A new kinetic method for the determination of magnesium and its application to natural waters

A kinetic method is described for the determination of trace amounts of magnesium in the presence of calcium. The procedure is based on the inhibition of the manganese(II) catalyzed aerial oxidation of 1,4-dihydroxyphthalimide dithiosemicarbazone reaction by

2. Effect of Transition Metals^a

Transition metal	Concentration (M)	Percentage inhibition	Mg(II) found (×l05M)
Fe(II)	3.6.10?5	54.1	4.62
Fe(III)	3.6.10?5	47.8	4.48
Co(II)	3.4.10?5	50.0	4.53
Ni(II)	3.4.10?5	50.0	4.53
Cu(II)	3.1.10?5	52.0	4.56
Zn(II)	3.0.10?5	54.1	4.62
Cd(II)	1.7.10?5	52.0	4.56
Hg(II)	9.9.10?6	45.8	4.44
Sn(II)	2.1.10?6	50.0	4.52
Pb(II)	1.2.10?6	54.1	4.62

a

Conditions: 4.53.10^?5M Mg(II), 35 ng Mn ml^?1, 0.429 M ammonia, 1.6.10^?4M OH-PDT.

3. Determination of Magnesium in Natural Waters

			Mg(II) found (M)b
Natural water	Ca(II) presenta		Atomic absorption
sample	M	Kinetic absorption	method
Commercial	3.45 · 10?4	1.65 · 10?3	1.74 · 10?3
Commercial	5.46 · 10?4	1.57 · 10?4	1.81 · 10?4
Untreated	6.13 · 10?4	2.16 · 10?4	2.40 · 10?4
Treated	4.95 · 10?4	1.93 · 10?4	2.17 · 10?4

a

EDTA titration less the magnesium.

b

Average of three separate determinations. traces of magnesium(II). The reaction is followed spectrophotometrically by measuring the rate of change in absorbance at 594 nm. The calibration graph (percentage inhibition vs magnesium concentration) is linear in the range 329–535 · 10^?5M with an accuracy and precision of 1.2%. The method has been applied to the determination of magnesium in natural waters at low concentrations.

     

Optimization of headspace solid-phase microextraction conditions for the determination of organophosphorus insecticides in natural waters

Headspace solid-phase microextraction (HS-SPME) has been developed for the analysis of seven organophosphorus insecticides, i.e. diazinon, fenitrothion, fenthion, ethyl parathion, methyl bromophos, ethyl bromophos and ethion in natural waters. Their determination was carried out using gas chromatography with flame thermionic and mass spectrometric detection. To perform the HS-SPME, two types of fibre have been assayed and compared: polyacrylate (PA 85 microm), and polydimethylsiloxane (PDMS 100 microm). The main parameters affecting the HS-SPME process such as temperature, salt additives, memory effect, stirring rate and adsorption-time profile were studied. The method was developed using spiked natural waters such as ground, sea, river and lake water in a concentration range of 0.05-1 microg/l. The HS-SPME conditions were optimized in order to obtain the maximum sensitivity. Detection limits varied from 0.01 to 0.04 microg/l and relative standard deviations (RSD <17%) were obtained showing that the precision of the method is reliable. The method showed also good linearity for the tested concentration range with regression coefficients ranging between 0.985 and 0.999. Recoveries were in relatively high levels for all the analytes and ranged from 80 to 120%. Water samples collected from different stations along the flow of Kalamas river (NW Greece) were analyzed using the optimized conditions in order to evaluate the potential of the proposed method to the trace-level screening determination of organophosphorus insecticides. The analysis with HS-SPME has less background interference and the advantage of its non-destructive nature reveal the possibility of the repetitive use of the SPME fibre.     

Transmission electron microscopy of the natural organic matter of surface waters

Some components of aquatic natural organic matter (NOM) can be analysed effectively by methods of particle analysis employing transmission electron microscopy in conjunction with multi-method analytical approaches in the field, minimum perturbation techniques for sample handling and technology transfer from the biomedical sciences. The NOM components, include fulvic acids, colloidal fibrils and organic polymers of MW > 30 000. The use of a water-compatible embedding resin permits shape and size analyses of colloidal NOM (1–1000 nm) in ultrathin sections which minimize the misleading dehydration artifacts of the past. Experimentally induced perturbations allow one to follow aggregation/coagulation events at 1 nm resolution, while permitting the analyst to relate some components of coagulum structure to chemical entities. This review presents the current status of attempts to optimize a combination of analytical chemistry and transmission electron microscopy for describing NOM and its behaviour in surface waters.     

Design of two-dimensional biomimetic uranyl optrode and its application to the analysis of natural waters

A two-dimensional biomimetic optrode for the detection and quantification of uranium in natural waters was fabricated. The sensing element was designed by the inclusion of uranyl ion imprinted polymer particles into polymethyl methacrylate followed by casting a thin film on a glass slide without any plasticizer. The ion imprinted polymer material was prepared via covalent immobilization of the newly synthesised ligand 4-vinyl phenylazo-2-naphthol by thermal polymerization. Operational parameters such as pH, response time and the amount of sensing material were optimized. The response characteristics of the imprinted and the corresponding non-imprinted polymer inclusion optrodes of uranium were compared under optimum conditions. The imprinted polymer inclusion optrode responds linearly to uranium in the concentration range 0–1.0 μg mL⁻¹ with a detection limit of 0.18 μg mL⁻¹, which is much better than the solution studies using 4-vinyl phenylazo-2-naphthol (1.5 μg mL⁻¹). Triplicate determinations of 100 μg of uranium(VI) present in 250 mL of solution gave a mean absorbance of 0.018 with a relative standard deviation of 8.33%. The superior sensitivity of imprinted polymer inclusion optrode is exemplified by lower detection limits and broader dynamic range over non-imprinted polymer inclusion optrode. The developed imprinted polymer inclusion optrode was found to give stable and precise response for 3 months and can be used without any loss in sensitivity. The applicability for analysing ground, lake and tap-water samples collected in the vicinity of uranium deposits was successfully demonstrated.     

The effect of organic matter and colloidal particles on the determination of chromium(VI) in natural waters

The chromium(VI) contents of two water samples, a river water and a sea-water, were determined by means of solvent extraction with APDC (ammonium pyrrolidinedithiocarbamate) into chloroform and by co-precipitation with iron(III) hydroxide. The analytical results depended on the separation method used, possibly because of differences in the behaviour of the chemical species of chromium in natural waters. Various chromium species, including simple inorganic ions, organic complexes, Cr(III) adsorbed on inorganic colloids and Cr(III) combined with organic polymers, were prepared, and their analytical characteristics were investigated.     

Measurement and computation of zinc binding to natural dissolved organic matter in European surface waters

The zinc binding characteristics of natural dissolved organic matter (DOM) from five representative European surface freshwater sources were studied by square wave anodic stripping voltammetry (SWASV) and model simulation. Water samples were titrated with zinc and free zinc ion activity {Zn²⁺}, was calculated from the measurement of labile zinc by SWASV and other system conditions. Measured values of {Zn²⁺}, which were in the range 10⁻⁷ to 10⁻⁵ M, were compared with those simulated using Humic Ion-Binding Models V and VI. It was assumed that zinc speciation was controlled by the organic matter, represented by fulvic acid (FA), together with inorganic solution complexation. The models were calibrated by adjusting the parameter DOMFA, the proportion of DOM considered to behave as FA. Two modeling scenarios were used to obtain DOMFA values, both considering and not considering the competitive effects of Al, Fe(II) and Fe(III). The default Zn-DOM binding strength in Model VI (log K_MA = 1.6) was not able to provide realistic values of DOMFA and a log K_MA of 1.8 was tentatively proposed as a more plausible value in these waters. Models V and VI gave very similar fits to the data after optimization of DOMFA, in contrast to recent findings for copper. This may be due to the fact that the additional strong binding sites provided by Model VI are not important in complexing Zn in the Zn concentration range investigated in this study. Computed free Zn activities from both modeling scenarios were very similar; however, the consideration of Al and Fe competition is more realistic for natural waters.     

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: application to the analysis of natural and waste waters

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L⁻¹ range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels.     

The determination of bromide in natural waters by flow injection analysis

Bromide can occur in well waters as a result of sea water intrusion. The phenol red method is adapted to a flow-injection system and interferences are studied by using a two-channel valve. Standards are injected from one loop of the valve while the possible interferent is injected from the other loop; this provides a fast means of evaluating interferences. Ammonia, cyanide and humic substances interfere. Bromide can be determined down to 2 μM at a rate of 80 samples per hour     

Differential pulse polarographic determination of inorganic and organic arsenic in natural waters

Summary As(III), As(V) and organic arsenic in water are determined by differential pulse polarography. As (III) is directly determined in 2M HCl as supporting electrolyte. Total inorganic arsenic [As (III) + As(V)] is measured after reduction of electro-inactive As(V) with sodium sulphite. Total arsenic is determined after oxidative treatment of the water residue with potassium permanganate and magnesium nitrate, and reduction of arsenic with sodium sulphite. Organic arsenic is evaluated by difference. The efficiency of the whole procedure is 78–80% and its detection limit is 1g/l. The relative standard deviation is better than ±1.5% at 50g/l. Interferences due to heavy metals are overcome by removing them by anionexchange or pre-electrolysis with a mercury cathode.

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Differential-puls-polarograpbische Bestimmung von anorganischem und organischem Arsen in natürlichen Wässern

Zusammenfassung As (III), As(V) und organisches Arsen in Wässern wurden differentialpuls-polarographisch bestimmt. As (III) wurde direkt in 2 M HCl als Trägerelektrolyt bestimmt. Das anorganische Gesamtarsen [As(III) und As(V)] wurde nach Reduktion des elektro-inaktiven As(V) mit Natriumsulfit gemessen. Nach der oxydativen Behandlung des Wasserrückstandes mit KMnO₄ und Magnesiumnitrat und nach Reduktion des Arsens mit Natriumsulfit wurde das Gesamtarsen bestimmt, und das organisch gebundene Arsen durch Differenzbildung ermittelt. Die Ausbeute des gesamten Verfahrens beträgt 78–80%, seine Erfassungsgrenze 1g/l Die relative Standardabweichung ist besser als ±1,5% bei 50g/l. Störungen durch Schwermetalle werden entweder durch deren Entfernung mittels Anionen-austauscher oder durch vorhergehende Elektrolyse mit einer Quecksilberelektrode beseitigt.

     

Electrochemical methodology to study labile trace metal/natural organic matter complexation at low concentration levels in natural waters

A new electrochemical methodology to study labile trace metal/natural organic matter complexation at low concentration levels in natural waters is presented. This methodology consists of three steps: (i) an estimation of the complex diffusion coefficient (D_ML), (ii) determination at low pH of the total metal concentration initially present in the sample, (iii) a metal titration at the desired pH. The free and bound metal concentrations are determined for each point of the titration and modeled with the non-ideal competitive adsorption (NICA-Donnan) model in order to obtain the binding parameters. In this methodology, it is recommended to determine the hydrodynamic transport parameter, α, for each set of hydrodynamic conditions used in the voltammetric measurements.The methodology was tested using two fractions of natural organic matter (NOM) isolated from the Loire river, namely the hydrophobic organic matter (HPO) and the transphilic organic matter (TPI), and a well characterized fulvic acid (Laurentian fulvic acid, LFA). The complex diffusion coefficients obtained at pH 5 were 0.4 ± 0.2 for Pb and Cu/HPO, 1.8 ± 0.2 for Pb/TPI and (0.612 ± 0.009) × 10⁻¹⁰ m² s⁻¹ for Pb/LFA. NICA-Donnan parameters for lead binding were obtained for the HPO and TPI fractions. The new lead/LFA results were successfully predicted using parameters derived in our previous work.     

Direct (1)H NMR spectroscopy of dissolved organic matter in natural waters

Nuclear magnetic resonance (NMR) spectroscopy arguably provides the greatest insight into the overall chemical composition of dissolved organic matter (DOM). However, in a standard 5 mm NMR probe, a sample of sea water at natural abundance only contains ca. 500-600 ng of organic matter, distributed among the heterogeneous components of DOM. Additionally, the intensity of the water signal, which may be many orders of magnitude greater than the signals from DOM, makes the detection and analysis of DOM at natural abundance extremely demanding. Here, we demonstrate, that although challenging, the application of an improved water suppression technique allows NMR spectra of DOM to be obtained directly (i.e without pre-concentration) for major bodies of water, including rivers, lakes and the ocean. The technique described here provides a compositional overview of an intact sample, permitting researchers to investigate and assess the impact of concentration, isolation and extraction procedures that are employed routinely. Also the technique permits NMR to be performed on 'precious' samples for which traditional isolations are not possible, for example, water from ice cores and pore water, which are key in hydrology and for paleoclimatic reconstruction.     

Optimization of the ICP working conditions for the analysis of waste waters and industrial solutions

Summary In order to optimize the working parameters of ICP analysis of waste waters and industrial solutions the spectral interferences and the effect of the carrier gas flow were studied. Special attention was paid to the influence of high contents of salt and H₂SO₄ in some samples. The use of a peristaltic pump, dilution or internal standardization enable reliable analytical results to be obtained. A direct ICP method for determination of Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb and Zn was worked out. Relative standard deviations were in the range of 0.5–5%.

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Optimierung der ICP-Arbeitsbedingungen für die Analyse von Abwasser und industriellen Lösungen

Zusammenfassung Zur Optimierung der ICP-Parameter wurden die spektralen Störungen sowie der Einfluß des Trägergasstromes untersucht. Der Wirkung hoher Salz- und Schwefelsäuregehalte wurde besondere Aufmerksamkeit gewidmet. Mit Hilfe einer peristaltischen Pumpe sowie durch entsprechende Verdünnung und Anwendung des Verfahrens des inneren Standards konnten zuverlässige Resultate erzielt werden. Eine Arbeitsmethode wurde entwickelt für die Bestimmung von Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb und Zn. Die Standardabweichungen lagen im Bereich von 0,5–5%.

     

Fluorimetric method for the determination of uranium in natural waters

A method is described for the fluorimetric determination of uranium in natural waters. The limit of detection is 0.3 ppM. Ion-exchange is used to preconcentrate the uranium by a factor of 22 and separate it from quenching ions in the sample. The fluorescence is measured in a medium that is 1.35M in both sulphuric and phosphoric acids. The uranyl ions are excited by radiation of wavelength 280 nm and bandwidth 40 nm. The emitted signal is scanned from 470 to 510 nm. After spiking of the sample solution with a small volume of standard uranium solution, the fluorescence signal is scanned again and the uranium content of the sample calculated from the two readings. The coefficient of variation is 8.5% for determinations of U in a synthetic water sample having a uranium content of 1.9 ppM. Destruction of organic matter in the eluates gives 0.1 ppM detection limit.     

The application of electrospray ionization coupled to ultrahigh resolution mass spectrometry for the molecular characterization of natural organic matter

Mass spectrometry has recently played a key role in the understanding of natural organic matter (NOM) by providing molecular-level details about its composition. NOM, a complex assemblage of organic molecules present in natural waters and soils/sediments, has the ability to bind and transport anthropogenic materials. An improved understanding of its composition is crucial in order to understand how pollutants interact with NOM and how NOM cycles through global carbon cycles. In the past, low-resolution (>3000) mass analyzers have offered some insights into the structure of NOM, but emerging ultrahigh resolution (>200,000) techniques such as electrospray ionization (ESI) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) have significantly advanced our knowledge of NOM chemistry. Here, a review of the recent literature on the advancements of NOM characterization and the applications of mass spectrometry to this central task is presented. Various methods for the analysis and display of the extremely complex mass spectra, such as the van Krevelen diagram and Kendrick mass defect analysis, are discussed. We also review tandem mass spectrometry techniques employed to gain structural information about NOM components. Finally, we show how ESI-FT-ICR-MS has been applied to examine specific issues that are important to the NOM scientific community, such as NOM reactivity, transport and fate, degradation, and existence of components, which are indicators of NOM origin. In general, ultrahigh resolution provided by FT-ICR-MS is essential for the complete separation of the thousands of peaks present in the complex NOM mixture and will clearly lead to additional future advancements in the areas of aquatic, soil, and analytical chemistry.     

Comparative study of separation and determination of triazines by micellar electrokinetic capillary chromatography and nonaqueous capillary electrophoresis: application to residue analysis in natural waters

The separation and determination of a mixture of chloro- and methylthiotriazines in water samples by both micellar electrokinetic capillary chromatography (MEKC) and nonaqueous capillary zone electrophoresis (NA-CZE) were compared. The characteristics of both methods proved to be very similar in terms of separation efficiency and analysis times, but application of these methods for the analysis of triazines in natural waters, with a prior preconcentration step, revealed significant differences. A preconcentration step by solid-phase extraction (SPE) with Oasis HLB cartridges was accomplished for the determination of triazines at sub-ppb levels in drinking and river waters; when NA-CZE was used after this SPE step, electropherograms with fewer interferences and more stable baselines were obtained than when separation was carried out using MEKC. Another aspect related to the application to real samples was the lack of precision encountered upon evaluating the electrophoretic signals generated when using SPE coupled with NA-CZE. Here, we demonstrate the importance of choosing an appropriate internal standard for analyte quantification. It is recommended that a triazine belonging to the same family as that of the triazine to be determined should be used as internal standard.     

Flow injection determination of aluminium by spectrofluorimetric detection after complexation with N-o-vanillidine-2-amino-p-cresol: the application to natural waters

An on-line flow injection spectrofluorimetric method for the direct determination of aluminium in water samples is described. The method is based on the reaction of aluminium with N-o-vanillidine-2-amino-p-cresol (OVAC) in acidic medium at pH 4.0 to form a water-soluble complex. The excitation and emission wavelengths were 423.0 and 553.0 nm, respectively, at which the OVAC-Al complex gave the maximum fluorescence intensity at pH 4.0 in a 50% methanol-50% water medium at 50 °C. An interference from fluoride ions was minimised by the addition of Be²⁺. Other ions were found not to interfere at the concentrations likely to be found in natural waters. The proposed methods were validated in terms of linearity, repeatability, detection limit, accuracy and selectivity. Under these conditions, the calibration was linear up to 1000 μg L⁻¹ (r = 0.999). The limit of detection (3σ) for the determination of Al(III) was 0.057 μg L⁻¹ and the precision for multiple determinations of 3 ng mL⁻¹ Al(III) prepared in ultra-pure water was found to be 0.62% (n = 10).The Schiff base ligand could be used to determine ultra-trace aluminium from natural waters. Analysis of environmental certified reference materials showed good agreement with the certified values. The procedure was found to be equally applicable to both freshwater and saline solutions, including seawater.