Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances

Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P _OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible. Received: 8 December 1997 / Revised: 2 March 1998 / Accepted: 4 March 1998     

Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances

Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P _OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible.     

On-line dual-precolumn-based trace enrichment for the determination of polar and acidic microcontaminants in river water by liquid chromatography with diode-array UV and tandem mass spectrometric detection

Dual-pre-column-based trace enrichment combined on-line with liquid chromatography-diode-array UV and tandem mass spectrometric detection was used to determine a wide polarity range of organic microcontaminants in river water. Various sorbents were studied for their extraction efficiency of (highly) polar and acidic compounds and their ability to selectively remove humic substances, which are normally co-extracted and interfere in the UV detection of polar microcontaminants. An optimised on-line dual-pre-column set-up with PLRP-S in the first pre-column and Hysphere-1 in the second pre-column was used to study the analytical performance of the procedure. Tandem MS was used for confirmation purposes and to quantify the organic microcontaminants in river water at the low-ng/l level. In addition, the influence of the type of sample (drinking and river water) on suppression of analyte responses in electrospray ionization MS was studied.     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

Chemical removal of humic substances interfering with the on-line solid-phase extraction—Liquid chromatographic determination of polar water pollutants

Summary Different methods for removing interference by humic substances in the analysis of polar pollutants have been compared in the analysis of environmental water by solid-phase extraction (SPE) with a chemically modified polymeric resin coupled on-line to liquid chromatography with UV detection. The methods were based on the use of chemical reagents. The best method was found to be addition of sodium sulphite to humic-containing water before SPE. The appropriate amount of sulphite depends on the amount of humic substances dissolved in the sample—for analysis of 50 mL tap and Ebro river water, respectively, 250 μL and 500 μL 10 % Na₂SO₃ solution had to be added. In both cases, the recovery values after chemical treatment were similar to those when a Milli-Q-quality water standard was analysed.     

Capillary electrophoretic separation of humic substances using hydroxyethyl cellulose as a buffer additive and its application to characterization of humic substances in a river water sample

We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated. Figure Addition of Fe(III) ions or EDTA to a solution containing fulvic acid (FA) results in a distinct change in the electropherogram pattern, which reflects the conformational change of FA: this forms the basis for the characterization of humic substances in river water samples     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Determination of benzoylureas in ground water samples by fully automated on-line pre-concentration and liquid chromatography-fluorescence detection

An on-line pre-concentration method for the analysis of five benzoylureas (diflubenzuron, triflumuron, hexaflumuron, lufenuron and flufenoxuron) in ground water samples was evaluated using two C(18) columns, and fluorescence detection after photochemical induced fluorescence (PIF) post-column derivatization. The trace enrichment was carried out with 35 mL of ground water modified with 15 mL of MeOH on a 50 mm x 4.6 mm I.D. first enrichment column (C-1) packed with 5 microm Hypersil Elite C(18). Retention properties of pesticides and humic acids usually contained in ground water were studied on C-1 at concentration levels ranging between 0.04 and 14.00 microg/L in water samples. The results obtained in this study show that the pesticides are pre-concentrated in the first short column while the humic acids contained in the ground water samples are eluted to waste. Pesticides recoveries ranged between 92.3 and 109.5%. The methodology proposed was used to determine benzoylureas in ground water samples at levels lower than 0.1 microg/L (maximum levels established by the European Union).     

The Singular Molecular Conformation of Humic Acids in Solution Influences Their Ability to Enhance Root Hydraulic Conductivity and Plant Growth

Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed.     

Interference of Humic Substances in the Spectrophotometric Determination of Bromate by Phenothiazines in Natural Waters

Abstract

The spectrophotometric method of bromate (BrO₃ ^?) determination by phenothiazines was applied to natural water samples and the interferences due to the presence of inorganic and humic substances were investigated. Common ions present in natural waters did not interfere and only the less abundant NO₂ ^? and Fe²⁺ exhibited strong interferences. Interferences of the two latter ions, if they existed, could be controlled and the method proved to be accurate and with a low detection limit. However, it was found that the presence of soluble humic substances resulted in positive interference, rendering the method unsuitable for bromate determination in natural waters and restricted its use in pure bromate solutions. This interference can be attributed to the electron acceptor groups invariably existing in the humic molecules. Since humic substances can remain in the water even after its ozonation, they will also contribute to a positive interference in bromate determination in potable waters.     

A comparison of various pyrolysis experiments for the analysis of reference humic substances

The interpretation of the results of pyrolysis studies of humic substances is fraught with difficulties if only a single analytical technique is employed for substructure analyses. In this paper we have carried out investigations into humic substances utilising the additional information from the combination of gas chromatography/infrared spectroscopy and gas chromatography/mass spectrometry detection following Curie-point pyrolysis at five different temperatures. The results were compared to those obtained from conventional flash pyrolysis. The aim was to ensure the validation of the results of the compounds identified by at least one other spectroscopic technique. Some 30 substances have been positively identified by infrared spectroscopy, although their appearance is dependent on pyrolysis method and temperature. Most assignments were validated by mass spectrometry or the substance class confirmed.     

A fluorescence method for studies of spent sulfite liquor and humic substances in sea water.

A fluorimetric method is described for the determination of lignin sulfonates and humic substances simultaneously in sea water. To express the concentrations in absolute values, dissolved humic substances were isolated from river water and used as a standard along with a lignin sulfonate standard. In the two-component system, measurements at two wavelengths were used to determine the concentrations or lignin sulfonates and humic substances in mixtures, since their fluorescence intensities were found to be additive. The method can be used to detect lignin sulfonates in sea water at concentration levels down to 0.01 p.p.m. when the content or humic substance is 3 p.p.m.     

Stability and Mobility of Metal-Humic Complexes Isolated from Different Soils

The contamination of potable water aquifers by heavy metals is one of the most severe environmental threats. For the transport of heavy metals from various types of contaminated sites into the ground water and also into surface water aquifers, humic substances (HS) are recognized to be of main importance. Dissolved in natural waters humic substances are readily complexed with a variety of metal ions. Therefore, humic substances are of cardinal importance for the migration and, consequently, the pollution of ground waters with heavy metals. Our paper presents the results of a comprehensive comparison of several isolated humic acids of soils of different origin (different geochemical milieu) and their metal complexes. Two polluted sites in Germany, which differ in their geochemical milieu (pH-value) were selected. The aim of our experiments was to describe the properties of terrestrial humic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon activation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded humic acid on an XAD-8 resin column, the partition of metals mobilized by humic acids could be quantified. There are correlations of the formation of metal-humic complexes with the soil pedogenes, with the pH-value as well as with the humic acid concentration.     

Association of Am with humic substances isolated from river waters with different water quality

The association properties of Am with aquatic humic substances in a 0.01M NaClO₄ solution at pH 6-8 were studied on the basis of molecular size distribution. Ten humic substances isolated from river water with different water quality (pH 3.9-8.0 and dissolved organic carbon (DOC) concentration of 2-40 mg/l) were used for comparing their effects on the association of Am. The molecular size distribution of Am in the presence of humic substances from an uncolored river water (DOC 2 mg/l) was different from that at the experimental systems using humic substances from brownish and high DOC (14-40 mg/l) river waters.     

Determination of Bismuth by Adsorptive Stripping Voltammetry Using Aluminum Oxide for Elimination of Environmental Sample Matrix Interferences

The aim of this work was to find a fast new and simple method for efficient elimination of negative influence of humic substances and synthetic surfactants in the voltammetric determination of bismuth. The negative influence of the organic matrix present in environmental water samples due to their adsorption on aluminum oxide was successfully evaluated. The organic compounds such as humic substances and surface active compounds were removed by adsorption on the surface of aluminum oxide from the water samples. The application of this method was the recovery of Bi(III) from spiked water samples.     

Application of Differential UV Spectroscopy to the Determination of Lignin Substances in Polluted Water

The absorption spectra of Bjorkman lignin, lignin sulfate, lignosulfonates, and humic substances in neutral and alkaline media are considered. It was found that the difference spectra of lignins (an alkaline solution with reference to a neutral solution) exhibited several intense bands, whereas humic substances exhibited equal shifts of the spectra over the entire spectral range. This distinctive property of the difference spectra of lignin substances, as compared to the spectra of humic substances, can be used for determining lignins in polluted water.     

Polymer film sensor for sampling and remote analysis of polycyclic aromatic hydrocarbons in clear and turbid aqueous environments

A sensor for remote analysis of polycyclic aromatic hydrocarbons (PAHs) has been developed. It is based on direct solid phase extraction of the pollutants on a polymeric film, followed by monitoring the laser induced fluorescence, emitted from the film, via optical fibers. The proposed sensor has been applied to direct PAH analysis in clear and turbid aqueous environments. Linear calibration plots have been obtained for PAH solutions containing both humic substances and clay suspensions. Detection limits in the range of 10 ppt have been achieved. Results are obtained almost instantaneously (in drinking water) or within minutes, in more complicated matrices. This set-up has provided considerable improvement of the detection limits, when compared to the traditional fiber-optic fluorescence probe. In case of pyrene, a 100-fold and a 250-fold improvement in the detection limits have been obtained for the clay and humic substances-containing water, respectively. The spectral response of the polymeric film has been studied under various conditions and the feasibility of the method for analysis of PAH mixtures has been addressed.     

Determination of heavy metal complexes with humic substances by HPLC/ICP-MS coupling using on-line isotope dilution technique

An isotope dilution mass spectrometric (IDMS) method has been developed for the simultaneous determination of the complexes of 11 heavy metals (Ag, Cd, Cu, Mo, Ni, Pb, Tl, U, W, Zn and Zr) with humic substances (HS) by coupling HPLC with ICP-MS and applying the on-line isotope dilution technique. The HPLC separation was carried out with size exclusion chromatography. This HPLC/ICP-IDMS method was applied to samples from a brown water, ground water, sewage and seepage water as well as for a sample containing isolated fulvic acids. The total contents of heavy metals and of their complexes were analyzed in these samples with detection limits in the range of 5–110 ng/L. The analysis of heavy metal/HS complexes from the different waters resulted in characteristic fingerprints of the distribution pattern of heavy metals in the separated HS fractions. A comparison between the total heavy metal concentrations and their portions bound to humic substances showed distinct differences for the various metals. Simultaneous ¹²C detection was used for the characterization of HS complexes not identified by UV detection and for the determination of relative DOC concentrations of chromatographic peaks. Received: 21 February 1997 / Revised: 27 May 1997 / Accepted: 28 May 1997     

A Multicolumn Ion Chromatographic Determination of Nitrate and Sulfate in Waters Containing Humic Substances

Abstract

A three-column ion chromatographic system for the removal of humic substances from natural waters, and subsequent on-line concentration and determination of nitrate and sulfate using non-suppressed ion chromatography is presented. Humic substances are removed using disposable adsorption columns packed with chemically bonded amine silica material. The sample is directly transfered to an ion exchange column where the anions are concentrated ca 10 times. After reversing the flow, the ions are transferred to a third column where they are separated and quantified. The detection limit is less than 1 mg L^?1 of nitrate or sulfate in water containing 45mgL^?1 of humic acid.     

Detoxification of AM-241 solutions by humic substances: bioluminescent monitoring

The study addresses the effect of humic substances on marine luminous bacteria Photobacterium phosphoreum exposed to Am-241 (3,000 Bq L⁻¹, water solution). Luminescent intensity of the bacteria was applied as a marker of their physiological activity. Humic substances have been found to reduce the effect of Am-241 on luminescence, decrease damage to cells, and change distribution of Am-241 between bacterial cells and intercellular media. It was shown that water-soluble humic substances, being products of natural transformation of organic substances in soil and bottom sediments, can serve as protecting agents for water microorganisms exposed to alpha radionuclides.