Vacancy Contents in MnZn Ferrites From TG Curves

Expressions for calculating the cation vacancy contents of MnZn ferrites from thermogravimetric curves are presented together with some experimental data. In a single-phase MnZn ferrite synthesized by conventional ceramic procedures, the O₂ evolution accompanying ferrite formation follows the formal equation. Mn²⁺ _σα Zn_σβ Fe³⁺ _2σ(1–γ) [V ]_{σ/4(1–2γ)} O₄ =σ'/σ Mn²⁺ _σ(α–2ϕ) Zn_σβ Fe²⁺ _2σθ Mn³⁺ _2σϕ Fe³⁺ _{2σ(1–γ–θ)} [V ]_{σ/4(1–2γ–3ϕ)} O₄ +σ'φ/2O₂ (g) where α and β denote the MnO and ZnO mole fractions in the primary mixture γ=α+β, θ and ϕ depend on the quantities of Fe²⁺ and Mn³⁺ formed, respectively, φ=θ–ϕ and σ'/σ is a function of the former parameters. Even though the relative amounts of Fe²⁺ /Fe³⁺ and Mn²⁺ /Mn³⁺ remain uncertain, the vacancy content [V ] of the ferrite can be determined because it depends on φ alone, which is related to the change in mass of the sample as the synthesis takes place through the equation φ=(1.5–γ) μ_β /μ_O2 (1–m _f /m _i ) Here, m _i and m _f are the masses of the sample before and after O₂ evolution, μ_B is the formula mass of the ferrite and μ_O2 is the O₂ molar mass. Practically vacancy-free single-phase MnZn ferrite samples were obtained by sintering in air at 1250°C and cooling in pure N₂ . This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoelectric power studies on MgO-stabilized β″-alumina

A study of the temperature dependence of thermopower is known to yield auxiliary information about the electronic conductivity of a mixed conductor. In light of the above, thermoelectric power (TEP) measurements were made on MgO-stabilized β″-alumina over the temperature range from 773 to 1223 K under conditions of different sodium activities in the ambient in order to substantiate the existing information on the electronic conductivity of sodium beta alumina (SBA). A mixture of Na _x Si _m O_{2 m + x /2} and SiO₂ in an environment of fixed served as electrodes reversible to Na⁺. The heat of transport obtained using the thermopower data at higher temperatures (973–1223 K) was in fair agreement with the activation energy of electrical conduction determined by other studies like impedance measurements and molecular dynamics simulation. It could be inferred from these results that there is negligible electronic conductivity in SBA under the conditions of measurement. The average TEP for SBA was determined to be 700–800 μV/K and the partial molar entropy of Na⁺ in SBA was found to be ~98 J mol^–1 K^–1. Electronic Publication     

Complexes of Zr<Superscript>IV</Superscript> and Hf<Superscript>IV</Superscript> with monolacunary Keggin-and Dawson-type anions

The reactions of the tetranuclear hydroxo complexes [M₄(μ₂-OH)₈(H₂O)₁₆]⁸⁺ (M = Zr or Hf) with the lacunary Keggin-type ([α-PW₁₁O₃₉]⁷⁻) and Dawson-type ([α ₂-P₂W₁₇O₆₁]¹⁰⁻) phosphotungstates in aqueous solutions produce the sandwich polyoxometalate complexes [M(α-PW₁₁O₃₉)₂]¹⁰⁻ (M = Zr (1) or Hf (2)) and [M(α ₂-P₂W₁₇O₆₁)₂]¹⁶⁻ (M = Zr (3) and Hf (4)). The complexes were isolated and structurally characterized as salts with potassium and dimethylammonium cations. The zirconium and hafnium atoms have a square antiprismatic coordination environment (coordination number is 8). In all complexes, the mutual arrangement of the ligands corresponds to the syn isomer. Hafnium complexes 2 and 4 are the first structurally characterized polyoxometalate complexes of this metal. The structures of the resulting compounds were confirmed also by ³¹P NMR spectroscopy in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 214–218, February, 2007.     

Synthesis,structure, and physicochemical properties of the Cr(<Emphasis Type="Italic">iso</Emphasis>-Bu<Subscript>2</Subscript>PS<Subscript>2</Subscript>)<Subscript>3</Subscript> chelate compound

A paramagnetic (μ_ef = 3.86 BM) complex Cr(i-Bu₂PS₂)₃ (I) has been synthesized. Single crystals I were grown, and the crystal structure of the compound was determined from X-ray diffraction data (X8 APEX diffractometer, MoK _α radiation, 4516 F _hkl , R = 0.0604). Monoclinic crystals, space group P2₁/n, unit cell parameters a = 14.2665(5) Å, b = 11.4400(4) Å, c = 23.1299(8) Å, β = 90.245(1)°, V = 3775.0(2) ų, Z = 4, d _calc = 1.196 g/cm³. The structure is based on discrete mononuclear molecules. The coordination polyhedron of the Cr atom is a distorted S₆ octahedron formed from the S atoms of three cyclic bidentate ligands — i-Bu₂PS ₂ ⁻ ions. Electron spectroscopy data correspond to the octahedral structure of the CrS₆ chromophore. Original Russian Text Copyright ? 2007 by E. A. Sankova, L. A. Glinskaya, T. E. Kokina, R. F. Klevstova, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 2, pp. 374–378, March–April, 2007.     

Cloning, expression, and characterization of thermostable region of amylopullulanase gene from Thermoanaerobacter ethanolicus 39E

The bifunctional activities of α-amylase and pullulanase are found in the cloned recombinant amylopullulanase. It was encoded in a 2.9-kb DNA fragment that was amplified using polymerase chain reaction from the chromosomal DNA of Thermoanaerobacter ethanolicus 39E. An estimated 109-kDa recombinant protein was obtained from the cloned gene under the prokaryotic expression system. The optimum pH of the recombinant amylopullulanase was 6.0. The most stable pH for the α-amylase and pullulanase activity was 5.5 and 5.0, respectively. The optimum temperature for the α-amylase activity was 90°C, while its most stable temperature was 80°C. Regarding pullulanase activity, the optimum temperature and its most stable temperature were found to be 80 and 75°C, respectively. Pullulan was found to be the best substrate for the enzyme. The enzyme was activated and stabilized by the presence of Ca²⁺, whereas EDTA, N-bromosuccinimide, and α-cyclodextrin inhibited its bifunctional activities. A malto-2–4-oligosac-charide was the major product obtained from the enzymatic reaction on soluble starch, amylose, amylopectin, and glycogen. A single maltotriose product was found in the pullulan hydrolysis reaction using this recombinant amylopullulanase. Kinetic analysis of the enzyme indicated that the K _m values of α-amylase and pullulanase were 1.38 and 3.79 mg/mL, respectively, while the V _max values were 39 and 98 μmol/(min · mg of protein), respectively.     

Synthesis and crystal and molecular structure of the mixed-ligand coordination compound ZnPhen(n-C4H9OCS2)2

A mixed-ligand complex ZnPhen(n-BuOCS₂)₂ has been synthesized. The structure of the compound was solved by X-ray diffractometry (X8 APEX diffractometer, MoK _α radiation, 4254 F _hkl , R = 0.0448). Triclinic crystals with the parameters a = 9.4464(3) Å, b = 11.0279(4) Å, c = 13.6528(6) Å;α = 106.940(1)°, β = 98.382(1)°, γ = 106.347(1)°; V = 1264.72(8) ų; Z = 2, space group 1. P1ˉ. The structure consists of discrete mononuclear molecules. The polyhedron of the Zn atom is a trigonal bipyramid N₂S₃ formed by coordination of the N atoms of the bidentate Phen molecules and the sulfur atoms of the monodentate and cyclic bidentate xanthate ligands. Dimer assemblies are formed in the structure due to π-π interactions of Phen molecules. Original Russian Text Copyright ? 2006 by R. F. Klevtsova, T. G. Leonova, L. A. Glinskaya, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 6, pp. 1189–1194, November–December, 2006.     

Effect of selenium oxidation state on cadmium translocation in chamomile plants

Syntheses and spectral characteristics of cadmium(II) compounds (CdSeO₄, CdSeO₃, and Cd(NCSe)₂(nia)₂) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)₂(nia)₂, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)₂(nia)₂ on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 μmol dm⁻³) Cd(NCS)₂(nia)₂ affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 μmol dm⁻³ and 60 μmol dm⁻³ significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF) and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values determined for Cd accumulation in shoots were obtained with CdSeO₄. Substitution of S with Se in the Cd(NCX)₂(nia)₂ (X = Se or S) caused an increase of Cd translocation into the shoots. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Thermal and Spectral Behaviour of 5-chloro-2-methoxybenzoates of Heavy Lanthanides and Yttrium

5-Chloro-2-methoxybenzoates of heavy lanthanides and yttrium were obtained as di- or tetrahydrates with a metal to ligand ratio of 1:3 and general formula: Ln(C₈H₆ClO₃)₃⋅nH₂O, where n=2 for Ln=Tb, Dy, Y and n=4 for Ln=Ho, Er, Tm, Yb, Lu. The complexes were characterized by elemental analysis, IR and FIR spectra, thermogravimetric studies, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical, bidentate, chelating ligand. All complexes are polycrystalline compounds. Their thermal stabilities were determined in air and in nitrogen atmospheres. When heated they dehydrate to form anhydrous salts which next in air are decomposed to the oxides of the respective metals while in nitrogen to the mixtures of carbon and oxides or carbon and oxychlorides of respective metals. The complexes are more stable in air than in nitrogen. The solubilities of yttrium and heavy lanthanide 5-chloro-2-methoxybenzoates in water at 293 K are of the order of 10^–3 mol dm^–3 The magnetic moments of the complexes were determined over the range 77–298 K. They obey the Curie–Weiss law. The values of μ_eff calculated for all compounds are close to those obtained for Ln³⁺ by Hund and Van Vleck. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pseudohexagonal motif of the arrangement of compex anions in the structure of [Ru(NH3)5Cl]2[Re6S8(CN)6]·3H2O

The [Ru(NH₃)₅Cl]₂[Re₆S₈(CN)₆]·3H₂O salt was obtained; its crystal structure was analyzed: a = 10.7713(9) Å, b = 13.9602(11) Å, c = 14.7956(11) Å, α = 91.961(3)°, β = 109.985(3)°, γ = 110.030(3)°, V = 1935.3(3) ų, space group P1ˉ, Z = 2, d _calc = 3.441 g/cm³. In the cluster anion, the Re-Re distances lie in the range from 2.594 Å to 2.612 Å. For two crystallographically independent complex cations, Ru-N_av is 2.105 Å, and Ru-Cl_av 2.329 Å. A pseudohexagonal motif of the structure was found. Original Russian Text Copyright ? 2008 by K. V. Yusenko, I. A. Baidina, E. A. Shusharina, and S. A. Gromilov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 1, pp. 178–181, January–February, 2008.     

Determination of Human Alpha-Fetoprotein (AFP) by Solid Substrate Room Temperature Phosphorescence Enzyme-Linked Immune Response Using Luminescent Nanoparticles

Luminescent nanoparticles of silicon dioxide (SiO₂) containing fluorescein isothiocyanate (FITC) with a particle size of 20 nm were synthesized using the Sol–Gel method (abbreviated FITC–SiO₂). FITC–SiO₂ nanoparticles whose surfaces are modified (FITC–SiO₂–S–CH₂COOH) can emit strong and stable solid substrate room temperature phosphorescence (SS-RTP) on acetyl cellulose membranes. When the original color-producing agent (R) in the enzyme-linked immunosorbent assay (ELISA) kits for determination of alpha-fetoprotein (AFP) was substituted with (FITC–SiO₂–S–CH₂COOH), the system maintained good FITC–SiO₂ phosphorescence properties. Furthermore, the phosphorescence intensity enhanced markedly after the ELISA reaction. The relationship between the phosphorescence intensity and the content of AFP obeyed Beer’s law. Based on the facts stated above, a new method for the determination of human AFP by SS-RTP-ELISA (using the luminescent nanoparticle as marker) was established. The linear range of this method is 0.040–16.0 pg of human AFP per spot (sample volume: 0.40 μL spot⁻¹, corresponding concentration: 0.10–40.0 ng mL⁻¹). The regression equation of the working curve is ΔIp = −6.289+18.075 m_AFP (pg spot⁻¹) (r = 0.9960, n = 6). The detection limit (LD) of this method calculated by 3 S_b/k is 6.7 fg spot⁻¹ (corresponding concentration: 17 ng L⁻¹). Compared to the ELISA method using a traditional color-producing agent, the new method exhibited a 34.8 times higher sensitivity and a wider linear range. The method has been successfully applied to the determination of human AFP in serum.     

High-Performance Liquid Chromatographic Determination of Isofraxidin in Rat Plasma

For the first time a high-performance liquid chromatographic (HPLC) method, with liquid-liquid extraction and ultraviolet (UV) absorbance detection, has been developed for quantification of isofraxidin in rat plasma. The analysis was performed on a Diamonsil C₁₈ column (200 mm × 4.6 mm i.d., 5 μm particle size) with acetonitrile–0.05% phosphoric acid, 26:74 (v/v), as isocratic mobile phase. The linear range was 0.05–8.0 μg mL⁻¹ and the lower limit of quantification was 0.05 μg mL⁻¹. The intra and inter-day relative standard deviation (RSD) for measurement of 0.25, 2.0, and 6.0 μg mL⁻¹ quality-control (QC) samples ranged from 5.7 to 6.4% and from 6.3 to 7.9%, respectively. Accuracy, as relative error (RE), was from ±5.8% to ±7.3%. The method was validated for specificity, accuracy, and precision and was successfully used in a pharmacokinetic study of isofraxidin in rat plasma after administration of Ciwujia extract.     

A resonance light scattering method for determination of DNA using Ru(bpy)2PIP(V)2+

A novel method for DNA detection is proposed that is based on the enhancement of resonance light scattering (RLS) of Ru(bpy)₂PIP(V)²⁺ at pH 2.7. Under optimum conditions, good linear relationships were obtained in the wide concentration range of 16–5120 ng mL⁻¹. The linear equation is I _RLS = 13.15 + 171.4 c (μg mL⁻¹), the correlation coefficient (r) is 0.9999. The detection limit of calf thymus DNA is 5.02 ng mL⁻¹. Plasmid DNA extracted from bacillus subtilis was determined by the method with satisfactory results.     

Dioxygen reactivity of laccase

A study was carried out on the dioxygen reactivity of the laccases from Trametes villosa, Rhizoctonia solani, Myceliophthora thermophila, Scytalidium thermophilum, and Coprinus cinereus. At pH 5.5, these laccases showed an apparently constant K _m (about 20–50 μM) for O₂ with either 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) or methyl syringate as the reducing substrate, in contrast to the k _cat , which varied up to 100-fold. O₂ reactivity of the Trametes and Myceliophthora laccases was also studied at various pH and NaF concentrations. The apparent K _m of Trametes and Myceliophthora laccases varied only slightly when pH changed from 3.0 to 8.0 or when the laccases were inhibited by F⁻ at pH 5.5, although the apparent k _cat were more significantly affected by both factors. The dependence of the apparent K _m on the source of laccase, pH, and F⁻ inhibition suggested that the fungal laccases might have a conserved O₂ pocket and that the F⁻ or OH⁻ inhibition might affect the O₂ reduction step (k _cat ) more than the O₂ binding step (K _m ) under steady-state conditions.     

Crystal and molecular structure and properties of [Ni(4-NH2Py)2(iso-Bu2PS2)2] and [Co(4-NH2Py)(iso-Bu2PS2)2]

The interaction of the Co(iso-Bu₂PS₂)₂ chelate with 4-NH₂Py afforded a paramagnetic complex [Co(4-NH₂Py)(iso-Bu₂PS₂)₂] (μ_eff = 4.53 BM). Single crystals of [Ni(4-NH₂Py)₂(iso-Bu₂PS₂)₂] (I) and [Co(4-NH₂Py)(iso-Bu₂PS₂)₂] (II) were grown and used for X-ray diffraction investigation (X8 APEX diffractometer, MoK _α radiation). Crystals I are monoclinic with unit cell parameters a = 12.5336(5) Å, b = 9.4356(4) Å, c = 16.4095(6) Å; β = 111.351(1)°; V = 1807.4(1) ų; Z = 2, ρ = 1.223 g/cm³, space group P2₁/n. Crystals II are triclinic with unit cell parameters a = 8.7572(4) Å, b = 9.6934(6) Å, c = 18.665(1) Å; α = 79.374(2)°, β = 87.049(2)°, γ = 75.640(2)°; V = 1508.6(1) ų; Z = 2, ρ = 1.259 g/cm³; space group . The structures of I and II are formed by isolated mononuclear molecules. The coordination unit is NiN₂S₄ (octahedron) in I and CoNS₄ (tetragonal pyramid) in II. The 4-NH₂Py molecule is coordinated through the N atom of the heterocycle. Electronic spectroscopy data for II agree with the symmetry of the NS₄ polyhedron found by X-ray diffraction (XRD) analysis. The noncoordinated amine groups link the complex molecules via N-H...S hydrogen bonds. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 6, pp.1072–1080, November–December, 2005. Original Russian Text Copyright ? 2005 by T. E. Kokina, L. A. Glinskaya, E. A. Sankova, R. F. Klevtsova, and S. V. Larionov     

Molecular structure of 2-methoxy-4-pyrrolidinyl-6-trinitromethyl-1,3,5-triazine

An X-ray diffraction study of 2-methoxy-4-pyrrolidinyl-6-trinitromethyl-1,3,5-triazine was carried out. The crystals are triclinic; C₉H₁₁N₇O₇; M = 329.25; a = 8.536(1) Å, b = 9.378(2) Å, c = 9.7401(8) Å; α = 79.13(1)°, β = 73.974(8)°; γ = 72.76(1)°; V = 710.8(2) ų, d _c = 1.54 g/cm³, Z = 2, space group P1ˉ. The molecule on the whole is planar, except the pyrrolidine ring, which has a twist conformation. No significant π-π interactions and hydrogen bonds of C-H⋯N or C-H⋯O type were found in the crystal, and the molecule packing is stabilized only due to van der Waals interactions. Original Russian Text Copyright ? 2008 by V. V. Bakharev, A. A. Gidaspov, I. A. Litvinov, and E. V. Mironova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 1, pp. 187–189, January–February, 2008.     

Crystal structure of bis(semicarbazido)copper(II) nitrate [Cu(NH<Subscript>2</Subscript>NHC(O)NH<Subscript>2</Subscript>)<Subscript>2</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

The crystal structure of bis(semicarbazido)copper(II) nitrate [Cu(NH₂NHC(O)NH₂)₂](NO₃)₂ has been studied by X-ray diffraction. Monoclinic crystals, a = 6.835(2) Å, b = 7.733(2) Å, c = 10.320(3) Å, β = 105.701(3)°, V = 525.1(2) ų, space group P2₁/c, Z = 2, d _msd = 2.136 g/cm³, μ(MoK _α) = 2.143 mm⁻¹. The structure was solved with the program for automatic analysis of Patterson’s function and refined by full-matrix least squares in an anisotropic approximation for all non-hydrogen atoms using 753 independent reflections; R ₁ = 0.0203. The square environment of the Cu atom is formed from the amino nitrogen atoms of the hydrazine fragments and the C=O oxygen atoms of the two semicarbazide bidentate molecules (Cu-N 1.928 Å, Cu-O 1.999 Å). The axial positions are occupied by the O atoms of the NO ₃ ⁻ outer-spheric anions (Cu-O 2.505 Å). In the structure, the complex cations and the NO ₃ ⁻ anions are linked into a framework by N-H...O type hydrogen bonds. Original Russian Text Copyright ? 2007 by G. V. Romanenko, Z. A. Savelieva, and S. V. Larionov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 2, pp. 370–373, March–April, 2007.     

Microdialysis sampling and chemiluminescence detection for in vivo and real-time study of the lead metabolism in rabbit blood

The chemiluminescence (CL) system K₂MnO₄-luminol is shown to be useful for the determination of lead(II). The method is based on the catalytic effect of Pb(II) on the CL reaction. The linear range was 3 × 10⁻³–9 × 10⁻¹ mg L⁻¹ (r = 0.9971) and the relative standard deviation (R.S.D.) for 5 × 10⁻² mg L⁻¹ Pb(II) measurement was 0.7% (n = 11). The detection limit was 3 × 10⁻⁴ mg L⁻¹ (3σ) Pb(II). Based on this, an in vivo, on-line, real-time analytical system for monitoring the metabolism of free lead(II) in rabbit blood was developed. A microdialysis probe, implanted in the vein of a rabbit, was perfused with perfusate at a flow rate of 5 μL min⁻¹. The concentration of free lead(II) in the dialysate was determined on-line with a flow-injection CL system. This system included microdialysis sampling, on-line separation and chemiluminescence detection. The concentration-time curve of lead(II) was in accordance with the one-compartmental open model, T_1/2 (elimination half-life), T_max (peak time) and C_max (peak concentration) were 37.77 min, 85.20 min and 0.137 mg L⁻¹, respectively.     

Phosphorus in biological standards and samples by thermal neutron irradiation and β-counting

A nondestructive NAA method based on the reaction ³¹P(n,γ)³²P (T _1/2 = 14.23 d) has been developed where the product nucleus, a pure β-emitter with end point energy 1.71 MeV is measured by using an end window G.M. counter and an Al filter of 27 mg·cm⁻². ³²P was identified by measuring E _β using Feather’s analysis and its half-life was found to be 15.3±0.2 days in standard reference materials (SRMs) and samples. For most reference materials (RMs) from NIST (USA) and IAEA (Vienna), our values agree within ±5% of the certified values. A variety of biological samples have also been analyzed and our values are in the range; medicinal herbs (n = 43), 0.29–5.23 mg/g; bhasmas (n = 19), 0.09–51.4 mg/g; vegetables (n = 8), 1.85–5.73 mg/g; lentils (n = 6), 2.1–5.5 mg/g; flours (n = 6), 1.3–3.3 mg/g; vegetarian diet (n = 5), 2.41–2.90 mg/g; fish (n = 43), 3.61–36.8 mg/g; human and animal milk (n = 6), 1.24–7.95 mg/g; commercial milk powders (n = 14), 2.76–11.9 mg/g; water from various sources (n = 14), 1–417 μg/l; human and animal blood (n = 9), 1.00–15.0 mg/g; cancerous and healthy breast tissue (n = 60), 1.00–8.63 mg/g; human hair (n = 43), 0.12–5.81 mg/g, where n is the number of samples analyzed. The method is simple, fast, and nondestructive and provides data within ±5% error limit with a detection limit of 0.1 mg/g.     

Pyrogallol Immobilized Amberlite XAD-2: A Newly Designed Collector for Enrichment of Metal Ions Prior to their Determination by Flame Atomic Absorption Spectrometry

 Pyrogallol is covalently linked with the benzene ring of Amberlite XAD-2, through an azo (–N=N–) spacer group and the resulting new polymer characterized by elemental analyses, thermogravimetric analysis (TGA) and infrared (IR) spectra. It has been used for separation and preconcentration of Cu(II), Cd(II), Co(II), Ni(II), Pb(II), Zn(II), Mn(II), Fe(III) and U(VI) prior to their determination by flame atomic absorption spectrometry (FAAS) or fluorimetry (for U(VI) only). The pH ranges for quantitative sorption are 5.5–6.5, 5.5–7.5, 5.5–7.0, 5.5–7.0, 5.5–6.5, 5.5–6.5, 5.5–8.0, 5.5–6.2 and 5.5–6.2, respectively, for the nine metal ions, which can be desorbed (recovery 90–99%) with 4 mol L⁻¹ HNO₃ or HCl. The sorption capacity of the resin has been found to be in the range 4.10 to 6.71 mg of metal g⁻¹ of dry resin. The loading half time (t_1/2) was ≤3.3 min for all the metal ions. The effects of NaF, NaCl, NaNO₃, Na₂SO₄, and Na₃PO₄ on the sorption of these metal ions (0.2 μg mL⁻¹) are reported. The Ca(II) and Mg(II) are tolerable up to a concentration level of 40–400 and 25–240 μg mL⁻¹, respectively. The enrichment factor for Cu(II), Cd(II), Co(II), Ni(II), Pb(II), Zn(II), Mn(II), Fe(III) and U(VI) has been found to be 65, 40, 65, 120, 25, 160, 120, 140, and 70 (concentration level 2–25 ng mL⁻¹), respectively. The limit of detection for these nine metal ions is 5.0, 1.3, 5.0, 4.0, 25.0, 0.5, 1.0, 2.0 and 1.0 ng mL⁻¹, respectively. After enrichment on the present matrix, the flame AAS method has been applied to determine these metal ions (except U) in river water samples (RSD ≤ 7%) and well water (RSD ≤ 8%). Uranium present in well water samples has been enriched on the present matrix and determined by a fluorimetric method (RSD ≤ 6%). The cobalt present in pharmaceutical vitamin tablets was also preconcentrated with the aid of the present chelating resin and determined by FAAS to be 1.93 μg g⁻¹ (RSD ∼4%). Received May 16, 2000. Revision April 3, 2001.     

A simple linear sweep voltammetric method for the determination of double-stranded DNA with malachite green

In pH 3.5 Britton—Robinson buffer solution double-stranded (ds) DNA can react with malachite green (MG) to form an interaction complex, which resulted in the decrease of the electrochemical response of MG, MG had a well-defined second-order derivative linear sweep voltammetric peak at −0.73 V (vs. SCE). After the addition of dsDNA into MG solution, the reductive peak current decreased with the positive shift of peak potential, which was the typical characteristic of intercalation. Based on the interaction, an indirect electrochemical determination method for dsDNA was established. The optimum conditions for the reaction were investigated and there were little or no interferences from the commonly coexisting substances. The decrease of peak current was linear with the concentration of dsDNA over the range of 0.8–12.0 μg cm⁻³ with the linear regression equation as ΔI _p″/nA = 91.70 C/(μg cm⁻³) + 74.55 (n = 10, γ = 0.990). The detection limit was calculated as 0.46 μg cm⁻³ (3σ). The method had high sensitivity and was further applied to the dsDNA synthetic samples with satisfactory result. The interaction mechanism was discussed with the intercalation of DNA-MG to form a supramolecular complex and the stoichiometry of the supramolecular complex was calculated by electrochemical method with the binding number 3 and the binding constant 2.35 × 10¹⁵ (mol dm⁻³)⁻³.