Zeev B. Alfassi

Determination of trace elements

Systematic errors in trace element analysis limits of detection and accuracy in trace element analysis sampling and sample preparation separation and preconcentration of trace elements determination of trace elements by atomic absorption spectrometry plasma optical emission and mass spectrometry instrumental neutron activation analysis (INAA) radiochemical neutron activation analysis determination of trace elements by electron spectrometry trace element determination by electrochemical methods determination of trace elements by chromatographic methods speciation of the elements trace element determination in environmental biology and health sciences.

Determination of antimony(III,V) in natural waters by coprecipitation and neutron activation analysis

Abstract A simple and quantitative method for separating antimony(III) from antimony(V) by coprecipitation with thionalide is described. The total concentration of antimony is determined through addition of tin(II) chloride followed by thionalide coprecipitation and antimony(V) is determined by substraction. The coprecipitation system was investigated with the use of 122 Sb radiotracer. The precipitate was collected on a membrane filter for neutron activation analysis. The dectection limit of antimony was found to be in the order of ng l −1 under the experimental conditions. The reliability was checked with National Research Council of Canada standard reference material.

Long range electron transfer between tyrosine and tryptophan in hen egg-white lysozyme

The azide, dibromide and dichloride radicals oxidize one or more tryptophan side chains in hen egg-white lysozyme. The indolyl radical produced in this second-order 1-electron oxidation subsequently oxidizes a tyrosine side chain to the phenoxy radical in an intramolecular reaction with a rate constant of 130 +/- 10 s-1 at pH 7, 25 degrees C. The final indolyl and phenoxy equilibrium mixture then decays with a t1/2 approximately 2 s. The faster intramolecular reaction exhibits a pH dependence; on decreasing the pH from 9 the first-order rate constant increases to a maximum near pH 5.4 and then declines as the pH is lowered further. In contrast, the first-order rate constant for the intramolecular electron transfer between the tyrosine and tryptophan of the peptide trpH-pro-tyrOH remains unchanged between approx. pH 11 and 6.5 and then increases as the pH is lowered further. This difference in the observed pH dependence suggests that changes in structure or ionization state influence the protein electron transfer rate. We also discuss the radiation inactivation of lysozyme in light of these observations.

Excitation functions and yields for cyclotron production of radiorhenium via nat W(p,ߙxn)181-186gRe nuclear reactions and tests on the production of 186gRe using enriched 186W

Abstract Excitation functions and thin-target yields for the 181-186gRe radionuclides have been measured by the stacked-foil activation technique on tungsten foils of natural isotopic composition for different proton energies up to 22.0 MeV. A further check on the cross sections was done by irradiation of thick-targets and comparing the irradiated thick-target yields with those calculated by analytical integration from the thin-target yields. The production of 186gRe was also studied by the irradiation of thick-target of enriched 186W with a 13.6±0.2 MeV proton beam. The results for 186W(p,ߙn)186gRe were compared also to those calculated by the EMPIRE II code (version 2.19), due to 186gRe extensive applications in nuclear medicine for metabolic radiotherapy of tumours. It was found that the maximum percentage of 186gRe by irradiation of natural tungsten is about 20% only, which confirms the conclusion that high radionuclidic purity and specific activity of 186gRe necessitate the use of highly enriched 186W target.

Off-center efficiency of HPGe detectors

The gamma ray detection efficiency of two HPGe detectors for off-center points was measured both on the detectors cap and outside the detectors cap. It was found that similar to measurements on the detector symmetry axis, for off-center measurements including those outside the detector cap also, the detector could be treated as an effective point detector. The virtual point detector was found to be almost at the same position for vertical and horizontal source displacements.

Statistical treatment of analytical data

Introduction. Statistics of Repeated Measurements. Significance Tests. Sampling. Statistics of Calibration Curves. Non Parametric Tests. Experimental Design. Basic Quality Control.

Simultaneous determination of sodium, magnesium, aluminium, silicon and phosphorus by instrumental neutron-activation analysis using reactor and epithermal neutrons

Sodium, magnesium, aluminium, silicon and phosphorus were determined simultaneously by measuring the activities of 24Na, 27Mg and 28Al produced by neutron activation once with reactor neutrons and once with epithermal neutrons (those neutrons from a nuclear reactor that are not absorbed by a cadmium sheet). The six countings gave six equations from which the required five quantities were calculated. Several known mixtures were checked, and the ranges in which Si and P could be determined were found (Si : Al and P : Al >10 : 1).

Off center gamma ray detection efficiencies of cylindrical single open ended (SOE) Ge(Li) detectors

Abstract The gamma ray detection efficiencies of off center points on the surface of a Ge(Li) detector, of a cylindrical single open ended (SOE) type, were measured relative to the efficiency of the center of the detector. The radial dependence of the efficiency e(r) can be approximated quite satisfactorily by the equation ϵ(r) = e0 exp (— Br2), were e0 is the efficiency at the center of the detector and B is a constant characteristic of the detector and the energy of the γ rays.

Detection and identification of cations and anions of ionic liquids by means of electrospray ionization mass spectrometry and tandem mass spectrometry

Electrospray ionization (ESI) and collision-induced dissociation (CID) spectra of nine ionic liquids have been measured. The main fragmentations of most of these ionic liquid cations were due to the loss of a butene molecule. In contrast to tetraalkylammonium ions, CID spectra of aromatic cations may represent insufficient information for unambiguous identification due to their only partial fragmentation. CID spectra of ionic liquid anions, however, allowed their reliable recognition, since isomers/isobars of such inorganic species are rare. Detection limits of cations and anions in a mixture of different ionic liquids seemed to depend on their surface activity as determined by the hydrophobicity of these species.

Direct determination of manganese in sea-water by electrothermal atomic absorption spectrometry with sodium hydroxide as chemical modifier for interference removal

A direct method was developed for the determination of Mn in sea-water by atomic absorption spectrometry (AAS) with a graphite furnace. The use of NaOH for chemical modification allowed the removal of the matrix major elements by prior ashing at a lower temperature (1400 °C) for at least 100 s. Manganese was subsequently volatilized at 2000 °C and determined by AAS. The proposed method was used for the direct determination of Mn in open ocean water by the calibration technique and the standard-additions method. CASS-2 reference sea-water was used for quality control; the results were in good agreement with the certified values. By using 80 µl injections, a detection limit of 0.051 ng ml–1 was achieved.