Mössbauer studies in an external field of well-crystallized Al-maghemites made from hematite

A series of hematites with up to 15 mol% Al substitution was converted to maghemites by reduction in the presence of organic matter, followed by slow oxidation. The maghemites formed were studied by Mössbauer spectroscopy in an external field of 60 kOe at 4 K. This technique allows the determination of site occupancy as well as the canting angle. The spectra are in agreement with a model having both vacancies and Al only in the octahedral sites and small canting angles for both sites. A small dipolar field at the tetrahedral sites was required to fit the line shape. The data indicate that about 10 mol% Al may be a solubility limit in maghemite.     

Improved quantitation of 13-cis- and all-trans-acitretin in human plasma by normal-phase high-performance liquid chromatography.

A reliable analytical method has been developed for measurement of 13-cis- and all-trans-acitretin (Neotigason) in human plasma by normal-phase high-performance liquid chromatography, with ultraviolet detection. Human plasma was obtained after centrifugation of whole blood samples and deproteinized by ethanolic denaturation. After liquid-liquid extraction with water-n-hexane, and aliquot ws chromatographed on a silica column using isocratic elution with n-hexane-methylsalicylate-acetic acid (200:18:0.6, v/v). The wavelength was set at 360 nm, and for plasma samples a limit of quantification of 3-4 ng/ml was obtained. All manipulations were carried out under dim light conditions to prevent photoisomerization.     

On the index of composition of integers from various sets

Given an integer n ≥ 2, let λ(n) := (log n)/(log γ(n)), where γ(n) = Π _p|n p, stand for the index of composition of n, with λ(1) = 1. We study the distribution function of (λ(n) – 1) log n as n runs through particular sets of integers, such as the shifted primes, the values of a given irreducible cubic polynomial and the shifted powerful numbers. Research supported in part by a grant from NSERC. Research supported by the Applied Number Theory Research Group of the Hungarian Academy of Science and by a grant from OTKA. Professor M.V. Subbarao passed away on February 15, 2006. Received: 3 March 2006 Revised: 28 October 2006     

The critical probability for random Voronoi percolation in the plane is 1/2

We study percolation in the following random environment: let Z be a Poisson process of constant intensity on ℝ², and form the Voronoi tessellation of ℝ² with respect to Z. Colour each Voronoi cell black with probability p, independently of the other cells. We show that the critical probability is 1/2. More precisely, if p>1/2 then the union of the black cells contains an infinite component with probability 1, while if p<1/2 then the distribution of the size of the component of black cells containing a given point decays exponentially. These results are analogous to Kesten's results for bond percolation in ℤ². The result corresponding to Harris' Theorem for bond percolation in ℤ² is known: Zvavitch noted that one of the many proofs of this result can easily be adapted to the random Voronoi setting. For Kesten's results, none of the existing proofs seems to adapt. The methods used here also give a new and very simple proof of Kesten's Theorem for ℤ²; we hope they will be applicable in other contexts as well. Research supported in part by NSF grant ITR 0225610 and DARPA grant F33615-01-C-1900 Research partially undertaken during a visit to the Forschungsinstitut für Mathematik, ETH Zürich, Switzerland     

Enantioseparation of Dencichine and D-Isomer on L-Cysteine Derivative Phase by Ligand-exchange Chromatography

Dencichine (β-N-oxalyl-L-α, β-diaminopropionic acid, L-ODAP), a nonprotein amino acid, is a haemostatic agent present in important Chinese medicinal herbs such as Panax notoginseng, as well as other Panax species1. It was first isolated from the seeds …     

Preconcentration of trace antimony in tap and sea water on activated alumina. Determination by graphite furnace atomic absorption spectrometry

Summary A method is described for antimony preconcentration based on retention on a column of activated alumina. Recovery is 80% when no pH-control and 4 mol/l HCl as eluent are used. The preconcentration factor is 400. The method was applied to the determination of antimony in spiked tap and sea water. The analytical performance of the method is discussed.     

Implementation of recycling routes for scanning probe microscopy tips.

In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route.     

Determination of iphosphamide and seven metabolites in blood plasma,as stable trifluoroacetyl derivatives,by electron capture chemical ionization GC-MS

A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C₁₈ adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma.