Peter Burba

Membrane filtration studies of aquatic humic substances and their metal species: a concise overview: Part 1. Analytical fractionation by means of sequential-stage ultrafiltration

A concise overview (75 references) of the analytical fractionation of aquatic humic substances using sequential-stage ultrafiltration is presented. First, humic substances in aquatic environments and actual problems connected with their fractionation and analysis are briefly considered. The molecular size classification of dissolved humic substances by means of multistage ultrafiltration, with special emphasis on on-line techniques, is the focal point of the discussion. In particular, the capabilities of ultrafiltration for the size fractionation and characterization of species formed between colloidal humic substances and pollutants (e.g. metals) are stressed.

Membrane filtration studies of aquatic humic substances and their metal species: a concise overview. Part 2. Evaluation of conditional stability constants by using ultrafiltration

The assessment of conditional stability constants of aquatic humic substance (HS) metal complexes is overviewed with special emphasis on the application of ultrafiltration methods. Fundamentals and limitations of stability functions in the case of macromolecular and polydisperse metal-HS species in aquatic environments are critically discussed. The review summarizes the advantages and application of ultrafiltration for metal-HS complexation studies, discusses the comparibility and reliability of stability constants. The potential of ultrafiltration procedures for characterizing the lability of metal-HS species is also stressed.

Labile complexes of trace metals in aquatic humic substances: Investigations by means of an ion exchange-based flow procedure

The lability/inertness of heavy metals bound in aquatic humic substances (HS) has been characterized by means of ligand exchange with cellulose-immobilized triethylenetetramine-pentaacetic acid (TETPA) applying a flow system. On the basis of high metal distribution coefficients, Kd of 103 to 104 (ml/g) on cellulose TETPA even in slightly acidic HS solutions, labile and inert metal fractions in HS are characterized by their different kinetics and degree of phase exchange in small TETPA columns. For traces of metals bound to dissolved HS, the lability order Cd ≈ Mn(II)>Zn>Pb>Co>Ni>Cu is revealed. Systematic variation of environmentally relevant parameters shows the strong influence of the pH value and the ratio of metal loading/complexing capacity on the metal lability in HS. Surprisingly, in the case of freshly formed HS/Ni and HS/Cu complexes, slow transformation processes occur which lower their initial lability by one order of magnitude and supposedly increase their thermodynamic stability.

Labile/inert metal species in aquatic humic substances: an ion-exchange study

SummaryAn ion-exchange procedure has been developed for the analytical fractionation of metals (e.g. Al, Co, Cu, Fe, Mn, Ni, Pb, Zn) forming labile/inert complexes with aquatic humic substances (HS) isolated (XAD 2, XAD 8, ultrafiltration) from bog, forest, ground and lake water. Using 1-(2-hydroxyphenylazo)-2-naphthol groups immobilized on cellulose (Cellulose HYPHAN™) as chelating collector (batch and column procedure, resp.) for reactive metal fractions in dissolved HS, the kinetics and the degree of separation (referred to the total metal content) serve for the operational characterization of the metal lability. According to the separation kinetics (96 h), mostly the reactivity order Mn>Zn>Co>Pb>Ni>Cu≫Al>Fe is observed for the above metals in HS, resulting in recoveries of >98% for Mn and Zn, but strongly varying for the other metals (e.g., 44–95% Cu, 18–84% Fe). By means of cellulose HYPHAN four metal fractions (e.g. Cu) can be distinguished kinetically: (a) about 50% of Cu freshly complexed with HS are directly exchanged (2nd order kinetics, k=0.275 1 · mol−1 · s−1) followed by (b) a less labile fraction (20–30%) of 1st to 2nd order exchange; (c) a hardly reactive fraction (5–10%) revealing uniform half times t1/2 of 25 h closes the Cu exchange from HS. Moreover the Cu fraction (d), being exchange-inert in HS, amounts to 5–10% and increases by slow transformation processes of the formed HS/Cu species.

Ultrafiltration and determination of Zn– and Cu–humic substances complexes stability constants

This study exhibits that size fractionation of humic substances (HS) and their metal complexes by ultrafiltration is an efficient procedure for simultaneous determination of stability constants. Using sequential-stage ultrafiltration and a radiotracer technique the HS-Cu and HS-Zn complexes studied can gently be size-fractionated and their free metal fractions simply be discriminated. The conditional stability constants Ki obtained for size fractions of these HS metal complexes exhibit a clear molecular size dependence. Accordingly, the highest Ki values (6.6 for Zn and 6.4 for Cu) are found in the HS fractions of >105 kDa. Moreover, the overall stability constants K found for Cu (log K=5.5) and Zn complexes (log K=4.5) of the aquatic HS complexes studied are quite comparable to those reported in the literature.

Abtrennung von Spurenelementen aus Wasser mit Hilfe von Celluloseaustauscher-Filtern und ihre Bestimmung durch Röntgenfluorescenzanalyse mit Radionuklidanregung

For the separation of trace elements from water cellulose containing chromotropic acid as functional group is used in form of thin filters (capacity 0.0075 mEq.). The time necessary for the filtration of 100 ml is about 10 min. The behaviour of the elements Fe, Cu, Zn, Sr and Hg is studied in detail. Fe, Cu, Zn and Sr are fixed on the filter in the range from pH 4–6.5 with a yield >90%, provided the content of the elements does not exceed the capacity of the filter. Larger amounts of calcium ions or sodium ions interfere considerably with the separation of the elements mentioned above. The filters are used directly for analysis by X-ray fluorescence. Calibration curves for the elements with atomic number 25–38 are presented. For comparison Chelex filters are investigated, too. The advantages and disadvantages in the use of the cellulose filters are discussed.ZusammenfassungFür die Abtrennung von Spurenelementen aus Wasser wird ein Celluloseaustauscher mit Chromotropsäure als funktioneller Gruppe in Form von dünnen Filtern verwendet (Kapazität etwa 0,0075 mÄq.). Die Filtrationszeit für 100 ml Wasser beträgt etwa 10 min. Das Verhalten der Elemente Fe, Cu, Zn, Sr und Hg wird näher untersucht. Fe, Cu, Zn und Sr werden im pH-Bereich von etwa 4–6,5 mit einer Filtrationsausbeute >90 % festgehalten, sofern der Gehalt die Kapazität des Filters nicht übersteigt. Größere Gehalte an Calcium-Ionen oder Natrium-Ionen stören die Abtrennung erheblich. Die Filter werden direkt für die Röntgenfluorescenzanalyse verwendet. Eichkurven für die Elemente mit den Ordnungszahlen 25–38 werden angegeben. Zum Vergleich werden Chelex-Filter herangezogen. Die Vor- und Nachteile der Verwendung von Celluloseaustauscher-Filtern werden diskutiert.

Analytische Multielement-Anreicherung an metallhydroxidbeladener Cellulose

SummaryThe analytical preconcentration of trace metals on metal hydroxide-coated cellulose is characterized. Metal hydroxides [e.g., Fe(OH)3, In(OH)3], in small amounts fixed on another adsorbent (e.g., cellulose), strongly bind many trace metals [e.g., Al, As, Be, Bi, Cd, Co, Cr(III), Cu, lanthanoids, Mn, Mo, Ni, Pb, Sn, Ti, V, Zn] in the ng/l to μg/l range. The sorption of trace metals on the synergistically acting collector [e.g., cellulose/1% Fe(III), cellulose/2% In(III)] proceeds with half times of some minutes. Furthermore, the element distribution coefficientsKd between adsorbent and strong saline solutions are of the order 104 to 105. Dissolved complexing matters (e.g., citrate, humic acid, phosphate) with the exception of chelating agents (e.g., NTA) do not interfere. The main advantages compared with the conventional ‘co-precipitation’ of trace metals with metal hydroxides, are a simplified procedure (batch method) and lowered metal amounts [e.g., some 100 μg Fe(III), In(III)]. After elution (2 M HCl) the preconcentrated trace metals are determined by flame-AAS (injection technique) and ICP-AES. With the analytical procedure developed for water analysis, detection limits (3σ) of 0.1 μg/l and relative standard deviations of 0.03 to 0.05 can be achieved for many elements in surface-, mineral- and sea-water.ZusammenfassungEs wird die analytische Multielement-Anreicherung an metallhydroxydbeladener Cellulose beschrieben. Metallhydroxide [z.B. Fe(OH)3, In(OH)3] in geringen Mengen auf einem anderen Spurenfänger (z. B. Cellulose) fixiert, zeigen ein hohes Sorptionsvermögen für Elementspuren [z. B. Al, As, Be, Bi, Cd, Co, Cr(III), Cu, Lanthanoide, Mn, Mo, Ni, Pb, Sn, Ti, V, Zn] im ng/l- bis μg/ l-Bereich. Die Spuren-VerteilungskoeffizientenKd an dem synergistisch wirkenden Mischkollektor [Cellulose/1% Fe(III) bzw. Cellulose/2% In(III)] erreichen auch in konzentrierten Salzlösungen Werte von 104 bis 105. Komplexierende Wasserinhaltsstoffe (z.B. Citrat, Huminsäure, Phosphat) stören die Spurenanreicherung kaum, abgesehen von starken Chelatbildnern (z.B. NTA). Hauptvorteile gegenüber der herkömmlichen „Mitfällung“ an Metallhydroxiden sind eine vereinfachte Handhabung (Schüttelverfahren) sowie erheblich verringerte Kollektormengen [z. B. einige hundert Mikrogramm Fe(III), In(III)]. Nach Elution mit 2 M HCl werden die angereicherten Elementspuren durch Flammen-AAS (Injektionsverfahren) bzw. ICP-AES bestimmt. Die Nachweisgrenzen (3σ) der wasseranalytischen Verbundverfahren liegen vielfach bei 0,1 μg/l, die relativen Standardabweichungensr bei 0,03 bis 0,05.

Extraction and exchange behavior of metal species in therapeutically applied peat

The binding and availability of metals (Al, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Zn) in therapeutically applied peat (Grosses Gifhorner Moor, Sassenburg/North Germany) was characterized by means of a versatile extraction approach. Aqueous extracts of peat were obtained by a standardized batch equilibrium procedure using high-purity water (pH 4.5 and 5.0), 0.01 mol l(-1) calcium chloride solution, 0.01 mol l(-1) ethylenediaminetetraacetic acid (EDTA) and 0.01 mol l(-1) diethylenetriamine pentaacetic acid (DTPA) solution as metal extractants. In addition, the availability of peat-bound metal species was kinetically studied by collecting aliquots of extracts after different periods of extraction time (5, 10, 15, 30, 60 and 120 min). Metal determinations were performed by atomic spectrometry methods (AAS, ICP-OES) and dissolved organic matter (DOM) was characterized by UV/Vis measurements at 254 and 436 nm, respectively. Of the extractants studied Ca, Mg and Mn were the most available metals, in contrast to peat-bound Fe and Al. The relative standard deviation s(r) of the developed extraction procedures was mostly in the range of 4 to 20%, depending on the metal and its concentration in peat. A pH increase favored the extraction of metals and DOM from peat revealing complex extraction kinetics. Moreover, a competitive exchange between peat-bound metal species and added Cu(II) ions showed that >100 mg of Cu(II) per 50 g wet peat was necessary to exchange the maximum of bound metals (e.g. 21.8% of Al, 3.9% of Fe, 79.0% of Mn, 81.9% of Sr, related to their total content).

Preconcentration and determination of trace elements in fresh water and sea water

Der Spurenelementgehalt in standardisiertem Wasser, in Rheinwasser und Meerwasser wird durch Neutronenaktivierungsanalyse (NAA), Rontgenfluorescenzanalyse (RFA) und Atomabsorption (AAS, mit Ausnahme von Meerwasser) bestimmt. Die Voranreicherung erfolgt fur NAA durch Gefriertrocknung und Schutteln mit einem Celluloseaustauscher (CA), fur RFA durch Abtrennung in CA-Saulen, Filtration durch CA-Filter oder Schutteln mit CA. Die Ergebnisse werden verglichen und diskutiert.ZusammenfassungDer Spurenelementgehalt in standardisiertem Wasser, in Rheinwasser und Meerwasser wird durch Neutronenaktivierungsanalyse (NAA), Röntgenfluorescenzanalyse (RFA) und Atomabsorption (AAS, mit Ausnahme von Meerwasser) bestimmt. Die Voranreicherung erfolgt für NAA durch Gefriertrocknung und Schütteln mit einem Celluloseaustauscher (CA), für RFA durch Abtrennung in CA-Säulen, Filtration durch CA-Filter oder Schütteln mit CA. Die Ergebnisse werden verglichen und diskutiert.SummaryTrace elements in standardized water, in Rhine water and sea water were determined by neutron activation (NAA), X-ray fluorescence (XFA) and atomic absorption (AAS, except for sea water). Preconcentration was effected for NAA by freeze-drying and shaking with a cellulose exchanger (CA), for XFA by separation in columns filled with CA, filtration through CA-filters or shaking with CA. The results obtained are compared and discussed.

Substâncias Húmicas: Sistema de Fracionamento Sequencial por Ultrafiltração com Base no Tamanho Molecular

A sequential system for fractionation by ultrafiltration (SSFU) equipped with advanced membranes filters (molecular size cut-off: 5, 10, 30, 50 and 100 kDalton) of the polyethersulfone type was developed for analytical fractionation of humic substances (HS) extracted from aquatic systems or soils. The device consists of five membrane filters (Sartocon® Micro) operated by a multi-channel peristaltic pump, enabling an easy handling, working in a closed system and with simple collection of the six obtained fractions (F1>100; F2: 100-50; F3: 50-30; F4:30-10; F5: 10-5 and F6 <5 kDalton). Then, the HS sample (250 mL solution 1.0 mg/mL, pH 5.0 to 6.0) to be fractionated is pumped by pump through the series of membrane filters with a tangential flow of 85 mL/min, initial pressure 0.2 to 0.3 bar and permeation flux through the membranes of 0.8 to 1.4 mL/min. The overall time for fractionation and cleaning of the device is about 10 h and 25 mL of each fraction is obtained.