Metallic impurities, determination

Since the potassium and sodium superoxides used for the experiment were reputedly to be of 96.5 and 90+ percent purity, respectively, it is likely that trace metal impurities present in the superoxides can quench the excited oxygen and nullify the deuterium effect. Composition of trace metal impurities, determined by X-ray fluorescence analysis of the alkali superoxides, is given in Table I. 

Rubidium metal is commeicially available in essentially two grades, 99 + % and 99.9 + %. The main impurities ate other alkali metals. Rubidium compounds are available in a variety of grades from 99% to 99.99 + %. Manufacturers and suppliers of mbidium metal and mbidium compounds usually supply a complete certificate of analysis upon request. Analyses of metal impurities in mbidium compounds are determined by atomic absorption or inductive coupled plasma spectroscopy (icp). Other metallic impurities, such as sodium and potassium, are determined by atomic absorption or emission spectrograph. For analysis, mbidium metal is converted to a compound such as mbidium chloride. 

MetaUic impurities in beryUium metal were formerly determined by d-c arc emission spectrography, foUowing dissolution of the sample in sulfuric acid and calcination to the oxide (16) and this technique is stUl used to determine less common trace elements in nuclear-grade beryUium. However, the common metallic impurities are more conveniently and accurately determined by d-c plasma emission spectrometry, foUowing dissolution of the sample in a hydrochloric—nitric—hydrofluoric acid mixture. Thermal neutron activation analysis has been used to complement d-c plasma and d-c arc emission spectrometry in the analysis of nuclear-grade beryUium. 

Commercially produced calcium metal is analyzed for metallic impurities by emission spectroscopy. Carbon content is determined by combustion, whereas nitrogen is measured by Kjeldahl determination. 

The paper describes the different chemical sensors and mathematical methods applied and presents the review of electronic tongue application for quantitative analysis (heavy metals and other impurities in river water, uranium in former mines, metal impurities in exhaust gases, ets) and for classification and taste determination of some beverages (coffee, bear, juice, wines), vegetable oil, milk, etc. [1]. 

Metal impurities can be determined qualitatively and quantitatively by atomic absorption spectroscopy and the required purification procedures can be formulated. Metal impurities in organic compounds are usually in the form of ionic salts or complexes with organic compounds and very rarely in the form of free metal. If they are present in the latter form then they can be removed by crystallising the organic compound (whereby the insoluble metal can be removed by filtration), or by distillation in which case the metal remains behind with the residue in the distilling flask. If the impurities are in the ionic or complex forms, then extraction of the organic compound in a suitable organic solvent with aqueous acidic or alkaline solutions will reduce their concentration to acceptable levels. 

The technique can be used to measure concentrations in the range 10 6-10 9M and as such is eminently suitable for the determination of trace metal impurities of recent years it has found application in the analysis of semiconductor materials, in the investigation of pollution problems, and in speciation studies. 

TXRF is frequently used for contamination control and ultrasensitive chemical analysis, in particular in relation to materials used in semiconductor manufacturing [278,279], and metallic impurities on resin surfaces, as in PFA sheets [279,280], TXRF has been used by Simmross et al. [281] for the quantitative determination of cadmium in the four IRMM polyethylene reference materials (VDA-001 to 004). Microsamples (20-100 ig) from each reference material were transferred by hot pressing at 130 °C as 3 xm thin films straight on to quartz glass discs commonly used for TXRF analysis. The results obtained were quite satisfactory (Table 8.50). Other reports of the forensic application to plastic materials by TXRF have appeared [282], including a study of PE films by elemental analysis [283],... 

For example, the industrial preparation of mineral acids, such as sulfuric, hydrochloric and nitric, inevitably leads to them containing small concentrations of metals as impurities. If the acid is to be used purely as an acid in a simple reaction, the presence of small amounts of metals is probably unimportant. If, however, the acid is to be used to digest a sample for the determination of trace metals by atomic absorption spectrometry, then clearly the presence of metallic impurities in the acid may have a significant effect on the results. For this latter application, high-purity acids that are essentially metal-free are required. 

It is ideally suited to the determination of metal impurities in AnalaR and other high-purity salts where the sample matrix... 

In direct titration, usually an appropriate buffer solution and a suitable indicator are added to the M2+ (metal-ion) solution and subsequently the resulting solution is titrated with previously standardized disodium-EDTA until the indicator just changes colour. Sometimes, a simultaneous blank determination is also recommended to have a check for the presence of traces of metallic impurities in the reagents. 

Determination of metallic impurities in some of the other inorganic salts used in preparing these solutions. 

A typical absorption curve for vitreous silica containing metallic impurities after x-ray irradiation is shown in Figure 12. As shown, the primary absorption centers are at 550, 300, and between 220 and 215 nm. The 550-nm band results from a center consisting of an interstitial alkali cation associated with a network substituent of lower valency than silicon, eg, aluminum (205). Only alkalies contribute to the coloration at 550 nm. Lithium is more effective than sodium, and sodium more effective than potassium. Pure silica doped with aluminum alone shows virtually no coloration after irradiation. The intensity of the band is determined by the component that is present in lower concentration. The presence of hydrogen does not appear to contribute to the 550-nm color-center production (209). 

A principal obstacle to identification of defects is the difficulty of comparing the results from EPR, luminescence, absorption, and deep state experiments. Probably the least ambiguous is that between EPR and luminescence when, as for transition metal impurities, it is possible for optical Zeeman measurements of a sharp luminescence line to determine the ground state g factor. If the optical and EPR measurements give the same value, then the correlation is made (Watts, 1977). In some cases, when optical excitation enhances or quenches the EPR signal, there may be a similar response in the photoconductivity or luminescence excitation spectrum. 

Numerous applications concern the mass spectrometric analysis of quite different gases and highly volatile compounds. For example, the determination of trace metal impurities in ethylene gas for... 

The chemical composition with respect to Si and metallic impurities (mainly Fe, Ca, Al) is generally determined by wet chemical methods in combination with standard spectroscopic techniques (AAS, AES, XRF) (Table 8) [224-226]. A precondition is the dissolution of the powder. Typical dissolving processes are fusion with sodium carbonate or mixtures of sodium carbonate and boric acid, with alkaline hydroxides [225, 226] and special acid treatments [225]. A more effective analysis based on optical emission spectroscopy allows the direct analysis of impurities in the solid state and requires no dissolution step [227]. 

This book discusses the methods currently available in the world literature up to 2005 for the determination of organic, organometallic and metallic impurities in soil and plant materials, vegetables and fruit. Radioactive substances and anions are also discussed. 

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