Cloud Point Extraction Coupled with Laser Thermal Lens Spectrometry for Determination of Trace Palladium in Environmental Water Samples

A highly sensitive, simple and safe method has been developed for the determination of trace palladium by cloud point extraction (CPE) combined with thermal lens spectrometry (TLS). The method is based on the fact that formation of the stable hydrophobic complex of palladium(II) with a newly synthesized reagent 2-(5-iodo-2-pyridylazo)-5-dimethylaminoaniline (5-I-PADMA), and then extraction into the micellar phase of non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) as extracting agent at pH 4.8. Parameters that affect extraction efficiency, such as solution pH, concentration of 5-I-PADMA and Triton X-114, and equilibration temperature and time on CPE, were investigated and optimized. The results showed that an efficient extraction of palladium could be achieved with the following conditions were as follows: pH = 4.8 acetic acid-sodium acetate (HAc-NaAc) buffer solution, 100 μL 5 × 10 –4 mol/L 5-I-PADMA, 800 μL 1.0% (w/v) Triton X-114, and heat-assisted at 60°C for 20 min. After phase separation, the surfactant-rich phase containing palladium complex was dissolved in 450 μL 2 mol/L HClO 4 -ethanol solution prior to its determination by TLS. A single mode He–Ne laser with 632.8 nm was employed for both excitation and probe beams. Under optimum experimental conditions, the calibration graph was linear over the range 0.1–7.5 ng/mL with a correlation coefficient of 0.9986. The detection limit was 1.0 ng/mL for palladium. The sensitivity enhanced by 558 times compared to that of the conventional spectrophotometry. The relative standard deviation (RSD) for elven replicate measurements of 1.0 ng/mL of palladium was 3.2%. The proposed method was applied to the determination of trace palladium in water samples.