The complex of the reagent 2,2′-dipyridyl-2-pyridylhydrazone with La(III) has been studied. Two lanthanum complexes were found to be formed in presence of excess lanthanum ions. The composition of these complexes have been determined. The stability of La:DPPH complex has been studied in both ethanolic and aqueous media. A sensitive (ε = 5.4 × 105 liters · mol−1 · cm−1) and precise method based on the spectrophotometric study of the La:DPPH complex has been proposed for the determination of a comparatively wide range of concentration of lanthanum (0–32 μg/ml). Comparison of the sensitivity of the proposed method with sensitivities of other methods cited in the literature for the spectrophotometric determination of lanthanum is included.

Microchemical Journal, Volume 33, Issue 2, April 1986, Pages 226-231