Indirect determinations with cerium

Both the cerium(IV)/arsenic(III) and the azide/io-dine systems have also been used for the indirect determination of metal ions that interact with the catalyst, thus inhibiting the catalytic cycle, by use of a kinetic method or catalytic titration. 

Method B Standardisation with sodium oxalate. Standardisation may also be carried out with sodium oxalate in this case, an indirect procedure must be used as the redox indicators are themselves oxidised at the elevated temperatures which are necessary. The procedure, therefore, is to add an excess of the cerium(IV) solution, and then, after cooling, the excess is determined by... 

The direct method for determining traces of fluoride is based on the coloured ternary complex formed by fluoride with Alizarin Complexone and lanthanum or cerium(III). Fluoride ions form stable complexes with some multivalent metals, namely Zr, Th, Ti, Fe(III), and Al. The colour changes resulting from the reactions of fluoride with coloured complexes of these metals provide indirect methods for the determination of fluoride. Examples of these methods are the Eriochrome Cyanine R-zirconium method, and the (less sensitive) Fe(III)-sulphosalicylate method. 

Indirect methods for the determination of carbohydrates, based on the consumption of an oxidant in their oxidation, have also been developed. For example, a method for the determination of n-glucose, n-fructose, and sucrose was developed, based on their oxidation with cerium (IV) perchlorate in M perchloric acid at 60° and the determination of the amount of unconsumed oxidant by titration with sodium oxalate, with... 

Silva et al.[44] developed an indirect Fl-AAS method for the determination of nitrate and nitrite in meats and vegetables following liquid-liquid extraction. Nitrate forms an ion pair with bis(2,9- dimethyl-l,10-phenanthrolinato)copper(l) which is extracted into IBMK. Copper is then determined in the separated mganic phase. When the nitrite is oxidized by cerium(VI) into nitrate before the extractirm, total nitrate is determined. When nitrite is ccmverted to nitrogen with sulfamic acid, only the origina] nitrate is determined. 

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