Sensitive Spectrophotometric Determination of La(III) with 1 (2 Pyridylazo)-2-napht-hol (PAN)

A simple and sensitive method for spectrophotometric determination of lanthanum has been developed. At pH 9.6, in presence of 50% ethanol, lanthanum reacts with 1-(-2-pyridylazo)-2-naphthol (PAN) to form a red complex which has two absorption maxima, at 545 and 510 nm. The molar absorptivity at 545 nm is 0.55 × 10^4 liters · mol−1 cm−1. On the other hand, lanthanum reacts with PAN in pure ethanol to form a red complex at 530 nm, with high molar absorptivity (8 × 10^4 liters · mol−1 cm−1).