Gravimetric analysis of high purity tellurium for purity evaluation

Gravimetric analysis was utilized for purity evaluation of high purity tellurium, which was a raw material of a tellurium standard solution. Using a method in which tellurium was precipitated as elemental tellurium with hydrazinium after dissolution of the high purity tellurium, an avoidable positive error (ca. 0.02%) was observed. It seems that a cause of the positive error is oxidation of the tellurium or occlusion of the solvent during the precipitation. On the other hand, when the precipitated elemental tellurium was further converted into tellurium oxide by heating at 600 °C, the positive error disappeared. Finally, the purity of the starting tellurium was evaluated from the recovery of tellurium oxide with sufficient accuracy for a raw material of a tellurium standard solution (0.017% expanded uncertainty (k = 2)).     

Preparation of high purity cobalt

A combination of anion exchange separation, electrolytic extraction, floating zone refining and dry hydrogen treatment was used to purify cobalt. The effectiveness of each purification process was confirmed by measurements of the residual resistivity ratio (RRR) and activation analyses. Proton activation analysis revealed that all the main metallic impurities except iron were effectively removed by a combination of these processes. The effective removal of oxygen, nitrogen and carbon by dry hydrogen treatment was confirmed by activation analyses using ³He ion beams, proton beams and γ rays. It was found that the rate-controlling step in the decarburization process was a surface reaction. The maximum RRR obtained for the purified specimen was 334, which is higher than previously reported values.     

Characterization of high purity gallium

Multi-step wet analytical procedures were tested on gallium samples of different purity grades. Results obtained were compared with those of spark source mass spectrometry (SSMS) and glow discharge mass spectrometry (GDMS). It was found that multi-step procedures, as applied, with preconcentration factors of 200 are suitable to determine most of the detectable elements in high purity gallium in the ng/g-range. The results thus obtained agree well with those obtained by mass spectrometry. The sensitivity of the multi-step and mass spectrometry methods is not sufficient to detect traces of the investigated elements in super purity gallium, i.e. better than 6 N. These qualities can be differentiated, however, by single crystal resistivity measurement.     

Preparation of high purity chromium

The purification of chromium is important in investigations of its true properties. High purity chromium was prepared by overlap floating zone refining in a dry hydrogen atmosphere at about 100 kPa. The purity was estimated from the values of the residual resistivity ratio RRR_4.2K and activation analyses using neutrons, charged particles and γ rays. The concentrations of residual carbon and oxygen were less than 10 ppm for purified chromium, and the highest value of RRR_4.2K was 667 which is higher than previously reported values. The rolling reduction of the purified chromium was over 50% at room temperature, showing a relatively good ductility.     

Differential scanning calorimetric assessment of high purity

The value and limitations of differential scanning calorimetry in the assessment of high-purity substances has been examined. In favorable cases, good agreement has been secured for polycyclic hydrocarbons between DSC purity values and GC assay values. For some halogenated benzoic acids, used as microanalytical reference standards, good agreement has been obtained between DSC purity values and acid—base titration results. DSC studies on cholesterol and urea, which have limited thermal stability, are presented. With the available instrument and technique, the practical upper limit of absolute DSC purity values may be 99.95 mole%, although higher numerical values can be obtained. Because the DSC technique is “blind” to equilibrium solid solution formation, DSC values should not be used as a sole criterion of purity; this recommendation is of special importance for compounds purified by fractional solidification processes.     

Method to obtain C-phycocyanin of high purity

A new approach is made for the purification of C-phycocyanin (C-PC), which is simple and more efficient than existing methods. The proposed method involves two steps: aqueous two phase extraction and ion-exchange chromatography. Crude extract of C-phycocyanin, of purity 1.18, obtained from Spirulina platensis is subjected to aqueous two phase extraction. C-phycocyanin obtained from this process showed a purity of 5.22, which is higher than the reported value till date. In order to explore the possibility of further purification, C-phycocyanin is subjected to ion-exchange chromatography and found that the purity increased from 5.22 to 6.69. The fluorescence, intactness of structure and purity of C-phycocyanin are confirmed using spectrofluorometry, circular dichroism spectra and sodium dodecyl sulfate-polyacrylamide gel, respectively.     

Spectrographic analysis of high purity manganese dioxide

The fluoride content of aqueous and organic Purex process solutions can be determined with good reproducibility and accuracy. The method includes a distillation separation of fluoride and its subsequent electrometric determination using a fluoride-selective electrode. The analytical range covers 5 to 500 μg of fluoride per aliquot and the concentration limit is 5×10^?5 M (1 ppm). Complexing cations like Al(III), Zr(IV), La(III), and U(VI) do not interfere.     

Synthesis of high purity single-walled carbon nanotubes in high yield

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.     

Search for uranium in high purity silicon

Detection of small quantities of uranium in silicon wafers has been carried out by neutron activation followed by observation of fission product¹⁴⁰La. Irradiations of about one week were made at a flux of 6·10¹⁴n cm⁻² s⁻¹ and the activity of the 1596 keV line was determined. Counting rates of as low as 1 count per minute have been observed. This indicates uranium concentrations of about 5·10¹⁰ atoms per cubic centimeter of silicon or about 0.01 mg/g, assuming activity from other fissionable nuclides to be negligible.     

Determination of trace metals in high purity gold

The possibility of using ETAAS or ICP-AES for the determination of trace amounts of Ag, Bi, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Pd, Pt and Sb in pure gold is investigated. The influence of the matrix element on the atomization of the trace analytes is studied and optimal instrumental parameters are defined. An analytical method based on matrix element reductive separation followed by spectrometric determination of trace analytes is proposed as an alternative for the analysis of high purity gold. Advantages and disadvantages of proposed analytical procedures from the viewpoint of achieved repeatability, reproducibility and detection limits and of the duration of analysis are discussed. Received: 16 August 1999 / Revised: 23 November 1999 / Accepted: 27 November 1999     

Measurement of trace impurities in high purity materials

Neutron activation analysis was used for the determination of 29 trace impurities is high-purity semiconductor grade Ge and Si. In order to determine very low contents of uranium and thorium,²³⁹Np and²³³Pa activation products were separated using anion exchange and LaF₃ coprecipitation methods. The impurity contents were found to be very low, and therefore their adverse effects would be negligible.     

Determination of trace metals in high purity gold

The possibility of using ETAAS or ICP-AES for the determination of trace amounts of Ag, Bi, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Pd, Pt and Sb in pure gold is investigated. The influence of the matrix element on the atomization of the trace analytes is studied and optimal instrumental parameters are defined. An analytical method based on matrix element reductive separation followed by spectrometric determination of trace analytes is proposed as an alternative for the analysis of high purity gold. Advantages and disadvantages of proposed analytical procedures from the viewpoint of achieved repeatability, reproducibility and detection limits and of the duration of analysis are discussed.     

Neutron activation analysis of high purity silver using high resolution gamma-spectrometry

A method of neutron activation determination of microimpurities in high purity silver has been developed. For matrix activity separation the extraction of silver by dibuthylsulfide (DBS) was employed. The purification coefficient was 10⁸ after triple extraction. Using Ge(Li) detector it was possible to determine 30 elements simultaneously in silver samples.     

Preparation and chemical characterization of high purity fluorapatite

High purity fluorapatite (FAP) was prepared by solid state reaction, in flowing argon gas, at 1370°C for 60 min. For chemical characterization of Ca₁₀(PO₄)₆F₂, the accuracy and reproducibility of different analytical methods were assessed. Methods with a good accuracy for the determination of Ca, P and F content were: titrations with EDTA for Ca determination (accuracy: −0.8%), spectrophotometric method for P determination (accuracy: +0.6%) and measurements with fluoride-selective electrode (accuracy +5.4%) for F determination.     

Preparation of high purity labelled Rose-Bengal with radioiodine

The exchange of Rose-Bengal in the mono-sodium salt with elementary¹³¹I in an organic medium allows for the preparation of a labelled product substantially higher in radiochemical purity than that produced by other methods. Purification of the starting material before the labelling process has been done by adsorption chromatography. Under the conditions described a radiochemical yield more than 97% can be obtained within 30–60 minutes. The product was stable during sterilization and storage for 10 days and was found to be free of¹³¹I.     

Activation analysis of mercury in high purity bismuth

A neutron activation method was developed for the determination of traces of mercury in high purity bismuth. After neutron irradiation at a flux of approx. 4.10¹¹ n/cm²/sec, mercury was separated from the matrix by displacement on metallic copper and subsequent distillation and amalgamation on silver foil. The γ-activity of the ¹⁹⁷Hg was counted in the 68–77 ke V region. The accuracy of the procedure was tested by an addition method of analysis. Bismuth samples with a mercury content in the 10 p.p.b. region were analysed.