Spectrochimica Acta Part A 74 (2009) 761–766 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Laser induced-thermal lens spectrometry after cloud point extraction for the determination of trace amounts of palladium N. Shokoufi a , F. Shemirani b,∗ , M. Shokoufi c a Department of Analytical Chemistry, Chemistry & Chemical Engineering Research Center of Iran, P.O. Box 14335-186, Tehran, Iran b Department of Analytical Chemistry, Faculty of Chemistry, University College of Science, The University of Tehran, P.O. Box 14155-6455, Tehran, Iran c Electron Pishro Pajohesh, Tehran, Iran article info Article history: Received 1 February 2009 Received in revised form 12 July 2009 Accepted 7 August 2009 Keywords: Thermal lens spectrometry Cloud point extraction Palladium Laser Microcell abstract Cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS) has been developed for the preconcentration and determination of palladium. TLS and CPE methods have good matching conditions for the combination because TLS is a suitable method for the analysis of low volume samples obtained after CPE. Palladium was complexed with 1-(2-pyridylazo)-2-naphthol (PAN) as a complexing agent in an aque- ous medium and concentrated by octylphenoxypolyethoxyethanol (Triton X-114) as a surfactant. After the phase separation at 60 ◦ C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 L of carbon tetrachloride. The obtained solu- tion was introduced into a quartz microcell and the analyte was determined by laser induced-thermal lens spectrometry (LI-TLS). The single-laser TLS was used as a sensitive method for the determination of palladium–PAN complex in 20 L of the sample. Under optimum conditions, the analytical curve was linear for the concentration range of 0.3–60 ng mL -1 and the detection limit was 0.04 ng mL -1 . The enhancement factor of 460 was achieved for 10 mL samples containing the analyte and relative standard deviations were lower than 5%. The developed method was successfully applied to the extraction and determination of palladium in water samples. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Spectrophotometric methods are the most commonly used techniques and continue to enjoy wide popularity. The common availability of the instrumentation, the simplicity of the proce- dures, speed, precision and accuracy of the technique still make spectrophotometric methods attractive. Thermal lens spectrometry as an indirect spectrophotometry has many advantages over direct spectrophotometry such as high sensitivity, low volume analysis and organic solvent enhancement effect. The thermal lens effect has been successfully applied to the spectrometric measurement of trace amounts of analytes [1–4]. The absorption of the laser beam with Gaussian profile by the analyte produces temperature gradient in sample. This temperature gradi- ent leads to the refractive index gradient that corresponds to the formation of thermal lens in solution. The strength of the lens is determined by its effect on the divergence of the same laser beam ∗ Corresponding author. Tel.: +98 21 61112481. E-mail addresses: shokoufi@khayam.ut.ac.ir (N. Shokoufi), shemiran@khayam.ut.ac.ir (F. Shemirani), info@electron-co.com (M. Shokoufi). [2] or on the divergence of a second laser beam [4]. A steady-state condition is obtained when the rate of laser heating equals the rate of heat loss due to the thermal conductivity of the solvent and the finite temperature rise. The build-up of the lens can take place on time scales from tens of microseconds to hundreds of millisec- onds, depending on the thermo-optical properties of the solvent and the radius of the laser beam through the sample [1,5]. Thermal lens takes time to develop into its full strength of thermal effect in solution (steady-state) [6], afterwards the thermal lens effect needs some time to relax in the solution [7]. The maximum signal is obtained when the steady-state condition is applied. The lack of tunability of the laser source precludes the mea- surement of spectra, therefore the selectivity of a method must be provided by chemical means, e.g., chromogenic reaction or separa- tion technique, while the thermal lens apparatus acts as a sensitive, quantitative system. The use of surfactants in analytical chemistry provides a lot of possibilities [8,9]. Separation and preconcentration based on the cloud point extraction emerges as an important practical technique. Aqueous solutions of most non-ionic surfactants possess the ability to decrease their solubility rapidly and become turbid when they are heated above a temperature called the cloud point tempera- 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.08.013