PRECONCENTRATION OF 1-(2-PYRIDYLAZO)-2-NAPHTHOL IRON(III) CAPRIQUAT ON A MEMBRANE-FILTER, AND 3RD-DERIVATIVE SPECTROPHOTOMETRIC DETERMINATION OF IRON(III)

Iron(III) was preconcentrated by collection on an organic solvent-soluble membrane filter (nitrocellulose (NC)) of the iron(III)-1-(2-pyridylazo)-2-naphthol (PAN) complex in the presence of capriquat as an oily quaternary ammonium salt. Third-derivative spectrophotometry was used for measurement of the third-derivative distance (d3A/dlambda3) between lambda1 = 520 nm and lambda2 = 590 nm or lambda3 = 660 nm and lambda4 = 724 nm of the iron(III)-PAN-capriquat complex or PAN-capriquat in dimethylsulfoxide (DMSO) following preconcentration. The calibration curve was linear in the range of 1-10 mug iron(III)/5.0 ml DMSO solution. The proposed method was about five-fold more sensitive and more selective than using zero-order spectrophotometry.