[en] This Final Graduation Work has focused on developing a method to determine cadmium in marine sediments by Electrothermal Atomic Absorption Spectroscopy (ETAAS) based on the Green Analytical Chemistry principles. For this, strategies were utilized to reduce the amount of reagents used and the residues generated as well as minimizing the time of the analysis. The experimental conditions for cadmium measurement by ETAAS were optimized for the analysis of acid extract of sediments, with the main objective of establishing a rapid temperature program for the graphite furnace; namely, eliminating the pyrolysis step in which the concomitants of the matrix are decomposed. Furthermore, the possibility of performing the instrumental measurement in absence of chemical modifiers (usually employed due to the volatility of cadmium) is evaluated. Diluted hydrochloric acid is employed for sample treatment in order to evaluate the bioavailable fraction of cadmium in these kind of samples. The extraction step was carried out in only 16 min and a minimum volume of reagent (1 mL) was used. A temperature program of the graphite furnace was established, with two drying steps, in order to achieve a gentle drying, avoiding sample projections into the atomizer; the atomization temperature was experimentally studied and set at 1300°C, and a final cleaning stage was included. The analysis was performed in the absence of chemical modifier, obtaining good absorbance profiles, both, for the standard solutions and the sediment extracts, with negligible background signals. The effect of the matrix components of the sediments in the determination of cadmium was evaluated by comparing the slopes of the calibration and addition lines applying the statistical t test. The experimental t value obtained was lower than the tabulated, which means that the matrix does not interfere and, therefore, the quantification can be directly performed using the calibration with standard solutions of cadmium. The analytical characteristics of the method established for cadmium measurement by ETAAS were studied. The method provided a good sensitivity, with characteristic mass values (0,48 ± 0,06 pg and 1,29 ±0,002 pg, respectively, for standard solutions and the sample) that are comparable to those reported in the bibliography for conventional furnace programs. Procedural Limits of Detection and Quantification achieved (0,56 μg/g and 1,07 μg/g, respectively) were adequate for cadmium determination in marine sediments. Regarding precision, the relative standard deviation (RSD) was lower than 3% and 10%, for the standard solutions and the overall procedure, respectively. In this study the reference sediment BCR 701 with certified cadmium contents of the three fractions of the standard protocol established by the Institute for Reference Materials and Measurements (IRMM, former BCR) was analyzed. According to literature, the sum of these three fractions is a good approximation of the bioavailable or labile content of cadmium in sediments. Thus, the content of cadmium obtained with the approach proposed in this study (11,39 ± 1,08 μg/g) was compared with the sum of the certified content of the three stages (11,34 ± 0,45 μg/g). The experimental and tabulated t values do not differ significantly, at a confidence level of 95%, so it can be concluded that the proposed method is a viable alternative to evaluate the bioavailable fraction of cadmium in marine sediments. Therefore, the aim of the work was achieved, developing a method based on Green Analytical Chemistry, both for the sample preparation step and the instrumental measurement, since it reduces the time of analysis, minimizes the amount of reagents used and the subsequent generation of residues.

[gl] O traballo presentado neste Proxecto de Fin de Grao centrouse no desenvolvemento dun método para determinar cadmio en sedimentos mariños mediante Espectroscopia de Absorción Atómica con Atomización Electrotérmica (ETAAS), basado na Química Analítica Verde. Para iso utilízanse estratexias que reducen a cantidade de reactivos empregados e de residuos xerados, así como minimizan o tempo de análise. Experimentalmente optimizáronse as condicións de medida do cadmio por ETAAS para a análise de extractos ácidos de sedimentos, tendo como principal obxectivo o establecemento dun programa rápido de temperaturas do forno de grafito. É dicir, eliminando a etapa de calcinación na cal se descompoñen os concomitantes da matriz. Ademais, evalúase a posibilidade de realizar a medida instrumental en ausencia de modificador químico, habitualmente empregado dada a volatilidade do cadmio No tratamento das mostras empregouse ácido clorhídrico diliuido con obxecto de evaluar a fracción biodisponible de cadmio neste tipo de mostras. A etapa de extracción levouse a cabo en tan só 16 min e empregouse un volumen mínimo de reactivos (1 mL). Estableceuse un programa de temperaturas do forno con dúas etapas de secado, para conseguir un secado suave e evitar proxeccións da mostra no atomizador; estableceuse experimentalmente a etapa de atomización en 1300°C e unha etapa final de limpeza. Levouse a cabo a análise en ausencia de modificador químico, obtendo un bó perfil atómico, tanto para as disolucións patrón como para os extractos de sedimentos, cunha señal de fondo despreciable. O efecto dos compoñentes da matriz de sedimento na determinación de cadmio evaluouse mediante comparación das pendentes das rectas de calibrado e de adición aplicando o test estadístico t. Obtivose un valor de t experimental menor que o da t tabulada, o cal permite considerar que a matriz non interfire e que, por tanto, pódese cuantificar directamente empregando o calibrado con disolucións patrón de cadmio. Estudáronse as características analíticas do método establecido para a medida de cadmio por ETAAS. O método proporcionou unha boa sensibilidade, con valores de masa característica (0,48 ± 0,06 pg e 1,29 ±0,002 pg, respectivamente, para disolucións patrón e para a mostra) que son comparables ós recollidos na bilbiografía para programas de forno convencionais. Tamén se alcanzaron Límites de Detección e Cuantificación do procedemento global axeitados para a determinación de cadmio en mostras de sedimentos marinos (0,56 μg/g e 1,07 μg/g, respectivamente). Con respecto á precisión, a desviación estándar relativa (DER) foi menor do 3% para as disolución patrón e inferior ao 10% para o procedemento global. No estudo analizouse o sedimento certificado BCR 701 o cal ten contidos certificados de cadmio das tres fracción do protocolo estándar establecido polo Institute for Reference Materials and Measurements (IRMM, antigo BCR). Dacordo coa bilbiografía consultada, a suma desas tres fracción é unha boa aproximación do contido biodispoñible ou lábil do cadmio en sedimentos. Desta forma, comparouse o contido de cadmio obtido co método proposto neste traballo (11,39 ± 1,08 μg/g) coa suma do contido certificado das tres etapas (11,34 ± 0,45 μg/g). A un nivel de confianza do 95%, os valores de t experimental e tabulada non difiren significativamente, polo que se pode concluir que o método proposto é unha alternativa viable para evaluar a fracción biodispoñible de cadmio en sedimentos mariños. Polo tanto, alcanzouse o obxectivo do traballo, ao desenvolver un método basado na Química Analítica Verde, tanto na etapa de preparación da mostra como na medida instrumental, reducíndose o tempo de análise, minimizándose a cantidade de reactivos usados e a xeración posterior de residuos.