Elemental speciation for chromium in chromium picolinate products

Chromium picolinate products have been examined for different forms of chromium, using chromatographic separation and inductively coupled plasma mass spectrometric detection. The brands we evaluated contained no detectable amount of elemental chromium(VI), the toxic form. Since chromium picolinate might have other chromium forms as impurities, different products may contain different forms of chromium species. Compared with ion-exchange, reversed-phase chromatography showed excellent chromium recovery based on the amount stated on the product label.     

The interconversion of orthorhombic chromium oxy-hydroxide and chromium dioxide

The thermal behaviour of CrOOH and CrO₂ in different atmospheres has been studied by means of DTA, TG and X-ray diffraction. The easy interconversion between the two substances at one atmosphere pressure is explained on the basis of the results obtained.

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Zusammenfassung Es wurde das thermische Verhalten von CrOOH und CrO₂ in verschiedenen Atmosphären mit Hilfe der Differentialthermoanalyse, Thermogravimetrie und Röntgendiffraktion untersucht und auf Grund der Ergebnisse die leichte Umwandlung wischen den zwei Verbindungen unter 1 Atm. Druck erklärt.

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Résumé Étude du comportement thermique de CrOOH et de CrO₂ dans différentes atmosphères, par ATD, TG et diffraction de rayons X. Interprétation de l'interconversion légère entre les deux substances sous une pression d'une atmosphère.

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lO₂ , -. , .

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Thanks are due to Prof. Dr. S. C. Bevan of Brunei University and to Dr. E. Hockings of RCA (USA) for valuable discussions, and also to the D.G.E.S.I. (Spain) for a grant (to M.A.A.F.).     

Microscopic detection of chromium as chromium(III)

Summary Trisodium phosphate is recommended as a reagent for the microscopic detection of chromium (III). Sensitivity of the test is 6 of chromium (III) in a volume of 0.01 ml. Of particular importance is the fact that aluminum and iron (III) do not react with the reagent to form crystalline precipitates.

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Zusammenfassung Tertiäres Natriumphosphat gibt mit Chrom(III)-Lösungen eine charakteristische Fällung, in der unter dem Mikroskop rechteckige Kristalle zu erkennen sind. Weder Aluminium noch Eisen(III) gibt mit diesem Reagens einen kristallinen Niederschlag. Die Reaktion gestattet den Nachweis von 6 Chrom in 0,01 ml Lösung. Auch Quecksilber(II) gibt charakteristische Kristalle.

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Résumé On recommande le phosphate trisodique comme réactif pour la recherche microscopique du chrome-III. La sensibilité de l'essai est 6 de chrome-III dans un volume de 0,01 ml. Le fait que l'alumine et le fer-III ne se combinent pas avec le réactif pour former des précipités cristallins présente une importance particulière.

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With 2 figures.     

The interconversion of orthorhombic chromium oxy-hydroxide and chromium dioxide

The thermal behaviour of CrOOH and CrO₂ in different atmospheres has been studied by means of DTA, TG and X-ray diffraction. The easy interconversion between the two substances at one atmosphere pressure is explained on the basis of the results obtained.     

Determination of chromium by atomic absorption spectrophotometry of chromium acetylacetonate : Determination of chromium in sea water

A sensitive atomic absorption method is described for the determination of chromium at sub-microgram levels. Chromium(III) is converted to its acetylacetone complex and extracted into MIBK. The atomic absorption sensitivity is thus en hanced two-fold compared to chromium (III) in aqueous medium. The detection limit of chromium is 0.015 p.p.m. with an acetylene-air flame; the sensitivity obtained with other chromium, methods under the same instrumental conditions is compared. The method can be applied to the determination of chromium in sea water; at a level of ca. 1.6 μg Cr/1, the precision is ±0.06 μg/1.     

Rapid chelatometric estimation of chromium, iron and aluminium in chromium + iron and chromium + aluminium mixtures

Summary A study of the kinetics of the reaction of chromium(III) with EDTA [1,2] had shown that the rate of reaction, usually slow, can be accelerated in the presence of hydrogen carbonate, sulphite, nitrite and organic solvents like alcohols, ketone, dioxane, etc., or suppressed in the presence of oxalate, acetate, etc. Based on this principle, a rapid titrimetric method using EDTA was developed for the estimation of chromium(III), iron and aluminium in chromium(III) + iron and chromium(III) + aluminium mixtures. The method has been extended for the estimation of iron and chromium(III) in stainless steel. Results are satisfactory.

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Zusammenfassung Die Reaktion von Chrom(III) mit äDTA kann durch Hydrogencarbonat Sulfit, Nitrit sowie organische Lösungsmittel beschleunigt oder durch Oxalat, Acetat u. a. unterdrückt werden. Aufgrund dieser Erscheinung wurde ein chelatometrisches Verfahren zur Bestimmung von Chrom(III), Eisen und Aluminium in Gemischen von Cr + Fe oder Cr + Al ausgearbeitet, das auch auf die Bestimmung von Eisen und Chrom in rostfreiem Stahl angewendet wurde. Es wurden befriedigende Ergebnisse erhalten.

     

Synthesis of chromium N-heterocyclic carbene complexes using chromium Fischer carbenes as a source of chromium carbonyls

Chromium Fischer carbene complexes, [Cr{OMe(R)}(CO)₅] have been utilized as a source of chromium carbonyls in the synthesis of chromium NHC complexes. Using the synthetic method, chromium complexes of various NHC ligands were isolated in reasonable yields. Moreover, the method can be employed for the synthesis of molybdenum and tungsten NHC compounds.     

Removal and recovery of chromium and chromium speciation with MINTEQA2

Chromium(III) is commonly found in large quantities in tannery wastewaters. For this reason, the recovery of the chromium content of these wastewaters is necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using ion exchange resins. To this purpose, two weakly acidic exchange resins Amberlite IRC 76 and Amberlite IRC 718 and a strongly acidic exchange resin Amberlite IR 120 were used. Basic chromium sulphate [Cr(4)(SO(4))(5)(OH)(2)] solutions in different concentrations and pH were used in all experiments as tanning baths. The resins were prepared in two different ionic forms as Na(+) and H(+). The effects of concentration, pH, stirring time and resin amount were investigated. The concentration range varied between 5 and 100 mg l(-1), pH range was between 1 and 8, stirring time between 5 and 60, and resin amount was between 50 and 1000 mg. Stirring speed was 2000 rpm during all these experiments. Exchange capacities, moisture contents and optimum conditions of these resins were determined in batch system. The results obtained showed that Amberlite IRC 76 and 718 weakly acidic resins had shown better performance than Amberlite IR 120 strongly acidic resin for removal and recovery of chromium(III) in Na(+) form. Optimum conditions were found as concentration 10 mg l(-1), pH 5, stirring time 20 min, and resin amount 250 mg. Furthermore, chromium(III) speciation was investigated for optimum concentration and pH with MINTEQA2 computer programme. The studied pH range was between 1 and 8 and concentration range was between 5 and 100 mg l(-1). Cr(OH)(2+) species were found to be dominant at pH 5 and 10 mg l(-1) concentration in batch studies. There was a correlation between experimental and computerised results.     

Thermal characterisation of alumina supported chromium and platinum–chromium catalysts

This study presented results on reduction of alumina supported chromium and platinum–chromium catalysts using temperature programmed reduction method (TPR). It has been shown that catalysts after earlier oxidation step but without calcinations one undergo reduction in lower temperature in comparison to calcined only catalysts. Moreover, addition platinum to Cr/Al₂O₃ catalysts also caused decrease of reduction temperature. It has been observed that over the examined catalysts oxidation CO to CO₂ and reduction CO to CH₄ occurs. However, on Pt–Cr catalysts both reactions proceed at lower temperature compare to Cr catalysts.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Isotope shift in chromium

Thirty-three spectral lines of chromium atom in the blue-violet region (425–465 nm) have been investigated with the method of laser-induced resonance fluorescence on an atomic beam. For all the lines, the isotope shifts for every pair of chromium isotopes have been determined. The lines can be divided into six groups, according to the configuration of the upper and lower levels. Electronic factors of the field shift and the specific mass shift (F_ik and M_ik^SMS, respectively) have been evaluated and the values for each pure configuration involved have been determined. Comparison of the values F_ik and M_ik^SMS to the ab initio calculations results has been performed. The presence of crossed second order (CSO) effects has been observed.     

Quantification of total chromium and hexavalent chromium in UHT milk by ETAAS

Procedures for the quantification of total chromium and hexavalent chromium in UHT milk samples are presented. Total chromium was determined directly in milk with the addition of a surfactant and a mixture of Pd and Mg as a chemical modifier. For the selective separation of hexavalent chromium, the sample pre-treatment consisted in precipitation of proteins and elution of the supernatant through a Chromabond NH2 column. The metal was eluted with nitric acid. Both total chromium and hexavalent chromium were evaluated by atomic absorption spectrometry with electrothermal atomization using the same instrumental conditions. The detection limits were 0.2 and 0.15 microgram l-1 for total chromium and hexavalent chromium, respectively. The linearity ranges under the optimized conditions were 0.2-20 and 0.15-50 micrograms l-1. For total chromium the precision was 4.9 and 5.7% for the analytical and the over-all procedure, respectively, and for hexavalent chromium 4.3 and 4.9%, respectively. The validation of both procedures was performed by the standard additions method and the recoveries were higher than 93% in all cases. For total chromium, a certified reference material was also used to validate the methodology. The methods were applied to the determination of total chromium and hexavalent chromium in 60 UHT milk samples.     

Triamidoamine complexes of chromium(III) and chromium(IV)

Treatment of [CrCl3(THF)3] with slightly more than 1 equiv of Li3(N3N) [(N3N)(3-) = ((Me3SiNCH2CH2)3N)(3-)] affords the triamidoamine complex [Cr(N3N)] (1) in 75% yield. 1 is oxidized by PhICl2, CuCl2, or AgCl to give the chromium(IV) complex [Cr(N3N)Cl] (2) in moderate yields. Alternatively, complex 2 is obtained directly from [CrCl3(THF)3] in 50% yield after treatment with 0.5 equiv of Li3(N3N). Both compounds are high-spin complexes bearing three and two unpaired electrons, respectively. Their molecular structures are described revealing a trigonal monopyramidal and trigonal bipyramidal coordination geometry of the chromium center, respectively.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Substoichiometric extraction of chromium

Substoichiometric extraction of chromium with tetraphenylarsonium chloride (TPACl), tri-n-octylamine (TNOA), diethylammonium diethyldithiocarbamate (DDDC) and ammonium pyrrolidinedithiocarbamate (APDC) was examined in detail. Chromium can be extracted substoichiometrically in a pH range, which is 1.1–2.6 for the TPACl compound, 0.6–2.3 for the TNOA compound, 5.1–6.4 for the DDCC chelate and 3.9–4.9 for the APDC chelate. Chromium in high-purity calcium carbonate, Orchard Leaves (NBS SRM-1571) and Brewers Yeast (NBS SRM-1569) was determined by neutron activation analysis combined with substoichiometric extraction by DDDC and APDC. The values of 2.0±0.02 ppm and 2.6±0.2 ppm were obtained for Brewers Yeast and Orchard Leaves, respectively. These values were in good agreement with the values reported by NBS. The reaction mechanism and the reaction ratio between hexavalent chromium and dithiocarbamate were also discussed.     

Coulometric determination of chromium

This paper describes an accurate and precise method for the determination of chromium by coulometry at controlled potential. A solution of the sample in 6M hydrochloric acid is electrolyzed at a large stirred mercury cathode whose potential is maintained constant at —1.10 V vs. S.C.E. ;this reduces the chromium quantitatively to the +2 state. Copper, lead, and a number of other elements are next eliminated by simply discarding the mercury and replacing it with fresh mercury ;then uranium is re-oxidized to non-interfering uranium(IV) by a second controlled-potential electrolysis at —0.80 V vs. S.C.E.; and finally the solution is electrolyzed at a working electrode potential of —0.40 V vs. S.C.E. This serves to re-oxidize the chromium quantitatively to the +3 state, and the analysis consists of measuring the quantity of electricity consumed in this oxidation.Of the elements commonly associated with chromium, only vanadium (and, when it is present in large amounts, molybdenum) interfere in this procedure.     

Oxidation of chromium carbide

The oxidation of chromium carbide has been studied gravimetrically. Products of reaction have been examined by gas sorption analysis and X-ray diffraction. Changes in phase composition, crystallinity and crystallite size are correlated with the reaction conditions.Chromium carbide, Cr₃C₂, differs from most of the transitional metal carbides in that it forms stable films of metal oxide (Cr₂O₃) around the remaining carbide particles, inhibiting further oxidation. Thus chromium carbide additive inhibits oxidation of interstitial zirconium carbide, ZrC, by forming some chromic oxide which stabilises the zirconia (ZrO₂) layer around the remaining carbide crystallites.     

Substoichiometric determination of chromium

The present work deals with the determination of Cr/III/ by means of the substoichiometric isotope dilution method, using PAN, 1-/2-pyridylazo/-2-naphthol as a complexing agent. Chromium forms a 12 complex with PAN. Heating to 90°C for 3 min was necessary for complete complexation. The complex was extracted into chloroform at pH 3.5 /acetate buffer/. Tens of micrograms of chromium could be determined. Effect of diverse metal ions was also studied.     

Studies of chromium stearate

Evidence is presented which throws doubt on the preparation of chromium III tri-stearate by aqueous metathetic reaction.