Affinity-based impurities

Most base-metal sulfides are very insoluble compounds and, in principle, processes based on the differences in their solubilities can be used in the selective precipitation of sulfides. For example, the strong affinity of copper ions for sulfide ion is used to good effect in the removal of traces of copper from leach liquors in the recovery of nickel,406 cobalt407 and manganese.408 For manganese, other impurity metal ions such as cobalt, nickel and zinc are also selectively precipitated by the use of sulfide ions. 

Higher alkoxides, such as tetra(2-ethylhexyl) titanate, TYZOR TOT [1070-10-6]9 can be prepared by alcohol interchange (transesterification) in a solvent, such as benzene or cyclohexane, to form a volatile azeotrope with the displaced alcohol, or by a solvent-free process involving vacuum removal of the more volatile displaced alcohol. The affinity of an alcohol for titanium decreases in the order primary > secondary > tertiary, and branched > unbranched. Exchange processes are more convenient than direct synthesis of tetraalkoxide from TiCl an alcohol, and a base because a metal chloride need not be handled. However, in general, traces of impurities of mixed tetraalkyl titanates can result. 

Thus, the selective enrichment of the target analyte was successfully demonstrated using the imprinted polymer. Conventional SPE sometimes needs to be combined with a different type of SPE or other separation steps to complete pre-purification, because compounds with similar chemical properties may accompany the analyte as impurities. On the other hand, imprinted polymer is an affinity-type SPE sorbent that exhibits specificity for an analyte therefore, the imprinted polymer-based SPE is able to streamline the whole procedure of analysis. Although aqueous conditions were employed here, it is also notable that the utility in organic solvents is one of the useful characteristics of imprinted polymers as SPE sorbents [18,19]. 

Lutzenkirchen. J.. Influence of impurities on acid-base data for oxide minerals-analysis of observable surface charge and proton affinity distributions and model calculations for single crystal samples, Croat. Chem. Acta, 80, 333, 2007. 

As a further chemical tracer method enabling ppm-resolution we have employed gas chromatography (GC). In combination with mass spectrometry this allows for material selective quantification of chemical impurities. The GC technique is based on the retention time of a given speeies on a functionalised column and varies with the respective molecular affinity to the column surfactants. By subsequent cycles of solvation and rinsing it is possible to obtain a depth profile of the ehemical impurities contained in the crystalline host [10]. The main requirements imposed by gas chromatography arc a sufficient solubility and separability of the analysed molecular species. For example, for tet-racene to be solvable to an adequate amount, saturation in toluene is reached at 150 ng/1 pL [31]. 

As sodium can be used to eliminate impurities contained in metals, one could consider it as a means for producing wanted compounds and alloys. This field of application is rather large and the following cases of alloy production, mainly based on the strong halogen affinity of this metal, may be examined alkaline earth metal alloys, calcium sodium alloys and calcium metal derived from them, and sodium alloys, especially those with potassium, when calcium, magnesium, cerium, aluminum, uranium, thorium, and titanium, for instance, are introduced into a base metal. 

Carbon-based traps have a lower affinity for water than does Tenax, but they must be purged with ultra-pure helium while being heated to drive off adsorbed impurities. Surrogates should be added before this clean-up procedure to determine the efficiency of the purge. After activation, sorbents must be handled with care as they may adsorb organic vapors from the air, thus resulting in adsorption artifacts. 

The Ti-C system consists of one cubic compound having the general formula TiC. A probable phase diagram based on various measurements is shown in Fig. 1. Because of the great affinity this system has for oxygen and nitrogen and the marked influence these impurities have on the various physical and chemical properties, the accuracy of most measurements is considerably poorer than would be suspeeted. 

Thus, the formation of powerful electric double layer on the surfaces of floating air bubbles, covered by adsorbed surfactants, makes the removal of ions released from dissociated mineral impurities possible. The selected surfactants should be strong fatty acids, strong fatty bases, or other ionizable suitable compounds with high affinity to the air-water interface. 

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