Analysis of Pb in water samples with plastic scintillation resins

²¹⁰Pb is a radioactive lead isotope present in the environment as member of the ²³⁸U decay chain. Since it is a relatively long-lived radionuclide (T_1/2 = 22.2 years), its analysis is of interest in radiation protection and the geochronology of sediments and artwork. Here, we present a method for analysing ²¹⁰Pb using plastic scintillation resins (PSresins) packaged in solid-phase extraction columns (SPE cartridge). The advantages of this method are its selectivity, the low limit of detection, as well as reductions in the amount of time and reagents required for analysis and the quantity of waste generated. The PSresins used in this study were composed of a selective extractant (4′,4″(5″)-Di-tert-butyldicyclohexano-18-crown-6 in 1-octanol) covering the surface of plastic scintillation microspheres. Once the amount of extractant (1:1/4) and medium of separation (2 M HNO₃) were optimised, PSresins in SPE cartridges were calibrated with a standard solution of ²¹⁰Pb. ²¹⁰Pb could be fully separated from its daughters, ²¹⁰Bi and ²¹⁰Po, with a recovery value of 91(3)% and detection efficiency of 44(3)%. Three spiked water samples (one underground and two river water samples) were analysed in triplicates with deviations lower than 10%, demonstrating the validity of the PS resin method for ²¹⁰Pb analysis.     

Macroscopic and microscopic ionization constants of the thiol and amine groups in 1-methyl-4-mercaptopiperidine

The acid dissociation constants of 1-methyl-4-mercaptopiperidine (pK(1) = 9.51, pK(2) = 11.33), the 1,1-dimethyl-4-mercaptopiperidinium ion (pK(A) = 9.59) and 1-methyl-4-(methylthio)piperidine (pK(B) = 10.18) have been determined potentiometrically in 3M sodium perchlorate (10% methanol) medium. The ultraviolet absorption of the mercaptide ion has been used to determine the relative proton affinity of the sulphur and nitrogen functions in 1-methyl-4-mercaptopiperidine under the same conditions, and its four microscopic constants (pK(a) = 9.49, pK(b) = 10.23, pK(c) = 11.34, pK(d) = 10.60) have been calculated; pK(A) has also been determined spectrophotometrically. From the results obtained, it can be concluded that the thiol group is more acidic than the amine group and that the Adams relation, K(a) + K(b) = K(1), holds very well when it is assumed that the spectrophotometric values for K(a), and K(b), can be replaced by K(A) and K(B) respectively.     

Indium determination in different environmental materials by electrothermal atomic absorption spectrometry with Amberlite XAD-2 coated with 1-(2-pyridylazo)-2-naphthol

Methods were developed for indium (In) determination in complex ores by electrothermal atomization atomic absorption spectrometry using matrix modification after its separation with Amberlite XAD-2 coated with 1-(2-pyridylazo)-2-naphthol (PAN). Palladium-magnesium, nickel, and zinc nitrates were used as matrix modifiers and were compared in terms of maximum pyrolysis temperature, sensitivity and background signal. They have enhanced the absorption signals for indium, respectively eliminating the matrix interferences. The standard additions method was applied. The relative standard deviations for six replicate determinations were in the range 0.3-4.0% for indium in different ores samples for indium concentrations 7.6-209 μg g⁻¹. The recommended method was applied to the indium determination in real samples. The data obtained by this method were in good agreement with those obtained by ICP-AES.     

Direct copper determination in whole milk, non-fat milk and whey milk by electrothermal atomic absorption spectrometry

A method for the direct determination of copper in samples of whole milk, non-fat milk and whey milk by electrothermal atomic spectrometry (ETAAS) was studied. The fat separation by centrifugation at 3200 rpm and the separation of casein mycelles to obtain the whey milk by ultracentrifugation at 31 000 g were investigated. In all cases Mg(NO₃)₂ was used as chemical modifier and Triton X-100 (0.2% w/v) as emulsifying agent. The optimum pyrolysis temperature was 1500° C. The detection limit was 0.4 μg/l of copper. The precision was studied for the whole milk and the coefficients of variation (CV) were 5.7, 4.0, 2.4 and 2.8% for 0, 5, 10 and 20 μg/l of copper added. The accuracy was determined by using the Reference Material Milk A-11 (IAEA) with a certified content of 378.4 ± 24 ng Cu/g; 359 ± 16 ng/g were found. The method was applied to ten cow milk samples, the levels of copper being determined for whole milk, non-fat milk and whey milk. A statistical study was applied and it was concluded that the majority of copper is in the non-fat milk. Received: 29 February 1996 / Revised: 19 April 1996 / Accepted: 28 April 1996     

A recursive method for computing interpolants

In this paper, we describe a recursive method for computing interpolants defined in a space spanned by a finite number of continuous functions in R^d${\mathbb{R}}^d$. We apply this method to construct several interpolants such as spline interpolants, tensor product interpolants and multivariate polynomial interpolants. We also give a simple algorithm for solving a multivariate polynomial interpolation problem and constructing the minimal interpolation space for a given finite set of interpolation points.     

Structure characterization of copolymers of ethylene and 1‐octadecene

Four ethylene‐1‐octadecene copolymers and the corresponding polyethylene homopolymer, synthesized with a metallocene catalyst, have been analyzed by using three characterization techniques in the solid state: differential scanning calorimetry, wide‐angle X‐ray diffraction, and Raman spectroscopy. Very important annealing effects are observed in the copolymers with higher comonomer content while standing at room temperature, in such a way that the enthalpies of melting derived from the first and second melting are different. The X‐ray diffractograms have been analyzed in terms of amorphous and crystalline components, determining both the crystallinity and the position of the different reflections. The variation of the unit cell parameters has been calculated from those reflections. No indication of a possible participation of the relatively long 1‐octadecene branches in the crystallization can be deduced from the X‐ray data. The degree of crystallinity has also been determined from the Raman spectra, following two procedures. The results indicate that the crystallinities deduced from the band at 1416 cm⁻¹ are much lower than those derived from the other two characterization techniques. On the contrary, the data from the 1060 cm⁻¹ band are practically coincident with the X‐ray determinations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1440–1448, 2000     

Numerical calculation of the discrete spectra of one‐dimensional Schrödinger operators with point interactions

In this paper, we consider one‐dimensional Schrödinger operators S_q on with a bounded potential q supported on the segment and a singular potential supported at the ends h₀, h₁. We consider an extension of the operator S_q in defined by the Schrödinger operator and matrix point conditions at the ends h₀, h₁. By using the spectral parameter power series method, we derive the characteristic equation for calculating the discrete spectra of operator . Moreover, we provide closed‐form expressions for the eigenfunctions and associate functions in the Jordan chain given in the form of power series of the spectral parameter. The validity of our approach is proven in several numerical examples including self‐adjoint and nonself‐adjoint problems involving general point interactions described in terms of δ‐ and δ′‐distributions.     

The Role of Lignocellulosic Composition and Residual Lipids in Empty Fruit Bunches on the Production of Humic Acids in Submerged Fermentations

The aim of this research was to study the production of humic acids (HA) by Trichoderma reesei from empty fruit bunches (EFBs) of palm oil processing, with a focus on the effects of lignocellulosic content and residual lipids. EFBs from two different soils and palm oil producers were previously characterized about their lignocellulosic composition. Submerged fermentations were inoculated with T. reesei spores and set up with or without residual lipids. The results showed that the soil and the processing for removal of the palm fresh fruits were crucial to EFB quality. Thus, EFBs were classified as type 1 (higher lignocellulosic and fatty acids composition similar to the palm oil and palm kernel oil) and type 2 (lower lignocellulosic content and fatty acids composition similar to palm oil). Despite the different profiles, the fungal growth was similar for both EFB types. HA production was associated with fungal growth, and it was higher without lipids for both EFBs. The highest HA productivity was obtained from type 1 EFB (approximately 90 mg L⁻¹ at 48 h). Therefore, the lignocellulosic composition and the nature of the residual lipids in EFBs play an important role in HA production by submerged fermentation.

     

Trivariate near-best blending spline quasi-interpolation operators

A method to define trivariate spline quasi-interpolation operators (QIOs) is developed by blending univariate and bivariate operators whose linear functionals allow oversampling. In this paper, we construct new operators based on univariate B-splines and bivariate box splines, exact on appropriate spaces of polynomials and having small infinity norms. An upper bound of the infinity norm for a general blending trivariate spline QIO is derived from the Bernstein-Bézier coefficients of the fundamental functions associated with the operators involved in the construction. The minimization of the resulting upper bound is then proposed and the existence of a solution is proved. The quadratic and quartic cases are completely worked out and their exact solutions are explicitly calculated.     

A study of the synthesis and characterization of ethylene/dicyclopentadiene copolymers using a metallocene catalyst

Copolymers of ethylene/dicyclopentadiene were produced using a Me₂Si(Ind)₂ZrCl₂/methylaluminoxane catalyst system. The melting and crystallization points of the freshly prepared copolymers steadily decreased with increasing comonomer concentration. This was attributed to increased comonomer concentration in the polymer. When the comonomer incorporation, as measured by ¹³C NMR, is plotted against the comonomer concentration in the reactor, a plateau appears at concentrations higher than 0.12 mol/L. At concentrations greater than 0.12 mol/L time dependant crosslinking begins to be observed in the copolymers after exposure to air for several months. This crosslinking is also apparent in the thermosetting behavior of the copolymers when they are allowed sufficient time to crosslink. Copolymers with lower comonomer concentrations possess melting enthalpies even after several weeks, suggesting that there is a threshold concentration of 0.12 mol/L for the crosslinking process. Tensile tests of thermoplastic samples showed that incorporation of ca. 5 mol% of comonomer into the polyethylene main chain results in a semi-elastomeric material which possesses high strain recovery and whose strain hardening is similar to that observed for the homopolymer.