4, 5-dihydroxy-l, 3-benzenedisulfonic acid

The indicator substance for iron determination is Tiron [4,5-dihydroxy-l,3-benzenedisulfonic acid, disodium salt] (Acros Organics, Geel, Belgium). The stock solution used to prepare the calibration samples contains Ig Fe/L (solution of Fe(N03)3-4aq in HNO3 0.5N) (Panreac Quimica, Barcelona, SP). 

A post-column derivatization with subsequent photometric detection has also been developed for the determination of aluminium. Using a mixture of ammonium sulfate and sulfuric acid, aluminium is separated as A1S04+ ion on a cation exchanger. It forms a stable complex with the disodium salt of 4,5-dihydroxy-l,3-benzenedisulfonic acid (Tiron) at pH 6.2 which can be detected at 313 nm. 

Nowadays, the trend appears to be to determine simultaneously iron and other metals or Fe(II) and Fe(III) species. In the first case, some reagents such as l,5-bis(di-2-pyridylmethylene)thiocarbonohydrazide, 2,4,6-tri-(2-pyridil)-l,3,5-triazine are used. In the second case 4,5-dihydroxy-l,3-benzenedisulfonic acid, disodium salt (635 nm), l-(5-bromo-2-pyridyla-zo)-2-naphthol-6-sulfonic acid (765 and 850 nm), azide complexes in tetrahydrofuran (396 nm), etc. are used... 

The buffer mixture of ammonium sulfate and sulfuric acid can also be employed for the elution of aluminum. The specific detection of aluminum is carried out via derivatization with Tiron (4,5-dihydroxy-l,3-benzenedisulfonic acid disodium salt), with subsequent photometry of the complex formed at a... 

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