Automated radiochemical procedure for plutonium and americium measurement

A radiochemical separation method for plutonium and americium from aqueous medium has been developed using a pre-packed resin column, a peristaltic pump, and the necessary tubing and valves for flow injection technique. All the radioanalytical operations were conducted in-line. Samples made of plutonium and americium tracers in water were analyzed by this technique and counted by alpha spectroscopy. The results show that plutonium and americium can be measured simultaneously using this technique.     

Measurement uncertainty in the pH measurement procedure

A measured value without even an approximate knowledge of the uncertainty is worthless. The uncertainty is part of every measured value and specification of the uncertainty is part of every analytical procedure. The uncertainty makes the value independent of its origin. The basis for estimation of the uncertainty is the "Guide to the Expression of Uncertainty in Measurement ". For some procedures, however, for example pH measurement, several problems arise in practice. This article describes a practical and inexpensive way of calculating the uncertainty of pH values.     

Polymer-supported O-methylisourea: a new reagent for the O-methylation of carboxylic acids

[reaction: see text] A solid-supported O-methylisourea reagent has been prepared in one step starting from commercially available solid-supported carbodiimide. The isourea reagent has been successfully used for the preparation of methyl esters from the corresponding carboxylic acids. The crude products obtained after resin filtration and solvent evaporation are generally obtained in >98% purity.     

Development of a reference measurement procedure for the determination of methylmercury in fish products

The development of an analytical procedure for speciation analysis of methylmercury in fish products is presented. The method is based on high-performance liquid chromatography hyphenated to inductively coupled plasma-mass spectrometry. The metrological approach is stressed out in this paper, in order to provide reliable and comparable results. A complete uncertainty budget has been evaluated and the method has been validated by the use of a certified reference material. Moreover, the detection could rely on the isotope dilution mass spectrometry, a powerful strategy capable of highly accurate results traceable to the “Système International d’Unités” and recognised by the “Comité Consultatif pour la Quantité de Matière” as a primary method of measurement. Presented at MEFNM 2008, September 2008, Budapest, Hungary.     

Ion chromatographic precision measurement procedure for electrolytes in human serum: validation with the aid of primary measurement procedures

In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%.     

Ion chromatographic precision measurement procedure for electrolytes in human serum: validation with the aid of primary measurement procedures

In order to make analytical measurement results traceable to the SI units in the field of clinical chemistry, an ion chromatographic (IC) measurement procedure has been developed which allows the amount of substance of the four so-called electrolytes Na, K, Mg and Ca as well as that of Li to be determined efficiently in human serum and with high accuracy. The IC measurement procedure was validated using primary measurement procedures confirmed by international comparison measurements and is proposed for use as a transfer standard when comparing measurements with clinical reference laboratories. The solutions used for calibration were gravimetrically prepared from pure substances (salts). Their chemical compositions had been iteratively fitted to those of the samples. The serum samples were mineralized by microwave-assisted digestion. The following relative expanded uncertainties for the average elemental contents were obtained: Li 0.4%, Na 0.14%, K 0.6%, Mg 0.8% and Ca 0.4%.

     

A candidate reference measurement procedure for Cyclosporine A in whole blood

Monitoring of Cyclosporine A (CsA) concentrations in whole blood is widely performed due to the narrow therapeutic index of the drug. Required standardisation for routine analysis of CsA is still missing. The candidate reference measurement procedure presented here is designated for the assignment of CsA values in hemolysed blood associated with expanded measurement uncertainty. Separate stock solutions for calibration and control materials were prepared by spiking hemolysed blood with CsA under gravimetric control. The essential sample pretreatment step was protein precipitation. Analysis was performed using isotope dilution LC-MS/MS with online solid phase extraction. Interference by matrix components was investigated. Using [²H₄]-CsA as the internal standard, no interference from the investigated matrices were detected. Measurement repeatability using three pools of whole blood as samples revealed coefficients of variation (CV) ranging from 1.0 % to 1.6 %. Intermediate measurement precision was determined by repeated analysis of self-prepared control materials taken from different stock solutions of pooled whole blood. CVs were between 0.8 % and 2.4 %. Measurement accuracy was checked using three control materials prepared from three different stock solutions. The recoveries of the mean of mean values obtained on four measurement days ranged from 99.4 % to 101.3 %. The combined expanded uncertainty of measurement based on 5 days of measurement and was evaluated according to the GUM as U = 2.0 % (k = 2).     

An enantioselective voltammetric sensor for the recognition of propranolol stereoisomers

An enantioselective voltammetric sensor for the recognition of propranolol stereoisomers is developed based on a carbon-paste electrode modified with uracil supramolecular structures and the use of chemometric methods. The conditions for the formation of an enantioselective selector on the surface of graphite (graphene) particles and the selective registration of voltammograms of enantiomers, as well as the possibility of the recognition thereof, are studied by methods of molecular dynamics simulation and voltammetry.     

Theoretical study of the stereoisomers of tetrahydrocannabinols

A theoretical AM1 semiempirical study of the major active components of marijuana and their stereoisomers is presented. It was found that the calculated partition coefficients, dipole moments, heats of formation, volume, surface area, ovality, and conformation of the pyran ring cannot explain the activity differences between the stereoisomers. The major factor is the orientation of the carbocyclic ring and its C₁ substituent with respect to the phenyl group hydroxyl oxygen. Our study has revealed and supports the involvement of previously described steric features of cannabinoids in determining their biological potency. Based on these conclusions, we predicted the relative activities for the (+)-cis-δ¹-THC, (-)-cis-δ¹-THC, (+)-cis-δ⁶-THC, and (-)-cis-δ⁶-THC stereoisomers, which have not been synthesized. © 1997 John Wiley & Sons, Inc.     

Cysteine carboxyl O-methylation of human placental 23 kDa protein

C-Terminal carboxyl methylation of a human placental 23 kDa protein catalyzed by membrane-associated methyltransferase has been investigated. The 23 kDa protein substrate methylated was partially purified by DEAE-Sephacel, hydroxyapatite and Sephadex G-100 gel filtration chromatographies. The substrate protein was eluted on Sephadex G-100 gel filtration chromatography as a protein of about 29 kDa. In the absence of Mg2+, the methylation was stimulated by guanine nucleotides (GTP, GDP and GTPgammaS), but in the presence of Mg2+, only GTPgammaS stimulated the methylation which was similar to the effect on the G25K/rhoGDI complex. AFC, an inhibitor of C-terminal carboxyl methylation, inhibited the methylation of human placental 23 kDa protein. These results suggests that the substrate is a small G protein different from the G25K and is methylated on C-terminal isoprenylated cysteine residue. This was also confirmed by vapor phase analysis. The methylated substrate protein was redistributed to membrane after in vitro methylation, suggesting that the methylation of this protein is important for the redistribution of the 23 kDa small G protein for its putative role in intracellular signaling.     

Selective O-methylation of polyhydroxyflavan-3-ols via benzyl carbonates

The flavan-3-ols (+)-catechin and (−)-epicatechin were selectively transformed to their 3′,4′-di-O-methyl- and 5,7-di-Omethyl-ethers respectively via benzyl carbonates. Such a regioselectivity is facilitated by marked differences in the pKa values of the phenolic hydroxyl groups and by the ability of the o-dihydroxy funtionality of the pyrocatechol B-ring to form borate complexes under mild basic conditions.     

Two stereoisomers of the rat toxicant norbormide

The structures of two diastereoisomers of norbormide {systematic name: 5‐[hydroxy­(phenyl)(2‐pyridyl)­methyl]‐8‐[phenyl(2‐pyridyl)­methyl­ene]‐3a,4,7,7a‐tetra­hydro‐4,7‐methano‐1H‐iso­indole‐1,3(2H)‐dione}, viz. the unsolvated mol­ecule, C₃₃H₂₅N₃O₃, and the ethyl acetate hemisolvate, C₃₃H₂₅N₃O₃·0.5C₄H₈O₂, have been determined unambiguously. They differ in the relative stereochemistry about the exocyclic double bond and the relative conformations of the aryl rings. Each compound exhibits both intra‐ and intermolecular hydrogen bonding.     

Validation of an in-house measurement procedure for determination of selected priority hazardous substances in water and estimation of measurement uncertainty

Accreditation and Quality Assurance - This study investigates measurement procedure validation for the determination of hexachlorobenzene, pentachlorobenzene and trifluralin as priority hazardous...     

Development of a rapid procedure for the measurement of uranium in drinking water by PERALS® spectrometry

A new method has been developed for the measurement of U in water samples by selective and quantitative extraction from DTPA solution into an extractive scintillator containing HDEHP and alpha-counting by PERALS^® spectrometry. Because this method offers several advantages over the current EPA and ASTM standard test methods for U in drinking water, including speed, simplicity and isotopic information, it has been proposed as a new ASTM standard test method. Sample preparation requires from 1–4 h. Less than 0.5% of Am, Pu, Po, Ra and Th were found to extract under the prescribed conditions. Typical backgrounds are ≤0.01 cpm. A comparison of this method with EPA standard method 908.0 and the results of two interlaboratory tests of this method are reported.     

Asymmetric synthesis of all the stereoisomers of tarchonanthuslactone

We describe herein an efficient synthesis of all the four stereoisomers of tarchonanthuslactone from (R)-3-hydroxy butanoate, easily prepared from l-threonine. The approach involves the use of a β,γ-unsaturated δ-lactone as an intermediate, obtained via a Kulinkovich reaction followed by a ring-closing metathesis strategy.     

Gamma-spectrometric measurement procedure for a clearance concept of radioactively contaminated mercury from nuclear facilities

Journal of Radioanalytical and Nuclear Chemistry - Radioactive mercury waste constitutes a significant challenge, as no approved disposal concept yet exists for such waste in Germany. This work...