Synchronous Scanning Fluorescence Spectroscopy Research Articles

Identification of milk types using two different fluorescence spectroscopy techniques

Fluorescence spectroscopy is a technique used to determine fluorescence spectrum that emits by fluorescent compounds. Milk had more than one fluorescent compounds such as tryptophan, vitamin A and etc. Quick identification of milk types is needed in dairy plants for milk quality control and safety. The ability of two different fluorescence spectroscopy techniques (front face fluorescence spectroscopy and synchronous scanning fluorescence spectroscopy) was determined to discriminate 40 milk samples according to milk species (10 samples for each of buffalo's, cow's, goat's and sheep's milk). The statistical methods, principal component analysis PCA and factorial discriminant analysis FDA, were used for more illustrating the obtained results. FDA was applied separately on the first five principal components obtained from PCA which performed on the two different fluorescence techniques. Results obtained from FDA showed that 100% of correct classification was obtained for data sets from the two different fluorescence techniques. The obtained results confirmed that the front face fluorescence spectroscopy and synchronous scanning fluorescence spectroscopy were capable of differentiate milk species.

Ozonation of natural organic matter and aquatic humic substances: the effects of ozone on the structural characteristics and subsequent trihalomethane formation potential

Abstract The effect of ozonation on the structural and chemical characteristics of natural organic matter (NOM) and its isolated humic fractions, humic acid (HA) and fulvic acid, were studied using Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), ultraviolet/visible (UV/Vis) spectroscopy, and synchronous scanning fluorescence (SSF) spectroscopy. The results were linked to the effect of ozonation on trihalomethane formation potential (THMfp) reduction for water standards with high THM precursors. Results showed that ozonation at a dose of 1 mg ozone/mg dissolved organic carbon (DOC) was capable of reducing DOC, UV absorbance at 254 nm (UV254), and THMfp by up to 42%, 95%, and 89% for the HA water standard, respectively. The study of UV/Vis, FTIR-ATR, and SSF revealed trends showing that ozone can alter the composition of DOC in the water standards, causing a significant reduction in aromaticity. The reduction of UV254 for each ozonated sample also affirms that ozone mainly targets aromatic moieties contained in NOM. FTIR-ATR results showed that the reduction of unsaturated functional groups, including aromatic rings and C = C bonds in the water standards tested, were the main components impacted by ozone application. SSF results also revealed that ozonation decreases the fluorescence intensity of the maximum peak – as well as the whole spectra.

Analysis of Australian Beers Using Fluorescence Spectroscopy

Classification of a series of Australian beers was performed using synchronous scanning fluorescence spectroscopy and emission-excitation matrices based on the IR fingerprint regions. The results indicate that synchronous scanning fluorescence spectroscopy is a robust and valuable method to discriminate between Australian lager beers based on their brand name. In addition, a subsequent spoiling study revealed that when beers are opened and stored at 4 °C for 4 weeks, the results demonstrated that the beers were not statistically different. The methods and techniques outlined may be of interest to brewing companies and microbrewers to determine the unique beer spectrum.

Effect of humic acid source on humic acid adsorption onto titanium dioxide nanoparticles

In many studies, different humic acid (HA) sources are used interchangeably to evaluate the effect of organic matter on geochemical processes in the environment. This research looks more specifically at the effect of HA source on HA adsorption onto nano-TiO2 and how HA adsorption affects the fate and transport of nano-TiO2. In this study, six humic acids (HAs) were studied which were derived from soils (SLHA), or from sediments (SDHA) all originating from the state of Florida. Humic acid adsorption onto titanium dioxide nanoparticles (nano-TiO2) and the sedimentation of HA-coated and uncoated nano-TiO2 were monitored by Ultraviolet–visible (UV–vis) spectroscopy. Synchronous scan fluorescence (SSF) spectroscopy was used to complement the study of HA adsorption onto nano-TiO2. Phosphate buffer was found to reduce the amount of HA adsorbed onto nano-TiO2 relative to solutions of NaCl of the same pH and ionic strength. Adsorption constant values (Kads) for HAs varied in the order SLHA>FSDHA (freshwater sedimentary HA)>ESDHA (estuarine sedimentary HA). SSF results suggested that the more highly conjugated fractions of HA, which are more prevalent in SLHAs versus SDHAs, were preferentially adsorbed. In order to better understand the relationship between adsorption and aggregation, sedimentation studies were conducted and it was found that the percentage of nano-TiO2 sedimentation was preferentially enhanced in the order of the presence of SLHA>FSDHA>ESDHA. The extent of nano-TiO2 sedimentation was decreased with increasing HA concentration. TEM imaging of nano-TiO2 confirmed that nano-TiO2 was aggregated in the presence of HAs. The findings in this study suggest that HAs from different sources influence the fate and transport of nano-TiO2 in the environment differently.

Organic matter source discrimination by humic acid characterization: Synchronous scan fluorescence spectroscopy and Ferrate(VI)

In this study, seven soil and sedimentary humic acid samples were analyzed by synchronous scan fluorescence (SSF) spectroscopy. The spectra of these humic acids were compared to each other and characterized, based on three major SSF peaks centered at approximately 281, 367 and 470nm. Intensity ratios were calculated based on these peaks that were used to numerically assist in source discrimination. All humic acid samples were then reacted with Ferrate(VI) and were again analyzed with SSF. Upon the addition of Ferrate(VI) SSF spectra were obtained which more readily differentiated humic acid source. This method will assist geochemists and water management districts in tracing sources of organic matter to receiving water bodies and may aid in the elucidation of the chemical nature of humic acids.

Nile Red Synchronous Scan Fluorescence Spectroscopy to Follow Matrix Modification in Sol–Gel Derived Media and its Effect on the Peroxidase Activity of cytochrome c

The highly solvatochromic dye Nile red is used in conjunction with synchronous scan fluorescence spectroscopy to elucidate changes in the internal environment of cytochrome c, upon incorporation into differently modified sol-gel derived media. Nile red was first studied in a variety of solvents in order to quantify changes in polarity. Matrix modifications involved the addition of several silanes, intended to interact with any unreacted hydroxyl entities left from the matrix forming reaction, while polymers were used to help reduce shrinkage and modify the internal pore environment. Slight unfolding of the protein was observed on incorporation into the sol-gel derived media. During the aging process further changes were monitored by using difference synchronous scan fluorescence spectra and complementary measurements of catalytic activity, expressed as the initial velocity. Combining Nile red synchronous scan fluorescence with cytochrome c activity data lead to a method to elucidate effects linked to protein conformation and those related to the sol-gel derived host.

Interaction between carbamazepine and humic substances: A fluorescence spectroscopy study

Carbamazepine is a popular drug that has been detected in natural environments, but little is known about its biogeochemical cycling, influencing factors, and eco-environmental effects in aquatic ecosystems. Interaction between carbamazepine and humic substances, including fulvic and humic acids, was studied using three-dimensional excitation-emission matrix fluorescence spectroscopy and synchronous-scan fluorescence spectroscopy. The intrinsic fluorescence of humic substances was quenched on the addition of carbamazepine, and static quenching was the primary mechanism. The binding parameters on their interaction, including the conditional binding constants (log K) and binding capacities (C(L)), were estimated by the Ryan-Weber nonlinear theory equation. Log K ranged from 3.41 to 5.04 L/mol at 25 degrees C and pH 7.0. The influence of pH on the complexation and the competition between carbamazepine and Cu(II) for fluorescence-binding sites also were discussed. The present results would be helpful in understanding the fate and biogeochemical cycling of other pharmaceuticals and personal care products in aquatic ecosystems.

Fluorescence spectroscopy in monitoring of extra virgin olive oil during storage

SummaryThe present study demonstrates the use of fluorescence spectroscopy for monitoring changes in virgin olive oil during storage. Total luminescence and synchronous scanning fluorescence spectroscopy techniques were tested with the purpose to check their ability to monitor changes occurring in olive oil during storage in different conditions: in clear and green glass bottles exposed to light, and in darkness. Total luminescence spectra of the initial oil samples in n‐hexane solutions exhibited intense peaks, one with a maximum appearing at 320 nm in emission and 290 nm in excitation, attributed to tocopherols, and another appearing at 670 nm in emission and 405 nm in excitation, belonging to the pigments of the chlorophyll group. The intensity of these emissions decreased during storage depending on the storage conditions. Additional bands appeared in oils exposed to light in the intermediate range of excitation and emission wavelengths, arising from unidentified compounds. Bands attributed to tocopherols, chlorophylls and those tentatively ascribed to phenolic compounds were observed in the synchronous scanning fluorescence spectra, allowing monitoring of the storage effects on these constituents and their quantitative assessment after appropriate calibration. The results presented confirm the capability of the fluorescence techniques to monitor the quality of oil products.

Effect of the labelling ratio on the photophysics of fluorescein isothiocyanate (FITC) conjugated to bovine serum albumin

The non-linearity of the fluorescence emission on increasing the probe to protein ratio has long been regarded as problematic and has lead to the development of dyes to overcome this effect. One of the causes of this non-linear response can be ascribed to the overlap of the label's own absorption and emission spectra. At higher labelling ratios, this affords the possibility of a reasonably efficient energy migration pathway, thus reducing the observed quantum yield of the dye. In this work we study the photophysics of fluorescein isothiocyanate (FITC) when conjugated to bovine serum albumin (BSA) at different labelling ratios (in the range FITC : BSA 1 : 17-15 : 1) using both steady state and time-resolved fluorescence techniques where on going from under labelled to over labelled samples a decrease in the initial (and steady state) anisotropy is observed, accompanied by an increase in the complexity of the decay kinetics and a decrease in the average lifetime. The band structure, elucidated by synchronous scan fluorescence spectroscopy, is also found to change on increased labelling. These results can be applied to the study of protein conformation and were confirmed by the analysis of denaturing BSA using urea.

Molecular characterization of dissolved organic matter in a North Brazilian mangrove porewater and mangrove-fringed estuaries by ultrahigh resolution Fourier Transform-Ion Cyclotron Resonance mass spectrometry and excitation/emission spectroscopy

Electrospray ionization (ESI) combined with ultrahigh resolution Fourier Transform-Ion Cyclotron Resonance mass spectrometry (FT-ICR MS) at 9.4 Tesla has been shown to be an ideal tool for the molecular characterization of dissolved natural organic matter (DOM). Here, we apply this technique for tracing DOM as it moves from mangrove porewaters into a Brazilian estuary and assess the changes that occur in the initial stages of outwelling. Comparisons of molecular features of DOM from the porewater and two sites within the adjacent estuary revealed that mass spacing patterns were far more pronounced in the mangrove porewater DOM, and the average molecular weights of estuarine DOM were lower. Calculation of double bond equivalents and Kendrick mass analysis normalized for both methylene (-CH 2−) and oxygen (O) substitution indicated that the lower molecular weights observed in the estuarine DOM were due primarily to loss of high molecular weight, highly unsaturated and/or aromatic components observed in the porewater DOM. Photodegradation is suggested as one mechanism that removes these high molecular weight components once mangrove-derived DOM reaches the estuary. The mass analyses were supported by UV–Vis and 3-D synchronous scanning fluorescence spectroscopy measurements to aid in the characterization of DOM in this unique ecosystem.

Synchronous-scan fluorescence as a selective detection method for sodium dodecylbenzene-sulfonate and pyrene in environmental samples

Synchronous-scan fluorescence spectra of dodecylbenzene sulfonic acid sodium salt (SDBS) and pyrene in aqueous solution were studied. The concentration ranges of SDBS and pyrene in aqueous solutions were 0.01–10.00 and 0.001–0.050 mg L −1, respectively. The optimized wavelength differences (Δ λ) of 46–55 and 38 nm were maintained between excitation and emission wavelengths for SDBS and pyrene, respectively, and they were found to be suitable for effective determination of SDBS and pyrene without mutual interferences; the peaks were observed at λ ex 229–232 nm (SDBS) and λ ex 335 nm (pyrene). Linear relationships between synchronous-scan fluorescence spectroscopy (SFS) intensity and concentration of SDBS or pyrene in aqueous solution (Milli-Q water, river water, and mucus of fish gills) were established. It was demonstrated that SFS method was effective for simultaneous analyses of SDBS and pyrene in mixed solution.

Synchronous-scan fluorescence spectra of Chlorella vulgaris solution

The characterization of the Chlorella vulgaris solution was carried out using synchronous-scan spectroscopy. The range of concentration of algae and Fe(III) in aqueous solutions were 5 × 10 8–8 × 10 9 cells l −1 and 10–60 μM, respectively. Effective characterization method used was synchronous-scan fluorescence spectroscopy. The wavelength difference (Δ λ) of 90 nm was maintained between excitation and emission wavelengths; 90 nm was found to be the best Δ λ for effective characterization of Chlorella vulgaris solution with or without quencher species (e.g., Fe(III), humic acid (HA)) for the first time. The peak was observed at about EX 236.6 nm/EM 326.6 nm for synchronous-scan fluorescence spectra. The fluorescence quenching of algae in system of algae–Fe(III)–HA was studied using synchronous-scan spectroscopy for the first time. Fe(III) was clearly the effective quencher. The relationship between I 0/ I (quenching efficiency) and c (concentration of Fe(III) added) was a linear correlation for the algae solution with Fe(III). Also, Aldrich humic acid was found to be an effective quencher. pH effect on synchronous-scan fluorescence intensity of algal solution with Fe(III) and/or HA was evident.

Characterization ofAnabaena cylindrica solution system using synchronous-scan fluorescence spectroscopy

The characterization of the algaeAnabaena cylindrica solution with Fe (III) was investigated using fluorescence emission and synchronous-scan spectroscopy. The ranges of concentrations of algae and Fe (III) in aqueous solutions were 5.0×108 2.5×108 cell/L and 1060 μmol/L. respectively. The effective characterization method used was synchronous-scan fluorescence spectroscopy (SFS). The wavelength difference (Δλ) of 90 nm, was maintained between excitation wavelength (λen) and emission wavelength (λen). The peak was observed at about (λex) (λem) 326 nm for synchronous scan fluorescence spectroscopy. The fluorescence quenching in system of algae Fe(III)-HA was studied using synchronous-scan spectroscopy for the first time, Fe(III) was clearly the effective quencher. The relationship betweenI I (quenching efficiency) andc (concentration of Fe (III) added) was, a linear correlation for the algae solution with Fe(III). Also, Aldrich humie acid (HA) was found to be an effective quencher.

Fluorescence study of the interaction of Suwannee River fulvic acid with metal ions and Al 3+-metal ion competition

In this study emission and synchronous-scan fluorescence spectroscopy have been used to investigate the interaction of the class A (oxygen seeking ‘hard acid’) metal Al 3+, with Suwannee River fulvic acid (SRFA), as well as competition between Al 3+ and several other metal ions (Ca 2+, Mg 2+, Cu 2+, Pd 2+, La 3+, Tb 3+ and Fe 3+) for binding sites on SRFA. Of the four metal ions possessing very similar (and relatively low) ionic indices (Ca 2+, Mg 2+, Cu 2+ and Pd 2+) only the latter two paramagnetic ions significantly quenched SRFA fluorescence emission intensity. Of the four metal ions possessing very similar (and relatively low) covalent indices (Ca 2+, Mg 2+, La 3+ and Tb 3+) only the last paramagnetic ion (Tb 3+) significantly quenched SRFA fluorescence. None of these metals was able to significantly compete with SRFA-bound Al 3+ Fe 3+, which differs substantially from all of the other metals examined in this study in that it possesses a relatively high ionic index (but not as high as Al 3+) and a relatively low covalent index (but not as low as Al 3+), was able not only to quench SRFA fluorescence but also to compete (at least to some extent) with SRFA-bound Al 3+. Synchronous-scan fluorescence SRFA spectra taken in the absence and presence of Fe 3+ and/or Al 3+ support the view that these two metal ions can compete for sites on SRFA. The results of these fluorescence experiments further confirm the Al 3+, and metal ions that have electronic properties somewhat similar to Al 3+ (such as Fe 3+) are somewhat unique in their ability to interact strongly with binding sites on fulvic acids.

Classification of edible oils using synchronous scanning fluorescence spectroscopy

Total luminescence and synchronous scanning fluorescence spectroscopy techniques were tested as regards their ability to characterize and differentiate edible oils, including soybean, sunflower, rapeseed, peanut, olive, grapeseed, linseed and corn oils. Total luminescence spectra of all oils studied as n-hexane solutions exhibit an intense peak, which appears at 290 nm in excitation and 320 nm in emission, attributed to tocopherols. Some of the oils exhibit a second long-wavelength peak, appearing at 405 nm in excitation and 670 nm in emission, belonging to pigments of the chlorophyll group. Additional bands were present in the intermediate range of excitation and emission wavelengths in some oils, arising from unidentified compounds. Similarly, bands attributed to tocopherols, chlorophylls and unidentified fluorescent components were detected in the synchronous-scanning fluorescence spectra. Classification of oils based on their synchronous fluorescence spectra was performed using a non-parametrical k nearest neighbours method and linear discriminant analysis. Both methods provided very good discrimination between the oil classes with low classification error. The results presented demonstrate the capability of the fluorescence techniques for characterizing and differentiating vegetable oils.

Characterization, differentiation and classification of aquatic humic matter separated with different sorbents: synchronous scanning fluorescence spectroscopy

Aquatic humic solutes were separated by the non-ionic macroporous XAD-8 and DAX-8 resins and a weakly basic DEAE cellulose anion exchanger from seven different fresh water sources. Synchronous fluorescence spectroscopy was applied for characterization, differentiation and classification of the different humic-solute aggregates. Fluorescence properties verified that humic-solute fractions isolated parallelly with the non-ionic XAD-8 and DAX-8 resins resembled very closely each other speaking strongly for their structural similarities. DAX-8 resin separated ca. 19% more aquatic humic matter than did the analogous XAD-8 resin. It was possible to tentatively differentiate the untreated water samples according to their fluorescent materials. Several distinct classes of chromophores were detected in both DOM and isolated humic fractions by the synchronous technique: λ ex/ λ em 280/298, 330/348, 355/373, 400/418, 427/445, 460/478, 492/510 and 516/534 nm.

Chemometric Evaluation of Synchronous Scan Fluorescence Spectroscopy for the Determination of Regulatory Conformance and Usage History of Insulation Oils

This paper describes the evaluation of synchronous scan fluorescence spectroscopy as a means of determining key characteristics of mineral insulating oils that are used in electrical apparatus around the world. Characteristics of interest to commercial operators include regulatory conformance, the history of the oil (whether it has been used or not), and, ideally, the identity and manufacturer of the oil. The oils analyzed in this study are highly relevant to real applications as they were acquired from actual high voltage power transformers operated in the United Kingdom (UK) or from stocks intended for future use in transformers. A small number of foreign oils that do not conform to UK regulations were also analysed. Principal components analysis (PCA) is used to evaluate the usefulness of the information contained in the acquired fluorescence spectra. This reveals that oils from different manufacturers can exhibit different types of spectra and that it may be possible to determine the identity of an oil from its spectral characteristics. It is also found that the spectra can be used to determine whether or not an oil has been used and whether it meets British regulatory standards. It is concluded that synchronous scanning fluorescence spectroscopy, combined with appropriate chemometrics, could provide the basis for a rapid screening test, capable of indicating whether or not a particular new or used transformer oil is suitable for initial use or continued use in high voltage equipment.

Monitoring laboratory-scale bioventing using synchronous scan fluorescence spectroscopy: analysis of the vapor phase

Bioventing is an improved method of soil remediation that is being used with increasing frequency. In this paper, we refine techniques to measure the progress of petroleum hydrocarbon decomposition by monitoring vapor phase composition with synchronous scan fluorescence spectroscopy (SSFS). Analysis of the vapor phase has advantages compared to standard extraction techniques that require extensive sample handling and clean up. For comparison, hydrocarbon contamination in the soil was measured by analysis of Soxhlet extractions with gas chromatography–mass spectrometry (GC–MS). Comparison of the GC–MS and SSFS data showed that changes in hydrocarbon composition measured in the vapor phase provide an accurate measure of decomposition reactions taking place in the soil.

A spectrofluorimetric study of the binding of carbofuran, carbaryl, and aldicarb with dissolved organic matter

This study examined the binding of carbamate pesticides with dissolved organic matter (DOM) using fluorescence quenching and synchronous scan fluorescence spectroscopy (SSFS). Fluorescence spectra of the three pesticides were characterized as follows: carbofuran and carbaryl fluoresce at 305 and 330 nm, respectively, upon excitation at 276–279 nm, whereas, aldicarb shows broad emission at 350–380 nm upon excitation at 326 nm. A fluorescence quenching technique was used to obtain conditional binding constants for the carbamate pesticides with Aldrich humic acid under fixed conditions of 22°C and pH 6. The binding constant of carbofuran with humic acid is greater than the binding constants of both carbaryl and aldicarb. Estimates were also obtained for the binding of carbofuran with DOM samples from a coniferous forest soil O horizon, a deciduous forest soil O horizon, a sedge marsh wetland, and a stream in the drainage sequence and their molecular weight (MW) fractions. Those conditional binding constants were used to predict the potential transport of carbofuran in the drainage sequence. When binding constants and DOM concentrations were both taken into account, it was found that DOM from the coniferous forest O horizon had the largest capacity to bind and to transport carbofuran in the drainage sequence. SSFS was used to probe the binding mechanisms of DOM with carbofuran. Overall, the potential mobility of carbofuran in the upland–wetland–stream drainage sequence was significantly enhanced via binding with DOM.

Variable-angle scanning fluorescence spectrometry for the simultaneous determination of three diuretic drugs

The applicability of variable-angle synchronous scanning (VASS) fluorescence spectroscopy has been demonstrated for the resolution of mixtures of three diuretics (furosemide, triamterene, piretamide) with closely overlapping fluorescence profiles. This technique permits linear or non-linear paths to be scanned at preselected angles through the excitation-emission matrix by scanning both monochromators at different speeds, in order to obtain the best variable-angle scanning spectra (highest signal values and interference-free bands). Such an approach has permitted the simultaneous determination of the three compounds at the μg to ng ml −1 level, with a relative standard deviation ≤ 5% ( n = 10). When applied to commercial pharmaceutical dosage forms, recoveries of the original drug between 98–101% have been obtained.