Coupling asymmetric flow-field flow fractionation and fluorescence parallel factor analysis reveals stratification of dissolved organic matter in a drinking water reservoir

Using asymmetrical flow field-flow fractionation (AF4) and fluorescence parallel factor analysis (PARAFAC), we showed physicochemical properties of chromophoric dissolved organic matter (CDOM) in the Beaver Lake Reservoir (Lowell, AR) were stratified by depth. Sampling was performed at a drinking water intake structure from May to July 2010 at three depths (3-, 10-, and 18-m) below the water surface. AF4-fractograms showed that the CDOM had diffusion coefficient peak maximums between 3.5 and 2.8 × 10⁻⁶ cm² s⁻¹, which corresponded to a molecular weight range of 680–1950 Da and a size of 1.6–2.5 nm. Fluorescence excitation–emission matrices of whole water samples and AF4-generated fractions were decomposed with a PARAFAC model into five principal components. For the whole water samples, the average total maximum fluorescence was highest for the 10-m depth samples and lowest (about 40% less) for 18-m depth samples. While humic-like fluorophores comprised the majority of the total fluorescence at each depth, a protein-like fluorophore was in the least abundance at the 10-m depth, indicating stratification of both total fluorescence and the type of fluorophores. The results present a powerful approach to investigate CDOM properties and can be extended to investigate CDOM reactivity, with particular applications in areas such as disinfection byproduct formation and control and evaluating changes in drinking water source quality driven by climate change.     

Determination of relative molecular weights of fluorescent components in dissolved organic matter using asymmetrical flow field-flow fractionation and parallel factor analysis

Dissolved organic matter in aquatic systems is of variable structure and composition. Asymmetrical flow field-flow fractionation coupled to UV/vis diode array and fluorescence detectors (AF4–DAD–EEM) was used to assess the size and optical properties of dissolved organic matter. The results were analyzed using parallel factor analysis (PARAFAC) and statistical fractogram deconvolution to correlate fluorescing components with molecular weight fractions. This coupling, which is shown for the first time in this work, is a powerful method capable of revealing novel information about the size properties of PARAFAC components. Tyrosine/polyphenol-like fluorescence (peak B) was significantly correlated (p < 0.05) with the smallest size group (relative molecular weight = 310 ± 10 Da), microbial humic-like and terrestrial visible humic-like fluorescence (peaks M, C, A) with the intermediate size group (1600 ± 150 Da), and terrestrial fulvic-like and tryptophan/polyphenol-like fluorescence (peaks A and T) with the largest size group (4300 ± 660 Da).     

Characterization of chromophoric dissolved organic matter (CDOM) in the East China Sea in autumn using excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC)

Samples of chromophoric dissolved organic matter(CDOM)in the East China Sea in autumn(October in 2011)were analyzed by excitation emission matrix(EEM)fluorescence spectroscopy combined with parallel factor analysis(PARAFAC).Three terrestrial humic-like components(C1,C2 and C3)and one protein-like component(C4)were identified.Based on spatial distributions,as well as relationships with salinity,the following assignments were made.The three humic-like components(C1,C2 and C3)showed conservative mixing behavior and came mainly from riverine input.The protein-like component(C4)was considered a combination of autochthonous production and terrestrial inputs and a biologically labile component.Path analysis of samples from the middle and bottom layers revealed that the causal effects on C1 were 78.46%for salinity,and 21.54%for apparent oxygen utilization(AOU);those on C2 were 76.43%for salinity,and 23.57%for AOU;those on C3 were70.49%for salinity,7.01%for Chl-a,and 22.50%for AOU;those on C4 were 55.54%for salinity,14.6%for Chl-a,and29.86%for AOU in middle layer;and those on C4 were 57.37%for salinity,29.02%for Chl-a,and 13.61%for AOU in bottom layer.Results indicated that CDOM in the East China Sea was mainly affected by terrestrial inputs,and microbial activities also played a key role in biogeochemical processes of CDOM.The application of the EEM-PARAFAC model presented a unique opportunity to observe compositional changes in CDOM in the East China Sea.In addition,the humification index(HIX)suggested that CDOM from the East China Sea was less stable and stayed shorter in the environment.     

Application of linear regression analysis for iron and copper removal process using natural zeolites

Natural zeolites (zeolitic volcanic tuffs) cropped out from three regions of Transilvania, Vultureni (V), Pagli?a (P) and M?cica? (M), were evaluated in the process of iron (V, P, M) and copper (M) removal from wastewaters. Iron and copper removal process was studied using a fixed bed column, when equilibrium and kinetic data were acquired. Four isotherms, Langmuir, Freundlich, Langmuir?CFreundlich and Redlich?CPeterson, were used to fit the experimental data obtained for each natural zeolite sample. Parameters of the adsorption isotherms were estimated from the experimental equilibrium data using MATLAB. Using these data the best fit with one of the chosen isotherm can be found. Isotherm constants were determined by linear regression analysis of the experimental data. We concluded that the mathematical model based on Freundlich isotherm is the most appropriate to describe the iron and copper exchange on our natural zeolite samples.     

Influence of acidification on the optical properties and molecular composition of dissolved organic matter

Acidification is a common method for preserving dissolved organic matter (DOM) in natural water samples until sophisticated laboratory analyses can be performed. However, little is known about the effects of this practice on the composition and optical properties of DOM. In this study, the effects of acidification on DOM in porewater samples collected from the RL IV bog system of the Glacial Lake Agassiz Peatlands in northern Minnesota were characterized. Molecular composition was determined by ultrahigh resolution mass spectrometry and optical properties by UV absorption and three-dimensional fluorescence spectroscopy. Excitation–emission matrix fluorescence spectroscopy results indicate that the fluorescence properties of the peatland porewater DOM were sensitive to pH and that the observed changes were fluorophore dependent. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed the appearance of newly formed, oxygen-rich compounds upon acidification. The extent to which these oxygen-rich compounds were formed was also dependent on the composition of the DOM.     

Simultaneous analysis of the photocatalytic degradation of polycyclic aromatic hydrocarbons using three-dimensional excitation-emission matrix fluorescence and parallel factor analysis

Polycyclic aromatic hydrocarbons (PAHs) may be photochemically degraded. Monitoring of degradation process of PAHs is carried out by traditional methods, which normally imply time-consuming procedures that do not allow the chemical process to be analyzed in real time. In the present study, photodegradation kinetics of dibenz[a,h]anthracene, benz[a]anthracene, benz[a]pyrene and benz[k]fluorantene were investigated in aqueous solutions under different conditions. A 2³ factorial design was used for optimizing the degradation process.Fluorescence spectroscopy is a fast, cheap and sensitive analytical method, attractive for use in conjunction with chemometric methods; in this case three-way analytical methodology based on fluorescence excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC) was employed. A four-factor PARAFAC model made it possible to resolve the species presents in the degradation mixture and quantify the relative concentration of the analytes throughout the degradation. Several different parameters, such as core consistency, percentage of fit and correlation coefficients between recovered and reference spectra were employed to determine the suitable number of factors for the PARAFAC model. This new methodology allows us to determine satisfactorily the PAHs concentration during the photodegradation in mixtures of arbitrary composition, representing an interesting alternative to the conventional techniques normally used for the monitoring of degradation reactions.     

Asymmetrical flow field-flow fractionation and excitation-emission matrix spectroscopy combined with parallel factor analyses of riverine dissolved organic matter isolated by tangential flow ultrafiltration

Asymmetrical flow field-flow fractionation (AF4) with sequential on-line UV/visible and fluorescence detectors was used to investigate the composition of dissolved organic matter (DOM) in permeate and retentate fractions isolated by tangential flow ultrafiltration (TFF) at various concentration factors (i.e. ratio of initial volume to the retentate volume; CF). The permeation coefficient model, which defines the log-log relationship between DOM in the permeate fractions and CFs, described the permeation behaviour of DOM with regression coefficients r ² > 0.99. The dominance of higher-molecular weight retentate chromophoric DOM (CDOM) observed in TFF was consistent with the results of AF4. The weight-averaged molecular weights (M _w) of the integral permeate and retentate at CF = 20 were determined to be 1160 and 2320 by AF4, respectively, while their molecular weight distributions (MWD) were centered at 1120 and 1600 Da. M _w, MWD, and aromaticity (i.e. ratio of absorbance at 250 and 365 nm; E2/E3) in permeate fractions were altered significantly during the early stages of TFF (CF < 9). These changes, however, were not evident in excitation-emission matrix fluorescence properties as determined using the parallel factor analysis model. The application of AF4 to TFF fractions suggests that the choice of CF may have an important impact on the size distribution and aromaticity of permeate fractions, whereas fluorescence properties appear insensitive to concentration factor. These results suggest that the choice of CF is crucial only in the study of the permeate fraction where similar CF (i.e. > 9) should be used to obtain meaningful comparison among samples.     

Effect of seasonal dynamics and chemical treatment on the quality of dissolved organic matter in water sources and potable water of Ufa

The structural-group composition and seasonal variations of organic matter dissolved in potable water and water sources of Ufa is studied. The efficiency of removal and destruction rate of dissolved organic matter at different technological stages of water treatment is evaluated for a surface water intake.     

Identification and quantification of carbamate pesticides in dried lime tree flowers by means of excitation-emission molecular fluorescence and parallel factor analysis when quenching effect exists

A non-separative, fast and inexpensive spectrofluorimetric method based on the second order calibration of excitation-emission fluorescence matrices (EEMs) was proposed for the determination of carbaryl, carbendazim and 1-naphthol in dried lime tree flowers. The trilinearity property of three-way data was used to handle the intrinsic fluorescence of lime flowers and the difference in the fluorescence intensity of each analyte. It also made possible to identify unequivocally each analyte. Trilinearity of the data tensor guarantees the uniqueness of the solution obtained through parallel factor analysis (PARAFAC), so the factors of the decomposition match up with the analytes. In addition, an experimental procedure was proposed to identify, with three-way data, the quenching effect produced by the fluorophores of the lime flowers. This procedure also enabled the selection of the adequate dilution of the lime flowers extract to minimize the quenching effect so the three analytes can be quantified. Finally, the analytes were determined using the standard addition method for a calibration whose standards were chosen with a D-optimal design.     

Spectrophotometric characterisation of surface lakewater samples: implications for the quantification of nitrate and the properties of dissolved organic matter

Filtered lakewater samples, mainly collected in the province of Torino (Piedmont, NW Italy) were characterised from a spectrophotometric point of view. Spectral data were then used for the direct determination of nitrate by three-wavelength photometry, which should account for the spectral interference by dissolved organic matter (DOM), and the results compared with nitrate quantification by ion chromatography. The spectrophotometric method proved very suitable for nitrate measurement, with unity slope (micro +/- sigma = 0.99 +/- 0.03) of the correlation plot (spectral vs. ion chromatography data) up to 0.1 mM nitrate, and with r2 = 0.97 for 26 data points. Lakewater spectra were also used for the characterisation of DOM by means of the specific absorption at 285 and 254 nm (absorbance vs. NPOC, the latter to quantify the DOM amount), and the E2/E3 and E3/E4 indexes. The latter two make only use of radiation absorption data (250 vs. 365 and 300 vs. 400 nm). It could be concluded that lakewater DOM is mainly composed of autochthonous material (biologically produced aliphatic compounds and only a minor fraction of aromatic groups), with generally low molecular weight and degree of aromaticity. Some exceptions could be found in high-mountain lakes, but it should also be considered that NPOC measurement cannot be avoided if DOM origin is to be studied. From the absorption spectrum alone it is possible to get indication on the aromaticity degree of radiation-absorbing DOM, but most of the autochthonous DOM would escape spectrophotometric characterisation.     

Assessing the dynamics of chromophoric dissolved organic matter (CDOM) in the Yellow Sea and the East China Sea in autumn by EEMs-PARAFAC

In this study we have successfully characterized the fluorescent components of chromophoric dissolved organic matter(CDOM) in the Yellow Sea and the East China Sea in autumn using excitation-emission matrix fluorescence spectroscopy(EEMs) combined with parallel factor analysis(PARAFAC).PARAFAC aids the characterization of fluorescence CDOM by decomposing the fluorescence matrices into individual components.Four humic-like components(C1,C2,C3,and C4),one marine biological production component(C6),and two protein-like components(C5 and C7) were identified by PARAFAC.We researched the distributional patterns of fluorescence intensity,regression analyses between salinity,chlorophyll a concentration and fluorescence intensities of individual fluorophore,and regression analysis between salinity and fluorescence intensities percent of individual fluorophore.The results revealed that C2 and C4 showed conservative mixing behavior,while C1 and C3 possessed conservative mixing behavior in high salinity region and additional behavior in low and middle salinity region,which were considered to be derived from riverine and degradation of organic matter from resuspended and/or sinking particles and show non-conservative mixing behavior.In addition to riverine sources,the tryptophan-like C5 may receive widespread addition(likely from photo-degradation or biodegradation),while the most likely sources for the one marine humic-like C6 and tyrosine-like C7 were biological activity and microbial processing of plankton-derived CDOM,which were suggested to be of autochthonous origin and biologically labile.The application of EEM-PARAFAC modeling presents a unique opportunity to observe compositional changes,different mixing behavior and temporal variability in CDOM in the Yellow Sea and the East China Sea.     

Predicting class I major histocompatibility complex (MHC) binders using multivariate statistics: comparison of discriminant analysis and multiple linear regression

The accurate in silico identification of T-cell epitopes is a critical step in the development of peptide-based vaccines, reagents, and diagnostics. It has a direct impact on the success of subsequent experimental work. Epitopes arise as a consequence of complex proteolytic processing within the cell. Prior to being recognized by T cells, an epitope is presented on the cell surface as a complex with a major histocompatibility complex (MHC) protein. A prerequisite therefore for T-cell recognition is that an epitope is also a good MHC binder. Thus, T-cell epitope prediction overlaps strongly with the prediction of MHC binding. In the present study, we compare discriminant analysis and multiple linear regression as algorithmic engines for the definition of quantitative matrices for binding affinity prediction. We apply these methods to peptides which bind the well-studied human MHC allele HLA-A*0201. A matrix which results from combining results of the two methods proved powerfully predictive under cross-validation. The new matrix was also tested on an external set of 160 binders to HLA-A*0201; it was able to recognize 135 (84%) of them.     

X-ray fluorescence determination of La,Ce, Pr,Nd, and Sm in industrial sediments of calcium sulfate using linear regression analysis

Industrial sediments of calcium sulfate semihydrate obtained from industrial extraction phosphoric acid and containing 0.3–4.5 wt % of impurity La?Sm are investigated by energy-dispersive X-ray fluorescence analysis (XRFA) and a procedure for the quantitative determination of cerium lanthanides in the sediments is developed. The use of linear regression analysis of X-ray fluorescence spectra of multielement industrial samples and models of individual compounds NaLn(SO₄)₂ · H₂O (cp grade) allowed us to resolve overlaps of spectral L-series lines for La–Sm, eliminate the background, and perform the regression assessment of line intensities of these elements. On this basis, we developed a procedure for the determination of La, Ce, Pr, Nd, and Sm in CaSO₄ · 0.5H₂O sediments with limits of detection (wt %): 0.022, 0.013, 0.011, 0.008, and 0.008, respectively. In concentration ranges (wt %) La (0.05–0.99), Ce (0.1–4.9), Pr (0.005–0.49), Nd (0.02–0.99), and Sm (0.005-0.19), the relative standard deviation RSD (n = 10, P = 0.95) was 18?27, 9?18, 20?31, 17?26, and 19?31%, respectively. A comparison of the results of XRFA with the data of inductively coupled plasma mass spectrometry confirms the accuracy of the results obtained according to OST (Branch Standard) 41-08-221-04.     

Application of unfold principal component analysis and parallel factor analysis to the exploratory analysis of olive oils by means of excitation-emission matrix fluorescence spectroscopy

Discrimination between virgin olive oils and pure olive oils is of primary importance for controlling adulterations. Here, we show the potential usefulness of two multiway methods, unfold principal component analysis (U-PCA) and parallel factor analysis (PARAFAC), for the exploratory analysis of the two types of oils. We applied both methods to the excitation-emission fluorescence matrices (EEM) of olive oils and then compared the results with the ones obtained by multivariate principal component analysis (PCA) based on a fluorescence spectrum recorded at only one excitation wavelength. For U-PCA and PARAFAC, the ranges studied were λ_ex=300-400 nm, λ_em=400-695 nm and λ_ex=300-400 nm, λ_em=400-600 nm. The first range contained chlorophylls, whose peak was much more intense than those of the rest of species. The second range did not contain the chlorophylls peak but only the fluorescence spectra of the remaining compounds (oxidation products and Vitamin E). The three-component PARAFAC model on the second range was found to be the most interpretable. With this model, we could distinguish well between the two groups of oils and we could find the underlying fluorescent spectra of three families of compounds.     

Spectrofluorimetric studies on the binding of salicylic acid to bovine serum albumin using warfarin and ibuprofen as site markers with the aid of parallel factor analysis

The interactions of salicylic acid (SL) and two different site markers (warfarin for site I and ibuprofen for site II) with bovine serum albumin (BSA) in pH 7.4 Tris–HCl buffer have been investigated with the use of spectrofluorimetry. An equilibrium solution of BSA and SA was titrated separately with the two markers. This initial work showed that the binding of SL with BSA could be quite complex, and that there was probably a competitive interaction occurring between ibuprofen and SL. However, the spectral results were difficult to interpret clearly for the interaction of warfarin and SL in similar circumstances.

To extract more information from the resolution of fluorescence excitation-emission spectra, the contour plots of the fluorescence spectra indicated that the optimal excitation wavelengths for BSA, SL, warfarin and ibuprofen were different, and were found to be at 278, 295, 306 and 218 nm, respectively. The spectral information was arranged into three-way excitation-emission fluorescence matrix (EEM) stack arrays, and was submitted for analysis by the parallel factor analysis (PARAFAC) algorithm. Firstly, it was demonstrated that the estimated excitation and emission spectral responses for SL, BSA and the site markers, warfarin and ibuprofen, agreed well with the measured spectra. Then, the interpretation of the plots of simultaneously extracted (by PARAFAC) equilibrium concentrations for the above four reactants, showed that: (i) the SL primarily appears to bind in site I but at a different location from the high-affinity binding site (HAS) for warfarin, and the interaction partially overlaps with the low-affinity binding site (LAS) for warfarin. (ii) The SL may have two LAS—one in site II where the HAS for ibuprofen is located, and the other in site I at the LAS for ibuprofen. Thus, application of the PARAFAC method for the study of competitive interaction of SL and BSA with the aid of two different site markers has extracted information unobtainable by traditional methods such as the Scatchard plot, and provided useful means of data visualization.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.