ELSEVIER Talanta 44 (1997) 1307-1312 Talanta Solvent extraction, spectrophotometric and inductively coupled plasma atomic emission spectroscopic (ICP-AES) determination of lanthanum(III) with crown hydroxamic acid Yadvendra K. Agrawal *, Pranav Shrivastav Chemistry Department, School of' Sciences, Gujaral UniversiO', Ahmedabad 380 009, India Received 17 July 1996; received in revised form 7 January 1997; accepted 8 January 1997 Abstract A new crown hydroxamic acid, 5,14-N,N'-hydroxyphenyl-4,15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTAHA) for the extraction and spectrophotometric determination of lanthanum(III) is described. Lanthanum(III) forms a yellow coloured complex with NHDTAHA, which is extracted with chloroform, having molar absorptivity 7.7 x 103 I tool- l per cm at 372 nm. The system obeys Beer's law in the range 1.2-20 ppm of lanthanum. The extract is directly aspirated for ICP-AES measurements, the limits for estimation are 5-140 ppb of lanthanum. Lanthanum has been determined in monazite sand and standard samples. © 1997 Elsevier Science B.V. Keywords: Crown hydroxamic acid; Inductively coupled plasma atomic emission spectrophotometry (ICP-AES); Monazite sand; Lanthanum(III); Spectrophotometry I. Introduction Liquid-liquid extraction technique is widely used for preconcentration and separation of vari- ous metal ions from an interfering matrix. Hy- droxamic acids are superior reagents for extraction and spectrophotometric determination of metal ions [1-5]. In recent years the macro- cyclic ligands, crown ethers, have been reported for metal complexation [6-10]. However, the methods for the extraction and determination of lanthanum with crown ethers suffer from low * Corresponding author. sensitivity and interference of diverse ions [11,12]. The direct atomic absorption and inductively cou- pled plasma emission determination of lanthanum is reported, but a prior ion exchange separation is required [13,14]. The complexities of lanthanum emission lines with large number of strong ionic lines cause some difficulties over line selection thereby causes overlaps and reduces the detection limits considerably [15,16]. The very low levels at which the lanthanum is sought and potential in- terference from major elements, have led to the use of separation method to remove the bulk of major elements and at the same time to concen- trate the lanthanum from the samples into small volume of solution. 0039-9140/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0039-91 40(97)00022-2