Separation of some platinum group metal chelates with 8-hydroxyquinoline by various high-performance liquid chromatographic methods

Different HPLC methodologies are employed to evaluate the separation and determination of some platinum metals (Pt, Pd, Ir and Rh) after the formation of 8-hydroxyquinolate chelates. With the aim of reducing the number of steps in treating the samples, the method developed did not include the elimination of excess chelating reagent before the analysis of metal chelates. Reversed-phase (RP), non-aqueous reversed-phase (NARP) and normal-phase (NP) HPLC are compared. The RP-HPLC method only permits the quantitative separation of Rh and Pd from the excess reagent. A silica column can be used to separate Ir and Rh by NP-HPLC. The NARP-HPLC method allows for the effective separation of the four elements tested, but the high detection limit (90 ng) for platinum and the peak width do not favour its application for quantitative measurement. Platinum group metals can be quantitatively separated and determined by NP-HPLC using a cyano column in less than 15 min. The broad linear range of all the elements (between 1 and 500 ng) is superior to that which has been previously reported and the detection limits (1.0 ng for Pt, 0.3 ng for Pd, 1.0 ng for Ir and 0.3 ng for Rh) are slightly lower.     

Application of the zone melting technique to metal chelate systems-IV Concentration of metal-8-hydroxyquinoline chelates in 8-hydroxyquinoline

The zone melting technique has been applied to 8-hydroxyquinoline containing trace amounts of various metal 8-hydroxyquinolates such as the nickel(II), cobalt(II), zinc(II) and copper(II) chelates. The metal chelate in each system was concentrated in the direction of zone travel. The highest concentrating effect was observed in the copper(II) chelate system. The concentration ratio, defined as the fraction of the metal chelate concentrated in the bottom 15% of the column, was determined after the 30th passage. A trace amount of copper ion extracted with a large excess of 8-hydroxyquinoline, was concentrated by means of the zone melting technique. The concentration ratio was 96%.     

Formation of metal chelates in solid state reaction between 8-hydroxyquinoline and carbonates of cadmium and zinc

The solid state reactions between 8-hydroxyquinoline (8-HQ) and CdCO₃ and ZnCO₃ have been studied. The Brounshtein-Ginstling rate equation is followed in both cases. The activation energy for CdCO₃-8-HQ and ZnCO₃-8-HQ are respectively 92.3 ± 3.3 and 86.6 ± 0.6 kJ mole⁻¹. The reaction products were characterized by elemental analysis, X-ray diffraction, and IR studies. Metal (Zn and Cd) carbonates and 8-HQ react in 1:2 molar ratio and the reaction proceeds via surface migration of 8-HQ.     

Capillary gas chromatographic analysis of pyrrolidinedithiocarbamate metal chelates

Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples.     

Thin-layer gel chromatography of 8-hydroxyquinoline metal complexes

Gel chromatographic behavior of 8-hydroxyquinoline (oxine, abbreviated HOx) complexes of zinc, copper, aluminum, gallium and indium has been investigated on thin layers of Styragel 60A and Merckogel OR-PVA 2000 mostly in chloroform and p-dioxan media. Except for the stable Cu(Ox)₂, the other oxinates exhibit either hydration or decomposition in gel-solvent-solute systems, which leads to strong retention or tailing on gel layers. An excess of 8-hydroxyquinoline present in solvents allows the oxinates to be stabilized, so that well-defined compact spots come out and migrate. For the Zn(Ox)₂ the formation of a self-adduct is strongly suggested on the basis of gel chromatographic behavior. Elution with the solvent containing pyridine also yields evidence of the adduct formation of zinc oxinate-nitrogen base.     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Aromatic properties of 8-hydroxyquinoline and its metal complexes

Chelatoaromaticity (aromaticity of chelate complexes) has been recently recognized as an important property influencing the stability of chelate compounds. In this paper, aromaticity of various forms of 8-hydroxyquinoline (anion, neutral molecule, zwitterion and cation) as well as its chelate complexes with magnesium and aluminium ions are investigated. Aromatic properties of these compounds are analyzed using several aromaticity indices based on energetic, geometric, magnetic and electronic physical manifestations of this phenomenon. Results of performed calculations have shown different aromatic properties for the two rings (pyridine and benzene) occurring in the studied ligand. Aromaticity of these rings in metal complexes of 8-hydroxyquinoline is significantly higher than that in corresponding ligand anion. This means that during complexation the aromaticity of the ligand increases and the chelatoaromatic effect stabilizes the studied metal complexes. In contrast, metallocyclic rings of studied metal complexes have non-aromatic properties, and, consequently, the metallocyclic ring is not stabilized by chelatoaromaticity. We conclude that, in the complex, every 8-hydroxyquinoline unit and the metal ion are separated p-electronic systems.      

Liquid adsorption chromatography of chelates : The effect of structure on the thin-layer chromatographic behaviour of chelates

The thin-layer chromatographic behaviour of chelates belonging to different classes is discussed. The major adsorption interactions of chelates are hydrogen bonding between the ligand donor atoms and the surface hydroxyl groups and reactions between the metal atom and the electron-donor active centres of the sorbent. Predominance of either of these general mechanisms depends on the chelate structure and particularly on the coordination saturation of the chelate. Coordination-saturated chelates are retained because of hydrogen bonding, while the metal atom does not participate directly but can influence sorption by affecting the electron density distribution in the chelating ring. Atomic electronegativity is used as a measure of the electron-acceptor ability of the metal. Electronegative atoms located outside the functional group of the chelate can participate in the adsorption either directly or by affecting the proton-acceptor ability of the donor atoms as a result of induction and steric effects. The relationship between chelate retention factors and the parameters characterizing the electron and spatial structure of ligands can be described quantitatively by an equation of the type log [(/R_f)?1] = A + Σσ. In the case of coordination-unsaturated chelates, adsorption interactions with participation of the metal atom predominate, either by ion exchange (with ligand replacement) or by a donor-acceptor mechanism (with introduction of the adsorption centre into the coordination sphere without decomposition). In general, the adsorbability of chelates is directly related to the proton-acceptor ability of donor atoms and the acceptor ability of the metal atom. Classification of chelates by their adsorption interactions is proposed. Recommendations are given for selecting the optimal chelating reagent for the separation of metals by liquid-adsorption chromatography.     

High-performance liquid chromatography of 8-hydroxyquinoline chelates of aluminium and cobalt(III)

Summary The 8-hydroxyquinoline chelates of Co(III) and Al(III) may be separated by high-performance liquid chromatography using a silica column and 5% methanol in chloroform as mobile phase. Using detection at 254 nm, the method provided detection limits of 0.9 ng of Co(III) and 17 ng of Al(III) in a 10 mm³ injection.     

Synthesis and characterization of hemicage 8-hydroxyquinoline chelates with enhanced electrochemical and photophysical properties

A new hexadentate, tripodal 8-hydroxyquinoline ligand (QH3) and its trivalent metal chelates (MQ, M=Al3+, Ga3+, In3+) with hemicage structures have been prepared and the electrochemical and photophysical properties systematically studied. The hemicage structure of the metal complexes was characterized by 1H NMR, indicating a pure facial geometry, in contrast to their uncaged cousins with 8-hydroxyquinoline (Mq3) and 3-methyl-8-hydroxyquinoline (M(3Meq)3), which all exist only as the meridional form in fluid solutions at room temperature. The photoluminescence quantum efficiency for the three hemicage complexes is 1.48, 1.79, and 1.26 times higher for AlQ, GaQ, and InQ, respectively, than their corresponding 3-methyl-8-hydroxyquinoline complexes, likely due to the rigidity of the ligand system, which can efficiently decrease the nonradiative decay of the excited states. The improved electrochemical stability of the hemicage complexes has been demonstrated by cyclic voltammetry, showing an increasingly reversible behavior from InQ to GaQ to AlQ (Ered=-2.15, -2.17, and -2.22 V vs Fc/Fc+ in DMSO). We infer that the degree of reversibility and redox potential result from the metal-ligand bond strength, which is largest in the case of aluminum.     

Polarographic behaviour of metal chelates of o,o'-dihydroxyazo dyes

The nature of complexes between various o,o'-dihydroxyazo dyes and metal ions, and their applications in polarographic chemical analysis, are described and discussed.     

Thermal studies of some divalent metal chelates of 8-mercaptoquinoline

Divalent metal chelates of 8-mercaptoquinoline (8-MQ) were prepared with copper, nickel, cobalt, zinc, lead, iron, cadmium, and mercury. The thermogravimetry and differential thermal analysis of each of the chelates were studied and a thermal stability order of Cd > Co > Ni > Zn > Pb > Hg > Fe > Cu was obtained. This order is compared with the order obtained with 8-hydroxyquinoline (8-HQ) chelates and the relative thermal stability temperatures of the chelate series are discussed in terms of ligand differences.

---

Zusammenfassung Zweiartige Metallchelate von 8-Mercaptochinolinen (8-MQ) wurden mit Kupfer, Nickel, Cobalt, Zink, Blei, Eisen, Cadmium und Quecksilber hergestellt. Die einzelnen Chelate wurden durch Thermogravimetrie und Differentialthermoanalyse untersucht und eine thermische Stabilitätsreihenfolge Cd > Co > Ni > Zn > Pb > Hg > Fe > Cu wurde erhalten. Diese Reihenfolge wird mit der für 8-Hydroxychinolin-Chelate (8-HQ) erhaltenen vergleichen und die relativen Thermostabilitätstemperaturen der Chelatreihen auf Grund der Ligand-Differenzen erörtert.

---

Résumé Des chélates de métaux bivalents de la mercapto-8 quinoléine (8-MQ) ont été préparés avec le cuivre, le nickel, le cobalt, le zinc, le plomb, le fer, le cadmium et le mercure. Chacun d'eux a été étudié par thermogravimétrie et par analyse thermique différentielle et l'ordre suivant de stabilité thermique a été obtenu: Cd > Co > Ni > Zn > Pb > Hg > Fe > Cu. Cet ordre de succession est comparé à celui obtenu pour les chélates de l'hydroxy-8-quinoléine (8-HQ); les stabilités thermiques des différents termes de la série des chélates étudiés sont comparées et examinées en considérant les différences de coordinants.

---

8- , , , , , , . Cd>Co>Ni> >Zn>Pb>Hg>Fe>Cu. , 8- .

---

---

P. W. B. would like to express his appreciation to the Armco Steel Corporation, the National Merit Scholarship Corporation, and the Dow Coming Corporation for their financial assistance during his career at the University of Notre Dame.     

β一二酮类金属螯合物的毛细管气相色谱行为研究

本文用毛细管气相色谱法研究了三氟乙酰丙酮、三氟-5,5-二甲基-2,4-己二酮及三氟-6-甲基-2,4-庚二酮与铍、铝、铬、铜、铁、钴、镍等金属离子生成螯合物的气相色谱行为,对部分螯合物做了碳氢分析及质谱鉴定,用热重量法考察了这些螯合物有适合于气相色谱法的热性质,采用WCOTOV-101,OV-17及SE-54等色谱柱对这些螯合物进行探讨,在不同柱上得到不同组合螯合物的分离。     

Analytic aspects of the chemical behaviour of 8-hydroxyquinoline (oxine)

As a result of the study of the chemical behaviour of some metallo-oxinates it is shown that : 1. A fluorescence test can be used to detect the presence of calcium, magnesium and aluminium in paper. The test is made by spotting the paper or its ash with a solution of oxine and examining tlie spot in the ultraviolet light. 2. A test for a fluoridc can be based on the inability of a qualitative filter paper which has been exposed to hydrogen fluoride to form fluorescent oxinate by spotting with oxine. 3. A test for a cyanide can be based on the liberation of oxine from coppcr(II)oxinate and the detection of the oxine by the formation of fluorescent aluminium oxinate. 4. Some non-fluorescent oxinates are able to quench the fluorescence of aluminium oxinate dissolved in chloroform. 5. The oxinates of aluminium, gallium, and iron(III) have a remarkable resistance to the action of 3N hydrochloric acid, whereas all other oxinates dissolve immediately. An explanation for this behaviour is proposed.     

Thermal behaviour of intercalated 8-hydroxyquinoline (oxine) in montmorillonite clay

The composite montmorillonite-8-hydroxyquinoline (Swy-1-8-HQ) was prepared by two different processes and studied by using thermogravimetric analysis (TG/DTG and DSC), as well as helpful techniques as fluorescence in the UV-visible region and X-ray diffraction. The composites developed fluorescent appearance, however with quantum poor efficiency and they exhibited distinct TG and DSC thermal behavior. The fluorescence data of spectra associated to the TG/DT curves allowed to suggest that the 8-HQ was present in the composites in two different circumstances: 1 - intercalated in the interlayer spaces (Swy-1-8-HQ2), rigidly associated to the substrate feasible as a monolayer with the aromatic rings parallel to the silica layer; and/or, 2 - adsorbed on the surface (Swy-1-8-HQ1), either as a bilayer formation or tilting of the molecules to the silicate layer sheet. All results confirmed above are in agreement with X-ray diffraction patterns, once the interlayer space increases when 8-HQ is incorporated. The experimental results confirm the formation of the composites in agreement with the method used in the preparation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spectra of 8-hydroxyquinoline

This paper reports the electronic absorption spectrum of 8-hydroxyquinoline in the liquid and vapour states in the region 50 000-28 000 cm⁻¹ and the i.r. absorption spectrum in the region 400–4000 cm⁻¹ in KBr and in the neat liquid.     

Chloromethylation of 8-hydroxyquinoline

The reaction of formaldehyde on a hydrochloric acid solution of 8-hydroxyquinoline, in the presence of hydrochloric acid gas, gave a chloromethyl derivative which is probably 7-chloromethyl-8-hydroxyquinoline hydrochloride. This compound is readily converted into the 7-hydroxymethyl derivative in alkaline solution. The 7-chloromethyl compound has been investigated as an analytical reagent for metal ions in acid solutions.