Platinum impurity determination

Area losses of carbon-supported platinum were determined [87] by electrochemical measurements and by X-ray diffraction. These losses cannot be due to adsorption of impurities since they were detected in roughly the same measure by both techniques. Recrystallization of the supported platinum was suggested [87] as the cause of the reduction of the surface area with time. 

Another example is the determination of pure silica in an impure ignited silica residue. The latter is treated in a platinum crucible with a mixture of sulphuric and hydrofluoric acids the silica is converted into the volatile silicon tetrafluoride ... 

The platinum electrode is also very convenient for investigating various adsorption phenomena in electrochemical systems. The surface of platinum is very stable and reproducible. As will be shown in what follows, the true working area can be determined with high accuracy for platinum surfaces with appreciable roughness and even for electrodes with highly dispersed platinum deposits. It is comparatively easy to clean the surface of adsorbed impurities and to control the state of the surface. 

Once the reaction conditions have been decided upon, the feed preparation steps and product purification steps must be determined. The designer must decide how much of which compounds must be removed from the feed and product streams. The latter has already been set by the product composition specified in the scope. The former is often determined by how the impurities affect the reaction. For instance, when platinum catalysts are used all sulfur and heavy metals must be removed or this very expensive catalyst will be poisoned. 

Trace impurities in noble metal nanoclusters, used for the fabrication of highly oriented arrays on crystalline bacterial surface layers on a substrate for future nanoelectronic applications, can influence the material properties.25 Reliable and sensitive analytical methods are required for fast multi-element determination of trace contaminants in small amounts of high purity platinum or palladium nanoclusters, because the physical, electrical and chemical properties of nanoelectronic arrays (thin layered systems or bulk) can be influenced by impurities due to contamination during device production25 The results of impurities in platinum or palladium nanoclusters measured directly by LA-ICP-MS are compared in Figure 9.5. As a quantification procedure, the isotope dilution technique in solution based calibration was developed as discussed in Chapter 6. 

The sulfur compounds contained as impurities in a substrate or solvent may have a profound effect on hydrogenation, particularly over platinum metals where the amounts of catalyst used are usually much smaller than in the case of base metals. An excellent way to remove such impurities is to treat the sample with Raney Ni at slightly elevated temperatures22 (usually 50-80°C). The impurities in benzene or cyclohexane can thus be removed simply by refluxing with Raney Ni for 0.5 h (see Section 13.3). Granatelli applied this desulfurization with Raney Ni to determine quantitatively as little as 0.1 ppm of sulfur contained in 50 g of nonolefinic hydrocarbons.23... 

Sodium polyphosphate.—Ignition of the residue left on evaporation of a solution of sodium hydroxide or carbonate with sufficient phosphoric acid gives a vitreous polyphosphate in an impure condition. It dissolves slowly in cold water, but more rapidly on warming. The solution is almost neutral to methyl-orange and to phenolphthalein. It has been found impossible to purify the substance or determine its composition, on account of its energetic action on vessels of glass, porcelain, silica, nickel, and platinum, but it probably has the formula Na4PG017.2... 

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