Avaliação do método de adição de padrão interno em técnicas espectroscópicas
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Data
2017-02-22
Autores
Fortunato, Felipe Manfroi [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O objetivo desta Tese de Doutorado foi avaliar o método de adição de padrão interno empregando técnicas espectroscópicas. Inicialmente o método de adição de padrão interno foi aplicado no modo convencional na determinação de Ca e Mg em amostras biodiesel e urina por espectrometria de absorção atômica em chama de alta resolução e fonte contínua e na determinação de ureia em urina por espectroscopia Raman. Para fins comparativos, todas as amostras e materiais certificados foram também analisados pelos métodos de calibração externa, adição de padrão e padronização interna. Nitrato, Sr e Mn foram selecionados como padrões internos para ureia, Ca e Mg, respectivamente. Para avaliar a exatidão do método na determinação de Ca e Mg foram analisados nove materiais de referência certificados (CRM) e os resultados obtidos foram concordantes a 95% de confiança com os valores certificados (teste t). Para ureia a exatidão foi avaliada por meio de comparação dos resultados obtidos pelo método de adição de padrão interno e por um método de referência. Todos os resultados obtidos foram concordantes entre si (teste t pareado) ao nível de 95% de confiança. A exatidão do método também foi checada por meio de testes de adição e recuperação: Ca (93 – 119%), Mg (100 – 116%) e ureia (99 – 105%). A desvantagem do método de adição de padrão interno convencional foi o volume total de amostra utilizado, a quantidade de soluções analíticas empregadas e a baixa frequência analítica. No entanto, este problemas foram solucionados com o desenvolvimento de sistemas em fluxo e pelo uso de um gradiente de concentração. O método de adição de padrão interno por gradiente de concentração em fluxo foi avaliado na determinação de Na e K em amostras de biodiesel e urina por espectrometria de emissão atômica em chama e na determinação de etanol em gasolina por espectroscopia Raman. Lítio foi empregado como padrão interno para Na e K, e acetona foi utilizada como padrão interno para etanol. A exatidão do método na determinação de Na e K foi avaliada por meio da análise de cinco CRMs, e os resultados obtidos para Na foram concordantes a 95% de confiança com os valores certificados (teste t), para K os resultados apresentaram valores subestimados ao longo do trabalho (em torno de 80% de recuperação). Para determinação de etanol em gasolina a exatidão foi avaliada por meio da comparação dos resultados obtidos pelo método proposto e pelo método de referência, e todos os resultados obtidos foram concordantes entre si (teste t pareado) ao nível de 95% de confiança. A exatidão do método de adição de padrão interno por gradiente de concentração em fluxo também foi avaliada por meio de testes de adição e recuperação: Na (94 – 110%), K (73 – 86%) e etanol (99 – 104%). Os resultados obtidos utilizando o método de adição de padrão interno (convencional e em fluxo) em todas as aplicações apresentaram precisão e exatidão melhores ou comparáveis aos métodos de adição de padrão, padronização interna e calibração externa, mostrando ser uma estratégia de calibração eficiente para técnicas espectroscópicas.
The aim of this Doctoral Thesis was to evaluation of the internal standard addition method employing spectroscopic techniques. Initially, traditional standard addition method was applied for Ca and Mg determination in biodiesel and urine samples by high-resolution continuum source flame atomic absorption spectrometry and for urea determination in urine samples by Raman spectroscopy. For comparison purposes, all samples and certified materials were also analyzed by external calibration, standard addition and internal standardization methods. Nitrate, Sr and Mn were selected as internal standards for urea, Ca and Mg, respectively. In order to verify the accuracy for Ca and Mg determination were analyzed nine certified reference materials (CRM), the results were in agreement with certified values at the 95% confidence level (t-test). For urea, the accuracy was evaluated by comparison of the results obtained by internal standard addition and a reference method. All results were in agreement at 95% confidence level (paired t-test) with each other. The accuracy was also checked by addition and recovery tests: Ca (93 - 119%), Mg (100 - 116%) and urea (99 - 105%). The drawbacks of traditional internal standard addition were the total volume of sample used, the amount of analytical solutions employed and the lower sample throughput. However, these problems were solved with the development of flow systems and the use of a concentration gradient. The internal standard addition by flow gradient concentration was evaluated for Na and K determination in biodiesel and urine samples by flame emission atomic spectrometry and for ethanol determination in gasoline by Raman spectroscopy. Lithium was selected as internal standard for Na and K, and acetone was selected as internal standard for ethanol. The accuracy of the method for Na and K determination was evaluated by five CRMs analysis, and the results obtained for Na were in agreement with certified values at the 95% confidence level (t-test), for K the results presented underestimated values throughout the study (around 80% recovery). The accuracy for ethanol determination in gasoline was evaluated comparing the results obtained by the proposed method with the reference method. All results were in agreement at 95% confidence level (paired t-test) with each other. The accuracy of internal standard addition by flow gradient concertation method was also evaluated by addition and recovery tests: Na (94 - 110%), K (73 - 86%) e ethanol (99 - 104%). The results obtained by internal standard addition (traditional and flow modes) for all applications showed accuracy and precision better or comparable with traditional calibration methods (standard addition, internal standardization and external calibration), revealing to be an efficient calibration strategy for spectroscopic techniques.
The aim of this Doctoral Thesis was to evaluation of the internal standard addition method employing spectroscopic techniques. Initially, traditional standard addition method was applied for Ca and Mg determination in biodiesel and urine samples by high-resolution continuum source flame atomic absorption spectrometry and for urea determination in urine samples by Raman spectroscopy. For comparison purposes, all samples and certified materials were also analyzed by external calibration, standard addition and internal standardization methods. Nitrate, Sr and Mn were selected as internal standards for urea, Ca and Mg, respectively. In order to verify the accuracy for Ca and Mg determination were analyzed nine certified reference materials (CRM), the results were in agreement with certified values at the 95% confidence level (t-test). For urea, the accuracy was evaluated by comparison of the results obtained by internal standard addition and a reference method. All results were in agreement at 95% confidence level (paired t-test) with each other. The accuracy was also checked by addition and recovery tests: Ca (93 - 119%), Mg (100 - 116%) and urea (99 - 105%). The drawbacks of traditional internal standard addition were the total volume of sample used, the amount of analytical solutions employed and the lower sample throughput. However, these problems were solved with the development of flow systems and the use of a concentration gradient. The internal standard addition by flow gradient concentration was evaluated for Na and K determination in biodiesel and urine samples by flame emission atomic spectrometry and for ethanol determination in gasoline by Raman spectroscopy. Lithium was selected as internal standard for Na and K, and acetone was selected as internal standard for ethanol. The accuracy of the method for Na and K determination was evaluated by five CRMs analysis, and the results obtained for Na were in agreement with certified values at the 95% confidence level (t-test), for K the results presented underestimated values throughout the study (around 80% recovery). The accuracy for ethanol determination in gasoline was evaluated comparing the results obtained by the proposed method with the reference method. All results were in agreement at 95% confidence level (paired t-test) with each other. The accuracy of internal standard addition by flow gradient concertation method was also evaluated by addition and recovery tests: Na (94 - 110%), K (73 - 86%) e ethanol (99 - 104%). The results obtained by internal standard addition (traditional and flow modes) for all applications showed accuracy and precision better or comparable with traditional calibration methods (standard addition, internal standardization and external calibration), revealing to be an efficient calibration strategy for spectroscopic techniques.
Descrição
Palavras-chave
Calibração, Adição de padrão interno, Técnicas espectroscópicas, Padronização interna, Adição de padrão, Calibration, Internal standard addition, Spectroscopic techniques, Internal standardization, Standard addition