Desenvolvimento de métodos analíticos para determinação de terras raras, Th, U e Y em rochas, solos e sedimentos por ICP-MS

Abstract

In this work, the introduction of dissolved geological certified reference materials in the plasma through pneumatic (PN) and ultrasonic (USN) nebulizers was studied, in order to compare both nebulizers performances in connection to the determination of rare earth elements (REE), U, Th and Y in geological samples by inductively coupledplasma mass spectrometry (ICP-MS). The best conditions for the nebulizer gas flow rate and the radiofrequency power were investigated for standard and samples solutions. The nebulizer gas flow rate was 1.05 and 1.10 L min-1 for PN and USN, respectively. The RF power was 1100 W for both nebulizers. Determinations and calibration curves werecarried out with aqueous standards using 10 ?g L-1 of Rh as internal standard for pneumatic nebulizer and without internal standard for ultrassonic nebulizer. The calibration curves correlation coefficients were better than 0.999 for all studied analytes, employing both nebulizations. Better detection power was obtained with the USN, whose LODs were between 0.01 ng L-1, for U, and 1.4 ng L-1 for Ce, while with the PN were between 0.2 ng L-1, for Lu and Tm, and 7.4 ng L-1, for Y. Slurry sample introduction with electrothermal vaporization (ETV) has been applied to inductively coupled plasma mass spectrometry (ICP-MS) for the direct determination of Dy, Sm, Eu, Tm and Yb in geological samples. The best conditions for sample preparation, the furnace temperature program, the nebulizer gas flow rate, the RF power and the amount of NaCl used as carrier were determined. The detection limits for 164Dy, 152Sm, 153Eu, 169Tm and 174Yb were of 200, 30, 20, 10 and 10 pg g-1, respectively. The precision was better than 10%.