Extraction-spectrophotometric investigation into the lanthanum-chlorophosphonazo 3-diphenylguanidine system and its use for determination of lanthanum

Lanthanum reacts with 2.7-bis-4-chloro-2-phosphonobenze--neazo)1.8-dihydroxynaphthalene-3.6-disulptonic acid (chlorophosphonazo 3) in the presence of diphenylguanidinium chloride to form a ternary complex (La:R:DPG=1:2:2) extracted into butanol. The optimal conditions are pH 2.5 - 3.5, 6-fold chlorophosphonazo excess, 0.06 M diphenylguanidinium chloride in the aqueous phase, the phase volume ratio being 1:1. The molar absorptivity for the butanol extract of the complex is 1.6x105. The reaction selectivity has been examined in the absence and presence of 1.2-cyclohexanediamine-N,N,N;N'-tetraacetic acid. An extraction-spectrophotometric procedure is suggested for determining lanthanum in the presence of ytterbium, lutecium, and calcium