Preparation,homogeneity and stability studies of a candidate LRM for Se speciation

A laboratory reference material (LRM) was prepared from Brazil nuts (Bertholletia excelsa) for quality control (QC) purposes of selenium speciation. The preparation of this LRM led through the usual operation steps applied during routine reference material production from biota samples-preparation of the raw material, homogenisation, storage design, checking of homogeneity, microbiological status and possible irradiation effects, and monitoring the species stability vs time at different storage temperatures. The selenium speciation studies to check species stability were carried out on a HPLC-UV-HG-AFS measurement set-up. Special attention was paid to the correct identification of selenium species by applying independent HPLC separation techniques (ion-pairing and anion-exchange chromatography). The concentration of selenomethionine (SeMet) and total Se content were quantified (79.9 microg g(-1) (calculated as Se) and 82.9 microg g(-1), respectively). The homogeneity and stability of this candidate reference material passed the relevant tests recommended by Bureau Communautaire de Référence (BCR).     

New human hair certified reference material for methylmercury and trace elements

 A new human hair certified reference material (NIES CRM No. 13) for mercury speciation and trace element analysis was prepared at the National Institute for Environmental Studies (NIES), Environmental Agency of Japan. Scalp hair from Japanese males, which is identical with the original material for the previous human hair CRM (NIES CRM No. 5), was used. Special attention was paid to reduce contamination from a grinding vessel during the preparation procedure. A newly-prepared ceramic/Teflon disc mill was used for cryogenic grinding of the hair. 1,000 bottles (3 g each) were produced after sieving and blending of the hair powder. Certified values for total mercury and methylmercury, as well as other trace elements of toxicological and nutritional significance (antimony, cadmium, copper, lead, selenium, and zinc), were determined based on analyses from extensive collaborations. Reference values for 12 elements (aluminium, arsenic, barium, calcium, cobalt, iron, magnesium, manganese, silver, sodium, sulfur and vanadium) were also given. Received: 8 February 1996/Accepted: 4 April 1996     

X射线荧光光谱法测定电解锰中锰、硅、磷和铁含量

熔融制样X射线荧光光谱法测定电解锰中锰、硅、磷和铁含量。用熔融后的四硼酸锂制作铂金坩埚保护层,以BaO2做氧化剂,在马弗炉内通过逐渐升温来氧化电解锰,然后熔融制取玻璃熔片,用X射线荧光(XRF)光谱法分析电解锰中锰、硅、磷和铁含量。锰、硅、磷和铁的相对标准偏差RSD分别为0.23%、2.82%、0.31%和0.53%。与其它分析方法比较,其结果更稳定。有效消除了电解锰熔融制样过程中的坩埚腐蚀问题,分析误差可完全控制在国家相关标准允许的范围内,实现了电解锰中各元素的快速准确测定。     

Calculating the thermodynamic parameters of the surface layer of the binary sodium-potassium system

The composition and number of surface monoatomic potassium layers in Na-K alloys are calculated on the basis of theory of the thermodynamic stability of surface layers of metal alloys with respect to their thickness. The surface layer of Na-K alloys is shown to be thermodynamically stable at surface layer thickness of two monoatomic potassium layers in the range of compositions with K in Na content of ∼13–15 at %. Good agreement is obtained using the surface activities of the components in binary metal melts as criteria.     

X-ray photoelectron study of relaxation processes in Ni72Mo14B14 and Ni72Nb14B14 melts

The time dependence of the chemical structure of the surface layers of nickel melts is investigated for the first time by X-ray photoelectron spectroscopy. Changes in the chemical structure of amorphous alloys obtained from the same melts are investigated according to depth. Translated fromZhumal Struktumoi Khimii, Vol. 39, No. 6, pp. 1103–1106, November–December, 1998.     

Certification of a second-generation biological reference material (freeze-dried human serum) for trace element determinations

The certification of a second-generation biological reference material (freeze-dried human serum) for trace element determinations is described. The material was prepared under rigorously controlled conditions to avoid extraneous additions. Analytical data were obtained by the authors as well as by numerous other intra- and extra-mural investigators, solicited on the basis of established experience in determining selected elements. For 14 trace elements (aluminium, chromium, manganese, iron, cobalt, copper, zinc, arsenic, selenium, bromine, rubidium, molybdenum, cadmium and caesium) certified values (in ng g^?1 or μg g^?1 dry weight) are listed; for an additional element (nickel) a best estimate (in ng g^? dry weight) is added. Trace element concentrations in the material, which is available to the scientific community, closely approximate those in normal, lyophilized blood plasma or serum samples. The material thus provides the means to check the accuracy and precision of analytical procedures for quantifying low-level trace elements in the best possible conditions and to detect errors that can easily be overlooked when reference materials with higher levels of trace elements are used. In addition, and in contrast to already existing biological reference materials with high levels of trace elements, it offers the possibility of identifying unsuspected errors at the sample preparation stage.     

New human hair certified reference material for methylmercury and trace elements

A new human hair certified reference material (NIES CRM No. 13) for mercury speciation and trace element analysis was prepared at the National Institute for Environmental Studies (NIES), Environmental Agency of Japan. Scalp hair from Japanese males, which is identical with the original material for the previous human hair CRM (NIES CRM No. 5), was used. Special attention was paid to reduce contamination from a grinding vessel during the preparation procedure. A newly-prepared ceramic/Teflon disc mill was used for cryogenic grinding of the hair. 1, 000 bottles (3 g each) were produced after sieving and blending of the hair powder. Certified values for total mercury and methylmercury, as well as other trace elements of toxicological and nutritional significance (antimony, cadmium, copper, lead, selenium, and zinc), were determined based on analyses from extensive collaborations. Reference values for 12 elements (aluminium, arsenic, barium, calcium, cobalt, iron, magnesium, manganese, silver, sodium, sulfur and vanadium) were also given.     

Determination of some trace elements in the industrial process of aluminium production

Some trace elements in samples from the aluminium industry (Aluminium Kombinat, Titograd, Yugoslavia) were determined by instrumental neutron activation analysis. Samples characteristic for alumina production (bauxite, red sludge), reduction cell components (alumina, anode, AlF₃, cryolite) and aluminium produced (purity 99.5–99.7%) have been analyzed. 10 trace elements were determined under a given set of working conditions and followed through the routine production.     

Meeting the Requirements of the Silver/Silver Chloride Reference Electrode

Potentiometric cells from which the pH values of standard buffer solutions are computed rely on the silver–silver chloride reference electrode which has proved to be convenient, reproducible and reliable. Of the various methods of preparation of silver-silver chloride electrodes only one concerns us here: the thermal–electrolytic type that has been used more extensively than any other form. Once prepared, the electrodes need to be equilibrated before use and between experiments. The equilibration technique must ensure voltage stability and inter-electrode, or bias, potential below 0.1 mV. In potentiometry the stability of a reference electrode is of utmost importance since an offset of 1 mV is equivalent to a deviation of about 0.02 in the pH value.     

The microchemical analysis of ferrous and non-ferrous alloys

Satisfactory methods are described for the determination of certain of the alloying constituents in small quantities of steels, aluminium alloys and white metals. In steels, lead is determined by using an extraction procedure with dithizone, whereas the stable colour produced by vanadium with 3 : 3' dimethylnaphthidine is used for determining this element. In aluminium alloys, absorptiometric procedures are recommended for determining copper, nickel, iron and manganese. The determination of silicon is advocated by the absorptiometric technique. For the determination of antimony, in white metals, a micro volumetric procedure with standard potassium bromate is recommended using α-naphthaflavone as indicator.     

Effect of the alkoxides addition order on the properties of Pd/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> catalysts used for methane combustion

A series of Pd/Al₂O₃–ZrO₂ catalysts were prepared to be used in methane oxidation. The effect of the addition order of metal alkoxides on the texture, structure and catalytic properties of the solids is studied. The control of the preparation parameters is achieved via sol gel way as an attractive route of the preparation of these catalysts. N₂ physisorption, XRD, Scanning Electronic Microscopy (SEM) and H₂ chemisorption are the main techniques used to characterize the prepared Pd/Al₂O₃–ZrO₂ catalysts. Textural analysis reveals the mesoporosity of all the catalysts independently of the addition order of alkoxides while surface area is more pronounced when the aluminium alkoxide is added before or with the zirconium precursor. XRD patterns show the development of the zirconia tetragonal phase for all the catalysts. Better metallic dispersion is obtained when aluminium alkoxide is added first which can be justified by the high homogeneity observed on the corresponding catalyst as revealed by SEM technique.     

Determination of manganese in brain samples by slurry sampling graphite furnace atomic absorption spectrometry

A simple procedure for the determination of manganese in different sections of human brain samples by graphite furnace atomic absorption spectrometry has been developed. Brain sections included cerebellum, hypothalamus, frontal cortex, vermix and encephalic trunk. Two sample preparation procedures were evaluated, namely, slurry sampling and microwave-assisted acid digestion. Brain slurries (2% w/v) could be prepared in distilled, de-ionized water, with good stability for up to 30 min. Brain samples were also digested in a domestic microwave oven using 5 ml of concentrated HNO₃. A mixed palladium+magnesium nitrate chemical modifier was used for thermal stabilization of the analyte in the electrothermal atomizer up to pyrolysis temperatures of 1300 °C, irrespective of the matrix. Quantitation of manganese was conducted in both cases by means of aqueous standards calibration. The detection limits were 0.3 and 0.4 ng ml⁻¹ for the slurry and the digested samples, respectively. The accuracy of the procedure was checked by comparing the results obtained in the analysis of slurries and digested brain samples, and by analysis of the NIST Bovine Liver standard reference material (SRM 1577a). The ease of slurry preparation, together with the conventional set of analytical and instrumental conditions selected for the determination of manganese make such methodology suitable for routine clinical applications.     

Intercalation materials for lithium rechargeable batteries

An overview is given of intercalation materials for both the negative and the positive electrodes of lithium batteries, including the results of our own research. As well as lithium metal as a negative electrode, we consider insertion materials based on aluminium alloys. In the case of the positive electrode metal-oxides based on manganese, nickel and cobalt are discussed. Received: 27 May 1997 / Accepted: 30 July 1997     

Evaluation of on-line coupling size exclusion chromatography electrothermal atomic absorption spectrometry for selenium speciation

 Chromatographic effluents were on-line analyzed by Zeeman-ETAAS, using a flow-through cell placed in a graphite furnace autosampler as interface. To obtain high sampling rates, the use of fast graphite furnace programmes was studied. Conventional programmes of 96 s were reduced to 18 s by using hot injection (120 °C) and reducing the charring step to 2 s. The increase of the injection volume from 20 to 60 μl lengthened the programme to 46 s. Nickel had to be added to get a comparable response for both inorganic and organic selenium species (selenite and selenomethionine) and to reduce the interferent effect produced in presence of the chromatographic eluent (TRIS 0.01 mol l^-1, NH₄NO₃ 0.1 mol l^-1, pH 7). The optimized conditions were applied to the speciation of selenium in human erythrocyte lysates by size exclusion LC-ETAAS. Using a high performance size exclusion column selenium could be assigned to proteins of 100 and 35 kDa. Detection limits in the range of 1 ng (2 μg l^-1 for 500 μl injection volume) were obtained for the combined technique. Received: 9 October 1996/Revised: 8 July 1996/Accepted: 14 July 1996     

Speciation of four selenium compounds using high performance liquid chromatography with on-line detection by inductively coupled plasma mass spectrometry or flame atomic absorption spectrometry

An analytical method for the speciation of selenomethionine, selenocystine, selenite and selenate by high performance liquid chromatography (HPLC) with atomic spectrometric detection is presented. An organic polymeric strong anion exchange column was used as the stationary phase in combination with an aqueous solution of 6 mmol L^–1 of salicylate ion at pH 8.5 as the mobile phase which allowed the isocratic separation of the four selenium analytes within 8 minutes. The separated selenium species were detected on-line by flame atomic absorption spectrometry (FAAS) or inductively coupled plasma mass spectrometry (ICP-MS). The signal-to-noise ratio of the FAAS detector was optimized using a hydrogen-argon entrained-air flame and a slotted-tube atom trap (STAT) in the flame. The limit of detection (3 σ) achieved by the HPLC-FAAS system was 1 mg L^–1 of selenium (100 μL injections) for each of the four selenium species. More powerful selenium detection was achieved using an ELAN 5000 ICP-MS instrument. Selenium was measured at m/z = 82. The ICP-MS signal intensity was enhanced by a factor of 3–4 after addition of 3% methanol to the chromatographic mobile phase and by using an increased plasma power input of 1300 W. The limit of detection achieved under these conditions was 1 μg L^–1 (100 μL injections). The HPLC-ICP-MS system was used for selenium speciation of selenite and selenate in aqueous solutions during a BCR certification exercise and for selenium speciation in the certified reference material, BCR No. 402 White Clover. Extraction experiments revealed that the selenium species in the biological material were extractable only in the presence of water in the extraction medium. The results indicated that selenate and a compound of unknown identity U were present in the plant sample. Received: 4 September 1996 / Accepted: 12 December 1996     

Exhaustive electrolysis for recovery of actinides from molten LiCl–KCl using solid aluminium cathodes

An electrorefining process in molten chloride salts using solid aluminium cathodes is being developed in Institute for Transuranium Elements in order to separate actinides (An) from spent nuclear fuel. In this process, the fuel including fission products (FP) is dissolved into an electrolyte. Without purification of the salt, the process would have to be stopped when the FP concentration would become too high to allow a selective deposition of An on the cathode. Exhaustive electrolysis is proposed as the first purification step, consisting of a group-selective recovery of An on solid aluminium cathodes. On the anodic side, chlorine gas is produced by electrochemical decomposition of the salt. In order to prove the feasibility of the method, two galvanostatic electrolyses were carried out and the potentials of both electrodes were constantly monitored. Uranium was recovered from LiCl–KCl melts containing UCl₃ and a mixture of UCl₃–NdCl₃, in which its concentration decreased from 1.7 to 0.1 wt% with no co-deposition of neodymium. Although the maximum applicable current densities were relatively low, the results are promising, demonstrating high current efficiency and selectivity of the proposed method. A design and application of a special chlorine gas producing inert anode is also discussed.     

Inductively coupled plasma compared with direct current arc spectrometry for analysis of minor elements in aluminium baths

A validation study was carried out in order to evaluate the efficiency of inductively coupled plasma-optical emission spectrometry (ICP-OES) for the analysis of minor elements (manganese, chromium, copper, iron, and titanium) in aluminium alloys. Aluminium casting samples were obtained by adding compressed powder compacts of each alloying element and aluminium (minitablets) to aluminum baths in a laboratory crucible furnace. Digestion of solid samples was performed using concentrated HCI and H202 35% (v/v) previous to analysis by ICP-OES without any matrix separation. This solution-based method was validated considering direct current arc spectrometry as the reference method based on direct analysis without any pretreatment of the solid samples considered. Univariate statistical procedures were carried out, for which precision <3% and trueness of the analytical results were taken into account.     

The preparation of a certified reference material of polar pesticides in freeze-dried water (CRM 606)

The preparation of a certified reference material of polar pesticides in freeze-dried water is described. The pesticides selected were atrazine, simazine, carbaryl, propanil, linuron, fenamiphos and permethrin which were added to 6000 litres of tap water at 50–80 μg · L^–1 (200–320 μg · L^–1 for permethrin) level in presence of NaCl (2.5 g · L^–1) prior lyophilization. After the freeze-drying process the residue was rehomogenized, filled into amber glass bottles and stored at –20 °C, +4 °C and +20 °C. All pesticides were determined by HPLC/diode array detector, except permethrin which was determined by GC/ECD. The results obtained for atrazine, simazine, carbaryl, propanil, linuron and fenamiphos showed no within- or between-bottle inhomogeneity, however the material was non-homogeneous for permethrin and therefore this was withdrawn from further studies. With respect to the stability for over one year, all pesticides were stable at –20 °C. At +4 °C all pesticides were stable for at least 9 months and at +20 °C the stability was demonstrated only during the first month of storage. The content (mass fractions) of atrazine, simazine, carbaryl, propanil and linuron in freeze-dried water (CRM 606) was certified by an interlaboratory testing and a certification campaign. Received: 7 September 1998 / Revised: 13 November 1998 / Accepted: 21 November 1998     

Long term stability of organic selenium species in aqueous solutions

Long term stability of organic selenium compounds (selenocystine, selenomethionine, trimethylselenonium ion) has been studied over a one year period for 2 analyte concentrations: 25 and 150 μg/L Se, at pH 4.5 in the dark, under different storage conditions: temperature of –20°C, 4°C, 20°C, 40°C; in Pyrex, Teflon, or polyethylene containers; in an aqueous matrix or in the presence of a chromatographic counter ion (pentyl sulfonate at 10^–4 mol/L concentration). Light effects have also been tested. The stability of the selenium species was monitored by HPLC-ICP/MS. Storage conditions can drastically alter the stability of organic selenium species. Organoselenium compounds were shown to be stable in the dark over a one year period in an aqueous matrix at pH 4.5 in Pyrex containers at both 4°C and 20°C. Pyrex vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid concentration. Teflon containers caused losses of less than 25% at both 4° C and 20° C in the dark. However, polyethylene vials presented, at all temperatures tested, a rapid decrease of the TMSe⁺ concentration. The stability of the Se species studied did not show significant differences between 4° C and 20° C in any container material used. Storage of solutions at 40° C led to slight differences between the Pyrex and Teflon containers. However, polyethylene presented a drastic decrease of the three species over time at this higher temperature. Solutions frozen at –20° C in polyethylene vials did not stabilize the TMSe⁺ signal. Finally, concentrations and matrices of the samples did not significantly affect the stability of the species. Received: 15 July 1996 / Revised: 14 July 1997 / Accepted: 18 July 1997     

DSC analysis of strengthening precipitates in ultrafine Al–Mg–Si alloys

Equal channel angular pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr and Al–Mg–Si–Zr–Sc alloys to achieve a substantial grain refinement of the materials. Post ECAP aging was then investigated on the ultrafine grained alloys by DSC and TEM analyses. DSC scans were carried out with heating rates ranging from 5 to 30°C min^–1. Peak identification was performed by the support of literature information and TEM analyses. Precipitation kinetics revealed to be similar for both alloys but the Sc-free alloy showed a recrystallization peak at temperatures ranging from 310 to 340°C, depending on the strain accumulated during ECAP. On the contrary, the Sc-containing alloy showed a greater grain stability. Analyses of peak positions and of activation energies as a function of ECAP passes experienced by the samples revealed large modifications of precipitation kinetics in the ultrafine-grained alloys with respect to the coarse-grained materials.