Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Study of Cr(VI)-2-oximinodimedone dithiosemicarbazone reaction and simultaneous determination of Cr(VI) and Fe(III)

Summary 2-Oximinodimedone dithiosemicarbazone reacts with Cr(VI) in strongly acid medium. The orange colour obtained has been used to propose a spectrophotometric method of Cr(VI) determination in the concentration range 0.40–9.5g ml^–1 (=5600 mole^–1-cm^–1 at 485 nm). The stoichiometry of the reaction is 32 (reagentCr(VI)) which is in accordance with the oxidation reaction of the reagent by Cr(VI). The method has been applied to the determination of Cr(VI) and Fe(III) in ceramic materials.

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Eine Studie zur Cr(VI)-2-oximinodimedondithiosemicarbazon-Reaktion und die simultane Bestimmung von Cr(VI) und Fe(III)

Zusammenfassung 2-Oximinodimedonedithiosemicarbazon reagiert in stark saurem Milieu mit Cr(VI). Die orange Farbe kann im Konzentrationsbereich von 0.4–9,5g/ml zur spektrophotometrischen Cr(VI)-Bestimmung verwendet werden (=5600 1 mol^–1cm^–1bei 485 nm). Die Stöchiometrie der Reaktion ist 32 (Reagens: Cr(VI)) und entspricht der Oxidation des Reagens durch Cr(VI). Die Methode wurde zur Bestimmung von Cr(VI) und Fe(III) in keramischen Materialien eingesetzt.

     

New specific methods for the detection of chromium(VI) and vanadium(V) using primaquin

Summary New specific methods have been developed for the detection of chromium(VI) and of vanadium(V), based on the formation of a purple color with primaquin in concentrated sulfuric acid solution. The identification limits and dilution limits have been determined to be 0.05g, 11 000 000 for chromium(VI) and 0.1g, 1500 000 for vanadium(V) respectively.

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Neue spezifische Methoden zum Nachweis von Cr(VI) und V(V) mit Primachin

Zusammenfassung Die neu ausgearbeiteten Methoden sind spezifisch und beruhen auf der Bildung einer Purpur-Färbung mit Primachin in konz. Schwefelsäure. Die Nachweisgrenzen und Verdünnungsgrenzen betragen 0,05g bzw. 11 000 000 für Cr(VI) und 0,1g bzw. 1500 000 für V(V).

     

A new spot test reagent for chromium(VI), vanadium(V), and hexacyanoferrate(III) ions: the schiff base from 4,4′-methylenedianiline and 4-dimethylaminobenzaldehyde

Summary A new Schiff base, bis(4-dimethylaminobenzylidine)4,4-methylenedianiline (I) has been prepared by reacting 4-dimethylaminoben-zaldehyde with 4,4-methylenedianiline. A 1% solution ofI in conc. sulphuric acid gives a deep red or blood red colour with Cr(VI), and V(V), and a deep rose red colour with [Fe(CN)₆]^3-. The limits of detection and dilution are 0.7 g, 171,000 for Cr(VI); 5 g, 110,000 for V(V); and 7 g, 17,100 for [Fe(CN)₆]^3-. Cr(III), V(IV), and [Fe(CN)₆]^4- do not interfere. The effects of common anions and cations are reported.

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Zusammenfassung Durch Umsetzung von 4-Dimethylaminobenzaldehyd mit 4,4-Methylen-dianilin wurde eine neue Schiffsche Base hergestellt, deren 1%ige Lösung in konz. Schwefelsäure eine tiefrote oder blutrote Farbe mit Cr(VI) und V(V), eine tiefrosa Farbe mit [Fe(CN)₆]^3– gibt. Die Nachweisgrenzen bzw. die Grenzkonzentrationen betragen: 0,7 g, 171000 für Cr(VI), 5 g, 110000 für V(V) und 7 g, 17100 für [Fe(CN)]₆ ^3–. Cr(III), V(IV) und [Fe(CN)₆]^4– stören nicht. Der Einfluß gängiger Anionen und Kationen wird angegeben.

     

Simultaneous determination of chromium (III) and chromium (VI) by reversed-phase ion-pair HPLC with chromium-specific detection

A method for the simultaneous determination of Cr(III) and Cr(VI) with reversed-phase ion-pair HPLC employing chromium-specific detection by flame atomic absorption spectrometry (FAAS) and inductively-coupled plasma mass spectrometry (ICP-MS) is presented. Experimental parameters of the chromatographic separation, such as concentration of the ion-pairing reagent, pH and polarity of the mobile phase have been optimized for two different ion-pairing reagents, tetrabutylammonium phosphate (TBA) and tetraethylammonium nitrate (TEA). Best chromatographic conditions have been obtained with a polymer-based reversed-phase column (Hamilton PRP1) and mobile phases containing either TBA (1 mmol/l) in methanol-water (60:40, v/v) or TEA (2 mmol/l) in water at a pH between 3 and 4. With FAAS the detection limits (3) have been found to be 24 g/l for Cr(III) and 40 g/l for Cr(VI). A detection limit of 0.3 g/l Cr(3) for both chromium species has been obtained when ICP-MS has been used for detection. The method has been applied to analyze tap- and groundwater and to investigate the behaviour of Cr(III) and Cr(VI) in spiked tap-water, as well as to analyze aqueous extracts of coal fly ash (NIST SRM 1633a) and of an ash from a wood treatment company.     

2-(α-Pyridyl)-thioquinaldinamide (PTQA)-A novel fluorimetric reagent in inorganic trace analysis. I: The nonextractive,nonquenching fluorescent method for the determination of chromium(VI)

A direct fluorimetric method for determining Cr(VI) in aqueous solutions is described. The nonfluorescent reagent 2-(-pyridyl)-thioquinaldinamide (PTQA) and Cr(VI) interact to produce an intensely fluorescent species [_ex(max) 360 nm; _em(max) 500 nm] showing constant and maximum fluorescence intensity in slightly acidic media (0.18N–1.08N H₂SO₄). The fluorescence attains its maximum value within 5 min and remains unchanged for 24 h. The system obeys Beer's law from 2 ng/ml to 0.8 g/ml of Cr(VI). Over sixty cations, anions and complexing agents are without any effect on the fluorimetric determination of 0.1 g/ml of Cr(VI). The method has been tested with synthetic mixtures, steels, solutions containing both Cr(III) and Cr(VI), and environmental samples.     

Controlled-potential coulometric studies on fluoride and sulphate complexes of neptunium (VI)

Fluoride and sulphate complexing of Np(VI) has been studied by controlled-potential coulometry at a constant ionic strength. The values of ₁ ^* and ₂ ^* for fluoride complexes were found to be 9.4 and 8.9, respectively, at an ionic strength =0.5. At an ionic strength =1.0, ₁ ^* and ₂ ^* obtained were 6.6 and 10.5, respectively. Sulphate complexing of Np(VI) was studied only at an ionic strength =0.5. The value of ₁ ^* obtained was 5.6.     

Human prostate specific antigen (hPSA) purification and establishment of hPSA radioimmunoassay

Human prostate specific antigen (hPSA) RIA was developed with hPSA and anti-PSA prepared in our laboratory. Its standard curve was linear with a sensitivity of 0.5 g/L. Serum PSA levels of 130 normal males ranged from 0 to 3.5 g/L (1.15±0.93 g/L), which are consistent with the results of other conventional RIA. The recovery, intra- and inter-assay coefficients of variation conform to the demands of RIA, and the results of 41 samples obtained by both the PSA RIA and PSA RIA of DPC were well correlated (=0.990). PSA level of 23 patients with prostatic carcinoma was 10400 g/L.     

Nickel(II) xanthates with nitrogen heterocycles as bridging ligands

New homopolynuclear nickel(II) xanthate complexes with nitrogen donor heterocycles as bridging ligands have been prepared, namely [Ni(Rxa)2(-L)]n and [Ni2(Rxa)4(-L1)], where R=i-Pr,i-Am; xa=OCS2– L=1,2-bis(4- pyridyl)ethane (bpe), 4,4-dithiodipyridyl (dtp), 1,2-bis(4- pyridyl)ethylene (dpe), 4,4-trimethylene-dipyridine (tmd); L1=2,3-bis(2-pyridyl)pyrazine (bpp), 2,4-bis(5,6- diphenyl-1,2,4-triazine-3-yl)pyridine (bdt), or 2,4,6-tris(2- pyridyl)-1,3,5-triazine (tpt). The compounds have been characterized by elemental analyses, i.r. and electronic spectroscopies, magnetochemical and conductivity measurements. The results show that the [Ni(Rxa)2(-L)]n complexes are linear polymers in which the nitrogen heterocycles bridge between the nickel(II) ions, which are coordinated by four sulfur and two nitrogen atoms and have trans-octahedral geometry. The nearly constant values of the effective magnetic moment (3.36–3.34 eff/B) over the 77–295 K temperature range indicate that exchange interactions are lacking among the paramagnetic centres in the linear structure, [Ni(i-Amxa)2(dpe)]n. The variable- temperature magnetic susceptibilities of the [Ni2(i-Prxa)4(bpp)] (3.00–2.95eff/B per Ni atom), [Ni2(i-Prxa)4(bdt)] (2.72–2.63 eff/B per Ni atom), and [Ni2(i-Amxa)4(tpt)] (2.76–1.87 eff/B per Ni atom) were measured down to liquid nitrogen temperature. In the case of binuclear nickel(II) complexes with bdt or tpt, antiferromagnetic coupling between the nickel(II) ions was detected, giving the exchange integral J=–4.0cm–1 and –29.6cm–1, respectively.     

Extractive spectrophotometric determination of dioxouranium(VI) with the sodium salt of hexamethyleneiminecarbodithioate

The optimum conditions for the extractive spectrophotometric determination of dioxouranium(VI) with hexamethyleneiminecarbodithioate(HMICdt) have been established. Dioxouranium(VI) reacts with this ligand at pH 4.5 to form a yellowish-orange uncharged 12 metal-ligand complex which can be extracted by chloroform. The calibration graph was linear in the range of 1–20 g ml^–1 of dioxouranium(VI) at 335 nm. The molar absorptivity of the extracted species is 5.952×10³ l mol^–1 cm^–1 with Sandell's sensitivity of 0.04 g cm^–2. The average of 10 determinations of dioxouranium was 49.75 g for the samples containing 50 g of U(VI) and the variation from the mean at 95% confidence limit was 49.75±0.5955.     

Simultaneous determination of chromium(VI) and chromium(III) by flame atomic absorption spectrometry with a chelating ion-exchange flow injection system

Summary Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h^–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml^–1 and 0.67% for Cr(III) (0.10,g ml^–1) and the corresponding limits of detection were 85 ng ml^–1, and 16 ng ml^–1, respectively.On leave from University of Belgrade.     

Certified reference materials (CRM 408 and 409) for quality control of main components (ammonium, calcium, hydronium, magnesium, nitrate, potassium, sodium and sulphate) in simulated rain water

Analyses of rainwater are routinely performed by a number of organisations to monitor the contribution from rainwater to the component occurrences in the environment and the acidification of the environment. To control the quality of such determinations, the Community Bureau of Reference (BCR) has organised a certification campaign to produce two simulated rainwater reference materials (CRM 408, low mineral content and CRM 409, high mineral content). The materials were carefully prepared (addition of pro analysis and supra pure reagents with the mentioned elements to silica-free deionised water) and its homogeneity and long-term stability were verified. The materials were certified for their contents of ammonium (106 mol/kg) (CRM 409), calcium (7.68 and 15.5 mol/kg), chloride (67.3 and 113 mol/kg), hydronium (16.6 and 48.0 mol/kg), magnesium (6.14 and 12.3 mol/kg), nitrate (20.1 and 78.1 mol/kg), potassium (4.25 mol/kg) (CRM 409), sodium (42.0 and 82.9 mol/kg) and sulphate (10.5 and 53.2 mol/kg). Indicative values (not certified) are given for ammonium and potassium in CRM 408. This paper presents the certification work performed, as well as the analytical work for the certification of the contents of relevant species.     

Effect of Surfactants on the Immobilization of 4-(2-Pyridylazo)resorcinol on Silochroms

The effect of cationic surfactants (cetyltrimethylammonium bromide, cetylpyridinium bromide, and tetrabutylammonium perchlorate) and a nonionic surfactant (OP-7) on the conditions of the immobilization of 4-(2-pyridylazo)resorcinol (PAR) on three types of silica gel (Silochrom S-120 (200–350 m), Silochrom S-120 (315–500 m), and Silochrom S-80 (200–350 m)) was studied. It was found that OP-7 does not affect the adsorption of surfactants. The effect of cationic surfactants increases in the order tetrabutylammonium perchlorate < cetyltrimethylammonium bromide < cetylpyridinium bromide. The adsorption activity of silica gels increases in the order Silochrom S-120 (315–500 m) < Silochrom S-80 (200–350 m) < Silochrom S-120 (200–350 m). Cetylpyridinium bromide provides full immobilization of PAR on silica gel Silochrom S-120 (200–350 m) in the pH range 2–9.     

Determination of Cd,Mo, Cr and Co in biological materials by RNAA

A method for the determination of trace amounts of Mo, Cd, Co and Cr in biological materials by neutron activation analysis with radiochemical separation is presented. The method is based on the ion-exchange scheme developed by SAMSAHL, where Co and Cr are trapped on BioRad Chelex-100 and Cd and Mo on BioRad AG2X8. The elements Mo, Cd and Co can be determined without systematic errors. For the element chromium the situation is less clear, partially due to lack of sufficient certified reference materials for Cr. The method has been used in the characterization of candidate reference materials. Detection limits in these materials range from 1.5 g/kg for Co to 10 g/kg for Cr. Actual levels as low as 8 g/kg for Cd and 7 g/kg for Co were measured.     

Chromogenic reaction of bromopyrogallol red with tri- and hexavalent chromium in the presence of cetyltrimethyl ammonium bromide and its application in Cr speciation

The coordination reactions of bromopyrogallol red (BPR) with tri- and hexavalent chromium in the presence of cetyltrimethylammonium bromide (CTAB) have been studied by absorption spectrometry. Results show that the reactions of Cr(VI) and Cr(III) with BPR in the absence or presence of CTAB have different temperature dependences. The reaction mechanism of Cr(VI) is that Cr(VI) is first reduced by BPR to Cr(III) and then the Cr(III) produced reacts with BPR. Based on the study on the coordination reactions and the effects of surfactants upon them, a simple, rapid, sensitive and accurate method for Cr speciation has been developed. Over the range of 0–8 g Cr(VI) or 0–12g Cr(III) per 25ml final volume, the calibration curve is linear with a detection limit of 3.5 × 10^–7 mol/1 for Cr(VI) or 4.4 × 10^–7 mol/1 for Cr(III).     

Role of metal center in reactions of polynuclear nickel(ii) and cobalt(ii) trimethylacetates with 8-amino-2,4-dimethylquinoline

The reactions of 8-amino-2,4-dimethylquinoline (L) (1) with polynuclear nickel(ii) and cobalt(ii) hydroxotrimethylacetato complexes under anaerobic conditions were studied. The nonanuclear cluster Ni₉(₄-OH)₃(₃-OH)₃(_n-OOCCMe₃)₁₂(HOOCCMe₃)₄ gave the mononuclear complex Ni(²-L)(²-OOCCMe₃)₂ (2). The tetranuclear complex Ni₄(₃-OH)₂(-OOCCMe₃)₄(²-OOCCMe₃)₂(EtOH)₆ produced the mononuclear complex Ni(²-L)(²-OOCCMe₃)(OOCCMe₃)L (3). At room temperature, the cobalt-containing polynuclear trimethylacetates, viz., the polymer [Co(OH) _n (OOCCMe₃)_2–n ] _x and the tetranuclear complex Co₄(₃-OH)₂(-OOCCMe₃)₄(²-OOCCMe₃)₂(EtOH)₆, were transformed into the trinuclear cobalt(ii) complex Co₃(₃-OH)(-OOCCMe₃)₄(²-L)₂(OOCCMe₃) (4). Meanwhile, at 80 °C these compounds generated the binuclear cobalt(iii) complex Co₂(₂²-(HN)C₉NMe₂)₂(-OOCCMe₃)(L)(OOCCMe₃)₃ (5). The structures of the resulting compounds were established by X-ray diffraction analysis. Compounds 2—4 exhibit the antiferromagnetic spin-spin exchange coupling, whereas compound 5 is diamagnetic.     

New Molybdenum(V) Complexes Prepared by the Oxidation of Dinuclear Quadruply-Bonded Molybdenum(II) Monothiocarboxylates

Oxidation of molybdenum(II) thiopivalate and thiobenzoate in the presence of -picoline or pyridine results in the formation of dinuclear molybdenum(V) complexes of the general formulae [Mo₂O₂(-O)₂(-SO₄)L₄] with L = -picoline or pyridine and [Mo₂O₂(-O)(-S)(-SO₄)L₄] with L = -picoline. As determined by X-ray structure analysis, two complexes with -picoline differ in their bridging cores: In one complex, two Mo atoms are doubly bridged through two oxygen atoms; in the other, one Mo atom is doubly bridged through oxygen and sulfur atoms. However, they both crystallize together. The product is solvated with -picoline and water molecules. Molybdenum atoms exhibit distorted octahedral coordinations. The same complexes were prepared also through direct reactions of [Mo₂O₃(O₂CCH₃)₄] with thiopivalic and thiobenzoic acid in the presence of -picoline or pyridine. The appearance of the oxo-oxygens and sulfido-sulfur as well as sulfato ligand is explained by the molybdenum-catalyzed oxidation of thiocarboxylates.     

Catalymetric trace determination of molybdenum(VI) based on a Landolt type peroxoborate-iodide reaction using an ion-selective electrode

Summary Trace amounts of molybdenum(VI) have been determined by means of its catalytic effect on the peroxoborate-iodide reaction in acidic medium. The indicator reaction is transformed to a Landolt reaction by the addition ofl-ascorbic acid which reduces iodine to iodide. The end-point of the reaction (decrease of iodide) is potentiometrically monitored by the aid of an iodide ion-selective electrode. The relationship between the time required to reach the end-point (t in seconds) and the concentration of molybdenum(VI) was found to be 1/t=4.79 [Mo(VI)]+0.598 in the range of 0.5–5.0 M Mo(VI). Tungsten(VI) interferes. The method has been applied to the determination of molybdenum(VI) in sea water after its concentration by the chelating resin Chelex-100 (standard deviation 0.52 g/l for 8.62 g Mo/l).

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Katalymetrische Bestimmung von Molybdän(VI)spuren durch die Landoltsche Peroxoborat-Iodid-Reaktion mit Hilfe der Iodid-Elektrode

Zusammenfassung Das Verfahren beruht auf der katalytischen Wirkung des Molybdäns auf die Peroxoborat-Iodid-Reaktion. Durch Zugabe einer definierten Menge von Ascorbinsäure, die das zunächst entstehende Iod sofort reduziert, wird eine Landolt-Reaktion aufgebaut. Der Endpunkt (Verminderung an Iodid) wird potentiometrisch mit der Iodid-Elektrode indiziert. Zwischen der Zeitdauer bis zum Endpunkt (t in Sekunden) und der Molybdänkonzentration besteht die Beziehung 1/t=4,79 [Mo(VI)]+0,598 im Bereich von 0,5–5,0 M Mo(VI). Wolfram(VI) stört. Molybdän kann nach diesem Verfahren in Meerwasser nach Konzentration am Chelationenaustauscher Chelax-100 bestimmt werden (Standardabweichung 0,52 g/l für 8,62 g Mo/l).

     

1D Polymeric copper(II) azido complexes. Synthesis,spectral and structural studies of [Cu(ethyl isonicotinate)2(N3)2]n and [Cu(methyl isonicotinate)2(NO3)(N3)]n complexes

Two new 1:2 polymeric complexes of copper(II) azide with ethyl isonicotinate (1) and methyl isonicotinate (2) have been synthesized and characterized by spectroscopic and crystallographic methods. The polymeric structure of complex (1) features six coordinated copper centers, a pair of trans-coordinated ligand molecules, and asymmetric ₂-1,1 and ₂-1,3-azido bridges resulting in a 1D chain structure. In complex (2), each copper atom which is located at an inversion center, is coordinated to a pair of trans ligand molecules, to the nitrogen atom of two -1,1-azido ligand and to an oxygen atom of a bridging (-O,O) nitrogen group. The i.r., electronic and e.s.r. spectra of the complexes are reported.     

Redox Properties of Trinuclear Osmium Carbonylhydride Clusters with Unsaturated Ligands

Schemes of redox transformations were proposed for osmium carbonylhydride clusters: trinuclear (-H)Os₃(-CR = CHR')(CO)_{1 0} (R = R' = H, Ph; R = H, R' = Ph), (-H)₂Os₃(₃-L)(CO)₉ (L = C = CHPh, CHCPh), tetranuclear CpMnOs₃ (-CH = CHPh)(-H)(-CO)(CO)_{1 1}, and trinuclear Os₃(₃-C = CHPh)(CO)₉. Two-electron reduction of the trinuclear clusters results in elimination of the unsaturated ligand with preservation of the metal framework.