Técnicas espectroanalíticas aliadas à química verde visando à determinação de V e Mo com procedimentos de extração e pré-concentração

Abstract

The goal of this PhD thesis was to propose alternatives to improve the analytical performance of F AAS (Flame Atomic Absorption Spectrometry) and LIBS (Laser Induced Breakdown Spectroscopy) aiming V and Mo determination. Some analytical procedures, in agreement with the Green Chemistry principles of, as the cloud point extraction (CPE) and dispersive liquid-liquid microextraction (DLLME) were evaluated in different kind of samples (mineral water, medicines and soil). First was evaluated some parameters concerning to the CPE and the instrumental parameters, using factorial design in order to obtain the better conditions for the extraction of V and Mo individually and simultaneously, as well as the minimum sample volume necessary to introduce in the nebulizer. The limits of detection (LOD) achieved with the CPE to extract individual V and Mo were 80 and 20 μg L-1, respectively. When the CPE procedure was applied for simultaneous extraction, the LODs were 80 and 70 μg L -1 to V and Mo, respectively. The developed procedure was applied in two real samples of medicines and the recoveries obtained were 107 ± 4 % and 98 ± 2 % for V and Mo, respectively. Measurements in presence of Fe (II) (possible interfering) in proportions higher than 1:10 (V: Fe and Mo: Fe) were performed and the absorbance signals of V and Mo decrease thereabout 30 and 50%, respectively. In the second work a procedure employing dispersive liquid-liquid microextraction for the determination of V and Mo by LIBS was developed and applied in water, medicines and soil samples. Some factorial designs were also performed to optimize the best conditions for DLLME procedure. After the optimization, a sample volume of 10 μL was dried in a piece of aluminum foil and submitted to determination by LIBS. The combination of DLLME-LIBS is quite feasible since microextraction is fast, easy to apply, low-cost, they have the possibility of automation, generates little waste and the small volume of the final extract is sufficient for the LIBS analysis. The LOD achieved with the proposed method were 5 and 30 μg L-1 for V and Mo, respectively. The procedure was applied to real samples of two medicines, where the recoveries obtained by comparing with the standard addition method and determination by ICP OES ranged 92-104% for V and 96% for Mo. In the soil sample recovery was 97 ± 15% for V and Mo was below the LOQ and a reference material NCS ZC 85005 (Beef Liver) where V was below the LOQ and the recovery obtained for Mo was 102 ± 21%.