Validation of an analytical method to quantify serum electrolytes by atomic absorption spectroscopy

Ciencias exactas e ingenierías   Validation of an analytical method to quantify serum electrolytes by atomic absorption spectroscopy   Validación de un método analítico para cuantificar electrolitos séricos por espectroscopia de absorción atómica   Alejandro Monserrat García-Alegría*, Agustín Gómez-Álvarez**, Leticia García-Rico***, Mercedes Serna-Félix****   * Chemical Department of Biological Sciences, University of Sonora, Hermosillo, Sonora, México, C.P. 83000. E-mail: ** Department of Chemical Engineering and Metallurgy, University of Sonora, Hermosillo, Sonora, México, C.P.: 83000. Phone: (662) 2592165. E-mail: *** Research Center for Food and Development Civil Association (CA), Hermosillo, Sonora, México, C.P. 83000. E-mail: **** School of Nursing of the Mexican Institute of Social Security, Hermosillo, Sonora, México, C.P. 83000. E-mail:   Recibido: 7 de abril de 2015 Aceptado: 8 de mayo de 2015   Abstract The objective of this research was to develop the procedure to validate an analytical method through the technique of spectroscopy by atomic absorption to quantify serum electrolytes. Quality parameters were used such as: accuracy, precision, repeatability, linearity, limit of detection, and limit of quantification. First some work was done in optimization of the analytical method in ideal conditions. Subsequently, some work was done with the validation of the method using a certified reference material National Institute Standard Technology (NIST) 2670a. Finally, the methodology was assessed in the determination of metals in a sample of human blood serum. The quality criteria evaluated showed consistent and acceptable values depending on the statistical test used for each parameter with a significance level of 5% (α = 0.05). The results obtained in this research can contribute to the beginning of the establishment of an official standard aimed at analysis of electrolytes (Na, K, Ca, Mg) in human blood serum so that can be used as reference by clinical laboratories, public health institutions, as well as in institutions of higher education and research centers. Keywords: Validation; optimization; serum electrolytes; atomic absorption spectroscopy.   Resumen El objetivo fue validar un método analítico mediante la técnica de espectroscopía de absorción atómica para cuantificar electrolitos séricos, utilizando parámetros analíticos como exactitud, precisión, repetitibilidad, linealidad, límite de detección y límite de cuantificación. Primeramente se trabajó en la optimización del método analítico en condiciones ideales. Posteriormente en la validación del método utilizando un material de referencia certificado por el National Institute Standard Technology (NIST) 2670a. Para finalizar, se evaluó la metodología en la determinación de metales en una muestra de suero sanguíneo humano. Los criterios de calidad evaluados mostraron valores consistentes y aceptables en función del estadístico de prueba empleado para cada parámetro con un nivel de significancia del 5% (α = 0.05). Los resultados obtenidos pueden contribuir al inicio del establecimiento de una norma oficial mexicana encaminada al análisis de electrolitos (Na, K, Ca, Mg) en suero sanguíneo humano para que pueda ser utilizada como referencia por laboratorios de análisis clínicos, instituciones de salud pública, así como en instituciones de educación superior y en centros de investigación. Palabras clave: Validación; optimización; electrolitos séricos; espectroscopia de absorción atómica.   INTRODUCTION The fundamental purpose of a clinical laboratory is to generate information that enables the diagnosis of diseases, as well as their prevention and treatment. In order to do so, it is necessary to use reliable, accurate and appropriate analytical methods for this purpose. It is required to optimize the experimental conditions, through the standardization of the analytical method, which determines the efficiency of the test from the different conditions in which the purpose is to quantify an analyte and then proceed to validation (Centro Nacional de Metrología-Entidad Mexicana de Acreditación [CENAM-EMA]), 2008a; Coy, 1999; Díaz-Romero, Henríquez-Sánchez, López-Blanco, Rodríguez-Rodríguez & Serra-Majem, 2002). Validation is confirmation that through provision of objective evidence they have met the requirements of the method for a specific application or intended use Intgernational Organization for Standardization/International Electrotechnical Commission ([ISO/IEC] 17025, 2005; NMX-Z-055-IMNC-1996; NMX-CH-152-IMNC-2005). Between the analytes that are determined in a clinical laboratory and that require the provision of safe and reliable data are the serum electrolytes (Na, K, Ca and Mg). These have important functions in the maintenance of body homeostasis. When the levels of these electrolytes increase or decrease problems such as diarrhea, dehydration, tachycardia, kidney failure, seizures, tetany, infarcts, and others might arise (Boetefür & Müller-Plathe, 1995; Spelch, Bousquet & Nicolas, 1980). Normally these electrolytes are quantified through spectrophotometric methods that have a lower sensitivity and low specificity, as well as a higher limit of detection and quantification and increased risk of interference compared to atomic absorption spectroscopy (Baruthio & Pierre, 1993; Olmedo et al., 2010). Additionally, there are differences in the concentrations of analyzed metals and reported inter-laboratory (Namkoong, Hong, Kim & Park, 2013). Due to the reasons mentioned above and to the need for a reference method to quantify metals, the aim of the present work is to validate the methodology to quantify serum electrolytes (Na, K, Ca and Mg) by atomic absorption spectroscopy.   MATERIALS AND METHODS Reagents and materials All the solutions were prepared with deionized water and chemical reagents used (HNO3 and H2O2) are high-purity (Merck). Standard solutions of each metal. They are prepared each time the determination by atomic absorption is made, from a stock solution of 1000 mg/L analytical grade (Na cas # 7440-23-5, K cas # 7440-09-7, Ca cas # 7440-70-2 and Mg cas # 7439-95-4 AccuStandard) in 0.2% of HNO3. Chemical modifiers such as LiCl and LaCL3 to 0.2% are used, to avoid ionic interference in Na and K, as well as chemical interference in Ca and Mg, respectively. Certified reference material of urine NIST 2670b. For this study a reference standard of human serum was not had, for that reason it was replaced by a standard certificate of urine, which despite of having a different matrix, by the large number of proteins present in the blood serum with respect to the urine, the process of digestion by the wet process eliminates the interference of matrix in both cases (serum and urine). Decontamination of materials. All the glassware (serological pipettes and volumetric imaging, beakers, flasks of aforacion), tiptoe to micropipette (...truncated)