Metal Analytical Reagents

Use Purification of hydrochloric acid and sulfuric acid, precipitating sulfides of metals, analytical reagent, source of sulfur and hydrogen. 

The combination of oxidi2ing effect, acidic strength, and high solubiHty of salts makes perchloric acid a valuable analytical reagent. It is often employed in studies where the absence of complex ions must be ensured. The value of wet ashing techniques, in which perchloric acid is used to destroy organics prior to elemental analysis for the determination of trace metals in organics, has been well estabHshed (see Trace and residue analysis). 

Bromine is used as an analytical reagent to determine the amount of unsaturation in organic compounds because carbon—carbon double bonds add bromine quantitatively, and for phenols which add bromine in the ortho and para positions. Standard bromine is added in excess and the amount unreacted is deterrnined by an indirect iodine titration. Bromine is also used to oxidize several elements, such as T1(I) to T1(III). Excess bromine is removed by adding phenol. Bromine plus an acid, such as nitric and/or hydrochloric, provides an oxidizing acid mixture usefiil in dissolving metal or mineral samples prior to analysis for sulfur. 

Ligands like (222) are useful analytical reagents for Cu(II) (64HC(20)l), whilst ligands (223) and (224) are used as dyes (Section 4.04.4.1.3). In dyes such as (223), which are applied to wool, the usual metal employed is chromium for cotton dyes like (224) it is more common to use copper. 

Hydrogen sulphide is used in the preparation of metal sulphides, oil additives etc., in the purification and separation of metals, as an analytical reagent and as raw material in organic synthesis. Physical properties are summarized in Table 8.11 and effects of temperature on vapour pressure are shown in Figure 8.4. 

Other transition metals have received much less attention. Complexes of palladium and 2-amino-phenyl-containing formazans have been reported.397 Mercury complexes of tridentate formazans have been studied.398 Silver complexes of tridentate benzothiazolyl-containing formazans have also been studied.399 Recently, alkali and alkaline earth metals have been the subject of many studies. Formazans such as 228 and 229 as well as the macrocyclic 204 have received considerable attention as metal-specific analytical reagents.400-41 1... 

Unlike the previously mentioned systems, compounds such as (191) and (192) show no tendency to yield 2 1 (L M) complexes. These compounds show much promise as analytical reagents for the alkali metals and, for instance, have been demonstrated to be suitable for the extraction and spectrophotometric determination of Na+ in human blood serum. 

More recently the introduction of an analytical reagent disodium ethylene-diaminetetraacetate, invariably termed as EDTA, an altogether latest titrimetric method has been used exclusively for the estimation of metals using metal-ion indicators. 

The kinetics of removal of iron(III) from its complexes with the aminocarboxylate-anthraquinone analytical reagent calcein and with the antitumor anthracycline doxorubicin by l,2-dimethyl-3-hydroxy-4-pyridinone (LI, (251) with R = R = Me) have been monitored. Rate constants for metal removal are almost independent of the concentration of the replacing ligand, indicating dissociative mechanisms they are approximately 1 x 10 s for displacement from doxorubin and between 12 x 10 s and 2 x 10 s from calcein. 

Hydroxyquinoline, whose chemistry has been reviewed (56CRV271), has found wide application as an analytical reagent, and is known as oxine . It forms insoluble complexes with a great many metal ions, coordinating at O and N, and can be used for the estimation of Mg, Zn, Al, Cu, Bi, Fe, Mn, Ni and others. 

Thioacetamide has been used for a long time as an analytical reagent to precipitate metal sulphides (see Ref. 2 for many relevant references). Thioacetamide can be hydrolyzed over a wide range of pH and is often used for CD in acidic baths. In a strongly acidic bath (pH < ca. 2), H2S is formed ... 

The principal use of 1,10-phenanthroline and several of its derivatives is, of course, as analytical reagents particularly for the determination of metals and in the form of their metal complexes as oxidation-reduction indicators. These uses of 1,10-phenanthrolines have been well... 

---