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Ultratrace Determination of Metals with Dithizone by Thermal Lens Spectrophotometry

Volume 42, Number 2 (Feb. 1988) Page 341-346

Ramos, G. Ramis; Alvarez-Coque, M. C. Garcia; Smith, B.W.; Omenetto, N.; Winefordner, J.D.


A pump-probe thermal lens instrument was constructed, evaluated, and applied to the determination of metals after extraction with dithizone in carbon tetrachloride. An argon-ion laser operated at 514.5 nm, with a power of just 22 mW at the cuvette position and chopped at 2 Hz, and a He-Ne laser were used as a pump and probe, respectively. The thermal lens effect was measured by a pinhole-photodiode and a lock-in amplifier. Evaluation of the setup with an iodine solution in carbon tetrachloride gave a minimum detectable absorbance of 5 × 10−6(S/N = 3), the upper limit of the dynamic range being 5.7 × 10−3. Relative standard deviation was about 3%. Calibration curves and limits of detection for several metal dithizonates were obtained. From extractions of cadmium dithizonate at concentrations lower than 2 ng mL−1, a LOD of 8 pg mL−1, corresponding to an absolute LOD of 4 fg of cadmium in the probe volume, was achieved.