Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.     

High performance liquid chromatography with an electrochemical detector in the cathodic mode as a tool for the determination of p-nitrophenol and assay of acid phosphatase in urine samples

Utilizing a commercially available helium-purging device and PEEK tubes for all tubing, especially for connection between the mobile phase and pump, high performance liquid chromatography with an electrochemical detector (ECD/HPLC) at the cathodic mode is a simple and precise method for the determination of p-nitrophenol (NP). Studies with cyclic and hydrodynamic voltammetry indicated that 25% aqueous MeOH containing 0.1% (v/v) CF(3)CO(2)H and -0.8 V vs. Ag/AgCl are the best mobile phase and detection potential for cathodic ECD/HPLC. With the present system, the limits of detection and determination were 0.2 and 0.25 microM, respectively, and up to 50 microM, a linear calibration curve was afforded. Within-day precisions for the analysis of 5 and 50 microM NP were 0.8 and 0.7% (n=6), respectively, and between-day precisions (n=6) for these samples were 3.5 and 2.2%, respectively. Compared with the commonly used Bessey-Lowry-Brock method, cathodic ECD/HPLC was useful for the assay of acid phosphatase in urine samples with p-nitrophenyl phosphate disodium salt as a substrate.     

Determination of phosphorus in biological material using electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser

Phosphorus has been determined by electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser. The effects of interferents on the phosphorus signal have been investigated. Chemical interferences were eliminated by high-temperature pyrolysis. The detection limit for the molybdenum tube system was 2.3 ng (corresponding to 2.3 micrograms ml-1 when 1 microliter was injected into the atomiser) and the characteristic mass was 1.9 ng of phosphorus. A calibration graph method combined with high-temperature pyrolysis has been evaluated through the determination of phosphorus in biological materials. The sensitivity, accuracy and precision of the method were superior to or nearly equal to those of graphite furnace atomic absorption spectrometry. The advantages of the high-temperature pyrolysis method are its simplicity and low cost.     

Highly Selective Separation of Rhodopsin from Bovine Rod Outer Segment Membranes Using Combination of Divalent Cation and Alkyl(thio)glucoside

The micellization process of bovine rod outer segment (ROS) membranes is investigated utilizing a series of neutral detergents. It is found that when alkyl(thio)glucosides with an appropriate hydrophilic–lipophilic balance (e.g. octylthioglucoside) are used in combination with a divalent cation, rhodopsin is selectively extracted from ROS membranes at a specific detergent-to-membrane ratio. This allows remarkable purification of rhodopsin by a single-step solubilization, because the residual membranes are heavily aggregated in the presence of divalent cation and are therefore easily sedimented by low-speed centrifugation. The absorption spectrum of the supernatant reproducibly exhibits an A₂₈₀/A₅₀₀ value of 1.6, an excellent value that could rarely be obtained by chromatographic purification. The degree of purification also depends on the type of divalent cation included in the solubilization solution; specific binding of IIB-series cations (Zn²⁺ and Cd²⁺) to ROS membranes is suggested to play an important role in the solubilization process. The present result represents a unique example of selective solubilization of a specific membrane protein from highly aggregated membranes.     

Chemistry of the neopolyoxins,pyrimidine and imidazoline nucleoside peptide antibiotics

New chitin synthetase inhibitors, neopolyoxins A, B, and C were isolated from the culture filtrate of Streptomyces cacaoi subsp. asoensis. Their absolute structures have been established on the basis of chemical and spectroscopic evidence. They are structural analogs of the polyoxins. As a nucleobase, neopolyoxin C possesses uracil, while neopolyoxins A and B contain the imidazoline moiety. A ring contraction reaction of pyrimidine nucleoside into imidazoline nucleoside played a key role in the structure determination of the nucleoside moiety. A similar transformation was suggested for the biosynthesis of neopolyoxins A and B.     

Chains of strongly non-reflexive dual groups of integer-valued continuous functions

Answering a question of Eklof-Mekler (Almost free modules, set-theoretic methods, North-Holland, Amsterdam, 1990), we prove: (1) If there exists a non-reflecting stationary set of consisting of ordinals of cofinality for each , then there exist abelian groups such that and for each . (2) There exist abelian groups such that for each and for each . The groups are the groups of -valued continuous functions on a topological space and their dual groups.

     

Coating and water permeation properties of SiO2 thin films prepared by the sol-gel method on nylon-6 substrates

Nylon-6 substrates were coated with SiO₂ thin films by the sol-gel method and their water permeability coefficient was evaluated. Methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) were used as starting materials. The addition of MTES to TEOS has enabled the formation of crack-free thin films on the substrates. The thin films strongly adhered to the substrates. The water permeability coefficients of nylon-6 substrates coated with these thin films decreased with the increase in the ratio of TEOS to the total alkoxides. The pretreatment of the nylon-6 substrates with -aminopropyltriethoxysilane was found to be effective to suppress the water permeability. The water permeability was suppressed by about 40% under the optimal condition.