Esma Tütem

Heavy metal cation retention by unconventional sorbents (red muds and fly ashes)

Toxic heavy metals, i.e. copper (II), lead (II) and cadmium (II), can be removed from water by metallurgical solid wastes, i.e. bauxite waste red muds and coal fly ashes acting as sorbents. These heavy-metal-loaded solid wastes may then be solidified by adding cement to a durable concrete mass assuring their safe disposal. Thus, toxic metals in water have been removed by sorption on to inexpensive solid waste materials as a preliminary operation of ultimate fixation. Metal uptake (sorption) and release (desorption) have been investigated by thermostatic batch experiments. The distribution ratios of metals between the solid sorbent and aqueous solution have been found as a function of sorbent type, equilibrium aqueous concentration of metal and temperature. The breakthrough volumes of the heavy metal solutions have been measured by dynamic column experiments so as to determine the saturation capacities of the sorbents. The sorption data have been analysed and fitted to linearized adsorption isotherms. These observations are believed to constitute a database for the treatment of one industrial plants effluent with the solid waste of another, and also to utilize unconventional sorbents, i.e. metallurgical solid wastes, as cost-effective substitutes in place of the classical hydrous-oxide-type sorbents such as alumina, silica and ferric oxides.

Adsorptive removal of chlorophenols from water by bituminous shale

Abstract Chlorophenols are among priority water pollutants which are taken up by aquatic fauna and flora and enriched in the food chains. Acid-activated bituminous shale has been used as an adsorbent for the removal of 2-chlorophenol (MCP) and 2,4-dichlorophenol (DCP) from water and the related process parameters were investigated. Kinetic analysis showed that the adsorption reaction could be approximated by a first-order rate equation for which pore-diffusion was the essential rate-controlling step. Adsorption was endothermic and basically of a physical character. Equilibrium modelling by linearized adsorption isotherms revealed that a Langmuir equation could well represent the observed data. The entropy change of adsorption was more positive for DCP due to its higher polarity. The saturation capacity of the sorbent for both chlorophenols were determined by dynamic column tests, this experimental capacity being lower than the theoretical monolayer capacity envisaged by the Langmuir equation. Adsorption was completely reversible as the retained DCP could be completely desorbed from the column with distilled water as eluant. The results were evaluated within the scope of utilization of cost-effective unconventional sorbents to remove chlorinated organics as possible substitutes for activated carbon.

Spectrophotometric determination of ascorbic acid using copper(II)–neocuproine reagent in beverages and pharmaceuticals

The proposed method for ascorbic acid (Vitamin C) (AA) determination is based on the oxidation of AA to dehydroascorbic acid with a Cu(II)-2,9-dimethyl-1,10-phenanthroline (neocuproine (Nc)) reagent in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. This chelate was formed immediately and the apparent molar absorptivity for AA was found to be 1.60 x 10(4)dm(3)mol(-1)cm(-1). Beers law was obeyed between 8.0 x 10(-6) and 8.0 x 10(-5)M concentration range. The relative standard deviation for 90mug AA was 3%. The Cu(II)-Nc reagent is a milder and therefore more selective oxidant than the conventional Fe(III)-1,10-phenanthroline (phen) reagent used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to a number of commercial fruit juices, pharmaceutical preparations containing Vitamin C, and red wine. The meta-bisulfite content of wine was removed with an anion exchanger at pH 3 prior to analysis, and a difference extractive-spectrophotometric method of AA assay in wine was developed so as to suppress the interferences caused by wine anthocyanins and polyphenols. The findings of the developed method for fruit juices and pharmaceuticals were also statistically compared with those of HPLC so as to establish it as a reliable novel method.

Spectrophotometric determination of trace amounts of copper(I) and reducing agents with neocuproine in the presence of copper(II)

The existing spectrophotometric method for the determination of total Cu with neocuproine (Nc) does not allow the differentiation of CuI and CuII. It is shown here that the use of a dilute (3.0 × 10–3 mol dm–3) Nc solution in weakly acidic or neutral media makes the determination of CuI feasible at the 1 × 10–5 mol dm–3 level in the presence of up to 0.1 mol dm–3 CuII. For the determination of trace amounts of CuI in the presence of 1 mol dm–3 CuII, the latter can be masked by NH3—NH4Cl buffer at pH 10, giving almost the same molar absorptivity for CuI, i.e., 7.5 × 103 dm3 mol–1 cm–1. The ability to measure the absorption due to CuI in the presence of an excess of CuII was exploited as the basis of an indirect method for the determination of trace amounts of reductants. Superior to the existing individual methods of determination, which are usually specific for a given reducing agent, the proposed system consists of treating the reductant with the CuII–Nc reagent in ammonium acetate buffered media, followed by measurement of the absorbance of the CuI–Nc chelate at 450 nm. The quantification of a given reductant in the concentration range 1 × 10–6–1 × 10–4 mol dm–3 usually takes 3 min with a mean relative standard deviation of 3%. The molar absorptivity of an n-electron reductant which has reacted stoichiometrically is approximately 7.5n× 103 dm3 mol–1 cm–1, i.e., n times that of CuI–Nc. Hence, hydrogen peroxide, ascorbic acid, cysteine, hydroxylamine, hydrazine, thiosulphate, dithionite, mitoxantrone, glutathione, iron(II) and thiourea were determined with theoretical molar absorptivities; carminic acid, sulphite, tin(II) chloride, 2,4-dinitrophenylhydrazine, sodium tetrahydroborate(III) and 2,3-dimercaptopropan-1-ol were determined with the aid of empirical linear absorbance–concentration plots. The proposed spectrophotometric method is rapid and allows the quantification of biologically important reducing agents.

Combined HPLC-CUPRAC (cupric ion reducing antioxidant capacity) assay of parsley, celery leaves, and nettle

This study aims to identify the essential antioxidant compounds present in parsley (Petroselinum sativum) and celery (Apium graveolens) leaves belonging to the Umbelliferae (Apiaceae) family, and in stinging nettle (Urtica dioica) belonging to Urticaceae family, to measure the total antioxidant capacity (TAC) of these compounds with CUPRAC (cupric ion reducing antioxidant capacity) and ABTS spectrophotometric methods, and to correlate the TAC with high performance liquid chromatography (HPLC) findings. The CUPRAC spectrophotometric method of TAC assay using copper(II)-neocuproine (2,9-dimethyl-1,10-phenanthroline) as the chromogenic oxidant was developed in our laboratories. The individual antioxidant constituents of plant extracts were identified and quantified by HPLC on a C18 column using a modified mobile phase of gradient elution comprised of MeOH-0.2% o-phosphoric acid and UV detection for polyphenols at 280 nm. The TAC values of HPLC-quantified antioxidant constituents were found, and compared for the first time with those found by CUPRAC. The TAC of HPLC-quantified compounds accounted for a relatively high percentage of the observed CUPRAC capacities of plant extracts, namely 81% of nettle, 60-77% of parsley (in different hydrolyzates of extract and solid sample), and 41-57% of celery leaves (in different hydrolyzates). The CUPRAC total capacities of the 70% MeOH extracts of studied plants (in the units of mmol trolox g(-1)plant) were in the order: celery leaves>nettle>parsley. The TAC calculated with the aid of HPLC-spectrophotometry did not compensate for 100% of the CUPRAC total capacities, because all flavonoid glycosides subjected to hydrolysis were either not detectable with HPLC, or not converted to the corresponding aglycons (i.e., easily detectable and quantifiable with HPLC) during the hydrolysis step.

Simultaneous derivative spectrophotometric determination of cobalt(II) and nickel(II) by dithizone without extraction

Dithizone (Dz), a common extractive-photometric ligand for Co(II) and Ni(II), has been dissolved in the water-miscible solvent tetrahydrofurane (THF) so as to constitute a reagent for both metals in aqueous phase without extraction. Complex formation was complete for both metals at pH 12.0 (adjusted by aqueous NH(3)) within 30 min, and the complexes were stable for at least 2 h. First-derivative spectra of the metal dithizonates (singly or as binary mixtures) were preferred to ordinary spectra, because working wavelength determination was more precise and spectral overlap was less. Two wavelengths at which the spectral overlap was minimum were selected as analytical wavelengths, i.e. 620 nm for Co and 740 nm for Ni, and the calibration curves drawn with zero-to-peak values as a function of concentration were linear for these wavelengths. Thus, the total (1)D values at 620 and 740 nm of the mixtures were used to determine Co and Ni concentrations. The relative standard deviation (R.S.D.) for the analysis of Co (3.0 mg l(-1)) individually was 3.5%, and for its admixture with Ni (3.5 mg l(-1)) was 2.5%. The R.S.D. for the analysis of Ni (5.9 mg l(-1)) individually and for its admixture with Co (1.8 mg l(-1)) were 5.5 and 5.8%, respectively. The linear range in (1)D evaluation was between 5.0x10(-6) and 1.0x10(-4) M for Co and 2.0x10(-5)-2.0x10(-4) M for Ni. Interference analysis was performed for individual metal (Co or Ni) determinations. Finally, the method has been applied to a Ni-Cr-based dental alloy (Wiron 99) successfully.

Sorptive Removal of Cesium-137 and Strontium-90 from Water by Unconventional Sorbents: II. Usage of Coal Fly Ash

It has been shown that coal fly ash is a good adsorbent for both radionuclides of 137 Cs and 90 Sr. Radiocesium adsorption is maximal around the neutral region whereas radiostrontium adsorption increases with pH, especially above pH 8. Cesium retention sharply drops with ionic strength while strontium adsorption increases sharply and steadily at low and moderate concentrations of the inert electrolyte, respectively. The suggested mechanisms of radionuclide retention by fly ash is specific adsorption of Cs + and irreversible ion-exchange uptake of Sr 2+ . The isotherm of adsorption is a Langmuir approximation of the B.E.T. multi-layered sorption. Acid pretreatment of fly ash, though not increasing radionuclide sorption capacity, may be useful in preventing the leach-out of other contaminants from the sorbent into water during the adsorption process.

Simultaneous spectrophotometric determination of cystine and cysteine in amino acid mixtures using copper(II)—neocuproin reagent

Biologically important sulphydryl compounds, e.g., e.g. were determined by treating the reductant thiol with copper(II)—neocuproin (Nc) reagent in ammonium acetate-buffered medium, followed by measuring the absorbance of the copper (1)—Nc complex at 450 nm. Cystine, if present in a mixture with cystein, was reduced to the latter with zinc—hydrochloric acid prior to the colour reaction. Many common amino acids (not containing the SH group) and reducing sugars did not interfere, and colour development took 2 min. Ascorbic acid, glutathione and penicillamine gave similar colour reactions to cysteine. For cysteine, the molar absorptivity was 7.5 × 103 1 mol−1 cm−1 with a relative standard deviation of 3%, rendering the method suitable for routine work with good precision. The method was successfully applied to the assay of cystine in soybean protein hydrolysate, and the results were compared to those obtained by liquid chromatography

Spectrophotometric determination of vitamin E (α-tocopherol) using copper(II)-neocuproine reagent

Abstract The possibility of the utilization of the copper(II)-neocuproine spectrophotometric method, which has previously been shown to permit the determination of various reducing agents, to the determination of vitamin E was investigated. The molar absorptivity for vitamin E was found to be (2.1 ± 0.1) × 104l mol−1cm−1 and Beers law was obeyed between 2.4 × 10−6 and 9.0 × 10−5M concentrations of α-tocopherol. The relative standard deviation of the slope of the absorbance vs. concentration plot was 2.1%. The results obtained by the copper(II)-neocuproine method were compared with those achieved by both the standard HPLC and the widely used iron(III)-bathophenanthroline method by means of a t-test which showed that the precision of the developed method was not essentially different from those of the others. The developed method was successfully applied to three commercial samples, two in dragee and one in ampoule form. The α-tocopheryl acetate contained in the samples, which did not respond directly to the Cu(II)-neocuproine reagent, was subjected to alkaline hydrolysis prior to the analysis of the hydrolysis product, i.e., α-tocopherol. The molar absorptivity due to Cu(I)-neocuproine at 450 nm against a reagent blank indicated a two-electron oxidation of vitamin E by Cu(II)-neocuproine, which may be slightly enhanced by solvent effects. Copper(II)-neocuproine is an oxidant of strength comparable to that of Fe(III)-bathophenanthroline. The developed method, although less sensitive, is easy to use in conventional laboratories, unlike the Fe(III)-bathophenanthroline method, which requires specially prepared reagents and solvents. The method is free from interferences from such common reductants as ascorbic acid and Fe(II) salts, found in pharmaceutical formulations, after washing the formulation with water and collecting vitamin E in the ether extract for subsequent analysis.

Sorptive Removal of Cesium-137 and Strontium-90 from Water by Unconventional Sorbents. I. Usage of Bauxite Wastes (Red Muds)

Bauxite wastes of alumina manufacture, i.e., red muds, have been tested for radiocesium and strontium removal from water. The red muds were water-washed, acid-, and heat-treated before usage to produce hydrous oxide like sorbents. Surface treatment of the sorbent was benefical for 137s uptake, while heat-treatment was detrimental to the -SOH surface sites responsible for high 90Sr affinity. Fractionation of the sorbent with respect to apparent grain size did not produce significant differences in the sorption efficiency. The distribution coefficients vs. equilibrium activity in solution showed a maximum with Cs, and a gradual decrease trend with Sr. The solution activity vs. adsorption data were fitted to B.E. T. (essentially types IV-V) isotherms for Cs and B.E. T.-Langmuir isotherms for Sr. Desorption, temperature-, pH-, and ionic strength-dependence tests revealed that the primary mode of sorption for both cations is specific adsorption while the secondary mode is ion exchange. A rise in pH favours the...