Selective sorption-spectrometric determination of nanogram amounts of vanadium(IV) and vanadium(V)

Conditions of the selective sorption-spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d = 1 cm, l = 0.1 mm, m = 2.7 mg). The flow rate is 10-20 mL/min. The detection limit is 5-7 no, of vanadium in the support zone or 0.2-0.5 ng/mL. The determination of 0.5-5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg.