Research ArticleExcitation-Dependent Fluorescence Quantum Yield forFreshwater Chromophoric Dissolved OrganicMatter from Northern Russian Lakes

Svetlana Patsaeva ,1 Daria Khundzhua,1 Oleg A. Trubetskoj,2 andOlga E. Trubetskaya3

1Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119992, Russia2Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, Russia3Branch of Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences,Pushchino, Moscow Region, Russia

Correspondence should be addressed to Svetlana Patsaeva; spatsaeva@mail.ru

Received 10 February 2018; Revised 11 April 2018; Accepted 2 May 2018; Published 4 June 2018

Academic Editor: Arnaud Cuisset

Copyright © 2018 Svetlana Patsaeva et al.%is is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Advanced fluorescence analysis within the wide range of excitation wavelengths from 230 to 510 nm accompanied withchromatography was used to study natural chromophoric dissolved organic matter (CDOM) from three freshwater Karelian lakes.%e influence of excitation wavelength (λex) on fluorescence quantum yield and emission maximum position was determined.%eCDOM fluorescence quantum yield has reached a minimum at λex∼270–280 nm and a maximum at λex∼340–360 nm. It wasmonotonously decreasing after 370 nm towards longer excitation wavelengths. Analytical reversed-phase high-performanceliquid chromatography with multiwavelength fluorescence detector characterized distribution of fluorophores betweenhydrophilic/hydrophobic CDOM parts.%is technique revealed “hidden” protein-like fluorophores for some CDOM fractions, inspite of the absence of protein-like fluorescence in the initial CDOM samples.%e humic-like fluorescence was documented for allhydrophilic and hydrophobic CDOM chromatographic peaks, and its intensity was decreasing along with peaks’ hydrophobicity.On contrary, the protein-like fluorescence was found only in the hydrophobic peaks, and its intensity was increasing along withpeaks’ hydrophobicity. %is work provides new data on the CDOM optical properties consistent with the formation of su-pramolecular assemblies controlled by association of low-molecular size components. In addition, these data are very useful forunderstanding the CDOM function in the environment.

1. Introduction

Chromophoric dissolved organic matter (CDOM) naturallyoccurring in all aquatic environments is colored and con-tains materials of different molecular sizes (MSs). %esechemically complex compounds of irregular structure exertphysical-chemical properties of water, affect sorption ca-pacity, and control transport of pollutants in different en-vironments. %e CDOM absorbs light in the UV andshortwave visible ranges and thus governs the opticalproperties for both freshwater and marine aquatic ecosys-tems directly influencing the spectral quality of the un-derwater light field. Because of its absorbance in the UV, it

can protect aquatic organisms being damaged by the UVradiation [1].

Emittance of fluorescence under UV light is one of themain properties of aquatic CDOM that allows its fast andhighly sensitive analysis [2–8]. Fluorescence measure-ments provide essential information about the chemicalstructure of aquatic CDOM and require small sampleamounts. It can be applied also in the remote sensing usinglidar systems for CDOM fluorescence detection from aboardthe ship or aircraft. As it is currently accepted, the fluo-rescence of aquatic CDOM consists of two main bands, theso-called protein-like and humic-like fluorescence comingfrom two main groups of fluorophores [2, 3]. Protein-like

HindawiJournal of SpectroscopyVolume 2018, Article ID 3168320, 7 pageshttps://doi.org/10.1155/2018/3168320

fluorophores usually have an excitation and emissionmaxima below 305 and 380 nm, respectively. %e othergroup corresponds to humic-like fluorophores and showsemission within the wavelength range 380–600 nm uponexcitation within the wavelength range 230–550 nm. Alongwith changing the excitation wavelength (λex) from 270 to310 nm, the humic-like emission maximum shifts towardsshorter wavelengths. Such a shift of the emission maximumwith increasing excitation wavelength was named the “blueshift” [4]. %is phenomenon has been described for varioustypes of natural waters [5–8] and during transformations ofhumic substances caused by microscopic fungi [9].

%e fluorescence quantum yield of SDOM has been anobject of several studies where it was found that it may varydepending on the excitation wavelength [7, 10, 11]. Itsvalues under excitation at discrete wavelengths 270, 310,and 355 nm were measured for the fractions of differentMSs obtained by filtration on 5 nm pore size membrane inriverine CDOM [5, 6] and various freshwater and marinesamples [7]. Low-MS fractions (<5 nm) demonstratedhigher fluorescence quantum yield in comparison with thehigh-MS fractions (>5 nm). Fluorescence quantum yieldwas found essentially dependent of excitation wavelengthwith increasing its value along with the excitation wave-length rising from 270 to 355 nm. Contrasting to aquaticCDOM, the terrestrial humic acids and industrial humicpreparations showed lower fluorescence quantum yield,values which practically did not depend on excitationwavelength altered within the range 270–355 nm [7, 12].However, until now, the chemical structure of fluorophoresof aquatic CDOM still remains unclear. Yet, to clear thelocalization of fluorescent species between differentstructural compounds should be very useful to understandthe origin of SDOM fluorescence and its functioning inaquatic environments.

%e current work is targeted to fluorescence measure-ments within the wide range of excitation wavelengths from230 to 510 nm focusing on fluorescence quantum yield es-timation. We used the reversed-phase high-performanceliquid chromatography (RP-HPLC) with online multiwave-length absorbance and fluorescence detections to analyzeprotein-like and humic-like fluorophores of the CDOM fromseveral lakes of northern Russia with the aim to generalizefluorescence distribution between hydrophilic/hydrophobicparts of CDOM in freshwater lakes.

2. Materials and Methods

2.1. CDOM Sample Preparation. %e samples of surfacewater were taken during an expedition (August 2013) inseveral freshwater lakes located in Karelia, the north of theEuropean part of Russia. %e Onego lake is the secondlargest freshwater body in Europe. In recent years, humanimpact on the ecosystem of Onego lake has increased, es-pecially in the northwestern part, where several industrialareas are located. %e two small ultrafresh lakes of marshorigin, Verhnee and Vodoprovodnoe, are located far fromindustrial facilities and can serve as a source of CDOM in theabsence of anthropogenic load. Water samples were stored

in the sealed plastic bottles in the dark at +4°C.%e 100ml oforiginal freshwater samples were filtered using cellulosefilters (Millipore) with a pore size of 0.45 μm. 50mL of eachfiltered natural water sample was freeze dried and dissolvedin 1.5–3ml of 10mM phosphate buffer (pH 6.5) prepared bymixing three volumes of 10mMNa2HPO4 solution (pH 9.8)and seven volumes of 10mM NaH2PO4 solution (pH 4.5).%e concentrated stock solutions of CDOMs were stored indark glass vials at +4°C before further spectroscopic andchromatographic analyses.

2.2. UV-Visible Absorption and Fluorescence EmissionSpectra. %e absorption spectra of original lake water, fil-tered samples, and CDOM dissolved in phosphate bufferwere measured in a quartz cuvette with optical path 1 cm or3 cm using the UV-Vis spectrophotometer Solar PB-2201(Belarus) within wavelength range 200–900 nm. %e 3 cm-cell was used to measure absorbance more accurately in thevisible range of the spectrum. For further applications, allabsorbances were related to 1 cm.

%e fluorescence emission spectra of CDOM sampleswere recorded in 1 cm standard quartz cuvette using a CaryEclipse fluorescence spectrophotometer (Varian, USA) atdifferent excitation wavelengths from 230 to 510 nmwith theinterval of 10 nm within the emission range of 200–700 nm.In order to minimize the inner-filter effect, all samples werediluted with 0.1mM phosphate buffer (pH 6.5) to reach anabsorbance of 0.05 at 270 nm.

2.3. Fluorescence Quantum Yield Measurement. %e fluo-rescence quantum yield was measured by the method of thereference compound applied earlier for the samples ofCDOM in natural water and commercial humic prepara-tions [6, 7, 12]. As the standard reference compound,quinine sulfate in aqueous 0.05M O2SO4 solution was usedbecause it is similar to aquatic humic substances in the shapeof emission spectrum with the emission maximum at450 nm.%e fluorescence quantum yield of quinine sulfate iswell known and equals to 0.546, or 54.6% under excitation at350 nm [13]. To obtain a calibration curve, the fluorescencespectra of quinine sulfate were measured at λex � 350 nm andconcentrations 3·10−7, 5·10−7, and 7·10−7M.

2.4. Analytical Reversed-Phase High-Performance LiquidChromatography (RP-HPLC). %e CDOM samples dis-solved in 10mM phosphate buffer were analyzed by using anACQUITY™ Ultra-Performance Liquid Chromatographicsystem (Waters Corp., Milford, MA, USA) on analyticalreversed-phase C18 column (UPLC© BEH C18, 2.1× 100mm,particle size 1.7 µm, Waters Corp., USA) as the stationaryphase. %e details of the chromatographic procedurewere described in [14, 15]. %e fluorescence of RP-HPLCchromatograms were monitored using an Acquity fluo-rescence detector (FLR) with λex � 270 nm and emissionwavelength range 300–600 nm. %e chromatograms withonline emission detection at 330 and 450 nm were analyzedfor detection of protein-like and humic-like fluorescence in

2 Journal of Spectroscopy

the same chromatographic run. %e elution rate was0.3mL/min. Methanol and 10mM phosphate buffer (pH 6.5)were used to form a stepwise gradient. %e fluorescencespectra for each RP-HPLC chromatographic peaks’ top wereextracted from the data of FLR detector.

3. Results and Discussion

3.1. UV-Visible Absorption Spectra. %e absorption spectraof each original and filtered freshwater sample were similar,demonstrating the low level of organic material in thesuspended form presented in the original natural water(Figure 1). All absorption spectra for original water andfiltered samples were featureless with a monotonic declinewith wavelength increasing from 200 to longer wavelengthswith the shoulder located around 260–290 nm. %e CDOMcontent in the lake Vodoprovodnoe was about twice higherthan that in two other lakes. %e absorption spectra differedin the slope of the curve as well. %e absorbance ratio at 230and 350 nm (A230/A350) was taken as a quantitative slopemeasurement. %is ratio was used to demonstrate essentialdifferences between the content of aliphatic bonds S-S,S-O, and S-P in CDOM of the lakes investigated. %ehighest value of A230/A350 ratio was noticed for the CDOMin the Onego lake (6.70) and was considerably less (4.77 and5.44) for the lakes Vodoprovodnoe and Verhnee, re-spectively. It means that the CDOM of the Onego lake isenriched in aliphatic compounds compared to other twolakes.

3.2. 8e Fluorescence Spectra and the Humic-Like Fluores-cence Emission Maximum as a Function of the ExcitationWavelength. %e emission spectra of the CDOM from threeKarelian lakes excited at wavelengths from 230 to 510 nm arepresented in Figure 2 after subtraction of the blank emissionat each excitation wavelength. We observed that the humic-like fluorescence was prevailing in all CDOM samples. In theexcitation region 230–280 nm, the CDOM exhibited broadhumic-like bands with the emission maxima from 425 to

450 nm and the protein-like fluorescence as a shoulderaround 330 nm. %e intensity of protein-like emission washigher being excited at λex 230, 270, and 280 nm. %e ratio

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Figure 2: Fluorescence emission spectra of CDOM samples fromthree Karelian lakes at excitation wavelengths varying from 230 to510 nm. (a) Verhnee lake. (b) Vodoprovodnoe lake. (c) Onegolake.

Journal of Spectroscopy 3

between protein-like and humic-like emission intensity wasthe highest in the Onego lake CDOM and much less in twoother samples.

%e fluorescence spectra of studied CDOM samplesfrom the lakes manifested a continuous red shift of humic-like emission maximum with increasing λex from 310 to510 nm (Figure 3), which is a common feature of theCDOM from rivers and coastal margins receiving terres-trial input [16, 17]. Additionally, all studied CDOMsamples showed the red shift of humic-like emissionmaximum with increasing λex from 230 to 270–280 nm,within the excitation range not yet analyzed before by otherresearchers. %e so-called “blue shift” was observed withchanging λex from 270 to 310 nm, which is typical fornatural water [5–7]. We did not find any informationpublished in scientific literature about excitation de-pendency of emission wavelength for the CDOM infreshwater lakes in the excitation range 230–510 nm, so webelieve that our results are the first to report this.

3.3. 8e Fluorescence Quantum Yield as a Function of Exci-tationWavelength. %e fluorescence quantum yield values forthe CDOM of three freshwater lakes showed nonmonotonousdependence with variation of λex from 230 to 510nm (Figure 4).%e highest fluorescence quantum yields in all the samples(2.3–3.4%) were obtained with λex around 340–360nm. Afterincreasing λex from 370 to 510nm, quantum yield values de-creased monotonically, demonstrating shoulders in 380–410and 420–470nm. From λex 230 to 270–280nm, the quantumyield values decreased to 1.2–1.7% and again increased to themaximum at 340–360nm. It should be noticed that the localminimum was detected in the similar excitation wavelengthrange (270–290nm), where themost significant “blue shift” wasfound. %is dependence is in agreement with our previousmeasurements of quantum yield values on coastal surfacewaters of the Kara Sea in the excitation region 250–550nm [8].

%e fluorescence quantum yield measurement issometimes used to characterize aquatic CDOM of marine,riverine, or coastal origin. %e overall shape of

dependencies of fluorescence quantum yield on excitationwavelength was found to be similar in different CDOMsamples: the maximum fluorescence efficiencies were ob-tained at excitation wavelengths between 340 and 380 nm.In [17], the dependence of fluorescence quantum yield onexcitation wavelength was used as an evidence of thepresence of terrestrial material in natural waters across theEquatorial Atlantic Ocean. %e fluorescence quantum yieldincreased from 280 nm to a maximum at 370–380 nmranging from 1.8 to 2.5% and decreased monotonicallythereafter. %e fluorescence quantum yield of CDOM inwaters from south Florida, Amazon, and Tamiami riversand fulvic acids isolated from the Suwannee River wasmeasured by Green and Blough [18]. During investigationperformed on water samples from the Equatorial AtlanticOcean [19], it was established that for excitation wave-lengths above 375 nm, the fluorescence quantum yielddecreased with decreasing λex and the emission maximumshifted continuously to the red. Additionally, maximum at∼340 nm was observed for the CDOM from a site influ-enced by the Congo River Plume. %e similar behavior offluorescence quantum yield of CDOM in deep and surfacewaters of the Norwegian Sea with maxima between 340 and380 nm was reported by Wunsch et al. [20]. In whole, ourdata corroborate with the other studies performed. How-ever, our results presented excitation dependence of theCDOM fluorescence quantum yield in the wavelengthrange below 280 nm for freshwater lakes CDOM for thefirst time. %is is important because the minimum fluo-rescence quantum yield around excitation at 280 nm wasfound. Moreover, it is valuable for further interpretation ofCDOM fluorescence origin because it is the same spectralrange of excitation where the blue shift of CDOM fluo-rescence emission is normally observed.

3.4. 8e Reversed-Phase High-Performance Liquid Chroma-tography (RP-HPLC) with Online Absorbance and Fluores-cence Detections. %e RP-HPLC with stepwise gradient

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4 Journal of Spectroscopy

formation using methanol and aqueous phosphate buffer gavepossibility to map the CDOM in terms of distribution ofhydrophilic/hydrophobic chromophores. %e chromato-grams with online absorbance detection resolved six peakswith different hydrophobic properties. %e hydrophobicityof peaks increased from the first to the last eluted peak dueto the increase of methanol concentration in the stepwiseseparation procedure. In our previous study [21], we havefound that the highest content of hydrophilic fraction wasin the CDOM from the Onego lake. In this research, we haveconfirmed this finding for all studied lakes by registration ofonline fluorescence (Figure 5). %e fluorescence detection atλex � 270 nm has shown that the CDOM in all three lakescontained humic-like fluorophores, for which the emissionmaxima depended on hydrophilic/hydrophobic properties.%e most intensive humic-like fluorescence with emissionmaximum at 420nm was found for the first hydrophilic peakin all three samples. Along with increasing the hydrophobicityof chromatographic fraction, the humic-like fluorescencemaximum shifted in 30nm towards longer wavelengths. SoRP-HPLC revealed the presence of at least two humic-like

fluorophores with different emission maxima (420 or 450nm)depending on their hydrophobicity. Fluorescence measure-ments were made not only for humic-like fluorescence but alsofor protein-like fluorescence. %e fluorophore emittinga maximum at around 345nm was found in the most hy-drophobic fractions of CDOM. %e highest amplitude ofprotein-like fluorescence was detected in the CDOM chro-matographic peaks #4–6 of the Onego lake (Figures 5(b) and5(d)), while in CDOM from two other lakes of marsh origin,the protein-like fluorophores were found in the peaks #5-6only in the trace amounts compared to humic-like fluo-rophores (Figures 5(a) and 5(c)).

3.5. Observation of “Hidden” Fluorophores Emitting Protein-Like Fluorescence. %e application of the RP-HPLC revealed“hidden” protein-like fluorophores in hydrophobic CDOMpeaks. %e local minimum in fluorescence quantum yielddependency on excitation wavelength for freshwater CDOMwas found at λex∼270–280 nm, where the “blue shift” ofCDOM fluorescence emission was typically observed as well

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Figure 5: RP-HPLC chromatograms of CDOM from the Verhnee (a) and Onego (b) lakes with online fluorescence detection at exci-tation/emission wavelength pairs 270/450 nm (red lines) and 270/350 nm (blue lines) for detection of humic-like and protein-like fluo-rescence, respectively. Inset zoom shows the zone of chromatograms from 3.5 to 8.5min. Normalized emission spectra of the peaks #1–6 offractionated CDOM from the Verhnee (c) and Onego (d) lakes. %e CDOM from the Vodoprovodnoe lake demonstrated similarchromatograms and emission spectra with that of the Verhnee lake.

Journal of Spectroscopy 5

[5–7]. On the contrary, the RP-HPLC with online fluores-cence detection has shown that the intensive humic-likefluorescence was found at all hydrophilic and hydrophobicchromatographic peaks (Figure 5). It should be stressed thatthe intensity of protein-like fluorescence increased with theincrease of peaks’ hydrophobicity, while the humic-likefluorescence decreased. %is effect was more pronouncedin the Onego lake CDOM (Figures 5(b) and 5(d)). Highamount of hydrophobic “hidden” protein-like fluorophores(i.e., fluorophores clearly detected by RP-HPLC but notso obviously visible in the original CDOM fluorescencespectra before fractionation) is one of the reasons of humic-likefluorescence quenching. We believe that the minimal CDOMfluorescence quantum yield observed at λex∼270–280nm couldbe partially resulting from absorption of light by chromophoricgroups similar to aromatic amino acids, short peptides, orproteins and thus leading to reduction in humic-like fluo-rescence excited at this wavelength range.

4. Conclusions

Fluorescence properties of natural CDOM from three Ka-relian freshwater lakes were examined within the excitationwavelength range 230–510 nm, and the influence of λex onfluorescence quantum yield and wavelength of emissionmaximum was determined. For all studied CDOM samples,the “blue shift” of humic-like fluorescence was observed at λexfrom 270 to 310 nm. On the contrary, a continuous “red shift”in emission maximum with increasing excitation wavelengthwas observed at λex from 230 to 270 nm and ≥310 nm. %equantum yield of CDOM fluorescence decreased startingfrom excitation at 230nm, showing aminimumat 270–280nm,then reaching a maximum at 340–360nm and further de-creasing towards longer excitationwavelengths.%ese results, forthe first time, demonstrated the excitation-wavelength de-pendence of fluorescence quantum yield in the spectral range ofexcitation below 280nm for freshwater CDOM. Analytical RP-HPLC with multiwavelength fluorescence and absorbance de-tectors was used to characterize CDOM in freshwater lakesand to determine distribution of fluorophores betweenhydrophilic/hydrophobic CDOM parts. %e intensive humic-like fluorescence was found at all hydrophilic and hydrophobicchromatographic peaks, while the protein-like fluorescence wasdetected only in the most hydrophobic peaks; the intensity ofprotein-like fluorescence increased with the increase of peaks’hydrophobicity, while the humic-like fluorescence decreased.%ese results are well consistent with the formation of supra-molecular assemblies by the CDOMmolecules, likely controlledby association of low-molecular size components. %e distri-bution of humic-like and protein-like fluorophores within theCDOM provides detailed information that may help to bettertrace the origin of CDOM and its biogeochemical trans-formations in the environment.

Data Availability

%e data used to support the findings of this study areavailable from the corresponding author upon request.

Conflicts of Interest

%e authors declare that they have no conflicts of interest.

Acknowledgments

%e authors express their gratitude to Dr. Elena Krasnova,Dr. Dmitriy Voronov, and Professor Igor Glushko for theirenthusiastic help in water sampling and very fruitful dis-cussions. %e authors thank the administration and the staffof N. A. Pertzov White Sea Biological Station of LomonosovMoscow State University for their kind support during thefield work. %is work was financially supported by theRussian Foundation for Basic Research (RFBR) (Grant no.18-016-00078).

References

[1] D. P. Hader, C. E. Williamson, S. A. Wangberg et al., “Effectsof UV radiation on aquatic ecosystems and interactions withother environmental factors,” Photochemical and Photobio-logical Sciences, vol. 14, no. 1, pp. 108–26, 2015.

[2] P. G. Coble, S. A. Green, N. V. Blough, and R. B. Gagosian,“Characterisation of dissolved organic matter in the Black Seaby fluorescence spectroscopy,” Nature, vol. 348, no. 6300,pp. 432–435, 1990.

[3] P. G. Coble, R. G. M. Spencer, A. Bakeret et al., “Aquaticorganic matter fluorescence,” in Aquatic Organic MatterFluorescence, P. G. Coble, J. Lead, A. Baker, D. A. Reynolds,and R. G. M. Spencer, Eds., pp. 75–122, Cambridge UniversityPress, New York, NY, USA, 2014.

[4] O. F. X. Donard, M. Lamotte, C. Belin et al., “High-sensitivityfluorescence spectroscopy of Mediterranean waters usinga conventional or a pulsed laser excitation source,” MarineChemistry, vol. 27, no. 1-2, pp. 117–136, 1989.

[5] O. M. Gorshkova, A. S. Milukov, S. V. Patsayeva et al.,“Fluorescence of DOM nanoparticles in natural water,” inProceedings of SPIE, Atomic and Molecular Pulsed Lasers VI,vol. 6263, pp. 248–255, Tomsk, Russian Federation, May 2006.

[6] A. S.Milyukov, S. V. Patsaeva, V. I. Yuzhakov, O.M.Gorshkova,and E. M. Prashchikina, “Fluorescence of nanoparticles of or-ganic matter dissolved in natural water,” Moscow UniversityPhysics Bulletin, vol. 62, no. 6, pp. 368–372, 2007.

[7] D. M. Shubina, O. M. Gorshkova, S. V. Patsaeva et al., “%e“blue shift” of emission maximum and the fluorescencequantum yield as quantitative spectral characteristics ofdissolved humic substances,” EARSeL eProceedings, vol. 9,pp. 13–21, 2010.

[8] A. N. Drozdova, S. V. Patsaeva, and D. A. Khundzhua,“Fluorescence of dissolved organic matter as a marker fordistribution of desalinated waters in the Kara Sea and bays ofNovaya Zemlya archipelago,” Oceanology, vol. 57, no. 1,pp. 41–47, 2017.

[9] D. Khundzhua, S. Patsaeva, V. Terekhova et al., “Spectralcharacterization of fungal metabolites in aqueous mediumwith humus substances,” Journal of Spectroscopy, vol. 2013,Article ID 538608, 7 pages, 2013.

[10] E. Parlanti, K. Woerz, L. Geoffroy et al., “Dissolved organicmatter fluorescence spectroscopy as a tool to estimate bi-ological activity in a coastal zone submitted to anthropogenicinputs,” Organic Geochemistry, vol. 31, no. 12, pp. 1765–1781,2000.

6 Journal of Spectroscopy

[11] R. Del Vecchio and N. V. Blough, “On the origin of the opticalproperties of humic substances,” Environmental Science andTechnology, vol. 38, no. 14, pp. 3885–3891, 2004.

[12] O. Gosteva, A. A. Izosimov, S. V. Patsaeva, V. I. Yuzhakov,and O. S. Yakimenko, “Fluorescence of aqueous solutions ofcommercial humic products,” Journal of Applied Spectroscopy,vol. 78, no. 6, pp. 884–891, 2012.

[13] R. A. Velapoldi and K. D. Mielenz, A Fluorescence StandardReferenceMaterial: Quinine Sulfate Dihydrate,NBS Spec Publ.260–64, National Bureau of Standards, Washington DC, USA,1980.

[14] O. E. Trubetskaya, C. Richard, and O. A. Trubetskoj, “Eval-uation of Suwannee River NOM electrophoretic fractions byRP-HPLC with online absorbance and fluorescence de-tection,” Environmental Science and Pollution Research,vol. 22, no. 13, pp. 9989–9998, 2015.

[15] O. E. Trubetskaya, C. Richard, and O. A. Trubetskoj, “Highamounts of free aromatic amino acids in the protein-likefluorescence of water-dissolved organic matter,” Environ-mental Chemistry Letters, vol. 14, no. 4, pp. 495–500, 2016.

[16] C. A. Stedmon, S. Markager, and R. Bro, “Tracing dissolvedorganic matter in aquatic environments using a new approachto fluorescence spectroscopy,” Marine Chemistry, vol. 82,no. 3-4, pp. 239–254, 2003.

[17] A. A. Andrew, R. Del Vecchio, A. Subramaniam, andN. V. Blough, “Chromophoric dissolved organic matter(CDOM) in the Equatorial Atlantic Ocean: Optical propertiesand their relation to CDOM structure and source,” MarineChemistry, vol. 148, pp. 33–43, 2013.

[18] S. A. Green and N. V. Blough, “Optical absorption andfluorescence properties of chromophoric dissolved organicmatter in natural waters,” Limnology and Oceanography,vol. 39, no. 8, pp. 1903–1916, 1994.

[19] E. S. Boyle, N. Guerriero, A. %iallet et al., “Optical propertiesof humic substances and CDOM: relation to structure,”Environmental Science and Technology, vol. 43, no. 7,pp. 2262–2268, 2009.

[20] U. Wunsch, K. R. Murphy, and C. Stedmon, “Fluorescencequantum yields of natural organic matter and organiccompounds: implications for the fluorescence-based in-terpretation of organic matter composition,” Frontiers inMarine Science, vol. 2, p. 98, 2015.

[21] D. A. Khundzhua, S. V. Patsaeva, O. A. Trubetskoj, andO. E. Trubetskaya, “An analysis of dissolved organic matterfrom freshwater Karelian lakes using reversed-phase high-performance liquid chromatography with online absorbanceand fluorescence analysis,” Moscow University Physics Bul-letin, vol. 72, no. 1, pp. 68–75, 2017.

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