INAA of fluorine in plastics using the medium-flux McMaster Nuclear Reactor

The fluorine contents of plastics, ranging from about 20 μg·g⁻¹ to 66%, may be measured instrumentally using a conventional research nuclear reactor, an automated sample irradiation and counting system, and a set of well-calibrated, in-house, fluorine standards. Plastics with low to medium fluorine contents may be analyzed using ²⁰F by placing the gamma-ray detector at appropriate distances from the irradiated sample. For high-F plastics, samples may be irradiated in a cadmium lined irradiation site, using ¹⁹O and ²⁰F. Counting statistics of <3% translate into reproducibility of measurements within ±3% and analytical accuracies of ±1% to ±10%.     

Polarographic Behavior of Gemfibrozil in the Presence of Dissolved Oxygen and Its Analytical Application

The polarographic behavior of gemfibrozil is investigated in 0.2 mol L^?1 KH₂PO₄‐Na₂HPO₄ (pH 5.8±0.1)‐8% ethanol supporting electrolyte in the absence and the presence of dissolved oxygen. The results demonstrate that the polarographic reduction peak at ca. ?1.17 V is a catalytic hydrogen wave after deaeration, and the enhanced reduction peak in the presence of dissolved oxygen is the so‐called parallel catalytic hydrogen wave. Based on the parallel catalytic hydrogen wave, a novel method has been developed for the determination of gemfibrozil by single sweep polarography. Calibration plot is linear in the range of 1.8×10^?7–2.4×10^?6 mol L^?1 and detection limit is 9.0×10^?8 mol L^?1. The proposed method is applied to the direct determination of the gemfibrozil in pharmaceutical preparations. The proposed method is simpler, faster and more sensitive than the known methods for gemfibrozil analyses.     

An improved method for the spectrophotometric determination of fluoride by addition of sodium dodecyl sulphate to the fluoride/lanthanum (III)/Alizarin fluorine blue system

The conventional spectrophotometric method for the determination of fluoride, based on the fluoride/lanthanum(III)/alizarin fluorine blue ternary complex, is improved by addition of sodium dodecyl sulphate. In 15% (v/v) acetone medium, the absorbance of the binary reagent complex is decreased and the reaction time is only 3 min under sonication. Beer's Law is obeyed at 574 nm for fluoride concentrations in the ranges 0.075–0.30 and 0.20–1.2 mg 1^?1; the apparent molar absorptivities are (1.6 ± 0.1) × 10⁴ and (1.5 ± 0.1) × 10⁴ mol^?1 cm^?1 fluoride levels, respectively. This method is applied to the determination of fluoride in bottled mineral waters.     

Thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) in nitrogen and oxygen

The thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) (parylene AF-4) films with thicknesses of ca. 7.5 and 10 μm has been studied by both dynamic (10°C min^?1) and isothermal TG in either nitrogen or oxygen atmospheres. In dynamic studies with nitrogen, gross decomposition occurs between 546.7±1.4 and 589.0±2.6°C, with 26.8±4.4% of the initial mass remaining at 700°C. With oxygen as the purge gas, the onset of decomposition shifts slightly to 530.8±4.2°C. The end of the transition at 587.4±2.6°C is within experimental error of the nitrogen value, but no polymer remains above 600°C. Isothermal data were obtained at 10°C intervals from 420 to 490°C in nitrogen, and from 390 to 450°C in oxygen. Plots of log(Δ%wt/Δt)vs. T^?1 are linear throughout the specified range for oxygen and from 420 to 470°C for nitrogen. The calculated activation energies of (147±16) kJ mol^?1 and (150±12) kJ mol^?1 in N₂ and O₂, respectively, are equal within experimental error.     

Zur gas-chromatographischen Bestimmung des Fluors

A fast, simple and accurate gas-chromatographic method for determination of fluorine in inorganic and organic substances is described. After dry ashing the fluorine reacts with triethylchlorsilane to triethylfluorsilane. The latter is determined by gas chromatography. The accuracy of the method is about ± 2%.     

Determination of fluorine by the spectrometry of prompt gamma-rays

The use, for analysis, of prompt gamma-rays excited by 5 MeV alpha-particles from the reactions¹⁹F(α,α′γ)¹⁹F,¹⁹F(α, nγ)²²Na and¹⁹F(α, pγ)²²NE, was studied. The precision of the analyses depended on the gamma-ray energy used for the measurement. Relative standard deviations were ±1.8, ±0.9 and ±1.3% using the 110-, 197- or 1275 keV gamma-rays. The method was tested with N. I. M. standard materials of calcium fluoride and fluorspar, and was used as a rapid method for the determination of fluorine in cements.     

Determination of calcium,phosphorus and fluorine in bone by instrumental fast neutron activation analysis

The determination of fluorine, calcium and phosphorus in bone by instrumental fast neutron activation analysis is described. Results for the IAEA standard material “Animal Bone” A3-74 re: Ca=313±10 mg/g, P=155±5 mg/g and F-613±20μg/g. The accuracy for all three elements is≤4%, precision being about 3%. The limit of determination for F is 120 μg, for Ca 30 mg and for P 1 mg in a sample of 500 mg.     

Simultaneous Detection of Homocysteine and Cysteine in the Presence of Ascorbic Acid and Glutathione Using a Nanocarbon Modified Electrode

The simultaneous electrochemical detection of homocysteine and cysteine using an absorbed ortho‐quinone species, catechol, at the nanocarbon modified glassy carbon electrode was achieved via 1,4‐Michael addition reaction. The detection was done in the presence and the absence of each other as well as with both glutathione and ascorbic acid present in order to investigate the selectivity of homocysteine and cysteine. A determination of homocysteine sensitivity is (0.882±0.296) nA nM^?1 with a LOD of ca. 11 nM and cysteine sensitivity is (7.501±0.202) mA µM^?1 with a LOD of ca. 5.0 µM within a range of 0–0.1 mM.     

Precise,non-destructive determination of fluorine by 14-MeV neutron activation analysis

A procedure is described for the precise determination of fluorine in organic and metal-organic compounds by 14-MeV neutron activation analysis using the reaction: ¹⁹F(n,2n)¹⁸F (β +, t_{$\text{1}\text{2}$} = 110 min).A relative standard deviation of better than ±0.5% is achieved by irradiating samples and standard simultaneously. Uniform neutron exposures were ensured by rotating the samples during irradiation. Positron emitters of short half-life are allowed to decay before counting. In metal-organic compounds, Sc, Zn, Ga and Ag cause the most serious interference; for organic compounds the method is rapid, and specific for fluorine.     

Separation radiochimique du fluor sur apatite

The radioisotope¹⁸F with a half-life of 110 min is produced in order to determine fluorine and oxygen by γ photon or charged particles activation. This radioisotope is a β⁺ emitter and must be separated from other radioisotopes produced from the analysed matrix. The separation was achieved by fixation of fluorine on a plombo-stronsic hydroxyapatite, prepared by synthesis in aqueous medium. Studies of the distribution of radioactive fluorine between the apatite and solutions of variable compositions, showed the optimal conditions, for the separation from the following metals: Al, Mg, Fe, Mo and from the Al−Mg alloy. The separation was applied to the determination of fluorine by γ irradiation and of oxygen by³He irradiation. Due to the great selectivity of this separation, radiochemically clean fluorine is obtained and the limit of detection is lowered.      

Rate constants for the reactions of O(3P) with selected monoterpenes

Rate constants for the gas-phase reactions of O(³P) atom with a series of monoterpenes have been determined at ambient temperature (ca. 302–309 K) and atmospheric pressure using a relative rate technique. Using the literature rate constants for O(³P) + isobutene, cis and trans-2-butene, 3-methyl-1-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene as the standards, the O(³P) rate constants derived for the terpenes (in units of 10⁻¹¹ cm³ molecule⁻¹s ⁻¹) are 2.8 ± 0.4 for α-pinene, 2.8 ± 0.5 for β-pinene, 3.1 ± 0.5 for Δ ³-carene, 3.5 ± 0.5 for 2-carene, 2.6 ± 0.5 for camphene, 7.6 ± 1.2 for d-limonene, 9.0 ± 1.6 for γ-terpinene, and 10.7 ± 1.6 for terpinolene. The relative rate constants in this work agreed with literature values to within ± 10% for the standard alkenes, and to within ± ca. 35% for the terpenes. © 1996 John Wiley & Sons, Inc.     

Determination of fluorine in geological samples using accelerator derived neutrons

A fast, neutron activation analysis technique is described for the determination of fluorine in geological samples. The method utilises the reaction¹⁹F(n,α)¹⁶N for the determination. However, it avoids the interference reaction from oxygen which produces the same radionuclide since the neutrons are derived from the bombardment of beryllium with 3 MeV deuterons. The maximum energy of the neutrons so produced is well below the threshold for the competing oxygen reaction. The results indicate that the method gives acceptable accuracy over the range of a few tens ppm to several percent fluorine content using suitable standards. Sample analysis time is only a few minutes allowing the analyses of large numbers of samples per day.     

Determination of fluorine in organic compounds by epithermal neutron activation analysis

Classical activation analysis of fluorine by thermal neutrons has a limited application because of frequent interference from chlorine, the short half life²⁰F (11.4 s) and too high dead time of detectors. A procedure is described for fluorine determination using¹⁹F (n,p)¹⁹O reaction. Use of a boron carbide shield has no effect on the activity of¹⁹O (boron ratio −1) but considerably reduces background and interference due to¹⁸O (n, γ)¹⁹O reaction. The technique has been successfully applied to the determination of fluorine in organic compounds even in the presence of large amounts of chlorine and oxygen.     

Fluorine analysis by activation with an isotopic fast-neutron source and counting Nitrogen-16

A rapid, nondestructive method has been developed for determination of fluorine by activation with fast neutrons from a²⁴¹Am-²⁴²Cm-Be source and counting the 6–7 MeV γ rays of the product nitrogen-16. The total neutron output of the source is 4.8·10⁹ unmoderated neutrons per second and the flux is 1.4·10⁸ fast n·cm⁻²· sec⁻¹. The γ-ray detectors consist of two opposing, matched cylindrical NaI(Tl) crystals 10 cm long and 10 cm in diameter. The sample is irradiated for 30 seconds, cooled for 4 seconds, and then counted for 30 seconds. The sensitivity is 4.8·10⁴ counts nitrogen-16 per gram fluorine, and the limit of detection is 0.4 mg fluorine in a 10-gram sample. A reproducibility of 0.24% is achieved. The relative standard deviation of the specific count rate of nitrogen-16 for 11 fluorine compounds is 1.31%.     

Crossed-beám chemiluminescence. II. Kinetics and mechanisms for reactions of group IIA Metals in ground and metastable states with fluorine

Visible chemiluminescence technique under crossed-beam conditions has been applied to the study of the reactions of the group IIA metal atoms Mg, Ca, Sr and Ba in their ground state (¹S₀) or in an excited metastable state (³P_i, ³D_i or ¹D₂) with F₂. The monofluoride emission bands are the most prominent features in the chemiluminescence spectrum. Using higher fluorine densities radiation is observed from excited alkaline earth difluorides, which are shown to principally originate from secondary reactions. Formations of MF* are determined to be first order with respect to both the metal atom and the fluorine molecule. Total cross sections for removal of ground state metal atoms from the beam by F₂ are 115 ± 15Ų for Ca, 125 ± 15Ų for Sr, and 160 ± 15Ų for Ba, which is consistent with an electron jump model. Chemiluminescence cross sections are reported for the reactions involving electronically excited reactants M*. Photon yields of 12 ± 3% for Mg*, 18 ± 5% for Ca*, 20 ± 5% for Sr*, and 15 ± 8% for Ba* reacting with F₂ are measured. These high photon yields are remarkable when compared with absolute photon yields for the ground state reactions which indicate that less than 2% of the products are MF* molecules. It was possible to obtain vibrational state distributions for some of the excited monofluorides which are found to be populated in a non-thermal manner. This strongly suggests that the dynamics of the reactions are governed by a direct mechanism. From the crossed-beam chemiluminescence spectra the dissociation energies of the ground state monofluorides are estimated. In addition, improved spectroscopic constants, dissociation energies and dissociation products of some of the excited electronic states of MF are given.     

Sulfur Concentration in Nanoporous Alumina Membrane

Nanoporous alumina membrane prepared by anodic oxidation using sulfuric acid electrolyte was subjected to TG-DTA and X-ray Photoelectron Spectroscopy (XPS or ESCA) to further study the distribution of sulfur. In XPS study, Ar⁺ ion bombardment was performed on the sample to etch the surface at a rate of 3 nm min^-1. As a result, sulfur was found to be concentrated within a depth of 3nm from the surface. The S content of the surface was found to be 2.7±0.5 wt%, and that at a depth of ca. 3 nm and ca. 10 nm was found to be as low as about 0.6±0.11 wt% (5.37±1.0 wt%→ 1.26±0.2wt% SO₂). In TG-DTA, the mass loss of 7.3% was in fair agreement with that calculated on XPS results (7.1±1.2%). This revised version was published online in July 2006 with corrections to the Cover Date.     

An oxygen standard for the determination of oxygen in steel by 14-MeV neutron activation analysis

A relative method for the determination of oxygen in steel via the ¹⁶O(n,p)¹⁶N reaction by means of 14-MeV neutrons is described. A standard is irradiated immediately behind the sample and the induced activities are counted simultaneously with two separate but identical detector systems. The standard mixture (ca. 5 g of graphite plus iron oxide containing 80 mg of oxygen per g) is compressed into a steel capsule of the same external dimensions as the samples (26 mm diameter, 9 mm thick). Dimensional tolerances, choice and purity control of the oxygen compound and preparation of the standard mixture are discussed. Fast neutron shielding, absorption of fast neutrons, self-absorption of the ¹⁶N /gg-rays and the average neutron flux in sample and standards are considered and a total correction factor is established. Flux inhomogeneities and differences in counting geometry and discriminator setting can be determined by irradiation and counting of two identical standards. The accuracy of this method was checked by comparison of the results with those of the reducing fusion method; satisfactory agreement was observed, although the activation results tended to be slightly higher. The mean long-term standard deviation for analysis of a given sample over a period of 6 months was found to be ±3%.     

Voltammetric Determination of Captopril on a Glassy Carbon Electrode Modified with Copper Metal‐organic Framework

We report in this work, a new method for the determination of captopril by differential pulse voltammetry using a glassy carbon electrode modified with a copper metal‐organic framework (H‐Kust‐1 or Cu₃(BTC)₂ or Cu‐BTC), immobilized on the surface by a copolymer of acrylamide and sodium acrylate. This compound is detected by the formation of a copper(II)‐captopril complex that is observed in an oxidation potential at ca. +0.28 V vs . Ag/AgCl. A linear dynamic range is obtained for a captopril concentration of 0.5 μM to 7.0 μM and the voltammetric response is highly reproducible within 3.52 % error. The sensitivity of 9.71±0.37 nA μM⁻¹ and the limit of detection of 0.20±0.01 μM make this methodology highly applicable for practical applications. The determination of captopril in a commercial pharmaceutical sample showed a recovery of 93.3 %.     

Röntgenspektrometrische bestimmung von blei in automatenstahl : Teil II. Sulfat-verfahren

A method is described for the x-ray spectrometric determination of 0.02–0.5% Pb in free-cutting steels. Lead in the sample solution is precipitated as sulphate with barium sulphate as collector, and the dried fixed precipitate is used for the X-ray Spectrometric measurement. The method shows a reproducibility (s) of ±0.002 % Pb. The time required is ca. 32 min for one determination and ca. 120 min for a series of 20 samples.     

Substoichiometric isotope-dilution determination of sulphur after conversion to methylene blue and ion-pair extraction with dodecyl sulphate

The proposed substoichiometric determination of sulphur includes two key steps: conversion of sulphur to methylene blue and ion-pair extraction of methylene blue into chloroform with a substoichiometric amount of dodecyl sulphate. The method, combined with isotope dilution is applied to the determination of total sulphur in NBS SRM Citrus Leaves and in a seaweed sample (Laminaria religiosa Miyabe). The mean values obtained were 0.401±0.008% S (RSD 2%; n=9; certified value 0.407±0.009%) for the SRM, and 0.756±0.012% S (RSD 1.6%; n=5) for the seaweed. A sample of 0.5–1 g containing ca. 100 μg of sulphur can be analysed.