Técnicas de titulación ácido-base: consideraciones metrológicas / Acid-base titration techniques: metrological considerations / Técnicas de titulação ácido-base: considerações metrológicas

Resumen Se evaluaron diferentes sistemas de medición para titulaciones ácido-base, con el propósito de determinar cuál presenta mejores características metrológicas. Estos sistemas incluyen volumetrías y gravimetrías, las cuales se combinaron con diferentes métodos de detección del punto de equivalencia: (i) potenciometría, (ii) indicador ácido-base y (iii) conductividad electrolítica. Este artículo propone una nueva aproximación para la estimación de la incertidumbre de medición asociada a la detección del punto de equivalencia. Los resultados indicaron que, para la determinación del punto de equivalencia, las incertidumbres más bajas se obtienen mediante el método potenciométrico en comparación con el método conductimétrico cuyo sesgo es hasta 78 veces mayor. Sin embargo, se encontró que el método potenciométrico es fuertemente dependiente de la resolución del instrumento y/o la cantidad de agente titulante que se adiciona en la cercanía al punto de equivalencia. También se encontró que la incertidumbre disminuye cerca del 40% empleando métodos gravimétricos en comparación con los volumétricos. Al realizar la evaluación del sesgo de los sistemas de medición acorde con la guía ISO 33:2015, los resultados mostraron que, de los métodos evaluados, el método gravimétrico con detección potenciométrica presentó las mejores características metrológicas, pues se obtuvieron sesgos e incertidumbres menores.

Abstract Different measurement systems for acid-base titrations were evaluated to determine which one had the best metrological characteristics. These systems included volumetric and gravimetric titrations, which were combined with different detection systems: (i) potentiometry, (ii) acid-base indicator, and (iii) electrolytic conductivity. This article proposes a new approach for estimating the measurement uncertainty associated with the detection of the equivalence point. The results showed that, for the determination of the equivalence point, the lowest uncertainties were obtained by the potentiometric method in comparison with the conductometric method, whose bias was 78 times higher. The potentiometric method, however, was strongly dependent on the instrument resolution and/or the titrant amount that is added close to the equivalence point. It was also found that uncertainty decreases about 40% using gravimetric methods as compared to volumetric methods. When performing bias evaluation of the measurement systems according to the ISO 33:2015 guide, results showed that, among the evaluated methods, the gravimetric method with potentiometric detection presented the best metrological characteristics, with the lowest biases and uncertainties.

Resumo Foram avaliados diferentes sistemas de medida para titulações ácido-base, a fim de determinar quais possuem as melhores características metrológicas. Estes sistemas incluem titulações e gravimétricas, que foram combinadas com diferentes sistemas de detecção do ponto de equivalência: (i) potenciometria, (ii) indicador ácido-base e (iii) condutividade electrolítica. Este artigo propõe uma nova abordagem para estimar a incerteza de medição associada à detecção do ponto de equivalência. Os resultados indicaram que, para a determinação do ponto de equivalência, as incertezas mais baixas são obtidas pelo método potenciométrico enquanto que a incerteza do método condutométrico é até 78 vezes maior que a obtida pela potenciometria. Além disso, a potencimetria é altamente dependente da resolução do instrumento e/ou da quantidade de titulante para ser adicionado na proximidade com o ponto de equivalência. Também verificou-se que a incerteza diminui em torno de 40% utilizando métodos gravimétricos. De acordo à guia de norma ISO 33:2015, os resultados mostraram que os métodos de titulação ácido-base avaliados gravimetricamente com detecção potenciométrica proporcionaram as melhores características de metrologia, porque obtiveram os menores distorções e incertezas.

A Study on the Statistical Method for the Target Component of a Glucose-lowering Functional Material in Extracts of Evening Primerose Seeds

BACKGROUND: The use of the extracts from evening primrose seeds as a health functional food has been gradually increased. Therefore, the monitoring and screening process has been considerably required for its quality control. OBJECTIVE: This study aimed to estimate the measurement uncertainty associated with determination of penta-o-galloyl β-D-glucose (PGG) in extracts from evening primrose seeds by high-performance liquid chromatography. METHODS: The sources of measurement uncertainty was expressed in accordance with mathematical/statistical theories of GUM & EURACHEM Guide. The expanded uncertainty was calculated by using the relative standard uncertainty between analytical result and sources of uncertainty in measurement (sample weight, final volume, extraction volume, standard solution, matrix and instrument etc). RESULTS: In the results of 95% confidence interval, the uncertainty in measurement was 10,253.34 ± 1,844.50 µg/kg (k = 2.0). CONCLUSION: In this study, it showed that the value of uncertainty in measurement for determination of PGG in extracts from evening primrose seeds by HPLC has about 18.0% influence on PGG contents of the analytical results. The results would be very useful for the monitoring and screening of evening primrose seeds marketed in Korea for its quality control as dietary supplement.

Uncertainty Measurement Evaluation of the Content Determination of Prednisolone API by HPLC / 中国药房

OBJECTIVE:To establish a method for the uncertainty measurement evaluation of the content determination of pred-nisolone API. METHODS:HPLC internal standard method was adopted to determine the content of prednisolone API,establish mathematical model for uncertainty evaluation,analyze influential factors and evaluate the factors. RESULTS:HPLC internal stan-dard method showed the contont was 98.8%,and expanded uncertainty of prednisolone API was 1.6%,and the determination result was(98.8±1.6)%,k=2. CONCLUSIONS:The method is suitable for the uncertainty measurement evaluation of the content deter-mination of prednisolone API by HPLC internal standard method.

Evaluation of uncertainty measurement in the assay of Danshu Capsule / 中成药

AIM: To establish a method for evaluating uncertainty of Danshu Capsule(peppermint oil). METHODS: The uncertainty originated from menthol in Danshu Capsule was analyzed by GC.The influencing factors on the uncertainty were evaluated, including solution strength of reference substance,sample weight,solution volume of sample,peak area of chemical reference substance,peak area of sample,average weight of capsule,etc. RESULTS: The expanded uncertainty U_95 was 1 mg(P=95%,k=2). CONCLUSION: It can be used for evaluation of uncertainty measurement by GC.