Zinc Identification Test

Since zinc, aluminium and lead(II) hydroxides are white, additional tests are needed to distinguish between them. A quick identification test for lead(II) ions depends upon the fact that lead(II) sulfate is insoluble in water, whereas aluminium and zinc sulfates are soluble. Addition of dilute sulfuric acid to lead(II) ions will therefore precipitate the lead(II) sulfate ... 

The methods for measuring impurities in samples should be sensitive. In contrast identification tests should be rather insensitive. For example the flame test for sodium ions will give a positive even with trace amounts present hence the use of the precipitation method with zinc uranyl acetate in pharmacopoeias. 

In the Franchimont test [42], nitramines are reduced to nitrite ions by zinc and acetic acid and then subjected to the Griess reaction. A modification of this test was used for the identification of nitramine impurities in RDX [43]. 

Elemental composition Zn 52.14%, C 9.58%, O 38.28%. Zinc carbonate is identified by effervescence produced upon adding dilute HCl. CO2 evolved is identified by the lime water test or by GC or GC/MS. Characteristic mass for identification of CO2 is 44. Zinc may be analyzed in an acid solution by AA, ICP, and other methods to measure zinc content of the compound. 

Identification Place a drop of a saturated solution of sample into a micro test tube, and add a drop of a 0.5% solution of ammonium chloride and several milligrams of zinc powder. Cover the mouth of the tube with a disk of filter paper moistened with a solution of 5% p-dimethylaminobenzaldehyde and 20% trichloroacetic acid in hexane. Heat with a small flame for about 1 min. A pink to red-violet stain appears on the paper. 

Identification A 1 20 aqueous solution gives positive tests for Zinc and for Sulfate, Appendix IIIA. 

The techniques used to obtain these data and to define the extended model of zinc metabolism are Important to define changes In zinc metabolism In both normal and pathological states and are particularly useful as an aid In definition of zinc deficiency. Human zinc deficiency has been difficult to Identify because Its symptoms are complex and variable (, 8-11) ranging from Impairments of taste and smell to skin rash and dwarfism. There Is presently no adequate clinical test for the diagnosis of zinc deficiency In humans, which further complicates Its Identification. Zinc content In serum, plasma, red blood cells,urine, saliva or hair have proven Inadequate for specific diagnosis of Individual cases of zinc deflclency(6,8-12). 

Tests for Identification of Some Synthetic Dyes. Two very simple reactions can confirm the presence of synthetic dyes. In the solvent stripping test, if the ammonia solution is heavily stained and it becomes irreversibly colorless upon the addition of zinc dust even at room temperature, the presence of an azo dye with sulfo group or groups is indicated (an acid or direct dye) (36, 37). The color of the solution in concentrated sulfuric acid can also be an important indication for identifying synthetic dyes. In this test, a few drops of concentrated sulfuric acid are dripped on a small sample of the dyeing, and the color of the sulfuric acid is observed after a few minutes. Intensive magenta red, red-violet, violet, blue, and green solutions indicate the presence of synthetic dyes (36, 37). 

Identifications and analyses of azo dyes can be performed by several techniques. These are absorption spectroscopy (i.e., visible, UV, and IR spectroscopy), fluorescence analysis, and GC. Chemical testings involve reduction methods. Reducing agents such as zinc dust, stannous chloride, and sodium hydrosulfite can split the azo linkage, producing the diazonium and the coupling fragments. The cleaved products may be... 

The Limit of Identification of this test is only 3 y potassium, which consequently can be detected directly in the presence of sodium only if not more than 10 times the quantity of the latter is present. Otherwise, sodium dipicrylaminate is salted out. If potassium is to be detected in the presence of greater amounts of sodium, the latter should be removed beforehand as sodium zinc uranyl acetate (see page 428). The filtrate is evaporated to dryness, ignited, and the residue subjected to the test for potassium. 

Flame tests are not commonly used to identify transition metals. The presence of a certain transition-metal ion in a solution is sometimes obvious from the solution s color. Some transition-metal ions can be more accurately identified using a procedure called qualitative analysis. Qualitative analysis is the identification of ions by their characteristic reactions. The transition-metal ions most often identified through qualitative analysis include copper, nickel, zinc, chromium, iron cobalt, cadmium, manganese, and tin. Most tests to identify the presence of an ion in a mixture involve causing the ion to precipitate out of solution. Some of the more dramatic precipitation reactions for transition metals are shown. 

---