Desenvolvimento e aplicação de métodos sustentáveis de geração de vapor para determinação de elementos traço por técnicas espectrométricas

Abstract

The analysis of trace elements using spectrometric techniques requires efficient sample introduction systems. However, conventional nebulizers have limitations for trace-level species such as Cr and Hg. Thus, this study proposed sustainable vapor generation methods as alternatives to traditional systems, reducing the use of expensive, unstable, and potentially toxic reagents. For Cr, a photochemical vapor generation (PVG) methodology coupled to Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) was proposed, using a UV reactor operating in continuous flow mode and using a standard Cr3+ solution of 50 µg L-1 in formic acid medium. The parameters evaluated included: formic acid concentration (10 - 40% v v-1), type of photochemical reactor, irradiation time (15 - 90 s), and N₂ carrier gas flow rate (20 - 60 mL min-1). The best conditions were obtained with a 19 W internal flow UV photoreactor, 30% v v-1 formic acid, an irradiation time of 60 s and a N₂ flow rate of 40 mL min-1. For Hg, the Thermochemical Vapor Generation (TVG) technique coupled with CV-AAS was applied to water and sediment samples from estuaries in Northeast Brazil. Hg concentrations in sediments ranged from 24.9 to 28.5 µg kg-1 in the Parnaíba Delta and reached 89.7 ± 7.1 µg kg-1 in the Cocó River. These values remained below the limits established by CONAMA Resolution No. 452/2012, indicating a low ecotoxicological risk associated with the analyzed sediment fraction. For water samples, concentrations between 2.2 ± 0.4 and 10.1 ± 1.2 µg L-1 were observed. When compared to the reference values defined by CONAMA Resolution No. 357/2005 for Class 1 brackish and saline waters (0.2 µg L-1), all results exceeded the established limit, highlighting the need for attention to the environmental quality of these estuarine ecosystems. The sustainability of the methods was evaluated using the AGREE tool, which integrates the 12 principles of Green Analytical Chemistry into a single metric (0 - 1). The results confirmed the green nature of the proposed approaches, highlighting their potential for efficient environmental monitoring of trace elements.