Determination of trace concentrations of hexavalent chromium

A simple and sensitive solvent extraction-atomic spectrometric technique has been developed for the determination of hexavalent chromium in fresh and saline waters. The technique is based on the reaction of chromium with diphenylcarbazide. The method has been tested on a variety of water samples over an analytical range of 0-2 microg l(-1). A limit of detection of 0.024 microg l(-1) was achieved. Spiking recoveries in the range 87-115% were achieved in river water, drinking water and marine waters.     

Determination of ultra trace concentrations of nitrite in polluted waters and soil

The nitrite is used to diazotize o-nitroaniline and the o-nitrophenyldiazonium chloride formed is coupled with N-(1-naphthyl)ethylenediamine dihydrochloride. The red-violet dye (absorption maxima at 545 nm) is stable and extractable into isoamyl alcohol. Beer's law is obeyed in the range 0.1-0.6 ppm nitrite in the original sample if the aqueous system is measured, and 0.025-0.15 ppm in the sample if extraction is used. The molar absorptivity is 6.04 x 10(4)l.mole(-1).cm(-1).     

Determination of trace concentrations of dissolved nitric oxide in a biological buffer

A new real-time method for measuring a trace concentration of nitric oxide (NO) in a complex matrix routinely used in pharmacological studies of its bioactivity is described. NO was quantified as a gas by chemiluminescence after extraction from a continuous liquid sample flow with a limit of detection of 0.042 nmol dm(-3) at a signal to noise ratio of 3. Theories to calculate the concentration of NO in the liquid sample flow from a direct measurement of NO in the extraction carrier gas are presented. The efficiency of extraction is determined by a stopflow experiment. An example is presented of the measurement of the steady-state concentrations of NO in Krebs-bicarbonate buffer at pH 7.4 and 37 degrees C when its liquid surface is sequentially exposed to gases containing various concentrations of NO in O2 plus CO2.     

水相合成CdTe量子点测定海藻中微量碲

以亚碲酸钠(Na2TeO3)为Te源,CdCl2为Cd源,水合肼(SHJ)为还原剂,3-巯基丙酸(3-MPA)为稳定剂,制得λEX=380 nm和λEM=608 nm的CdTe量子点(CdTe QDs),该量子点的荧光强度与合成前Na2TeO3浓度呈线性关系.在n(Cd)/n(SHJ)=1∶0.04,n(Cd)/n(3...     

Partition behavior and partial purification of hexokinase in aqueous two-phase polyethylene glycol/citrate systems

This study dealt with the partition behavior and partial purification of hexokinase (HK) from baker’s yeast by liquid-liquid extraction using aqueous two-phase polyethylene glycol (PEG)/citrate systems. First, we investigated the effect of agitation type (vortex and 8 rpm rotation) on the stability of the system, and then the effects of sodium citrate concentration, PEG concentration, and molar mass of PEG on the partition coefficient of this enzyme by using a 2⁵ factorial experimental design. The results of this factorial experiment showed the possibility of a partial purification of HK by using two extraction steps, since the enzyme preferentially migrated to the top phase and the total proteins (mainly contaminants) remained in the bottom phase. The purification factor (Pur _TOP) of the enzyme in the top phase was 1.87, and the partition coefficient of the total proteins (K _Prot ) was 0.47.     

Determination of trace concentrations of transmuted stable nuclides in TMD detectors using PGAA

The capability of prompt gamma-ray activation analysis (PGAA) for neutron fluence dosimetry by means of transmutation detectors is reported. The metallic foils of Ni, Au, Cu and Nb and the small piece of Ge crystal, which were irradiated at the LVR-15 reactor at ?e? for several days, were selected for analysis by PGAA technique. Concentrations of transmuted stable nuclides in these foils were measured using the PGAA facility installed at the research reactor FRM II in Garching.     

Determination of petroleum trace impurities in aqueous samples by chromatography in a steam flow

A procedure was developed for the determination of trace petroleum products in water by gas chromatography with steam as the carrier gas. Solid-phase microextraction was used for sample preparation. A method for the stabilization and homogenization of water samples before the analysis and a method for the removal of polar components of the sample were proposed. The precision and accuracy indices of the proposed procedure were estimated for aqueous solutions of a mixture of diesel fuel and oil with a concentration close to the maximum permissible concentration. The relative error in the measurement is no more than ～25% in the concentration range of petroleum products of 0.05–0.5 mg/L.     

Determination of trace concentrations of bromophenols in water using purge-and-trap after in situ acetylation

An analytical method that enables detection and quantification of bromophenols (BPs) at taste threshold concentrations (2,6-DBP: 0.5 ng/L) was developed. This method involves conversion of the BPs to their acetates, followed by isolation of the acetates by a modified purge-and-trap procedure, and analysis by gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode. Bromophenyl acetates were synthesized so that each of the two steps in the method could be developed and optimised in isolation to the other. Deuterated BPs (phenol-d5, 2-BP-d4, 4-BP-d2, 2,6-DBP-d3, 2,4-DBP-d3 and 2,4,6-TBP-d2) were synthesized to enable quantification of analytes using the deuterated analogues of analytes as internal standards. This method allowed quantification of BPs at concentrations ranging from the detection limits (3 ng/L for phenol and 0.1-0.5 ng/L for each of the BPs) to 1000 ng/L for each analyte, with repeatabilities of < or =14% (RSD) for concentrations of 1 ng/L and < or =9% (RSD) for concentrations of 10-1000 ng/L, with recoveries ranging from 91 to 97%.     

Effect of pH and reagent concentrations on gelation of magnesium-silicate aqueous systems

The rate of gelation of the maghesium-silicate aqueous systems was studied in relation to pH and concentration of particular magnesium salts. The magnesium and silicate ions were found to interact in solutions at low temperature.     

Preconcentration procedures for trace cadmium determination in natural aqueous systems prior to zeeman etaas

Nanotrace Cd determination in natural waters using two new flotation collectors, lead(II) heptyldithiocarbamate, Pb(HpDTC)₂, and cobalt(III) heptyldithiocarbamate, Co(HpDTC)₃, are presented. The optimization of the most important experimental parameters for flotation is given. Zeeman electrothermal atomic absorption spectrometry (ZETAAS) is used as an instrumental technique for Cd measurement. The results are compared with those obtained by other preconcentration procedures as independent methods. The limit of detection of ZETAAS using Pb(HpDTC)₂ as collector is 4.8?ng/L, while using Co(HpDTC)₃ it is 3.0?ng/L.     

Determination of trace element concentrations in meteorites by inductively coupled plasma — Mass spectromety

Determination of 25 trace elements in the meteorites Allende and Murchison by ICP-MS is described. Samples are digested using HF, HNO₃, and HClO₄ at 140°C and diluted into HNO₃. Element concentrations were determined using USGS terrestrial rocks as standards for calibration. Precision and accuracy of the technique, evaluated based on measurements of samples of known composition, are for 16 elements better than 10%.     

Determination of low concentrations of iodine-131 in fast-reactor coolant systems

A method has been devised for the determination of iodine-131 in the presence of mixed fission products in reactor coolants, by oxidation to elemental iodine followed by sublimation on to copper gauzes. The method reduces to a minimum contamination of the copper gauzes by ruthenium-103 and ruthenium-106 and eliminates contamination due to technetium-99 and caesium-137. It is possible to determine 10(2)cpm ml from iodine-131 in a total count of 2 x 10(6)cpm ml of fission products, with an accuracy of +/- 3%. The only activity collected on the copper gauzes was iodine-131 (62% collection efficiency) and ruthenium-103 (0.005% of total activity) which gave comparable count rates. The activity of these two isotopes was separated by single-channel gamma analysis.     

Determination of the concentrations of trace and doping elements in GaAs by neutron activation analysis

The concentrations of ten trace and dopant elements in GaAs semiconductor were determined by reactor neutron activation analysis after removal of As by evaporation of AsCl₃. The retentions of the elements of interest were measured using radiotracers. The concentrations of doping elements (Te, Cr and Zn) in commercial GaAs samples were compared to the limit of detection of these elements to analyze the possibility to use NAA for concentration depth profiling measurements. The NAA results were compared with those of electrical measurements and SIMS and the discrepancies found are discussed.     

The methods of determination of critical micellar concentrations of the amphiphilic systems in aqueous medium

Science is the attempt to make the chaotic diversity of our sense-experience to a logically unified system of thought. A sound theoretical basis and a rational physicochemical understanding based on experimental findings lead to a proper understanding of a topic. Colloid chemistry strengthened its footing by the extensive studies on gold sols by Michael Faraday in 1850s, however, the term “colloid” was coined by Thomas Graham in 1861. Historically, the Stone Age paintings in the Lascaux cave in France and the written records of Egyptian pharaohs were produced with stabilized colloid pigments. The part of colloid science dealing with amphiphilic molecules is so diverse on its own that it is dealt in a separate branch called the “association colloid”. A key development in the study of association colloids was the observation by James McBain that the osmotic pressure of salts of alkali metal fatty acid displayed a pronounced break in the concentration beyond a specific characteristic concentration, after which the osmotic coefficient remained almost constant (Evans and Wennerstrom, 1994). McBain attributed this fact to the self-association of these molecules among themselves (McBain, 1913, McBain, 1944) in solution. Here, we are providing a molecular as well as thermodynamic approach toward the micellization process.     

Speciation methods of actinides in trace concentrations

The development of actinide speciation methods in the environment is discussed. The results on speciation and migration of radionuclides in near-surface and deep conditions at the Krasnoyarsk mining and chemical plant and at the Production Association ‘Mayak’ (southern Ural) are reported. For surface conditions, the mobile plutonium fraction is mostly associated with inorganic complexes (carbonate) of the higher plutonium oxidation state, while less mobile fraction is associated with low-soluble Pu(IV) complexes with humic acids. The mobile fraction of americium consists of complexes with low molecular weight fulvic acids of non-specific nature with molecular weights lower than 10 kDa. Plutonium and americium behaviour in deep conditions is governed by colloid migration. To cite this article: A.P. Novikov et al., C. R. Chimie 7 (2004).

Résumé

Méthodes de spéciation des actinides en traces. Le développement de méthodes pour la spéciation des actinides dans l’environnement est discuté. Nous présentons des résultats concernant la spéciation et la migration des radionucléides dans des conditions de sub-surface et en milieux géologiques profonds à la mine de Krasnoyarsk et à l’usine chimique de Mayak (Oural du Sud). En conditions de sub-surface, la fraction mobile contient essentiellement des complexes inorganiques (carbonates) de Pu dans ses degrés d’oxydation élevés, tandis que la fraction moins mobile contient des complexes insolubles du Pu(IV), avec des acides humiques. La fraction mobile de Am comporte des complexes d’acides fulviques de nature non précisée, mais d’une masse molaire inférieure à 10 kDa. En conditions de milieu profond, le comportement de Am et de Pu est influencé par la migration des colloïdes. Pour citer cet article : A.P. Novikov et al., C. R. Chimie 7 (2004).     

Determination of trace element concentrations of indian cigarette tobacco by instrumental neutron activation analysis

Lung cancer and smoking are associated. Epidemiological studies show that not only lung cancer but other chest diseases have causative relationship with smoking. Cigarette tobacco and smoke contains many carcinogens. Inorganic and metallic constituents of cigarette tobacco and smoke have not been studied as extensively as the organic compounds. Since some of the metals are highly toxic and also carcinogenic, authors have attempted to measure the levels of some of the trace elements of Indian tobacco by instrumental neutron activation analysis, and compared the results with the tobacco of America, Germany, Iran and New Zealand.     

Determination of trace concentrations of thorium in uranium oxide matrix by epithermal instrumental neutron activation analysis

An epithermal instrumental neutron activation analysis (EINAA) method using cadmium filter was standardized to determine trace concentrations of thorium in four samples of uranium oxide (U₃O₈) samples. Samples and thorium standards, wrapped with cadmium foil, were irradiated at a reactor neutron flux of about 10¹² cm^?2 s^?1. Radioactive assay was carried out using a Compton suppressed anticoincidence gamma ray spectrometer consisting of HPGe-BGO detectors coupled to MCA. Concentrations of thorium in these samples were found to be in the range of 15–72 mg kg^?1. EINAA results were validated by determining thorium concentrations in uranium matrix by standard addition method. EINAA results were compared with those obtained by two wet chemical methods namely ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results obtained by the three methods were found to be in good agreement, indicating further validity of the proposed EINAA method.     

The effect of sample matrix quenching on the measurement of trace uranium concentrations in aqueous solutions using kinetic phosphorimetry

Sand samples collected on the beaches of the “radioactive” Brazilian town of Guarapari were first separated by flotation in bromoform and successively divided into various magnetic fractions with a Franz isodynamic separator. Concentrations of background radionuclides in samples of monazite, ilmenite, and zircon were determined by a γ-ray spectrometer. Chemical composition of monazite, ilmenite, and magnetite were assessed by means of an electron microprobe. Monazite resulted to be relatively rich in ThO₂ whose abundance ranged from 5.3 to 7.7 (wt%).     

Photometric determination of trace selenium in aqueous media

A new procedure is developed for the photometric determination of trace selenium in aqueous solutions. The selection of 2-(p-nitrophenyl)-3,5-diphenyltetrazolium chloride as a reagent for selenium is justified. The proposed sample preparation procedure involves gas extraction of selenium as hydrogen selenide followed by its liquid-adsorption extraction from the gas phase to an aqueous reagent solution with the formation of a water-insoluble formazan. Formazan formed upon the absorption of hydrogen selenide is extracted with isoamyl alcohol. The concentration of selenium is determined from the absorbance of the formazan extract in the isoamyl alcohol. The procedure allows the determination of 10–120 μg/L selenium.     

Statistical comparison of trace element concentrations

A method is proposed by which the significance of the differences between trace element concentrations of sample and control can be estimated without detailed knowledge of the distribution in the total population. Both sample and control are cut in half and the trace element concentrations of all four pieces are determined. The concentration values of the two halves of each sample are compared with each other and so are the concentration values of the two samples. This cross-comparison is essentially the application of Student's t-test to the smallest possible number of data. The calculation is reduced to a simple formula, and tables of confidence limits are not needed. The implications of lack of general background knowledge are discussed. Since it cannot always be known whether a certain trace element follows a normal or log-normal distribution pattern, or whether simultaneously determined concentrations of several trace elements are correlated with each other, the most cautious estimate of the significance is recommended.