Heterogeneous hydride generation in a packed membrane cell

Summary Volatilization of arsenic, selenium and antimony for sample introduction in atomic absorption spectrometry has been performed by pumping an acidic sample through an anion exchanger in the tetrahydroborate (III) form packed as a bed in the liquid channel of a gas-liquid separation membrane cell. The hydrides generated in the heterogeneous reaction between bound tetrahydroborate (III) ions and the analytes are rapidly transferred with the aid of the concomitantly generated hydrogen gas through the gas-permeable membrane into the gas phase and swept to the spectrometer by an additional hydrogen gas flow. This instant transfer of the hydrides to the gas phase kinetically discriminates the reaction of the hydride with metal borides and metal colloids, whose formation by reaction with tetra-hydroborate (III) is slower than the hydride reaction. The susceptibility to interference by transition metal ions is thus markedly reduced, as compared with both batch hydride generation methods and a previously presented heterogeneous reaction scheme. The detection limits for arsenic, selenium, and antimony were 1.2, 3.7, and 10 g/l, respectively. The calibration graphs were linear from the detection limit up to 125 g/l for arsenic, 150 g/l for selenium, and 250 g/l for antimony. The relative standard deviations at concentration levels of 10 and 100 g/l were 1.8 and 0.7% for arsenic and 2.3 and 1.2% for selenium. Corresponding figures for 50 and 100 g/l antimony were 2.5 and 1.6%.     

An oblique section hydride generator for the simultaneous determination of arsenic, antimony and bismuth in geological samples by inductively coupled plasma-atomic emission spectrometry

Summary An oblique section hydride generator is developed for use in combination with inductively coupled plasmaatomic emission spectrometry. The generator offers less interferences from concomitant ions and transition metal ions when compared with the conventional hydride generators reported in literature. The emission signals and the detection limits of the analytes are also improved. The recommended hydride generator has been applied to the determination of arsenic at g/g level and antimony and bismuth at subg/g level in geological standard reference materials. A good agreement is achieved between the data obtained by the present study and the certified values.

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Abgeschrägter Hydridgenerator für die Simultanbestimmung von As, Sb und Bi in geologischen Proben durch ICP-AES

     

Generation and enrichment of AsCl3 for interference-free determination of trace levels of arsenic in steel by atomic absorption spectrometry

Summary Arsenic was analysed after volatilization as arsenic trichloride, facilitated by evaporative concentration of hydrochloric acid. The generated gas was enriched in a cold trap and then revolatilized into a flame-in-tube atomizer for atomic spectrometric determination. No interference was observed at the 50 and 250 g/l As levels when the potential interferents Ni, Co, Cu, and Fe were added at 5000 mg/l each, or as a mixture containing all ions at 1000 mg/l. Standardization against aqueous acidified As(III) solutions was therefore possible without the use of making agents. Analyses of five reference samples of various steel alloys showed good agreement with certified values. The detection limit for As was 3.9 g/l in the dissolved sample, or 0.39 g/g in the steel.     

Mechanism of metal-ion sorption on hydrous metal oxides

A model for treating the sorption of metal ions on hydrous metal oxides was established based on the assumptions that these materials are weakly acidic cation exchangers and have a discrete exchanger phase. The experimental results of the sorption of metal ions on the hydrous niobium(V) and tin(IV) oxides are found to be consistent with the formulas derived from the model by considering that the charge balance and the mass action law hold in the exchanger phase and cations are sorbed by the distribution between this phase and the bulk aqueous phase.     

Laser induced breakdown spectroscopy (LIBS) as an analytical tool for the detection of metal ions in aqueous solutions

Laser induced breakdown spectroscopy (LIBS) is applied to analyze aqueous solutions of Li⁺, Na⁺, Ca²⁺, Ba²⁺, Pb²⁺, Cd²⁺, Hg²⁺ and Er³⁺ and suspensions of ErBa₂Cu₃O_x particles (d=0.2 m). An excimer (308 nm) pumped dye laser with laser pulse at 500 nm and pulse energy at 22±2 mJ is used to produce plasma in aqueous solution. Plasma emission lines of the elements are detected by a photodiode array detector. Detection limits of the metal ions are 500 mg/l for Cd²⁺, 12.5 mg/l for Pb²⁺, 6.8 mg/l for Ba²⁺, 0.13 mg/l for Ca²⁺, 13 g/l for Li⁺ and 7.5 g/l for Na⁺. No mercury and erbium emission can be detected, even at Hg²⁺ and Er³⁺ concentrations of up to the g/l range. On the other side, for Er in suspensions of ErBa₂Cu₃O_x particles a more than 10³ times higher sensitivity is found than for dissolved Er³⁺. This result gives a possibility to analyze colloid-borne metal ions with an increased sensitivity.     

Coprecipitation with metal hydroxides for the determination of beryllium in seawater by graphite furnace atomic absorption spectrometry

Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater.     

Simultaneous ion-chromatography of alkali, alkaline earth and heavy metal ions with conductivity and indirect UV detection: Comparison of eluents containing organic complexing acids and copper sulfate

Summary The simultaneous ion-chromatography of mono-and divalent metal ions on the weak cation-exchange column Nucleosil-PBDMA (polymer coated silica with polybutandiene-maleic acid) with conductivity and indirect UV-detection is presented. The influences of eluents containing organic complexing acids (-hydroxy-isobutyric, tartaric, citric, oxalic, pyridine-2,6-dicarbonic acid and EDTA etc.) as well as UV-absorbing, displacing counterions [Cu(II), Ce(III) etc.] on the retention times of metal ions was investigated in detail. With the combination of citric acid-PDCA as eluent all alkali and alkaline earth ions could be completely separated within 12 min. Alkali, alkaline earth and heavy metal ions [Cu/Zn/Co/Fe(II)] were separated by the combination of tartaric and oxalic acid as eluent in a single run. Trace amounts of Na, K and Ca were successfully separated from the Mg-matrix by an EDTA-PDCA eluent. For the IC with indirect UV-detection the eluent consisting of CuSO₄ or CuCl₂ was used to separate Na, K, Mg and Ca with baseline resolution within 10 min.The detection limits of metal ions with conductivity detection were found beween 0.5 g/l for Li and 8 g/l for Cs. They were 10 times more sensitive than those with indirect UV-detection.This IC-method was applied to determine alkali, alkaline earth and Mn ions in the water, food, ore-cinder and sole-brine samples with satisfactory results.Dedicated to Prof. Dr. G. Schulze on the occasion of his 60th birthday     

Determination of trace arsenic in hydrofluoric acid by hydride generation and atomic absorption spectrometry

Practical procedures are given for determination of arsenic(III) and (V) in hydrofluoric acid by means of hydride generation and atomic absorption spectrometry. Arsenic(III) can be determined by direct generation of arsine with sodium borohydride in hydrochloric/hydrofluoric acid medium, arsenic(V) being only slightly reduced under the conditions used. For its determination, arsenic(V) has to be prereduced with potassium iodide, and even then its reduction to arsenic(III) and then arsine is far from complete. It is possible to determine it in presence of arsenic(III) by a difference method, but this is recommended only if the As(V)/As(III) ratio is greater than 1. Total arsenic can be determined after oxidation of As(III) and evaporation of most of the hydrofluoric acid. The limit of determination is 5 g/l for arsenic(III) and 0.25 g/l for total arsenic; the relative standard deviation is about 10%.     

Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.     

Cationic and anionic contributions to the crystal lattice energy and the heat of solution of salts

Up to now values of H, S, and G have been determined for individual ions in the gaseous state and in aqueous solution at infinite dilution. Values of S have also been determined for individual ions entering into a crystal lattice. The Born-Mayer-Huggins crystal lattice theory has been used to calculate the enthalpy of individual ions in the crystal lattice of alkali metal halides. A formula has been derived on the basis of this theory for the difference between the enthalpies of the cation and anion in the crystal lattice. This difference depends on the van der Waals forces resulting from dipole-dipole and dipole-quadrupole interactions and on the quantum mechanical repulsive forces between the electron clouds of the ions. The enthalpy difference between ions in the lattice varies from +3.1 (LiCl) to -10.1 (KCl) kJ/g-ion. Values of H and G for ions in the crystal lattices of twenty alkali metal halides are presented in tabular form. It is found that the lattice energy is almost equally divided between the cations and anions.The heats of hydration and entropies of solution of ions were calculated from the data obtained and from the known heats of solution of electrolytes. They are presented in tables of H and G of solution, i.e., of the change from a crystal lattice to the aquated state, for the individual ions of twenty alkali metal halides.     

Effect of Ag+ Concentration on the Uptake Rate of Tracer Elements During the Somatic Embryogenesis of Lycium Barbarum L

Multitracer technique and -ray energy spectrum analysis was used to study the effect of Ag⁺ on the uptake of some tracer metal ions in the somatic embryogenesis of Lycium barbarum L. The results show that in the case of some metal ions the uptake changes are selective, cooperative and interactive in somatic embryogenesis due to Ag⁺ influence. To 50 mg/l Ag⁺ concentration, the uptake and the frequency of somatic embryogenesis increases along with increasing concentration. Ag⁺ could speed up cell differentiation and somatic embryogenesis. Above 50 mg/l Ag⁺ concentration, Ag⁺ has a poisonous effect, influences tracer element absorption and inhibit the frequency of somatic embryogenesis.     

Determination of total arsenic in serum and packed cellsof patients with renal insufficiency

In order to investigate the arsenic level in serum and packed cells of patients with renal insufficiency, total arsenic (As) concentrations were determined with hydride generation atomic absorption spectrometry (HGAAS) in serum (S) and packed cells (PC) of 31 non-dialyzed patients. The accuracy of the method was tested by the analysis of arsenic in 3 certified reference materials. Patients showed a three-fold increase of arsenic concentrations in serum and a two-fold increase of arsenic in packed cells compared with controls. Patients (n=10) with higher serum creatinine (>2.0 mg/dL), urea (>0.70 g/L) and urinary protein (mean ±SD: 1.12±0.82 g/L) showed higher arsenic concentrations (5.8±3.3 g/L in serum and 18.0±16.7 g/kg in packed cells) compared with those with lower creatinine (<1.6 mg/dL), urea (<0.6 g/L) and urinary protein (mean ±SD: 0.27±0.82 g/L) (n=16, serum arsenic 1.2±1.2 g/L, packed cells arsenic 2.6±1.9 g/kg). The significant differences (both p<0.001) in S and PC-arsenic levels of patients in group I and II implies a relationship between the arsenic level and the degree of chronic renal insufficiency.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday     

Determination of trace metals in sea waters of the Albanian coast by energy-dispersive X-ray fluorescence

Preconcentration of trace transition and heavy metal ions by precipitation with APDC has been combined with energy-dispersive X-ray fluorescence for environmental sea water analysis. The preconcentration procedure implies adding of 500 g Mo ion and 10 ml of 1% water solution of APDC to a 500 ml water sample at pH 4, filtering off on a Millipore filter and analyzing after drying. Realistic detection limits are at 1 g·l^–1 level and precision varies between 10–25% at about 5 g·l^–1 level, depending on the element. Eleven sea water samples, covering Albanian Adriatic and Ionian coast, are analyzed for trace metal ions.     

Complexometric determination of copper(II) in ores,alloys and complexes using 2-mercaptoethanol as indirect masking reagent

A complexo-titrimetric method for the determination of copper(II) in the presence of other metal ions is described, based on the selective masking ability of 2-mercaptoethanol towards copper(II). Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with zinc sulfate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10%) is then added, the mixture is shaken well and the released EDTA from the Cu-EDTA complex is titrated against standard zinc sulfate solution. The interferences of various ions are studied and the method is applied to the determination of copper in its ores, alloys and complexes. Reproducible and accurate results are obtained for 2.5–40 mg of Cu with relative errors 0.4% and standard deviations 0.04 mg.     

Metabolomic study in plasma,liver and kidney of mice exposed to inorganic arsenic based on mass spectrometry

The mechanism of arsenic toxicity still remains unclear, although enzymatic inhibition, impaired antioxidants metabolism and oxidative stress may play a role. The toxicological effects of trivalent inorganic arsenic on laboratory mouse Mus musculus after oral administration (3 mg/kg body weight/day) were investigated along 12 days, using a metabolomic approach based on direct infusion mass spectrometry to polar and lipophilic extracts from different organs and fluids (liver, kidney, and plasma). Positive and negative acquisition modes (ESI⁺/ESI^?) were used throughout the experiments. The most significant endogenous metabolites affected by exposure were traced by partial least square-discriminant analysis and confirmed by tandem mass spectrometry (MS/MS) and gas chromatography coupled to MS. In this work, the toxic effect of arsenic has been related with important metabolic pathways, such as energy metabolism (e.g., glycolysis, Krebs cycle), amino acids metabolism, choline metabolism, methionine cycle, and degradation of membrane phospholipids (cell apoptosis). In addition, this work illustrates the high reliability of mass spectrometry based on a metabolomic approach to study the biochemical effects induced by metal exposure.

Arsenic(III) as a non-metallic atom in heteropolytungstates: Toward very large polyanions

A review of the synthesis and structures of polytungstate ions containing arsenic(III) is presented. The lone pair of electrons on the As(III) inhibits formation of the classic Keggin structure of these ions. However, this site of unsaturation may be used to construct novel high nuclearity species. Application of this concept has led to the formation of a phospho(V)polytungstate ion containing 48 tungsten atoms.     

Indirect determination of arsenic by flotation spectrophotometry

An indirect method of arsenic determination in the submicrogram range via the determination of molybdenum is presented here. High sensitivity is achieved by combination of the chemical amplification during formation of dodecamolybdoarsenic acid (arsenic: molybdenum ratio 1 12) with multiplication due to the formation of ion-association complexes during flotation-spectrophotometric molybdenum determination with crystal violet (molar ratio 1 2). Thus, the amplification factor relating to arsenic is 24.Dodecamolybdoarsenic acid is formed in a weakly acidic medium and is quantitatively extracted byn-butanol. Back extraction of the heteropoly acid to the aqueous phase and its simultaneous destruction provides the basis for the reaction of released molybdate ions with thiocyanate ions. The molybdenum-thiocyanate complex forms a sparingly soluble ion-association complex with crystal violet which can be floated with toluene on the phase boundary (film flotation). After separation of the aqueous phase the floated molybdenum compound is dissolved in acetone and the resulting free crystal violet ions are subjected to photometric determination at 590 nm as equivalent of the concentration of arsenic. The molar absorptivity of crystal violet is 3.2 · 10⁵1 · mol^–1 · cm^–1. Beer's law is obeyed in a concentration range from 0.01 to 1 g Mo · ml^–1 (0.001–0.1 g As · ml^–1). The resulting detection limit for arsenic is 1 ng · ml^–1.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 g/l for Cr(VI) and 5 g/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Bestimmung toxikologisch wichtiger Elemente in biologischem Material mittels R?ntgenfluorescenz- Analyse

Zusammenfassung Die bisherige Anwendung der Röntgenfluorescenz-Analyse auf biologisches Material beschränkte sich auf die Bestimmung klinisch wichtiger Elemente in sehr kleinen Probenmengen. Durch systematische Untersuchungen und Verbesserungen der handelsüblichen Geräte war es möglich, die Röntgenfluorescenz-Analyse auch in der forensischen Toxikologie einzusetzen. Die Nachweisgrenzen betragen 1 g Brom in 5 g Urin, 1,8 g Blei in 10 g Vollblut und 0,025 g Arsen in 10–30 mg Haaren. Die Standardabweichungen liegen bei 1–5%. Bei der hohen Spezifität der Röntgenfluorescenz-Analyse wird diese Methode auch den hohen Anforderungen der forensischen Toxikologie gerecht.

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Determination of elements of toxicological importance in biological material by means of X-ray fluorescence analysis

The application of X-ray fluorescence analysis till to day is restricted to the determination of elements of clinical importance in very small samples. By systematical investigations and improving industrial equipment it could be achieved to adapt X-ray fluorescence analysis to forensic toxicology. The limits of detection are 1 g of bromine in 5 g of urine, 1,8 g of lead in 10 g of blood, and 0,025 g of arsenic in 10 to 30 mg of hair. The standard deviation is 1 to 5%. Because of its high specifity X-ray fluorescence analysis satisfies the high standards claimed for forensic toxicology.

     

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.