Differential Dual-Beam Thermal Lensing Spectrometry: Determination of Lanthanides

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Abstract
This paper describes a differential dual-beam thermal lensing setup which involves two continuous lasers and two cells placed one just behind the other on the beampath. A tunable excitation laser creates the thermal lensing effect in the two cells, whereas the (He-Ne) laser, colinear to the excitation beam, probes the variation of the index of refraction due to the absorption in each cell. The differential response is achieved by placing the solvent in the first cell and the solvent with analyte in the second cell. The positions of the two cuvettes are optimized in order to maximize differential thermal lensing effect detection. This differential instrument allows compensation of 95–98% of the thermal lensing solvent effect. Thermal lensing spectra of two lanthanide ions (Nd3+, Pr3+), both in no complexing solution (HClO4) and in carbonate medium, are discussed. Analytical determinations of these elements with detection limits in the range of 10−6 mole per liter are observed.