Microdetermination of aromatic nitro compounds with iron(II) in alkaline sorbitol media

In titrations with iron(II) sulphate in alkaline solutions of sorbitol, the iron(III) formed is bound in a strong complex and the formal redox potential of the Fe(III)/Fe(II) system is decreased to —1.10 V (SCE; 0.5 M sorbitol, 2 M KOH). This permits reducing titrations with a stable reagent, of systems which would otherwise require unstable strong reductants (e.g. Cr(II), Sn(II), V(II), etc.). Determinations of organic mono-, di- and tri-nitro compounds are described; these can be carried out directly on the microscale, with potentiometric, bipotentiometric or biamperometric end-point detection. Nitrate does not interfere; the method can also be employed for indirect determinations of various aromatic compounds after their conversion to nitro derivatives.