Synchronous Molecular Fluorescence Research Articles

Synchronous Fluorescence Spectrometry (SFS) with Multivariate Calibration for the Determination of Polycyclic Aromatic Hydrocarbons (PAHs) and Their Oxygen Analogs in Printer Toner

Synchronous molecular fluorescence with multivariate calibration was investigated to assay seven polycyclic aromatic hydrocarbons (PAHs) and three oxygenated derivatives (O-PAHs) in printer toner. Great sensitivity and a good data compression capacity were achieved; therefore, a relatively small number of factors were used. Correlation coefficients above 0.95 for the calibration functions were obtained, and recoveries lie between 70 and 130% in analyzing synthetic samples (13 PCs). For the real samples assayed, recoveries between 81 and 125% were obtained when compared to the results obtained by gas chromatography – tandem mass spectrometry (GC-MS/MS). Despite a certain loss in accuracy when compared to chromatography, the proposed methodology is faster, simpler, and lower in cost. The multivariate tool proved to be an expeditious alternative for screening toner in relation to the presence and abundance of PAHs and derivatives.

Direct solid sample analysis using synchronous fluorescence spectroscopy coupled with chemometric tools for the geographical discrimination of coffee samples

This work aims the study chemometric methods for the classification of the origin of coffee samples. Samples of finely pulverized coffee grains were analyzed by synchronous molecular fluorescence spectroscopy to carry out the classification. The spectral data of the samples were obtained in triplicate in two offsets: 10 nm (with emission wavelengths from 240 nm to 600 nm) and 40 nm (from 240 nm to 560 nm), all with 1 nm resolution. Different strategies were performed using the spectra obtained with the offsets of 10 nm and 40 nm and fused data at mid-level (10 nm + 40 nm). The performances of linear and nonlinear methods were compared, the best results were obtained from the raw data from the fusion at low-level of the 10 nm and 40 nm offset spectra with the Pareto optimization criterion.

Fluorescence and DOC contents of estuarine pore waters from colonized and non-colonized sediments: Effects of sampling preservation

The influence of the colonization of salt marsh sediments with Halimione portulacoides was evaluated by analysing the fluorescent dissolved organic matter (FDOM) in sediment pore waters from a salt marsh at different depths. Cores of sediments at colonized and non-colonized sites were collected from a coastal lagoon (Ria de Aveiro, Portugal). The DOC content of extracted pore waters was determined and characterized by synchronous molecular fluorescence (Δ λ = 60 nm) and UV–visible spectroscopies. The common practice of freezing sediment cores for further and later chemical investigation was shown not to be an appropriate methodology of sample preservation. On the contrary, freezing of extracted and filtered pore water seemed not to affect either the DOC content or the fluorescence properties of pore waters. Two types of fluorescent substances were found in the pore waters spectra; one corresponding to humic-like substances and another one resembling proteins. However, major differences were found in the spectra of pore waters depending on both depth and the presence/absence of vegetation colonization.

Spectroscopic properties of sedimentary humic acids from a salt marsh (Ria de Aveiro, Portugal): comparison of sediments colonized by Halimione portulacoides (L.) Aellen and non-vegetated sediments

The influence of the colonization of salt marsh sediments with Halimione portulacoides, on the composition of the sedimentary humic acids was evaluated. For this purpose, cores of colonized and non-colonized sediments from a salt marsh in Ria de Aveiro (Portugal) were collected, and the humic acids of different layers were extracted and characterized by Fourier transform infrared, synchronous molecular fluorescence (Δλ = 60 nm) and UV-visible spectroscopies and also by elemental analysis. The infrared spectra suggest the presence of more peptide residues and carbohydrates in the sedimentary humic acids from surface and around the plant roots at the site colonized by H. portulacoides, when compared with the humic acids from the depth-equivalent sediment layers at the non-colonized site. The higher content of protein-type materials is confirmed by the lowest values of C/N ratios and the highest relative intensities of a band at λexc = 280 nm in the fluorescence spectra. The lowest e280 values obtained in the UV-visible spectra, and the infrared spectra suggest a lower aromatic content of the humic acids from the colonized site.

Method for the differentiation of leaf litter extracts and study of their interaction with Cu(II) by molecular fluorescence

Six leaf litter extracts (LLE) (eucalyptus (Eucaliptus globulus), fern (Pteridium aquilinium), oak (Quercus robur), chestnut (Castanea sátiva), laurel (Laurus nobilis), and ulex (Ulex europoeus) canopies) were isolated following an extraction procedure similar to that used for fulvic acids (FA) and were characterized by elemental analysis and UV-Vis, FT-IR, and synchronous molecular fluorescence (SyF) spectroscopies. Moreover, information about their interaction with the Cu(II) ion in aqueous solution (100 mg yL of LLE in 0.1 M KNO3 at pH = 6) was obtained from the measurement of SyF spectra at increasing concentrations of Cu(II). These spectral sets were treated by a self-modeling mixture analysis method (SIMPLISMA) to obtain improved quenching profiles to be used in the estimation by the method of Ryan and Weber of the conditional stability constants (Kc), concentration of binding sites, and percentage of fluorescent binding sites accessible for complexation. For comparison purposes, two samples of FA extracted from two horizons of an oak forest soil (0-5 cm and 5-15 cm) were also studied. The spectroscopic data obtained for LLE and FA were different. The results suggest that LLE are characterized by relatively high concentrations of individualized simple molecules and include reactive structures (alkene and protein residues). The ratio of aliphatic yaromatic structures was higher in LLE than for FA. Both LLE and soil FA form stable complexes with Cu(II), but the logarithm of the conditional stability constant of the 1:1 complexes is larger for LLE (about 5) than for the soil FA (about 4.5).Key words: leaf litter extracts, soil fulvic acids, synchronous fluorescence, Cu(II) complexation, SIMPLISMA, spectral pattern recognition.

Effect of the pH on the complexation of Cu(II), Ni(II) and Fe(III) Ions by a vine leaf litter extract by fluorescence quenching

An extract of dead vine leaves (vitis viniferal) (VLE) was obtained by the extraction procedure for fulvic acids and its interaction (at a concentration of 25mg/L in 0.1 M KNO3) with the Cu(II), Ni(II) and Fe(III) ions was studied in the pH range between 3 and 6. This interaction was monitored by synchronous molecular fluorescence, since bands due to the fluorescent ligands undergo quenching upon complex formation. After the chemometric isolation of the quenching profiles from the raw spectra by a self-modeling mixture analysis, SIMPLISMA, they were analyzed by two methods: (i) graphical procedures based on the Stern-Volmer model; and (ii) a non-linear least-squares procedure. For the Cu(II) and Ni(II) ions, the treatment by these two methods provided similar values both for the logarithm of the conditional stability constants (log Kc) and the percentage of fluorescent structures that do not participate in the complexation. The log Kc were (standard deviations in parenthesis): Cu(II) ion, 2.4 (3), 3.37(3), 4.4(1) and 4.92(9), respectively, for pH = 3, 4, 5 and 6; Ni(II)ion, 2.9(1), 3.3(2), and 4.09(3), respectively, for pH = 4, 5 and 6. For Fe(III) an interaction with VLE was observed, but no values for Kc could be obtained.

Acid-base properties of fulvic acids extracted from an untreated sewage sludge and from composted sludge

The acid-base properties of two samples of anthropogenic fulvic acids (FA) extracted from the untreated sewage sludge (rsFA) of a municipal wastewater treatment plant and from the compost (csFA) obtained in the aerobical digestion of this sludge were studied. Potentiometric titrimetry, infrared spectroscopy and synchronous molecular fluorescence (SyF) spectroscopy were used to obtain experimental information about the acid-base properties of the samples. Moreover, the SyF spectral data which were collected as function of the pH were analysed by a self-modelling curve resolution technique, evolving factor analysis with a gradient concentration window (EFA-GCW), to calculate the number of acid-base systems, their SyF spectra and the corresponding distribution diagrams, from which the p K a values were estimated. Two acid-base systems with p K a values about 6.2 and 8.9 were detected for rsFA and three systems with p K a values about 3.8, 6.6 and 9.4 for csFA. The amounts of acid groups directly titrated in water were (standard deviations in brackets) about 6.8(1) for rsFA and 6.73(3) for csFA. This information for rsFA and csFA was compared with similar information for natural soil FA samples extracted from a pinewood soil. Beyond different structural composition, this comparison showed that the anthropogenic samples have a higher amount of acid structures, but the structures of natural samples have stronger acid properties.

Method for the differentiation of leaf litter extracts and study of their interaction with Cu(II) by molecular fluorescence

Six leaf litter extracts (LLE) (eucalyptus (Eucaliptus globulus), fern (Pteridium aquilinium), oak (Quercus robur), chestnut (Castanea sátiva), laurel (Laurus nobilis), and ulex (Ulex europoeus) canopies) were isolated following an extraction procedure similar to that used for fulvic acids (FA) and were characterized by elemental analysis and UV-Vis, FT-IR, and synchronous molecular fluorescence (SyF) spectroscopies. Moreover, information about their interaction with the Cu(II) ion in aqueous solution (100 mg yL of LLE in 0.1 M KNO3 at pH = 6) was obtained from the measurement of SyF spectra at increasing concentrations of Cu(II). These spectral sets were treated by a self-modeling mixture analysis method (SIMPLISMA) to obtain improved quenching profiles to be used in the estimation by the method of Ryan and Weber of the conditional stability constants (Kc), concentration of binding sites, and percentage of fluorescent binding sites accessible for complexation. For comparison purposes, two samples of FA extracted from two horizons of an oak forest soil (0-5 cm and 5-15 cm) were also studied. The spectroscopic data obtained for LLE and FA were different. The results suggest that LLE are characterized by relatively high concentrations of individualized simple molecules and include reactive structures (alkene and protein residues). The ratio of aliphatic yaromatic structures was higher in LLE than for FA. Both LLE and soil FA form stable complexes with Cu(II), but the logarithm of the conditional stability constant of the 1:1 complexes is larger for LLE (about 5) than for the soil FA (about 4.5).Key words: leaf litter extracts, soil fulvic acids, synchronous fluorescence, Cu(II) complexation, SIMPLISMA, spectral pattern recognition.

Trilinear PARAFAC decomposition of synchronous fluorescence spectra of mixtures of the major metabolites of acetylsalicylic acid.

Mixtures of the three major metabolites of acetylsalicylic acid (salicylic, gentisic and salicyluric acid) were analyzed by synchronous molecular fluorescence spectroscopy. Three-way data matrices were generated by acquisition of spectra as a function of the pH (between 2 and 11) and of different relative concentrations of the three components. The PARAFAC trilinear model, without restrictions and using one factor per metabolite, was used in the data analysis. A full decomposition of the data matrices into the spectra, concentration and pH profiles was obtained. This result shows that molecular fluorescence spectroscopy can be used for the development of robust analytical methods for the simultaneous determination of the three major metabolites of acetylsalicylic acid in complex background samples.

Study of the complexation of Cu(II) by fulvic acids extracted from a sewage sludge and its compost

The complexation of Cu(II) by two samples of fulvic acids (FA) extracted from the raw sewage sludge (RsFA) of a waste water processing plant and from the composted sludge (CsFA) obtained upon aerobical digestion was studied at pH 6.0. Synchronous molecular fluorescence spectroscopy was used to monitor the association of FA with Cu(II) and a self-modelling mixture analysis method (SIMPLISMA) was used to preprocess the spectral data to calculate the number of components with different quenching profiles as function of the Cu(II) concentration and their spectra. The stability constants and a rough estimation of the binding site concentrations were obtained by a Stern-Volmer analysis, by a non-linear least-square method and by a linear procedure. The analysis of the SyF spectra allowed the identification of two binding sites for both samples. The logarithm of the conditional stability constant corresponding to the 1:1 complex formed between the stronger binding site and Cu(II) is about 4 for both samples.

Procedure for the Classification of Fulvic Acids and Similar Substances Based on the Variation With pH of Their Synchronous Fluorescence Spectra

A method for the classification of fulvic acids (FA) and similar substances is presented. It consists of three steps: (i) for each sample, sets of synchronous molecular fluorescence spectra as the pH is changed are acquired; (ii) the spectral set is reduced to a small number of spectra and concentration profiles of the detected components by evolving factor analysis with a gradient concentration window (EFA–GCW) are obtained; (iii) the spectra of the components of the samples are subjected to pattern recognition analysis by cluster analysis and multi-dimensional scaling. The procedure was tested with 13 samples of FA of natural and anthropogenic origin. Classification rules as a function of the origin and acid–base properties of the samples, in the form of figures with spectra and tables with spectral characteristics, were obtained. The classification according to the origin of the FA samples is useful for the evaluation of the extent of humification of FA. The following information on the acid–base properties of the fluorescent fractions of FA was obtained: only FA extracted from soil have fluorescent fractions with relatively strong acid character (pKa ≈ 3.2); all FA extracted from different origins have similar fluorescent structures with relatively weak acid character (pKa ≈ 6.2); in addition, FA extracted from low humified materials (leaf litter and composted wastes) have another set of similar fluorescent structures with weak acid character (pKa ≈ 9.2).

Study of the interaction of a soil fulvic acid with UO2 2+ by self-modelling mixture analysis of synchronous molecular fluorescence spectra

The interactions between UO22+ and fulvic acids (FUA) were studied by a methodology that involves synchronous molecular fluorescence spectroscopy, to monitor the quenching of the intrinsic fluorescence of FUA by UO22+, and a self-modelling mixture analysis method (SIMPLISMA), to treat spectroscopic data. This methodology was applied to the analysis of the interaction of UO22+ with salicylic acid at pH 3.5 and with a soil FUA at pH 3.5 and 7.0, in this case in the presence of various concentrations of carbonate ion (10–5, 10–4 and 10–3 mol l–1). From the calculated quenching fluorescence intensity profiles, using either the Stern–Volmer relationship or a non-linear least-squares method, mean conditional stability constants (log values with standard deviations in parentheses) were estimated for salicylic acid [respectively 2.72(4) and 2.77(6)], for FUA at pH 3.5 [3.93(2) and 4.4(1)] and pH 7.0 [4.06 and 4.1 (average values for the various concentrations of carbonate ion)]. The non-linear least-squares method also allowed the estimation of the number of binding sites that exist in FUA (0.11 and 0.24 mol g–1 at pH 3.5 and 7.0, respectively).

Simultaneous use of evolving factor analysis of fluorescence spectral data and analysis of pH titration data for comparison of the acid-base properties of fulvic acids

Three fulvic acids (fua) extracted from a Portuguese pinewood soil (dry pine needles, fual, leaf litter, fua2, and lower soil horizon, fua3) have been studied by synchronous molecular fluorescence spectroscopy (SyF) at variable pH and by potentiometric pH titrations. The number of macroscopic acid-base systems and their p K a s were calculated by analysis of the SyF-pH hyphenated data with a self-modeling curve resolution technique (evolving factor analysis, EFA). Four macroscopic acid-base systems were detected in the fulvic acid samples (with p K a s around 3.0, 4.5, 7.0 and 9.0). The concentrations of the groups responsible for the acid-base systems were calculated by a standard non-linear least squares adjustment of pH potentiometric titration curves using the p K a values obtained by EFA. The procedure detected differences between the three fua: the concentration of carboxylic groups increased from fual to fua3 but, in contrast, the concentration of the phenolic groups decreased. These results correlate well with the expected extent of humification of the samples.

Beryllium(II) as a Probe for Study of the Interactions of Metals and Fulvic Acids by Synchronous Fluorescence Spectroscopy

The interaction of Be(II) with two samples of fulvic acids (fua), extracted from materials present in a pinewood soil (fua2 from upper and fua3 from lower soil horizons), was followed by synchronous molecular fluorescence spectroscopy at pH = 6 and 11. The variations observed in the spectral data were analyzed by evolving factor analysis (EFA). It was found that Be(II) is a useful probe for detecting different ligand structures in complex mixtures of the fua type. The existence of common ligand structures in the two fua samples at both pH values studied was observed. These are probably of the salicylic acid type. Dihydroxylic structures of the catechol type were also detected. The logarithm of the mean conditional stability constants for coordination of the fua ligand structures of the salicylic acid type and Be(II) were obtained (at a pH of 6 and 11, respectively): fua2, 5.85(2) and 5.24(9); fua3, 6.5(1) and 5.08(4). This strong coordination indicates that fua can have an important function in the immobilization of Be(II) dispersed into the environment.