Indirect complexometric determination of palladium usingl-histidine as masking agent

An indirect complexo-titrimetric method is described for the determination of palladium in the presence of other metal ions, L-histidine being used as the masking agent. Palladium(II) and other metal ions are initially complexed with an excess of EDTA and the surplus EDTA titrated with standard zinc sulfate solution at pH 4.5–5.5 using xylenol orange as indicator. An excess of 1 % L-histidine solution is then added, and the released EDTA is titrated with standard zinc sulfate solution. Accurate and reproducible results were obtained for 2–15 mg of Pd with relative errors 0.4% and standard deviations < 0.02mg. Sn(IV) and Au(III) interfere, but can be easily masked. The method is successfully applied for the determination of palladium(II) in alloy compositions.     

Critical study of fluorimetric determination of selenium in urine

Different steps for the fluorimetric determination of Se in urine have been investigated. A HNO₃---HClO₄ (4:1) mixture is useful for urine digestion, and reduction of Se(VI) to Se(IV) is effectively carried out with HCl (6M). Selenium(VI) present after the digestion process constitutes 14.5–36.6% of total Se. An optimum pH of 1.80±0.05 and the addition of 1 ml of 2,3-diaminonaphthalene (DAN) (0.1%, w/v) are established in the formation of Se—DAN complex. Heating to 60°C, a time of incubation of 15 min is recommended to assure the complete formation of Se—DAN complex. A volume of 5 ml of cyclohexane and vigorous shaking for 45 sec is necessary for the extraction process. With this optimized method, the detection limit of selenium was 0.82 μg/l., within-day precision for a 50.0 μg/l. standard solution and urine (27.3 μg/l.) were 2.4 and 2.7% and between-day for the urine was 3.9% (33.9 μg/l.). Analytical recovery of 0.5 ml of Se standard (250 μg/l.) added to 1 ml of urine was 99.9±2.9% (95.8–104.4, n = 12). Normal levels of selenium excretion in urine obtained from healthy people were 27.9±8.7 μg/day (13.2–44.1), not observing significant differences (P < 0.05) between sexes.     

Indirect complexometric determination of palladium(II) using sodium nitrite as a selective masking reagent

A selective complexometric method is described for the determination of palladium, sodium nitrite being used as masking reagent. Palladium(II) in a given sample solution is initially cornplexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 4.5–5.5 (acetic acid-sodium acetate buffer), using xylenol orange as indicator. An excess of sodium nitrite is then added, the mixture is shaken well and the EDTA released from the Pd-EDTA complex is titrated with a standard zinc sulfate solution. Results are obtained for 2.5–27.5 mg of Pd with relative errors 0.5% and standard deviations 0.05 mg. The interferences of various ions are studied. The method is applied for the determination of palladium(II) in alloys and complexes.     

Methods for separation of trace amounts of platinum and investigation of the influence of interfering elements during platinum determination in copper ores and copper concentrates by graphite furnace atomic absorption spectrometry

A THGA graphite furnace with Zeeman background correction has been used to determine platinum content in copper ore and copper concentrate at the part per billion (ppb) concentration level. Two different procedures for the separation of trace platinum have been applied: (i) use of an ion exchange resin; and (ii) a two-stage method based on platinum separation on inorganic carriers. The influence of interfering elements in the matrix (Cu, Pb, Fe, Ti, V, Au, Pd, Ir, Rh and Al) has been examined using a graphite furnace. It was found that the presence of Cu (12.5–100 mg l⁻¹), Pb (100–500 mg l⁻¹), Fe (100–2000 mg l⁻¹), Ti (25–100 mg l⁻¹), V (25–100 mg l⁻¹), Au (25–300 mg l⁻¹), Pd (20–250 mg l⁻¹), Ir (0.5–3.5 mg l⁻¹) and Rh (0.025–1 mg l⁻¹) in the samples analyzed has no effect on the platinum absorption signal when using a recommended temperature program (T_pyr=1300°C, T_at=2450°C). Spectral interference was observed, which was due to aluminum, as a result of the close neighborhood of the Pt 265.945-nm and Al 266.039-nm lines. This interference could not be eliminated by the Zeeman background correction.     

Diphenic acid as a selective reagent for the amperometric determination of thorium(IV)

Th(IV) has been titrated amperometrically at an applied e.m.f of −1.0 V (dropping mercury electrode vs. SCE) with diphenic acid (neutralized with sodium hydroxide). Th(IV) in the range 8.0–60.0 mg/100ml can be determined with an error of ±0.5%. A number of foreign ions including Ce(IV), Zr(IV), La(III), U(IV), U(VI) do not interfere even if present in excess but traces of Ti(IV) do. The method is rapid and selective and has been used for the determination of Th(IV) in monazite sand.     

Selective complexometric determination of mercury using sodium nitrite as masking agent

A complexo-titrimetric method for the determination of mercury(II) in the presence of other metal ions is described based on the selective masking ability of sodium nitrite. Mercury and other ions are initially complexed with an excess of EDTA and the surplus EDTA is titrated with Pb(NO₃)₂ solution at pH 5.0–6.0 using xylenol orange as indicator. An excess of solid NaNO₂ is then added to decompose the Hg(II)-EDTA complex and the released EDTA is titrated with standard Pb(NO₃)₂ solution. Accurate results were obtained for 10–65 mg of mercury with relative errors <0.3% and standard deviations < 0.03 mg. Sn(IV) and Pd(II) interfere but can be easily masked. The method is applied for the determination of Hg(II) in its alloy compositions and complexes.     

Indirect complexometric determination of cadmium(II) using 1,10-phenanthroline as selective masking agent

An indirect complexometric method is described for the determination of cadmium(II), 1,10-phenanthroline being used as masking agent. Cadmium(II) in a given sample solution is initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 1,10-phenanthroline is then added and the EDTA released from the Cd-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 1.5–57 mg of Cd with relative errors 0.90% and standard deviations 0.06 mg. Cu(II), Co(II), Hg(II), Ni(II), Zn(II), Pd(II), Tl(III), Au(III) and Sn(IV) interfere, but can be easily masked. The method is applied for the determination of cadmium in synthetic alloy solutions.     

Photometric determination of micro amounts of thiosulphate by means of its cyanolysis with lanthanum(III) as catalyst

Lanthanum(III) has been found to catalyse the reaction of thiosulphate with cyanide. The effects of pH, reaction time and temperature, amount of cyanide and lanthanum, and order of addition of reagents have been investigated. Temperature has little effect in the range 10–30°, but at both 35° and 40° the rate is noticeably faster. Reaction is complete at room temperature in 1.5 hr at pH 9.3–9.6, and in 3 hr at pH 9.1–9.6. The method can be applied to the determination of 1.0 × 10⁻⁵−6.0 × 10⁻⁴M thiosulphate, with a relative standard deviation of 0.3% for 4 × 10⁻⁴M thiosulphate.     

Spectrophotometric determination of tin in copper-based alloys using pyrocatechol violet

In the present paper, a new procedure using Pyrocatechol Violet (PCV) for the determination of tin in copper-based alloys is proposed. The use of HEDTA as masking agent allowed tin to be determined in the presence of large amounts of copper, without any separation procedure. The method is more selective than previous methods. Cetyltrimethylammonium bromide (CTAB) and Tween-20 are used to increase the stability of the system.

The method can be applied directly to an acidic solution of Sn(IV) in the range 2.0–60.0 μg with a final volume of 50 ml. The pH is adjusted to 2.0 ± 0.2 with glycine buffer and, after 30 min, the absorbance is measured at 660 nm. Al(III), Cd(II), Co(II), Mg(II), Ca(II), Mn(II), Ni(II) and Pb(II) do not interfere at the 500 mg level; 20 000 μg of Cu(II) and 400 μg of NaCl can be present. The interference at 100 μg of Fe(III) can be masked with ascorbic acid. Bi(III), Sb(V), Ti(IV), Mo(VI), EDTA, tartrate, citrate and iodide interfere. The proposed method was used for tin determination in several copper-based alloys and a comparison of the analytical results with certified values indicates that the procedure provides accurate and precise results.     

Detection and spectrophotometric determination of EDTA with cobalt(II) and phosphomolybdic acid in urine and detergents

A simple, rapid, sensitive and selective method for the microgram detection and spectrophotometric determination of EDTA in water, human urine and detergents, based on its reaction with Co(II) and phosphomolybdic acid at pH 0.5–2.0 is reported. Absorbance is measured against Co(II)–phosphomolybdic acid reference solution at 750 nm. The effect of time, temperature, pH and Co(II) or phosphomolybdic acid concentration is studied, and optimum operating conditions are established. Beer's law is applicable in the concentration range 0.3–1.9 μg ml⁻¹ of 10⁻⁵M EDTA. Its detection limit is 0.14 μg in the solution phase and 0.03 μg in the resin phase. The relative standard deviation is ±0.13 μg. Ag(I), Zn(II), Cu(II), Ni(II), Pb(II), Cd(II), Ca(II), Mg(II), Fe(III), Cr(III), U(VI), chloride, nitrite, phosphate, oxalate, borate and amino acids do not interfere.     

Polarographic chemometric determination of zinc and nickel in aqueous samples

Polarographic chemometric methods were applied to the determination of zinc and nickel in aqueous solutions previously acidified with 0.1 M acetate buffer (pH 4.2). The studied methods are multivariate methods including classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS); derivative ratio methods (first, ¹D and second, ²D derivative ratio). A comparative study was considered. The studied chemometric methods do not need the presence of any reduction potential shift reagent in spite of the great overlap between the two metals polarograms. A training set consisting of 10 binary mixture solutions in the possible combinations containing 0.13–9.30 μg/ml Zn(II) and 0.20–12.25 μg/ml Ni(II) was used to develop the chemometric calibrations (CLS, PCR and PLS). A validation set containing the synthetic mixtures in the range of 0.29–9.00 μg/ml for Zn(II) and 0.30–11.60 μg/ml for Ni(II) was used to validate the multivariate calibrations. Same mixtures were used to develop the derivative ratio methods. The polarograms were recorded and their current values were measured within the potential range −920 to −1052 mV at 2 mV intervals. The mean percentage recoveries obtained using CLS, PCR and PLS were found to be 99.5 ± 1.5%, 100.0 ± 1.1% and 100.0 ± 1.0% for Zn(II) and 99.4 ± 1.3%, 99.7 ± 1.2% and 99.9 ± 1.0% for Ni(II), respectively. The mean percentage recoveries obtained using ¹D at −950 mV, ¹D at −1010 mV, ¹D at −950 mV–¹D at −1010 mV and ²D at −986 mV for Zn(II) were found to be 99.7 ± 1.2%, 99.2 ± 1.6%, 99.4 ± 1.4% and 99.4 ± 1.4%; and using ¹D at −1030 mV and ²D at −1010 mV for Ni(II) were found to be 100.5 ± 1.3% and 100.4 ± 1.3%, respectively. Interferences due to the presence of Cd, Co, Pb, Fe, Mn, Ca, Mg, Cu and Al were studied. The applicability of the proposed methods was assessed through the determination of both metals in tap drinking-water. Samples were subjected if required up to a 20-fold preconcentration step by microwaving in pyrex vessels. The results were compared with those obtained using the zincon and the heptoxime colorimetric reference methods for the determination of zinc and nickel, respectively.     

Extraction chromatography of palladium and platinum complexes with nitroso-R-salt

The retention of palladium and platinum complexes with nitroso-R-salt on silica gel treated with Aliquat 336 has been investigated. The complexation of platinum with nitroso-R-salt (NRS) requires heating of H₂PtCl₆ with an excess of NRS at 100°. The affinity of the complexes for an Aliquat 336 stationary phase increases in the following order: PdCl₄²⁻ ˜ Pt-NRS < PtCl₆²⁻ Pd-NRS. The complexes of palladium and platinum can be separated by column chromatography on silica treated with Aliquat 336 and eluted with 0.25M perchloric acid (Pt) and 1M perchloric acid (Pd).     

Determination of palladium(II) using thiosemicarbazide as a replacing reagent

A simple, rapid, accurate, and selective complexometric method is proposed for the determination of palladium(II). Palladium(II), with associated diverse metal ions, is first complexed by adding a known excess of EDTA, and the uncomplexed EDTA is back titrated with lead nitrate solution in acetic acid-sodium acetate buffer (pH 5.0–6.0) until the end-point. Thiosemicarbazide (1%) solution in water is added to displace EDTA from the Pd-EDTA complex. The released EDTA is then titrated with the lead nitrate solution. Reproducible and accurate results are obtained in the concentration range of 1–10 mg of palladium with a relative error of less than 0.4% and a standard deviation of less than 0.02. The interference of many commonly associated metal ions was also studied. Advantages of this method over other complexometric methods of palladium determination are high-lighted.     

Towards the understanding of molecular mechanisms in the early stages of heat-induced aggregation of beta-lactoglobulin AB

Heat-induced aggregation of bovine β-lactoglobulin AB (10 mg/ml) was studied at 68.5 °C at two different pH values (6.7, 4.9) using gel electrophoresis techniques and matrix-assisted laser desorption ionization mass spectrometry (MALDI–TOF MS). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) analysis under non-reducing and reducing conditions showed that in the early stages of the aggregation of β-lactoglobulin disulfide linked aggregates were formed on heating at pH 6.7, but not at pH 4.9. We related this result to the pH-dependent activity of the free thiol group at C121. Mass spectrometric analyses were conducted in two steps. The first involved the analysis of intact non-native monomers and dimers following their ultrasonic passive elution into a suitable solvent mixture in order to confirm the identity of the different gel bands. The second step comprises the analysis of in-gel digests for the determination of disulfide patterns in non-native monomers, covalent dimers and trimers. The results of in-gel digestions analyzed by mass spectrometry suggest that non-native dimers could result from the formation of inter-molecular disulfide bonds C121–C66, C160–C160, or C121–C160. Moreover, two inter-molecular bonds C121–C66 and C160–C160 between two and the same monomer units have been detected, which may play an important role in limiting the process of covalent β-lactoglobulin network formation. The combination of SDS–PAGE and MALDI–TOF MS enables us to understand the mechanism of β-lactoglobulin aggregation at the macromolecular level.     

Solid–solid interactions between ferric and cobalt oxides as influenced by Al2O3-doping

The solid–solid interactions between pure and alumina-doped cobalt and ferric oxides have been investigated using DTA, IR and XRD techniques. Equimolar proportions of basic cobalt carbonate and ferric oxide and different amounts of aluminum nitrate were added as dopant substrate. The amounts of dopant were 0.75, 1.5, 3.0 and 4.5 mol% Al₂O₃.

The results obtained revealed that solid–solid interaction between Fe₂O₃ and Co₃O₄ takes place at temperatures starting from 700°C to produce cobalt ferrite. The degree of propagation of this reaction increases progressively as a function of precalcination temperature and Al₂O₃-doping of the reacting solids. However, the heating of pure mixed solids at 1000°C for 6 h. was not sufficient to effect the complete conversion of the reacting solids into CoFe₂O₄, while the addition of a small amount of Al₂O₃ (1.5 mol%) to ferric/cobalt mixed solids followed by precalcination at 1000°C for 6 h conducted the complete conversion of the reacting solids into cobalt ferrite. The heat treatment of pure and the 0.75 mol%-doped solids at 900 and 1000°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for the CoFe₂O₄ structure. An increase in the amount of Al₂O₃ added from 1.5–4.5 mol% to the mixed solids precalcined at 1000°C led to the disappearance of all bands of free oxides and appearance of all bands of cobalt ferrite. The promotion effect of Al₂O₃ in cobalt ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of CoFe₂O₄ phase was determined for pure and doped solids. The computed values of ΔE were, respectively, 99.6, 87.8, 71.9, 64.7 and 48.7 kJ mol⁻¹ for the pure solid and those treated with 0.75, 1.5, 3 and 4.5 mol% Al₂O₃.     

Determination of oxygen in zirconium by the platinum flux technique

The platinum flux technique, well established for the determination of oxygen in titanium, was successfully applied to the analysis of zirconium for its oxygen content after a systematic study of the optimum experimental conditions. The extraction of oxygen was complete in 20 min in the temperature range of 1850 to 2100° with a ratio of flux to sample of about 4.5:1 to 8:1. Statistical analysis of the results on a homogeneous sample gave a standard deviation of 0.0038 weight % and a coefficient of variance of 2.9%atalevelof 0.131 weight % of oxygen in zirconium. The recommended experimental conditions are a 0.1-g sample, a 5:1 flux-to-sample ratio, and 20 min extraction at 1900°–1950°.     

Selective complexometric determination of copper in ores and alloys using 2,2′-bipyridyl as masking agent

An EDTA titration method is described for the determination of copper(II) in the presence of other ions based on the selective masking ability of 2,2′-bipyridyl. Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as an indicator. A known excess of 2,2′-bipyridyl solution (1% in 50% alcohol) is then added, the mixture is shaken well and the released EDTA from the Cu–EDTA complex is titrated against standard lead nitrate solution. The interference of various ions are studied and the method is applied to the determination of copper in its ores and alloys. Reproducible and accurate results are obtained for 2.54–25.40 mg of copper with S.D. values <0.04 mg.     

Über peroxo-mischkomplexe von titan, niob und tantal—III Die chelometrische titration von fünfwertigem niob

A chelatometric method for the titration of Nb^v, using nitrilotriacetic acid is described. This forms a 1:1 complex with the peroxy-Nb^v ion. NTA is added in excess, and the excess is backtitrated with Cu solution at pH 5·0–5·5 using the metallofluorescent indicator, Methylcalcein, under UV illumination. The reproducibility, for amounts of 4·56–23·68 mg of Nb is 0·07 mg of Nb. N-Hydroxyethylethylenediamine-N,N',N'-triacetic acid forms a similar 1:1 complex, and can be used instead of NTA, but with little advantage.

Résumé

On décrit une méthode de dosage du Nb (V) par formation de chélates. L'acide nitrilotriacétique, qui forme un complexe 1/1 avec les ions peroxoniobium (V) est utilisé comme agent chélatant. On ajoute du NTA en excès er l'on dose en retour par une solution de cuivre en utilisant comme indicateur de fluorescence la méthylcalcéine sous irradiation ultra-violette. Les analyses d'essais portant sur des échantillons variant de 4,56 mg à 23,68 mg de niobium fournissent une reproductibilité de ± 0,07 mg. L'acide N-hydroxyéthyléthylénediamine-N,N'.N'-triacétique forme également un complexe 1/1 avec les ions peroxoniobium (V) et peut être utilisé à la place du NTA mais ne présente pas d'avantages particuliers.     

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium—I Titrimetr1c determination of manganese

A new method has been developed for the direct titrimetric determination of manganese^II, depending on its oxidation to manganese^III with potassium dichromate at room temperature in a strong phosphoric acid medium using a potentiometric or photometric endpoint. Oxygen of the air does not interfere. The potentiometric method gives results to an accuracy within ± 0.3% for 20–150 mg of manganese/50 ml of titration solution; with the photometric method 5–17 mg of manganese/40 ml of titration solution can be determined with an error of 0.3–1.0% depending on the amount present. Potassium dichromate in 12.0M phosphoric acid has a formal redox potential of about 1.5 V and this reagent appears to have great possibilities in titrimetric analysis.     

Separation of yttrium and neodymium from samarium and the heavier lanthanides by cation-exchange chromatography with hydroxyethylenediaminetriacetate in monochloroacetate buffer

Trace and mg amounts of yttrium and neodymium are separated from samarium and the heavier lanthanides by elution of the latter with hydroxyethylenediaminetriacetate (HEDTA) in a chloroacetate buffer of pH 2.85 from a column containing 68 ml (20 g) of AG 50W-X4 resin of 200–400 mesh particle size. Yttrium and neodymium (and also praeseodymium, cerium and lanthanum) are retained and can be eluted with 0.01M HEDTA in 0.20M ammonium acetate (pH 6). The separations are reasonably sharp and quantitative: only 3–15 μg of samarium was found in the yttrium fraction and 0.8–3.4 μg of yttrium in the samarium fraction when 4.41 mg of yttrium and 7.12 mg of samarium were present originally. Control of the pH during the column operations is essential because the peak positions are very sensitive to change in pH. The relevant distribution coefficients, elution curves of pairs of elements and results for the analysis of synthetic mixtures are presented. Also included is a method for separating yttrium and the lanthanides from HEDTA and sodium and ammonium ions.