Aquatic photochemistry of paracetamol in the presence of dissolved organic chromophoric material and nitrate.

PURPOSE: This study contains some new findings connected to the photolysis of the drug paracetamol (hereinafter APAP) especially in light of estimating natural conditions, and it will offer information to better evaluate environmental problems connected with this widely used analgesic agent. Only a few studies, so far, have focussed on the photodegradation process of APAP in the natural environment, and the question about the role of the colored/chromophoric dissolved organic matter (CDOM) and nitrate (NO3-) as photoinductors is almost open. METHODS: APAP dissolved in freshwater and pure laboratory water in the presence and absence of CDOM and NO3- ions was irradiated using weak-energy photon energies simulating natural conditions. RESULTS: CDOM and NO3- as photoinductors produced only the slow phototransformation of APAP under weak energy radiation, and APAP seemed to be practically resistant to direct photolysis under weak radiant energies available in natural conditions. The estimated reaction efficiencies, in addition to half-lives, speak for that NO3- and CDOM do not act as quite independent photoinductors but their effect in conjunction (CDOM-NO3- -water) is stronger than the separate ones. The principal phototransformation intermediates of APAP were mono-hydroxy derivatives, depending on available photon energies formed via ortho- or meta-hydroxylation, possessing substantial power of resistance to further specific transformation reactions. CONCLUSIONS: The estimated half-life of the phototransformation of APAP in the natural aqueous environment and in the presence of suitable photoinductors will be about 30 days or more.

Advanced TMAH and TMAAc thermochemolysis-pyrolysis techniques for molecular characterization of size-separated fractions from aquatic dissolved organic matter.

The structural similarities and differences between the original DOM and the eight size fractions separated were studied in detail with the pyrolysis technique in combination with gas chromatography and mass spectrometry (Py-GC-MS) using two alkylating reagents: TMAH (tetramethylammonium hydroxide), to find both esterified and free carboxylic acids; and TMAAc (tetramethylammonium acetate), to specify only free carboxylic acids. A statistical analysis of the original multidimensional TMAH and TMAAc pyrograms disclosed that the overall structural compositions of the five most important size fractions, accounting for 84% of the original DOM, greatly resembled each other. The remaining three minor size fractions were not classified as homogeneous associations, but they also contained the same total, covalently bound and free carboxylic acid species as the other size fractions and the original DOM mixture, thus representing some kind of intermediate forms. This fundamental outcome strongly supports the opinion that the native dissolved humic-like macromolecules resemble supramolecular associations of smaller molecular size moieties with similar structural functionalities. The concentrations of free aliphatic and aromatic dicarboxylic acids in the DOM solution were so low that their effects on the potential formation of multiply charged ions in electrospray ionization-MS (ESI-MS) studies are likely insignificant.

NMR spectroscopy study of freshwater humic material in light of supramolecular assembly.

The structural similarity-dissimilarity of several humic-type derivatives, separated from a strongly colored freshwater sample by different sorbing solid techniques, tangential-flow ultrafiltration (UF), and large-scale preparative high-performance size-exclusion chromatography (HPSEC), were in detail studied with one-dimensional liquid 1H and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, especially in light of the native humic-type dissolved organic matter (DOM-HM). The results support the applicability of functional cross-linked poly(vinylpyrrolidone) (PVP) or diethylaminoethyl-cellulose (DEAE) sorbents in concentrating representative integrated wholes of aquatic humic-type material along with a conventional nonionic XAD-8/DAX-8 (polymethyl methacrylates) technique. Apart from the fact that the acidification of the original humic water before a separation procedure seems not to be so destructive to the original structural composition of the DOM-HM as expected, the refinement of aquatic humic solutes, independent of the selected sorbing solid technique, will cause structural changes in the separated humic complexes in comparison with the situation predominating in the original starting material. Tangential-flow ultrafiltration (UF) proved an overpowering reliability to concentrate the aquatic DOM-HM. Most fundamental is the combined outcome of different HPSEC experiments and determined structural functionalities which indicate that almost all original DOM-HM solutes are aggregated mixtures consisting of structurally similar associations possessing various molecular size ranges, which can be separated from their integrated whole as nearly homogeneous and uniform species. This finding permits a reasonable starting point to go on working with more advanced multidimensional NMR techniques in resolving the uncertainty about supramolecular assembly of dissolved humic material. The tested conformity between the obtained molecular NMR descriptors and the corresponding previously collected FT-IR parameters was acceptable thus speaking for the fact that the less sensitive FT-IR spectroscopy can also provide valuable information on the structural and functional properties of heterogeneous humic-type mixtures.

Comparative study for separation of aquatic humic-type organic constituents by DAX-8, PVP and DEAE sorbing solids and tangential ultrafiltration: elemental composition, size-exclusion chromatography, UV-vis and FT-IR.

Aquatic humic-type solutes were separated in parallel from the same fresh water source by four different procedures: non-ionic polymethyl methacrylate (DAX-8) and functional cross-linked polyvinylpyrrolidone (PVP) resins, functional diethylaminoethyl cellulose (DEAE) and tangential ultrafiltration completed with a weakly basic anion exchange resin (IRA-67). The similarity-dissimilarity between the quantities and qualities of the different humic samples is discussed, especially in the light of the original dissolved organic matter (DOM). During the past two decades, a significant progress has occurred in the aquatic humic research due to the so-called hydrophobic-hydrophilic properties possessed by certain non-ionic sorbing solids. As a result of many coincidences, it may be justifiable to examine critically the prevailing isolation techniques of aquatic humic solutes and to try to update their complicated definitions. For that reason, it is reasonable to summarize the leading principles of different isolation techniques in Section 1 of this article. The results of the present study strongly support the applicability of the PVP resin, alone or completed in sequence with a suitable non-ionic sorbing solid, for isolation of aquatic humic-type solutes from both quantitative and qualitative points of view. In certain cases, the DEAE cellulose gives a useful alternative for conventional sorbing solids in the isolation of the bulk of aquatic humic solutes. The base-catalyzed ester hydrolysis of the HM during the chromatographic isolation of the DOM seems to be relative minor.

Comparative study for differentiation of aquatic humic-type organic constituents by capillary zone electrophoresis using polyvinyl alcohol-coated capillary.

Capillary zone electrophoresis (CZE) with UV detection (254nm) was applied to characterize aquatic dissolved humic matter (DHM) from different environmental sources (lake, river and sea waters, in all 15 different samples). A series of separation examples of DHMs using a polyvinyl alcohol (PVA)-coated silica open tubular capillary were carried out in a phosphate buffer (40mM) as a background electrolyte at neutral acidity (pH 6.8). The separative power of electropherograms was reasonable and the reproducibility was above the mark. Each electropherogram was characteristic of the corresponding humic sample. Special functional fulvic and humic acids or their overall mixtures separated with XAD, DAX and DEAE sorbing solids as well as the original dissolved organic matter (DOM) were nicely differentiated according to their environmental sources. The PVA coating of open tubular silica capillaries seems to be very potential in electrophoretic characterization and separation of different humic solutes at neutral acidities with low sample concentrations thus permitting a workable technique, in a growing series of CZE studies, for better compared results from different studies.

Preliminary study of lake dissolved organic matter in light of nanoscale supramolecular assembly.

Large-scale preparative high-performance size-exclusion chromatography (HPSEC) was performed to separate different molecular size fractions in milligram quantities from strongly colored dissolved organic matter (DOM) of a freshwater using a very mild conjugate acid-base pair (10 mM acetic acid-sodium acetate solution at pH 7.0 with an ionic strength of 6 x 10(-5)) as the mobile phase. The homogeneity-uniformity of different molecular size fractions in relation to their combined original mixture was verified by an analytical HPSEC system. In addition to molecular size distribution and basic spectroscopic characteristics, Fourier transform infrared spectroscopy was applied to specify structural features for different size fractions. The results demonstrate clearly that only a very small amount of conjugate organic acid-base pair is required to generate a powerful resolution for a DOM mixture, and very strong treatments with organic acids are not necessarily needed to reach a better SEC resolution. Most essential is the combined outcome of different HPSEC experiments and determined structural functionalities which indicate that almost all original DOM solutes are aggregated mixtures consisting of different associations possessing various molecular size ranges, which can be separated from their integrated whole as nearly homogeneous and uniform species. In summary, the present study strongly speaks for the need to direct the research of natural dissolved and colloidal organic carbon more strongly toward a nanoscale study of supramolecular assemblies. More precise knowledge about the primary, secondary, and tertiary structure of dissolved DOM constituents has its essential function, e.g., for environmental protection and utilization of surface waters.

Comparative study for separation of aquatic humic substances by capillary zone electrophoresis using uncoated, polymer coated and gel-filled capillaries.

Several comparative capillary zone electrophoresis (CZE) experiments were carried out by means of uncoated, polyvinyl alcohol (PVA) and polyacrylamide (PAA) coated silica open tubular capillaries and gel-filled capillaries (linear non-cross-linked polyacrylamide, PAGE, by a pre-coated PAA capillary) using different kinds of background electrolytes (BGEs) and organic modifiers for characterization of aquatic dissolved humic matter (DHM). Organic compounds, such as acetic acid, acetate buffer, methanol, ethylene glycol, acetonitrile, dimethylsulphoxide, 5 M urea and sodium dodecyl sulphate (SDS) were tested as sample modifiers to improve the separative power. The fractionation mode by a PVA coated open tubular capillary using 40 mM phosphate buffer at pH 6.8 and 5 M urea-water as the sample modifier turned out to be fairly practical as well as its PAA homologue. Linear non-cross-linked PAGE with 10% gel concentration and 5 M urea-water as the sample modifier using 40 mM phosphate buffer at pH 6.8 produced the most reliable results as to the adaptation of physical gels, especially if the interactions of humic solutes with the gel matrix are not critical. The addition of SDS in the linear PAGE gel increased the interaction of humic solutes with the gel matrix but also improved the separative power and strengthened the chaotropic effect of the urea modifier.

Critical comments on accuracy of quantitative determination of natural humic matter by solid state (13)C NMR spectroscopy.

Structural information of natural organic matter (NOM) at the molecular level is very essential in understanding their nature and reactivity. Nuclear magnetic resonance (NMR) is an excellent tool for estimating the gross chemical composition of the very complex humic matter (HM). A well-known fact is that the solid state (13)C NMR spectral analysis is very parameter-sensitive especially in the study of the heterogenous HM (e.g. baseline corrections, different pulse techniques and spinning rates of the rotor vs. different disruptive sidebands in the spectra). This being the case, it has been emphasized the importance of qualitative and quantitative analyses for generating as real spectra as possible by means of different pulse and polarization techniques, sampling spinning rates as well as certain correction factors. In the present study a practical accuracy for quantitative determination of NOM type material by solid state (13)C NMR spectroscopy was assessed using a known HM sample. Different magnetic-field strengths, sampling spinning rates, single and ramped amplitude cross polarization techniques and TOSS pulse sequence were applied for obtaining a more reliable insight into the disruptive effect of the chemical shift anisotropy (CSA), especially the most disturbing first order spinning side bands (SSB). The results demonstrated that the SSB problem is not so significant as sometimes stated, at least in the context of HM samples and in the light of the overall reproducibility and uncertainty connected with the sample itself.

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: lambda(ex)/lambda(em) 280/298, 330/348, 355/373, 400/418, 427/445, 460/478, 492/510 and 516/534 nm.

Sediment-dissolved organic matter equilibrium partitioning of pentachlorophenol: the role of humic matter.

The dissolved humic matter (HM) has an essential influence on the release of the bound pentachlorophenol (PCP) from the solid sediment. It was studied how the increase of the dissolved HM concentration affects the equilibrium partitioning of PCP between the solid sediment matter and dissolved HM. The lake sedimentary and dissolved HM were isolated and their structural compositions were compared with elemental analyses, solid-sate 13C NMR spectroscopy and degradative analyses by pyrolysis-GC/MS. At the beginning of the equilibrium experiment, the PCP contaminant (200 microg l(-1)) was added into the water-sediment slurry system having an initial dissolved HM concentration. After 35 days, the system has reached an equilibrium and 75.5% of PCP was bound to the total solid sediment, 1.5% to dissolved HM and 23.0% remained free in water. The dissolved HM content was increased by 150% and, at the second equilibrium state after 91 days, only 63.8% of PCP was bound to the total sediment, and even 6.5% to the dissolved HM and 29.7% was free. The structural analyses indicated that the contents of aliphatics, aromatics and carboxylic carbons are lower in sediment than in dissolved HM, the content of carbohydrates in turn is higher in sediment than in dissolved HM, as well as that of different protein descriptors. The closely related partition coefficients for the sediment and dissolved HM, however, implied that the structural dissimilarity of these sorbents does not play so strong roles in the binding affinity of PCP as it would be postulated. The relatively great sorption coefficient of the minor colloid-like particle fraction in water implied its special but quantitatively quite immaterial roles in the partitioning cycle of PCP.

Sorption behaviour of some chlorophenols in lake aquatic humic matter.

The sorption behaviour of 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) and pentachlorophenol (PCP) with an aquatic humic sorbent (HS) was examined in their single and mixed solutions at different acidities (pH 3, 5.5 and 7). The binding capacities and equilibrium coefficients (K(OC)) obtained were fairly close to the literature values but still underline HS's structural and steric influence on the sorption. The most acidic carboxylic (COOH) groups of the HS structure have unquestionably an essential role in the sorption. The amounts of different chlorophenols bound onto the constant quantity of the aquatic HS were in reality very low demonstrating that the amount of the dissolved organic carbon (DOC) in the environment plays a greater role than the value of K(OC). The ability of the aqueous phase to force chlorophenols to associate with the HS becomes at more neutral acidities weaker and weaker and other binding mechanisms become favoured in comparison to hydrogen or hydrophobic bonds. Sorption isotherms were constructed from sorption data, and conformity to a linear model, non-linear Freundlich equation and Langmuir equation was checked.