Desenvolvimento de um método de extração e pré-concentração em fluxo para determinação de cádmio em amostras de interesse alimentício utilizando a palha do café como adsorvente
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Data
2017-03-29
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Universidade Federal de Goiás
Resumo
The present work presents a study on the use of dry coffee straw and straw from sticky coffee, also known as "bark" of the coffee as adsorbent for metallic ions. Initially, the experiments were carried out in batch and the metal quantification before and after the adsorption experiments was done using Atomic Flame Absorption Spectrometry (FAAS). The adsorption of the ions Cd (II), was evaluated and the results indicated that the coffee straw dried in natura, presented an outstanding performance.
The optimization parameters studied in the adsorption of the corresponding ion were the pH of the solution and time of contact, presenting the maximum adsorption occurrence in the pH value between 5 to 9 and better contact time starting from 60 minutes. The physical-chemical characterization of the material was done through the use of Infrared Spectroscopy, X-ray Dispersive Energy Analysis, X-Ray Diffraction Analysis, EDX Elemental Analysis and the zero load point determination. The adsorption kinetics best fit the pseudo-second order model and the adsorption isotherms developed with the objective of determining the maximum adsorptive capacity showed a better fit to the Langmuir model.
From data obtained in the batch experiments, the dry coffee straw was used in the development of a solid phase extraction method for adsorption of cadmium. In order to evaluate the chemical and flow variables that possibly influence the system, the multivariate method was used. The variables studied were adsorbent mass, eluent concentration, eluent volume and pre-concentration flow, through a factorial design 24, indicating the eluent volume and pre-concentration flow as the significant variables, which were studied later by means of Doehlert planning. Thus, the best conditions for flow system operation were: adsorbent mass 25 mg, (HCl) eluent concentration 1.0 mol L-1, eluent volume 250 μL and pre-concentration flow 2.0 mL min-1.
For the purpose of analyzing the selectivity of the method, a study of the possible interferences was done, based on the calculation of the interference factor (IF). The Cu+2, Fe+2, Mn+2, Zn+2, Ca+2, Mg+2, Na+1, K+1, Cr+3 ions were analyzed in different proportions.
The pre-concentration factor was calculated as being equal to 20.4; Limit of detection (LD) 7,86 μg L-1, Limit of quantification (LQ) 26,20 μg L-1, precision (DPR) 0,11, linear range between 26,20 - 2000 μg L-1.
The accuracy of the method was tested through the analysis of the certified water reference material (APS - 1071).The recovery tests were carried out on samples of cashew, pineapple, orange and guava juices, and the values found were ranged from 100,72 to 109,7%.
The method developed was satisfactory for pre-concentration of Cd (II) ions, for the simplicity, efficiency, low cost. Also, the used adsorbent can be easily found in nature and it can be reused.
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Palavras-chave
Cádmio, Palha do café, Adsorvente, Extração em fase sólida, Cadmium, Coffee straw, Adsorbent, Solid phase extraction
Citação
SOARES, Maria Dalva Americano. Desenvolvimento de um método de extração e pré-concentração em fluxo para determinação de cádmio em amostras de interesse alimentício utilizando a palha do café como adsorvente. 2017. 106 f. Dissertação (Mestrado em Química) - Universidade Federal de Goiás, Catalão, 2017.