Influence of hydrofluoric acid on extraction of thorium using a commercially available extraction chromatographic resin

The dependence of Th recovery on hydrofluoric acid (HF) concentration in nitric acid (HNO₃) solutions (1–5 mol/dm³) containing 1 × 10⁻⁶ mol/dm³ of Th and various concentrations of HF and the elution behavior were studied using a commercially available UTEVA (for uranium and tetravalent actinide) resin column. Thorium recovery decreased with an increase in HF concentration in the sample solutions. The concentration of HF at which Th recovery started to decrease was ∼1 × 10⁻⁴ mol/dm³ in 1 mol/dm³ HNO₃ solution, ∼1 × 10⁻³ mol/dm³ in 3 mol/dm³ HNO₃ solution, and ∼1 × 10⁻² mol/dm³ in 5 mol/dm³ HNO₃ solution. When Al(NO₃)₃ (0.2 mol/dm³) or Fe(NO₃)₃ (0.6 mol/dm³) was added as a masking agent for F⁻ to the Th solution containing 1 × 10⁻¹ mol/dm³ HF and 1 mol/dm³ HNO₃, Th recovery improved from 1.4 ± 0.3% to 95 ± 5% or 93 ± 3%. Effective extraction of Th using UTEVA resin was achieved by selecting the concentration of HNO₃ and/or adding masking agents such as Al(NO₃)₃ according to the concentration of HF in the sample solution.     

Crystallization and microstructure of Li2O-Al2O3-SiO2 glass containing complex nucleating agent

The crystallization and microstructure of Li₂O-Al₂O₃-SiO₂ (LAS) glass ceramic with complex nucleating agents (TiO₂ + ZrO₂ + P₂O₅ +/or F⁻) are investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the effects of P₂O₅ and F⁻ on the crystallization of LAS glass are also analyzed. The introduction of both P₂O₅ and F⁻ promotes the crystallization of LAS glass by decreasing the crystallization temperature and adjusting the crystallization kinetic parameters, allows a direct formation of β-spodumene without the transformation of LiAl(SiO₃)₂ into β-spodumene and as a result, increases the crystal size and crystallinity of LAS glass ceramic.     

Gamma radiation induced synthesis of gold nanoparticles in aqueous polyvinyl pyrrolidone solution and its application for hydrogen peroxide estimation

Gold nanoparticles (Au nps) have been synthesized in aqueous solution of polyvinyl pyrrolidone (PVP) by gamma radiolysis from HAuCl₄·3H₂O precursor and in presence of small concentrations of Ag⁺, 2-propanol and acetone. The effect of different experimental parameters, such as concentration of reactant, molecular weight of PVP on nanoparticle formation was studied. TEM image confirmed that spherical Au nps were formed when PVP of molecular weight 360,000 Da was used as capping agent. H₂O₂ is a reactant in the enzyme catalyzed reaction of o-phenylene diamine (o-PDA). The reaction product has a weak absorption in the yellow region of the spectrum. When this product interacts with Au nps, it leads to enhancement of the absorption peak. The nanoparticles synthesized by radiation method were used for estimation of H₂O₂. The absorbance value of this peak at λ_max was observed to change with H₂O₂ concentration, which was monitored for estimation of H₂O₂. The response is linear in the range of 2.5×10⁻⁶ mol dm⁻³ to 2×10⁻⁴ mol dm⁻³ and 1×10⁻⁷ mol dm⁻³ to 3×10⁻⁶ mol dm⁻³ H₂O₂ in two separate sets of experimental parameters with detection limit 1×10⁻⁷ mol dm⁻³.     

K2B12F12: A rare A2X structure for an ionic compound at ambient conditions

The anhydrous salt K₂B₁₂F₁₂ crystallized from aqueous solution and its structure was determined by single crystal X-ray diffraction. The Ni₂In-type structure it exhibits is rare for an A₂X ionic compound at 25 °C and 1 atm., consisting of an expanded hexagonal close-packed array of B₁₂F₁₂²⁻ centroids (cent?cent distances: 7.204-8.236 Å) with half of the K⁺ ions filling all of the O_h holes and half of the K⁺ ions filling all of the D_3h trigonal holes in the close-packed layers that are midway between two “empty” T_d holes. The structure is also unusual in that the bond-valence sum for the K⁺ ions in O_h holes is less than or equal to 0.73 (the bond-valence sum for the other type of K⁺ ion is 1.16). A variation of the Ni₂In structure is exhibited by the previously published monohydrate Cs₂(H₂O)B₁₂F₁₂, for which an improved structure is also reported here. For K₂B₁₂F₁₂: monoclinic, C2/c, a = 8.2072(8), b = 14.2818(7), c = 11.3441(9) Å, β = 92.832(5)°, Z = 4, T = 120(2) K. For Cs₂(H₂O)B₁₂F₁₂: orthorhombic, P2₁2₁2₁, a = 9.7475(4), b = 10.2579(4), c = 15.0549(5) Å, Z = 4, T = 110(1) K.     

Reaction between carbon dioxide and elementary fluorine

Reactions between carbon dioxide and fluorine were examined at temperatures of 303-523 K under various pressure and mixture ratios of both gases. Reactions were carried out similarly under the existence of NaF, CsF and EuF₃.After the reaction, fluorine was removed and the reaction products were analyzed using FT-IR, GC/FT-IR and GC/MS. The major products were CF₃OF, COF₂, CF₄ and CF₂(OF)₂.The best yield of COF₂ was 11.1% under the reaction condition of CO₂/F₂ = 76 kPa/76 kPa with temperature of 498 K for 72 h in a direct reaction. The formation rate of COF₂ in the direct reaction was estimated as 0.232 dm³ mol⁻¹ h⁻¹ under the reaction conditions of CO₂/F₂ = 76 kPa/76 kPa, at 498 K. In the presence of CsF, it was estimated as 1.88 dm³ mol⁻¹ h⁻¹ at CO₂/F₂ = 76 kPa/76 kPa at 498 K.The activation energy of the COF₂ formation in the direct reaction was estimated as 45.7 kJ mol⁻¹ at CO₂/F₂ = 76 kPa/76 kPa at 498 K. In addition, 24.2 and 38.9 kJ mol⁻¹ were evaluated at CO₂/F₂ = 76 kPa/76 kPa at 498 K, respectively, in the presence of CsF and EuF₃.     

Comparison of microwave-assisted digestion procedures for total trace element content determination in calcareous soils

The aim of the study was to determine total trace (Cd, Co, Cr, Cu, Mn, Pb and Zn) and major (Al and Fe) element concentrations in calcareous soils using microwave-assisted digestion procedures. The literature showing lack of consensus regarding digestion procedures and unsatisfying recoveries for calcareous materials, four procedures using various acid combinations (HCl, HNO₃, H₂O₂, HF) and volumes were tested using a certified reference material (CRM 141R) and natural calcareous soil samples. Digests were analysed by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Repeatability (R.S.D. <5%) and recoveries (82-116%) showed that the procedures were precise and accurate for most elements. Five calcareous soil samples from a Champagne vineyard plot were, then, subjected to these procedures. In calcareous materials, the presence of HF resulted in Al being severely underestimated (recovery <5%) and Co overestimated (recovery >124%) due to complex formation or spectrochemical interferences, respectively. As digestion was not significantly influenced by the addition of H₂O₂, the procedure corresponding to Aqua regia (HCl-HNO₃) appeared as the best compromise and was selected for further multielemental environmental studies on calcareous materials, even if the absence of HF could lead to incomplete digestion of accessory silicate minerals. Results for a vineyard plot showed that the soils were contaminated (3.65 mg kg⁻¹ Cd, 67 mg kg⁻¹ Cr, 278 mg kg⁻¹ Cu, 143 mg kg⁻¹ Pb and 400 mg kg⁻¹ Zn) as a consequence of urban waste and copper-treatment applications.     

Segregated aromatic π-π stacking interactions involving fluorinated and non-fluorinated benzene rings: Cu(py)2(pfb)2 and Cu(py)2(pfb)2(H2O) (py = pyridine and pfb = pentafluorobenzoate)

The syntheses, physical characterization and crystal structures of two new molecular copper(II) complexes of composition [Cu(C₅H₅N)₂(C₇F₅O₂)₂] (1) and [Cu(C₅H₅N)₂(C₇F₅O₂)₂(H₂O)] (2) (C₅H₅N = py = pyridine and C₇F₅O₂⁻ = pfb = pentafluorobenzoate) are reported. Single-crystal X-ray structure determinations revealed that in 1, the Cu²⁺ ion, which lies on a crystallographic inversion centre, is coordinated to two py molecules and two oxygen atoms from two monodentate pfb anions, resulting in a trans-CuN₂O₂ square planar geometry. In 2, the Cu²⁺ ion is also coordinated to two py and two pfb species in addition to a water molecule in the apical site of a distorted CuN₂O₃ square pyramid. In the crystal packing, both 1 and 2 show segregated aromatic π-π stacking interactions in which (py + py) and (pfb + pfb) ring-pairings are seen, but no (py + pfb) pairings occur. Crystal data: 1: C₂₄H₁₀CuF₁₀N₂O₄, M_r = 643.88, space group , a = 8.0777 (3) Å, b = 8.0937 (3) Å, c = 10.5045 (5) Å, α = 90.916 (3)°, β = 93.189 (2)°, γ = 118.245 (3)°, V = 603.36 (4) Å³, Z = 1. 2: C₂₄H₁₂CuF₁₀N₂O₅, M_r = 661.90, space group , a = 7.5913 (5) Å, b = 15.6517 (6) Å, c = 21.1820 (14) Å, α = 95.697 (4)°, β = 94.506 (2)°, γ = 91.492 (4)°, V = 2495.2 (3) Å³, Z = 4.     

A chemiluminescence biochemical oxygen demand measuring method

A new chemiluminescence biochemical oxygen demand (BOD_CL) determining method was studied by employing redox reaction between quinone and Baker's yeast. The measurement was carried out by utilizing luminol chemiluminescence (CL) reaction catalyzed by ferricyanide with oxidized quinone of menadione, and Saccharomyces cerevisiae using a batch-type luminometer. In this study, dimethyl sulfoxide was used as a solvent for menadione. After optimization of the measuring conditions, the CL response to hydrogen peroxide in the incubation mixture had a linear response between 0.1 and 100 μM H₂O₂ (r² = 0.9999, 8 points, n = 3, average of relative standard deviation; R.S.D._av = 4.22%). Next, a practical relationship between the BOD_CL response and the glucose glutamic acid concentration was obtained over a range of 11-220 mg O₂ L⁻¹ (6 points, n = 3, R.S.D._av 3.71%) with a detection limit of 5.5 mg O₂ L⁻¹ when using a reaction mixture and incubating for only 5 min. Subsequently, the characterization of this method was studied. First, the BOD_CL responses to 16 pure organic substances were examined. Second, the influences of chloride ions, artificial seawater, and heavy metal ions on the BOD_CL response were investigated. Real sample measurements using river water were performed. Finally, BOD_CL responses were obtained for at least 8 days when the S. cerevisiae suspension was stored at 4 °C (response reduction, 69.9%; R.S.D. for 5 testing days, 18.7%). BOD_CL responses after 8 days and 24 days were decreased to 69.9% and 35.8%, respectively, from their original values (R.S.D. for 8 days involving 5 testing days, 18.7%).     

Thermochemistry of NaRb[B4O5(OH)4]·4H2O

The enthalpies of solution of NaRb[B₄O₅(OH)₄]·4H₂O in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of RbCl in aqueous (hydrochloric acid + boric acid + sodium chloride) were determined. From these results and the enthalpy of solution of H₃BO₃ in approximately 1 mol dm⁻³ HCl(aq) and of sodium chloride in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(5128.02 ± 1.94) kJ mol⁻¹ for NaRb[B₄O₅(OH)₄]·4H₂O was obtained from the standard molar enthalpies of formation of NaCl(s), RbCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of NaRb[B₄O₅(OH)₄]·4H₂O was calculated from the Gibbs free energy of formation of NaRb[B₄O₅(OH)₄]·4H₂O computed from a group contribution method.     

Polyethyleneimine-capped silver nanoclusters as a fluorescence probe for sensitive detection of hydrogen peroxide and glucose

In this work, we utilized polyethyleneimine-capped silver nanoclusters (PEI-Ag nanoclusters) to develop a new fluorometric method for the determination of hydrogen peroxide and glucose with high sensitivity. The PEI-Ag nanoclusters have an average size of 2 nm and show a blue emission at 455 nm. The photostable properties of the PEI-Ag nanoclusters were examined. The fluorescence of the PEI-Ag nanoclusters could be particularly quenched by H₂O₂. The oxidization of glucose by glucose oxidase coupled with the fluorescence quenching of PEI-Ag nanoclusters by H₂O₂ can be used to detect glucose. Under optimum conditions, the fluorescence intensity quenched linearly in the range of 500 nM–100 μM with high sensitivity. The detection limit for H₂O₂ was 400 nM. And a linear correlation was established between fluorescence intensity (F₀ − F) and concentration of glucose in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁵ M and 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a detection limit of 8.0 × 10⁻⁷ M. The method was used for the detection of glucose in human serum samples with satisfactory results. Furthermore, the mechanism of sensitive fluorescence quenching response of Ag nanoclusters to glucose and H₂O₂ has been discussed.     

The mercury chromates Hg6Cr2O9 and Hg6Cr2O10—Preparation and crystal structures, and thermal behaviour of Hg6Cr2O9

The basic mercury(I) chromate(VI), Hg₆Cr₂O₉ (=2Hg₂CrO₄·Hg₂O), has been obtained under hydrothermal conditions (200 °C, 5 days) in the form of orange needles as a by-product from reacting elemental mercury and K₂Cr₂O₇. Hydrothermal treatment of microcrystalline Hg₆Cr₂O₉ in demineralised water at 200 °C for 3 days led to crystal growth of red crystals of the basic mercury(I, II) chromate(VI), Hg₆Cr₂O₁₀ (=2Hg₂CrO₄·2HgO). The crystal structures were solved and refined from single crystal X-ray data sets. Hg₆Cr₂O₉: space group P2₁2₁2₁, Z=4, a=7.3573(12), b=8.0336(13), , 3492 structure factors, 109 parameters, R[F²>2σ(F²)]=0.0371, wR(F² all)=0.0517; Hg₆Cr₂O₁₀: space group Pca2₁, Z=4, a=11.4745(15), b=9.4359(12), , 3249 structure factors, 114 parameters, R[F²>2σ(F²)]=0.0398, wR(F² all)=0.0625. Both crystal structures are made up of an intricate mercury-oxygen network, subdivided into single building blocks [O-Hg-Hg-O] for the mercurous compound, and [O-Hg-Hg-O] and [O-Hg-O] for the mixed-valent compound. Hg₆Cr₂O₉ contains three different Hg₂²⁺ dumbbells, whereas Hg₆Cr₂O₁₀ contains two different Hg₂²⁺ dumbbells and two Hg²⁺ cations. The Hg^I-Hg^I distances are characteristic and range between 2.5031(15) and 2.5286(9) Å. All Hg₂²⁺ groups exhibit an unsymmetrical oxygen environment. The oxygen coordination of the Hg²⁺ cations is nearly linear with two tightly bonded O atoms at distances around 2.07 Å. For both structures, the chromate(VI) anions reside in the vacancies of the Hg-O network and deviate only slightly from the ideal tetrahedral geometry with average Cr-O distances of ca. 1.66 Å. Upon heating at temperatures above 385 °C, Hg₆Cr₂O₉ decomposes in a four-step mechanism with Cr₂O₃ as the end-product at temperatures above 620 °C.     

A widely varying range of products in reactions of C6F5BrF2, C6F5IF2, and C6F5IF4 with Lewis acids of different strength

The relative fluoride donor ability: C₆F₅BrF₂ > C₆F₅IF₂ > C₆F₅IF₄ was outlined from reactions with Lewis acids of graduated strength in different solvents. Fluoride abstraction from C₆F₅HalF₂ with BF₃·NCCH₃ in acetonitrile (donor solvent) led to [C₆F₅HalF·(NCCH₃)_n][BF₄]. The attempted generation of [C₆F₅BrF]⁺ from C₆F₅BrF₂ and anhydrous HF or BF₃ in weakly coordinating SO₂ClF gave C₆F₅Br besides bromoperfluorocycloalkenes C₆BrF₇ and 1-BrC₆F₉. In reactions of C₆F₅IF₂ with SbF₅ in SO₂ClF the primary observed intermediate (¹⁹F NMR, below 0 °C) was the 4-iodo-1,1,2,3,5,6-hexafluorobenzenium cation, which converted into C₆F₅I and 1-IC₆F₉ at 20 °C. The reaction of C₆F₅IF₄ with SbF₅ in SO₂ClF below −20 °C gave the cation [C₆F₅IF₃]⁺ which decomposed at 20 °C to C₆F₅I, 1-iodoperfluorocyclohexene, and iodoperfluorocyclohexane. Principally, the related perfluoroalkyl compound C₆F₁₃IF₄ showed a different type of products in the fast reaction with AsF₅ in CCl₃F (−60 °C) which resulted in C₆F₁₄. Intermediate and final products of C₆F₅HalF_n−1 (n = 3, 5) with Lewis acids were characterized by NMR in solution. Stable solid products were isolated and analytically characterized.     

A new structure type of RE4B4O11F2: High-pressure synthesis and crystal structure of La4B4O11F2

The first lanthanum fluoride borate La₄B₄O₁₁F₂ was obtained in a Walker-type multianvil apparatus at 6 GPa and 1300 °C. La₄B₄O₁₁F₂ crystallizes in the monoclinic space group P2₁/c with the lattice parameters a=778.1(2) pm, b=3573.3(7) pm, c=765.7(2) pm, β=113.92(3)° (Z=8), and represents a new structure type in the class of compounds with the composition RE₄B₄O₁₁F₂. The crystal structure contains BO₄-tetrahedra interconnected with two BO₃-groups via common vertices, B₂O₅-pyroborate units, and isolated BO₃-groups. The structure shows a wave-like modulation along the b-axis. The crystal structure and properties of La₄B₄O₁₁F₂ are discussed and compared to Gd₄B₄O₁₁F₂.     

Synthesis, crystal structure and mono-dimensional thallium ion conduction of TlFe0.22Al0.78As2O7

A new solid solution TlFe_0.22Al_0.78As₂O₇ has been synthesized by a solid-state reaction. The structure of the title compound has been determined from a single-crystal X-ray diffraction and refined to final values of the reliability factors: R(F²)=0.030 and wR(F²)=0.081 for 1343 independent reflections with I>2σ(I). It crystallizes in the triclinic space group P-1, with a=6.296(2) Å, b=6.397(2) Å, c=8.242(2) Å, α=96.74(2)°, β=103.78(2)°, γ=102.99(3)°, V=309.0(2) Å³ and Z=2. The structure can be described as a three-dimensional framework containing (Fe/Al)O₆ octahedra connected through As₂O₇ groups. The metallic units and diarsenate groups share oxygen corners to form a three-dimensional framework with interconnected tunnels parallel to the a, b and c directions, where Tl⁺ cations are located. The ionic conductivity measurements are performed on pellets of the polycrystalline powder. At 683 K, The conductivity value is 5.23×10⁻⁶ S cm⁻¹ and the ionic jump activation energy is 0.656 eV. The bond valence analysis reveals that the ionic conductivity is ensured by Tl⁺ along the [001] direction.     

Synthesis, vacuum ultraviolet and near ultraviolet-excited luminescent properties of GdCaAl3O7: RE (RE=Eu, Tb)

Vacuum ultraviolet (VUV) excitation and photoluminescent (PL) properties of Eu³⁺ and Tb³⁺ ion-doped aluminate phosphors, GdCaAl₃O₇:Eu³⁺ and GdCaAl₃O₇:Tb³⁺ have been investigated. X-ray diffraction (XRD) patterns indicate that the phosphor GdCaAl₃O₇ forms without impurity phase at 900 °C. Field emission scanning electron microscopy (FE-SEM) images show that the particle size of the phosphor is less than 3 μm. Upon excitation with VUV irradiation, the phosphors show a strong emission at around 619 nm corresponding to the forced electric dipole ⁵D₀→⁷F₂ transition of Eu³⁺, and at around 545 nm corresponding to the ⁵D₄→⁷F₅ transition of Tb³⁺. The results reveal that both GdCaAl₃O₇:RE³⁺ (RE=Eu, Tb) are potential candidates as red and green phosphors, respectively, for use in plasma display panel (PDP).     

Investigation of Fe-based oxyhydroxy-fluoride with hollandite-type structure

Well crystallized Fe-based oxyhydroxy-fluoride with the FeO(OH_0.2F_0.8)·0.2H₂O chemical composition has been prepared from hydrolysis of Fe trifluoride under supercritical CO₂ conditions. Investigation by Mössbauer spectroscopy and neutron diffraction show that this compound crystallize in the monoclinic symmetry (SG: I2/m, a = 10.447(7) Å, b = 3.028(2) Å, c = 10.445(4) Å, β = 90.00(3)°). Taking into account the Fe-O(F) bond distances, F⁻ anions are mainly located on the common vertices of Fe octahedra whereas OH⁻ groups occupy mainly the shared edges of the Fe octahedra. Two various highly distorted octahedral sites have been identified with Fe-O/F bond distances varying from 1.90 Å to 2.31 Å. One Fe site is more distorted than in FeO_0.8OH_1.2·0.2Cl akaganeite because of the random distribution of F⁻/OH⁻/O²⁻ in the vicinity of this Fe cation.     

Sequential injection method for the direct spectrophotometric determination of bismuth in pharmaceutical products

A spectrophotometric method is reported for the determination of bismuth in pharmaceutical products using sequential injection analysis. Methylthymol blue (MTB) was used as a color forming reagent and the absorbance of the Bi(III)-MTB complex was monitored at 548 nm. The various chemical and physical variables that affected the reaction were studied. A linear calibration graph was obtained in the range 0.0-75.0 mg l⁻¹ Bi(III) at a sampling frequency of 72 h⁻¹. The reagent consumption was considerably reduced compared to conventional flow injection systems, as only 150 μl of MTB were consumed per run. The precision was very satisfactory (s_r=0.5%, at 50.0 mg l⁻¹ Bi(III), n=12) and the limit of detection, c_L, was 0.250 mg l⁻¹. The developed method was applied successfully to the analysis of various pharmaceutical products containing Bi(III). The relative errors e_r, were <1.5% in all cases and were evaluated by comparison of the obtained results with those found using atomic absorption spectrometry as the reference method.     

Thermochemistry of dicesium calcium tetraborate octahydrate

The enthalpies of solution of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) in approximately 1 mol dm⁻³ aqueous hydrochloric acid and of CsCl(s) in aqueous (hydrochloric acid + boric acid + calcium oxide) were determined. From these results and the enthalpies of solution of H₃BO₃(s) in approximately 1 mol dm⁻³ HCl(aq) and of CaO(s) in aqueous (hydrochloric acid + boric acid), the standard molar enthalpy of formation of −(10328 ± 6) kJ mol⁻¹ for Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) was obtained from the standard molar enthalpy of formation of CaO(s), CsCl(s), H₃BO₃(s) and H₂O(l). The standard molar entropy of formation of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) was calculated from the thermodynamic relation with the standard molar Gibbs free energy of formation of Cs₂Ca[B₄O₅(OH)₄]₂·8H₂O(s) computed from a group contribution method.     

Synthesis and luminescent properties of Tb-activated yttrium indium germanate phosphor

An yttrium indium germanate YInGe₂O₇ and YInGe₂O₇:Tb³⁺ was synthesized using a vibrating milled solid-state reaction with metal oxides. The structure was characterized by its X-ray powder diffraction pattern. All of the peaks can be attributed to the monoclinic YInGe₂O₇ phase, as increasing the Tb³⁺ ion concentrations and the full-width of the half-maximum (fwhm) of these peaks did not cause any obvious differences in the increase in Tb³⁺ concentration. The CIE color coordinates were all in the green region. The phosphor exhibited a bright green emission at 542 nm under excitation at 378 and 258 nm, which belongs to the ⁵D₄→⁷F₅ transition of Tb³⁺ ions. There were two kinds of emission mechanism in YInGe₂O₇:Tb³⁺: (1) under excitation at 378 nm, time-resolved ⁵D₄→⁷F₅ transition shows a single exponential decay even when all sites are occupied by Tb³⁺ ions; (2) under excitation at 258 nm, the excited energy was absorbed by the host crystal then transferred effectively to the Tb³⁺ ion which caused the decay curves for the ⁵D₄→⁷F₅ transition to show non-exponential behavior. There is a maximum value for photoluminescence intensity when the Tb³⁺ concentration is 100 mol% with CIE color coordinates of x=0.252; y=0.595. The concentration quenching effect was not observed, because the YInGe₂O₇:Tb³⁺ structure gradually changed to a thortveitite-like structure with increasing Tb³⁺ concentration.     

Flow-injection methylene blue-based spectrophotometric method for the determination of peroxide values in edible oils

A flow-injection method for measuring the peroxide value (PV, mequiv. O₂ kg⁻¹) in edible oils is described. The technique is based on spectrophotometric monitoring at 660 nm of methylene blue (MB), generated from leucomethylene blue (LMB) oxidation with peroxides present in oil samples. After being optimized, the method was validated in terms of linearity, precision sensitivity and recovery.Linear calibration graph was obtained in the range 0.1-5 mequiv. O₂ kg⁻¹, with a detection limit (S/N  =  3) of 0.014 mequiv. O₂ kg⁻¹. The precision of the method (R.S.D., n = 9) for within and between-days is better than 1.5% and 2.2%, respectively at 0.4 mequiv. O₂ kg⁻¹. The method was applied successfully to the determination of PV in six edible oil samples, and compared to the classical official method. Using the linear regression test, Student's t-test and variance ratio F-test, there was no significant difference between the compared methods. The proposed method is accurate, simple, cheap and could be used to control edible oil rancidity with a high sample throughputs (30 samples h⁻¹).