Anwendbarkeit der Zeeman-Effekt/Atomabsorption in der Komplexchemie und Spurenanalyse

The compensation of non specific background absorption is the main problem connected with determinations of traces of metals in the presence of large amounts of concomitants which volatilize together with the metal to be determined. This analytical problem manifests itself especially in flameless atomic absorption spectrometry used in coordination chemistry and trace analysis and can be very effectively mastered by the use of the Zeeman-effect atomic absorption spectrometry. This method works very well in the presence of 0.1 m KNO₃ or NAClO₄, where the most commonly used method, the deuterium background compensation, fails at this concentration of supporting electrolytes in most cases. The high compensating power of the Zeeman-effect method is also demonstrated by the determination of mercury in urine after a simple matrix modification by addition of HNO₃, Br₂ and KBr. The mechanism of the stabilization of mercury by this matrix modification is also discussed. The deuterium system failed in these determinations.     

Micro Dry Ashing for Trace Selenium Determination in Organic Matrices

Abstract

A specific sample treatment method was established for determination of ng levels of Selenium in microquantities of organic compounds. Our task was determination of Selenium traces, in a new pharmaceutical product, as a result of a laboratory scale synthesis, in an amount of several tens of mg. GFAAS was chosen as an analysis method, due to its sensitivity and rapidity. Among the wet and dry methods for organic material digestion tried, the low temperature dry ashing using ashing aid, was the only one which gave satisfactory recoveries of Selenium. Micro dry ashing was performed, using an Ethanol solution of Magnesium Nitrate on samples spiked with Selenium Nitrate in the range of concentration of 1–6ng mg^?1 at a temperature of 450°C for two hours. The presence of Magnesium Nitrate and the heating suppress the atomization with approximately 15–25%. Recoveries of Selenium varies as a function of the organic matrix: for polyaromate compounds as Chrysene and Fluoranthene they lie between 90–103% and for oxygenated compounds as Dimethoxybenzoic acid or Phthalates 23–50% respectively.

Another aspect of chemical interference by organic matrices and the way how to overcome it, has been clarified.     

Determination of order parameters from carbon–fluorine dipolar coupling

Abstract

A convenient NMR method for the determination of the order parameters for liquid crystals containing a fluorinated phenyl ring is described. The technique consists of measuring the carbon-fluorine dipolar coupling constants in the one-dimensional C-13 spectrum of the molecule. The order parameters may then be calculated for the fluorine-containing ring with a high degree of precision because of the excellent resolution afforded by the 1-D C-13 spectra. The method is used to determine the core order parameters for 4-n-hexyloxybenzilidene-4′-fluoroaniline (FAB-OC6). The results of the carbon-fluorine dipolar coupling method are compared with two established methods for determining the core order parameters of phenyl rings, namely deuterium NMR spectroscopy and SLF/VAS, a two-dimensional C-13 NMR spectroscopy. Some comments about the orientational properties of the fluorinated liquid crystal FAB-OC6 are made.     

Appraisal of different electrothermal atomic absorption spectrometric methods for the determination of strontium in biological samples

A comparative study of various potential chemical modifiers (La, Mg, Pd, Ni, Ta, Lu, Sm, Eu, Ho, Er, Tm and Tb) as well as of different background correction procedures (deuterium and Zeeman effect) and atomization techniques (wall and platform) for the direct determination of strontium in biological samples was carried out. Two instruments, one with deuterium and the other with Zeeman effect background corrections have been used to perform the experiments. Although La, Mg, Pd, Ta and Lu had a positive effect, lanthanum alone provided the best performance for the determination of strontium in whole blood, urine and bone digests using wall atomization without deuterium background correction. However, neither chemical modifier produced any significant improvement in sensitivity when Zeeman effect background correction with integrated platform atomization was used. Under the optimized conditions, the characteristic masses were 0.82 and 2.20 pg and the detection limits (3σ) were 0.13 and 0.30 μg l⁻¹ with wall atomization and with Zeeman effect background correction respectively. Recovery studies and analysis of standard reference materials certified for strontium were performed to assess the accuracy. The results for the determination of strontium in real samples with wall atomization and lanthanum as chemical modifier, agreed well with those obtained with Zeeman effect background corrector with a precision typically between 0.5 and 3%. Both procedures can be recommended, and the choice will depend on instrument availability.     

Determination of very low/levels of selenium(IV) in sea water by differential-pulse cathodic stripping voltammetry after extraction of the 3,3′-diaminobenzidine piazselenol

Selenium(IV) is determined by cathodic stripping voltammetry after the formation of a piazselenol with 3,3′-diaminobenzidine. The selenium is then accumulated as HgSe on a mercury electrode by deposition at ?0.45 V. The differential-pulse cathodic stripping peak allows a detection limit of 0.01 μg l^?1. For the determination of selenium in natural waters, interferences can be avoided by extraction of the piazselenol into toluene followed by a back-extraction into 0.5 M hydrochloric acid. The accuracy of the overall procedure was checked by analyses of a standard reference material. The method was applied to the determination of selenium(IV) in sea-water samples at levels as low as 20 ng l^?1 with a concentration factor of 10 during the extraction procedure.     

Speciation analysis of selenium in natural water using square-wave voltammetry after preconcentration on activated carbon

A simple, accurate, sensitive and selective method was described for rapid determination of ultra-trace quantities of selenium. Selenium(IV) was collected on activated carbon (AC) after reduction to elemental Se by l-ascorbic acid. The collected selenium was then dissolved by oxidation reaction with bromate in acidic media and was indirectly determined through the bromide formation using square-wave voltammetry (OSWV). The total amount of Se(IV) and Se(VI) was collected on AC after its reduction by hydrazine. Selenium in the range 0.01-20 μg L⁻¹ could be determined by this method. The method was used to the determination of Se(IV) and Se(VI) in natural water with satisfactory results.     

The problem of arsenic interference in the analysis of Cd to evaluate its extractability in soils contaminated by arsenic

The arsenic (As) spectral interference observed in the determination of cadmium (Cd) by inductively coupled plasma atomic emission spectrometry (ICP-AES) was studied in atomic absorption spectrometry (AAS) using flame (FAAS) and graphite furnace (GFAAS) as atomizers. The soils of 15 kitchen gardens located near two smelters in the North of France were selected according the ratio As/Cd. Four different extracting solutions usually used to evaluate the mobility of Cd were chosen to extract Cd from these soil samples: citric acid 0.11 M, acetic acid 0.11 M, calcium chloride 0.01 M and water. The quantitative determinations of Cd in the 15 soils for each solvent were investigated by ICP-AES at two lines (228.802 and 214.438 nm) and by FAAS or GFAAS with two-way background compensation. Compared to the Cd concentrations measured in the acid solutions and in the CaCl₂ solution after the addition of a chemical modifier, it was clearly demonstrated that the high-speed self-reversal background compensation (HSSR-method) was the method of choice to eliminate the spectral interference of As during Cd determination by FAAS and by GFAAS. In water, it was shown that the deuterium lamp used for the background compensation (D₂-method) was able to eliminate the most of the As interference. In comparison with Cd concentrations in water after adding a chemical modifier, those obtained with the HSSR-method were similar and a very good correlation was obtained between these two methods (R² = 0.995). It was therefore established that the HSSR-method would be able to replace the chemical modifiers to eliminate As interference in the determination of Cd-extractable from As contaminated soils.     

Determination of Thallium In Solid Environmental Samples By Electrothermal Atomic Absorption Spectrometry

Abstract

A method for the determination of thallium in solid environmental samples is developed. After destruction of the sample, TI(III) is extracted from 0.5 M hydrobromic acid solution into diisopropyl-ether. the organic phase is evaporated and the residue taken up in a mixture of sulfuric and nitric acids. Measurements are carried out with an atomic absorption spectrometer with Zeeman background corrector. the accuracy of the method is tested by analysis of certified reference materials and the method is applied to fly ash and emitted particulate matter from a municipal refuse incinerator and to soil samples.     

A critical study on the determination of selenium in gallium arsenide by polarographic techniques

A simple voltammetric method is described for the determination of traces of selenium in gallium arsenide. Differential-pulse cathodic stripping voltammetry permits a direct determination of selenium without preliminary enrichment or separation processes. Selenium can be determined down to levels of 1–2 μg g^?1, with relative standard deviations of about 10%, in ? 100-mg samples of gallium arsenide. Results for gallium arsenide doped with 7–75 μg g^?1 selenium agree in most cases with those obtained by spectrophotometry based on 4-chloro-o-phenylenediamine.     

Selenium Determination in Serum by Graphite Furnace Atomic Absorption Spectrometry

Selenium concentration in serum has been proposed as the most valuable indicator of human selenium status. In this work, the concentration of selenium in serum is measured by GFAAS using longitudinal Zeeman-effect background correction, a highly sensitive technique that can be used to determine selenium at sub-ppb level. Standard reference materials are analyzed to verify the accuracy and precision of this technique. The direct method proposed in this study is used for the determination of selenium in human serum collected from healthy people of 19–25 years and women of 21–34 years in the First trimester of pregnancy. The method developed in this study, which can quickly and accurately measure serum selenium, is suitable for applications in clinical diagnosis or biological monitoring.     

Precision Considerations in the Determination of Manganese in Mouse Brains by Furnace Atomic Absorption with Zeeman Background Correction

Abstract

A method is presented for the determination of manganese in mouse brains by furnace atomic absorption with Zeeman background correction. Precision for the method of standard additions is compared with that of aqueous calibration curves. NBS bovine liver SRM is analyzed to verify the accuracy of the method.     

Coprecipitative Preconcentration and Differential Pulse Cathodic Stripping Voltammetric Determination of Selenium (IV)

Abstract

A DPCSV procedure for the determination of selenium (IV) with a prior preconcentrative coprecipitation on iron (III) hydroxide has been developed. The experimental conditions for coprecipitation of selenium (IV) onto iron (III) hydroxide, viz. pH, iron (III) concentration, volume of aqueous phase and selenium concentration, were optimized. The coprecipitated selenium (IV) is dissolved in 10 ml of 0.1 M HCl and analysed using DPCSV in the presence of copper (II). Selenium concentrations as low as 10–100 ng present in 500 ml of the aqueous phase could be determined. The method is precise and has been applied to the analysis of sea water and reference material samples.     

Practical aspects of simultaneous determination of selenium and ytterbium by neutron activation analysis

An instrumental method for the simultaneous determination of selenium and ytterbium by thermal neutron activation analysis is described. Selenium and ytterbium were determined via the 400.7 keV photopeak of⁷⁵Se and the 177 keV photopeak of¹⁶⁹Yb. The accuracy of this instrumental method has been examined; as a result, it has been proved that this method is most exact and accurate when the gamma-ray counting is carried out after the decay of¹⁷⁵Yb.     

Method for Determination of Selenium and Arsenic in Human Urine by Atomic Fluorescence Spectrometry

Abstract

The study presents the method for simultaneous determination of selenium and arsenic in human urine by atomic fluorescence spectrometry (AFS). According to the procedure developed, a sample is first digested in the microwave system, then chemically treated in the flow through a hydride generation system, and finally exposed to measurements in a double‐channel atomic fluorescence spectrometer. It has been revealed that selenium and arsenic can be accurately determined with detection limit of 0.13 and 0.16 µg/L and repeatability (RSD) of 1.0 and 1.2%, respectively. The urine samples taken from a control group and from persons subjected to a special diet were analyzed. The obtained results proved that the method developed was capable of controlling reliably even slight changes of both elements in a wide range of their concentrations, and, as such, that it can be recommended to be used for clinical and toxicological purposes.     

Elemental Analysis by Gas Chromatography-Atomic Emission Detection for the Control of a Deuterated Derivatization Reagent

Abstract

Methyl iodide is a derivatization reagent often used to methylate molecules with amine, hydroxyl or carboxylic groups before a gas chromatographic analysis. In order to improve the analytical qualities of quantitative determination by gas chromatography mass spectrometry, derivatization with reagents labelled with stable isotopes can be used. Deuteromethyliodide can be used instead of methyliodide to obtain labelled compounds easily detected, as far as the reagent is pure enough.

This paper illustrates the use of the gas chromatography atomic emission detection coupling (GC-AED) for the study of the purity of a reagent labelled with deuterium (IC²H3) used for the derivatization of a new immunoenhancer (sodium ditiocarb - lmuthiol^R) before the GC-MS determination of the parent drug and its methylated metabolite. The elements monitored simultaneously are: carbon (193.03 nm), hydrogen (656.3 nm), deuterium (656.04 nm), iodine (183.1 nm) and sulfur (180.7 nm). The chromatograms corresponding to these various elements obviously show the presence of compounds containing deuterium and I or hydrogen associated with iodine and make easier and faster the determination of the chemical pollution of the IC²H3 batch. The monitoring of the specific wavelength associated to the atomic emission of sulfur (180.7 nm) allows easy detection o f ditiocarb and its metabolite from the chromatogram made very complex by the reagent pollution.     

Specifically deuteriated intermediates for the synthesis of liquid crystals and liquid-crystalline polymers

Abstract

The recent developments in solid state N.M.R. techniques have rendered deuterium a most attractive nucleus for use in the study of liquid crystals and other ordered systems. Its application often requires that the deuterium be positioned at specific sites in the molecule. Here, the preparation of such specifically labelled compounds for use in liquid crystal research is discussed. It is shown that many deuteriated liquid crystals can be prepared from a limited set of labelled intermediates. Strategies for the labelling of such intermediates in both aromatic and aliphatic sites based on experience gained in the author's laboratory during the last years are discussed. In the experimental section more than fifty procedures for obtaining specifically deuteriated intermediates and mesogens are described in detail.     

Kinetic Determination Of Nitrite Based On The Griess Reaction And The Stopped Flow Technique

Abstract

A kinetic method for nitrite determination in solution is described. The method is based on the Griess reaction and the stopped-flow technique. The time between two preset levels of the output signal is used as a measure of the nitrite concentration. The determination involves only one step and is independet on the background absorption of the reagents. The working curve can be made with only 2 or 3 points. No blank value is shown. The method can be applied to dilute or(more) concentrated nitrite solutions by appropriate change of their pH. Concentrations as low as 1.10^?6M NO₂ ^? can be determined.     

The determination of selenium in water samples from the environment

A method for the determination of selenium by preconcentration and thermal neutron activation is presented. Selenium is adsorbed on active charcoal after reduction to the elemental state. By varying the conditions of the reduction, it is possible to measure the total selenium content and tetravalent selenium separately. The contribution of hexavalent selenium is obtained by substraction. The lower limit of determination is 5 ng°1⁻¹. About 40 samples per day can be handled by one analyst. The preconcentration can be performed at the sampling site resulting in samples, which can be stored easily for later analyses by neutron activation.     

Analysis of Dexamethasone Acetate in Pharmaceutical Formulations by HPLC

Abstract

A rapid and effective high-pressure liquid chromatographic method has been developed for the quantitative determination of dexamethasone 21 acetate in pharmaceutical formulations. Sample preparation employs a simple extraction procedure and analysis is carried out on a reversephase chromatographic system using a LiChrosorb RP 18 column and a water-acetonitrile as mobile phase. The extraction procedure gives quantitative recovery and chromatographic results show that drug levels of as 0.1 ppm can be conveniently analyzed without significant background interferences.     

Quantitative <Superscript>2</Superscript>H NMR spectroscopy

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by ²H-{¹H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group. For Part 2, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008.