Spectrophotometric bipyridine method

The widespread occurrence of iron ores, coupled with the relative ease of extraction of the metal, has led to its extensive use as a constructional material with the result that the analysis of steels by both classic wet and instrumental methods has been pursued with vigour over many years.3 Iron complexes are themselves widely used as the basis of convenient analytical methods for the detection and estimation of iron down to parts per million. Familiar tests for iron(III) in aqueous solution include the formation of Prussian blue as a result of reaction with [Fe(CN)6]4, and the formation of the intensely red-coloured [Fe(H20)5SCN]2+ on reaction with thiocyanate ion.4 Iron(II) forms particularly stable red tris chelates with a,a -diimines such as 1,10-phenanthroline or 2,2 -bipyridine that have been used extensively in spectrophotometric determinations of iron and in the estimation of various anions.5 In gravimetric estimations, iron(III) can be precipitated as the insoluble 8-hydroxyquinoline or a-nitroso-jS-naphthol complex which is then ignited to Fe203.6 In many situations the levels of free [Fe(H20)6]3+ may be controlled through complex formation by addition of edta. 

Venumadhav et al. [28] described two simple and sensitive visible spectrophotometric methods for the determination of lornoxicam in bulk and pharmaceutical dosage form. Method 1 is based on oxidation of fhe drug with ferric chloride and subsequent complexation of Fe(II) with 2,2 -bipyridine to form a blood red colored species (520 nm). Method 2 is based on oxidation of fhe drug wifh ferric chloride and chelation of Fe (II) with bathophenanthroline to produce a blue colored chromogen (610 nm). These two methods were extended to the analysis of pharmaceutical formulations and results compared with the reference method. 

Emmerie and Engel (1938) devised the most widely used procedure for the determination of vitamin E in biological materials. The determination was based on the reduction of iron(III) to iron(II) ions in the presence of tocopherol and formed a colored complex with 2,2-bipyridine the absorbance was measured at 520 or 534 nm and is an AOAC official method (1995). The existing spectrophotometric methods for vitamin E determination made use of the oxidizability of the 6-hydroxychroman ring of a-tocopherol to the... 

When complexed with bipyridine or phenanthroline, strongly coloured complexes of Fe(II) or Fe(lII) are formed. These are the basis of spectrophotometric methods of their determination. 

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