarkable contribution from periphyton-produced DOM. Higher total protein, carbohydrate, and thiol contents in periphyton pore water than in surface water and periphyton overlying water underscored the possibility of periphyton pore water DOM leached from periphyton. These results agreed with 3-D EEM and ATR-FTIR analyses that showed the prevalence of possible microbial source of periphyton pore water DOM as indicated by higher fluorescence index (FI) than surface water and periphyton overlying water. Similarly, the size-fractionated DOM from surface water demonstrated terrestrial sources, and periphyton pore water demonstrated microbial sources regardless of their differences in size based on their FI values. The types of periphyton affect the production and composition of DOM, as evidenced by higher total protein, carbohydrate, and chlorophyll-a (Chl-a) contents in floating mat on the water surface than in epiphyton attached to submerged phytoplankton, probably because the former is photo-synthetically more productive than the latter due to different light availability. This study provided fundamental information on periphyton DOM that is essential for further investigating its role in carbon cycle and its biogeochemistry.

Chemometrics-assisted excitation-emission matrix fluorescence spectroscopy for real-time migration monitoring of multiple polycyclic aromatic hydrocarbons from plastic products to food simulants

Polycyclic aromatic hydrocarbons (PAHs), as a class of organic pollutants that have attracted much attention, are likely to be formed with the production and processing of plastic products, and they may migrate from contaminated plastic products to food, causing the risk of poisoning or cancer. In this study, migration tests were carried out on disposable plastic products for food contact, and a novel strategy that combines excitation-emission matrix (EEM) fluorescence spectroscopy with the advanced second-order calibration method based on the three-direction resection alternating trilinear decomposition (TDR-ATLD) algorithm was used to monitor the migration of three PAHs anthracene (ANT), pyrene (PYR), and phenanthrene (PHE) from the plastic products to food simulants in real-time. With the “second-order advantage”, even if the fluorescence spectra of the target analytes overlapped seriously, and other unknown substances migrated from the plastic products to food simulants, accurate qualitative and quantitative results were still obtained by the proposed method. In the static system, the coefficient of determination (R2) of the three PAHs within the calibration range were all greater than 0.99, and the average spiked recoveries were 99.5-107.1%, with the standard deviation lower than 8.9%. The figures of merit (FOMs) and intra- or inter-day precision also showed good feasibility and reliability of the method. In the simulation study of the migration kinetic process, three PAHs can be quantified in real-time in complex matrix, then the related migration equations were established. The results indicate that the proposed method can be used for real-time migration quantitative monitoring of PAHs, providing a potential and available method for the study of the migration kinetics of hazardous substances from food contact materials to food or food simulants.

Integrating biological ion exchange with biological activated carbon treatment for drinking water: A novel approach for NOM removal, trihalomethane formation potential, and biological stability

Ion exchange resins (IEX) are used in drinking water utilities to remove natural organic matter (NOM) from surface water; however, the disposal of used brine can be a major drawback. Recently, biological ion exchange (BIEX) has been proposed as an alternative to biological activated carbon (BAC) for removing natural organic matter (NOM). The present study is, to the best of our knowledge, the first attempt to use a hybrid BIEX and BAC (BIEX+BAC) system for drinking water treatment. The removal of NOM, assimilable organic carbon, and trihalomethane formation potential was investigated by operating four columns comprising IEX, BIEX, BAC, and BIEX+BAC with 18,000 bed volumes. The BIEX+BAC system was the most effective at removing dissolved organic carbon (59.9%). Based on fluorescence excitation-emission matrix spectroscopy, the BIEX+BAC column showed the maximum removal rates in all peak regions of T1, T2, and A. Using liquid chromatography-organic carbon detection, resin-containing columns were found to effectively remove humic substances, which are the principal precursors of trihalomethanes. The lowest potential for trihalomethane formation was observed in BIEX+BAC. BIEX+BAC also had the highest assimilable organic carbon removal efficiency (61.2%) followed by BIEX (52.3%), BAC (49.5%), and IEX (47.1%). The BIEX+BAC hybrid was found to be the most effective method for removing NOM fractions and reducing the formation of disinfection byproducts.

Distribution, characteristics and fate of fluorescent dissolved organic matter (FDOM) in the Bay of Bengal

The Bay of Bengal (BoB) is the largest sink to retain discharges from major rivers and the Sundarbans Mangrove Forest in Bangladesh and upholds significant ecological and resource diversity. This study aims to characterize, and identify sources, spatial dynamics, and the fate of the principal ecological web driver that is fluorescent dissolved organic matter (FDOM) in the BoB using advanced techniques of excitation-emission matrix (EEM) fluorescence spectroscopy and multivariate parallel factor (PARAFAC) analyses. The identified four protein-, two humic- and one detergent-like FDOM components mostly showed higher abundance in the shallow water than deep unlike a protein-like component. Such exceptional protein-like component was identified to form colloidal structure under elevated salinity in deep water. Autochthonous humic-like FDOM originated from primary production and water temperature counteracted microbial polymerization in shallow and deep water, respectively. The annual mass deposition indicated the influx of anthropogenic pollutants from both terrestrial and internal marine systems.

Molecular insight into DOM fate using EEM-PARAFAC and FT-ICR MS and concomitant heavy metal behaviors in biologically treated landfill leachate during coagulation: Al speciation dependence

Various combined processes with pre-coagulation have been developed for biologically treated landfill leachate, but the microscopic-level processes occurring during coagulation remain largely unknown. Herein, dissolved organic matter (DOM) fate using fluorescence excitation emission matrix spectroscopy combined with parallel factor analysis and electrospray ionization coupled Fourier transform-ion cyclotron resonance mass spectrometry and concomitant heavy metal (HM) behaviors were explored at the molecular level. In addition, AlCl3 and two polyaluminum chloride (PACl) species (dominated by [AlO4Al12(OH)24(H2O)12]7+ and [(AlO4)2Al28(OH)56(H2O)26]18+, respectively) were used. The results show that all coagulants are efficient at removing DOM. PACl was found to be advantageous over AlCl3 in overcoming pH fluctuation, which is ascribed to the different dominant mechanisms, namely, entrapment and sweep flocculation for AlCl3 and charge neutralization for PACl. Consequently, PACl was more effective at removing humic substances, usually high-molecular-weight, oxygen-rich and unsaturated, than protein substances. For HM removal, PACl was likewise better and more stable, where As, Cu, Ni, Co and Hg were removed predominantly via adsorption, and Cr, Zn, Pb, Cd and Mn were removed via coprecipitation. Correlation analysis showed that humic substances tended to complex with HMs and be removed synergistically due to the ubiquitous occurrences of aromatic structures and oxygen-containing functional groups.

Spatial variation of dissolved organic matter in the Tuojiang River Basin in Chengdu, China: insights based on EEMs-PARAFAC analysis.

Three-dimensional excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis was adopted to investigate the characteristics of dissolved organic matter (DOM) components in water samples collected from the Tuojiang River Basin in Chengdu, including its main stream and tributaries. Four DOM components that matched with three fluorescence peaks were identified in the whole river basin and tributaries; while three components corresponding to four fluorescence peaks were identified in the main stream. In all cases, humic-like components accounted for high proportions of the DOM. Correlation analysis revealed the same sources for four components in the whole river basin and its tributaries, whereas two components had different sources in the main stream. Ultraviolet absorbance parameters (SUVA254, SR) and fluorescence parameters (BIX, HIX, FI, β:α) indicated the dominant autochthonous sources of DOM in the whole river basin. Higher terrestrial inputs of DOM were observed in the tributaries than in the main stream. In the areas influenced by human activities (6#, 17#, 18#), the sources of DOM showed strong terrestrial characteristics and high degrees of humification and aromatization, as well as serious pollution. The results of this study have potentially far-reaching implications for environmental water management in the area.

Rapid Fluorescence EEM Spectroscopy Using Super-Cycle Hadamard-Transform Multiplexing.

Hadamard-transform (HT) multiplexing has recently been applied to increasingly complex spectroscopic techniques. It had been shown that the data acquisition time for fluorescence excitation emission matrix (EEM) spectroscopy can be reduced by 1 or 2 orders of magnitude using HT multiplexing of the excitation light using a programmable light source. In these previous studies, the data acquisition rate had been limited by the time it took to record an EEM, that is, to complete one cycle of multiplexed excitation spectra. The extraction of chemical information, such as concentration and chemical identity, is then obtained from parallel factor (PARAFAC) analysis of the sequence of EEMs. In this contribution, we increase the data acquisition rate by another order of magnitude, limited ultimately by the time it takes to record a single excitation spectrum. Our algorithm is entirely based on improved data processing, that is, it can be applied to previously recorded HT multiplexed data sets. The algorithm is based on three previously unexplored approaches: (1) we perform a PARAFAC multivariate analysis on the raw (multiplexed) data set, (2) the time-independent PARAFAC loading vectors are obtained prior to obtaining the time-dependent score vectors, and (3) when loading vectors are difficult to obtain from the EEMs, we instead use a rolling-average approach to considerably increase the stability of the fit. Analysis of experimental data shows that the scores of fluorescence EEMs with seven excitation wavelengths and over 1000 emission wavelengths can be obtained in less than 20 ms.