Colors inorganic ions

Gathodically Colored Inorganic Films. The generalized cathodic, monovalent ion-iasertion reaction for inorganic thin films is... 

The effect of intensive drying is another example of the intimate relationship between colorant and turbidity. Depending on the conditions of drying, a sugar, crystallized from a colored but brilliant solution and then dried, may give a turbid solution when redissolved. The type of inorganic ions present has a decided effect on the extent of this phenomenon, in a manner not yet completely clear, but the extent is certainly related to the valence and coordinating power of the ions. 

Aside from these three classes (species with unfilled inner subshells, with unpaired electrons, or with two different oxidation states of the same element), there are a number of colored inorganic substances about which generalizations may be set up only with difficulty. Among these are many of the elementary nonmetals, a large number of covalent salts (such as mercuric iodide, cadmium sulfide, silver phosphate and lithium nitride), a number of nonmetal halides (iodine monochloride, selenium tetrachloride, antimony tri-iodide, etc.), and the colored ions, chromate, permanganate, and Ce(H20) v, whose central atoms presumably have rare-gas structures. 

Organolithium species may form coloured and EPR-active intermediates not only with conventional acceptors such as carbonyl or imine compounds [14-16] but also with unsaturated inorganic ions such as ambidentate thiocyanate-SCN the reaction between n-BuLi and NH4SCN in the presence of strongly ion-stabilizing hexamethylphosphoric triamide 0 = P(NMe2)3 (HMPA) eventually produced LiNCS 2 HMPA via some unusually colored intermediates and thiocyanate-based radical species [62]. 

TABLE 1.3 Colors of Select Aqueous (Uncomplexed) and Other Simple Monodentate" Ligand-Complexed Inorganic Ions. Note How Color Changes with Ligand... 

Physical separation of inorganic ions and other low-molecular analytes from the particulate and dissolved macromolecular fractions of the sample is useful in different flow instruments. Dialysis and UF membrane cells are amongst practical systems for flow injection analysis (FIA), which serve to exclude any unwanted sample material so that only the analyte reaches the reaction or sensing zone. SoHd particles and large interfering molecules can be separated using membranes from the smaller species of analytical interest. Such cells can also be used in the continuous-flow, stopped-flow, and sequential injection modes of flow analysis. The membrane preseparation units are very attractive because they are simple, repeatable, require little or no pretreatment of sample, and show no interferences from sample color and turbidity in most cases no reaction in the membrane interface is involved. 

Anthocyanins are stored in an organized aqueous medium in the cell vacuoles. A slightly acidic environment (pH 3-5 Stewart et al, 1975) rich in inorganic ions and other polyphenols is essential for the transformations in these pigments that enable the formation of molecular complexes and subsequent color changes and stabilization (Brouillard Dangles, 1993). 

An amino acid sample thought to be pure should be a pure-white solid devoid of any suggestion of color and it should yield a crystal-clear aqueous or HCl solution free entirely from specks of carbon, shreds of filter paper or toweling, or other visible insoluble impurities. It has been found futile to analyze further any sample which does not conform to this standard. Subjection of the sample to the qualitative tests described in a later section has been found to be an informative second step in the analysis. If the proportions of ammonia and the inorganic ions are below the allowable limits it can be reasonably expected that the high purity of the product will be bbme out by the subsequent analyses. The presence of an excessive quantity of any one of these impurities indicates that the product should be further purified. 

Oxidation. Hydrogen peroxide is a strong oxidant. Most of its uses and those of its derivatives depend on this property. Hydrogen peroxide oxidizes a wide variety of organic and inorganic compounds, ranging from iodide ions to the various color bodies of unknown stmcture in ceUulosic fibers. The rate of these reactions may be quite slow or so fast that the reaction occurs on a reactive shock wave. The mechanisms of these reactions are varied and dependent on the reductive substrate, the reaction environment, and catalysis. Specific reactions are discussed in a number of general and other references (4,5,32—35). 

---