Potentiometric E-Tongue System for Geosmin/Isoborneol Presence Monitoring in Drinkable Water.

A potentiometric E-tongue system based on low-selective polymeric membrane and chalcogenide-glass electrodes is employed to monitor the taste-and-odor-causing pollutants, geosmin (GE) and 2-methyl-isoborneol (MIB), in drinkable water. The developed approach may permit a low-cost monitoring of these compounds in concentrations near the odor threshold concentrations (OTCs) of 20 ng/L. The experiments demonstrate the success of the E-tongue in combination with partial least squares (PLS) regression technique for the GE/MIB concentration prediction, showing also the possibility to discriminate tap water samples containing these compounds at two concentration levels: the same OTC order from 20 to 100 ng/L and at higher concentrations from 0.25 to 10 mg/L by means of PLS-discriminant analysis (DA) method. Based on the results, developed multisensory system can be considered a promising easy-to-handle tool for express evaluation of GE/MIB species and to provide a timely detection of alarm situations in case of extreme pollution before the drinkable water is delivered to end users.

Procedimiento de validación de magnitudes bioquímicas en un gasómetro. Aplicación al alcance flexible en la Norma ISO 15189 / Validation procedure of biochemical parameters in a gasometer. Application to the flexible scope in the standard ISO 15189

Objetivos. Diseñar un procedimiento de validación de 4 magnitudes bioquímicas en un gasómetro frente a un analizador acreditado que sea sencillo, consistente y aceptable según la Norma ISO 15189:2007 y que pueda servir como método de acreditación flexible. Métodos. Medición secuencial en los analizadores Dimension RxL y GEM 4000 de glucosa, sodio (Na+), potasio (K+) y lactato en 91 muestras de plasma (heparina de litio) de pacientes entre marzo y junio de 2009 (EP-9). Se chequearon outliers y error sistemático. Los pares de resultados se estudiaron mediante análisis de regresión lineal y gráficos de Bland-Altman. Métodos. El criterio de aceptación fue obtener un error sistemático inferior a las especificaciones de calidad definidas en el laboratorio acreditado. Resultados y discusión. Los resultados de glucosa y K+ fueron aceptables según el procedimiento 6.1 de la guía EP-9, mientras que Na+ fue aceptable según el procedimiento 6.2. En cuanto a lactato, se detectó un error sistemático superior a la especificación del laboratorio. Conclusiones. Se han validado los métodos de determinación de glucosa, Na+ y K+ en un gasómetro GEM 4000 mediante la aplicación de la norma EP-9 con respecto a los del Dimension RxL (métodos de referencia). El lactato no se pudo validar porque el error sistemático superó la especificación del laboratorio. Conclusiones. Este procedimiento se propone como herramienta de validación de métodos para laboratorios acreditados con alcance flexible según la Norma UNE EN ISO 15189 (AU)

Objectives. Designing a 4 biochemical parameters validation procedure in a gasometer versus an accredited analyzer. This procedure is simple, robust and acceptable according to the standard ISO 15189: 2007 and that can serve as flexible accreditation method. Methods. Sequential measurement in Dimension RxL and GEM 4000 analysers of glucose, Na+, K+ and lactate in 91 patients plasma samples (Lithium heparin) between March and June 2009 (EP-9). Checked outliers and bias results pairs were studied using linear regression analysis and Bland-Altman graphics. Methods. The acceptance criterion was to get a bias lower than quality specifications defined in the accredited laboratory. Results and discussion. The results of glucose and K+ were acceptable, following the procedure 6.1 of EP9 guideline, while for Na+ it was acceptable by the procedure 6.2. For lactate, a superior to the specification of the lab bias was detected. Conclusions. Measuring methods of glucose, sodium and potassium in a GEM 4000 gasometer applying standard EP9 versus Dimension RxL as reference methods have been validated. Lactate could not be validated because the bias exceeded the specification of the laboratory. Conclusions. This procedure is intended as validation tool of methods for laboratories accredited with flexible scope according to UNE EN ISO 15189 standard (AU)

Beyond potentiometry: robust electrochemical ion sensor concepts in view of remote chemical sensing.

For about 100 years, potentiometry with ion-selective electrodes has been one of the dominating electroanalytical techniques. While great advances in terms of selective chemistries and materials have been achieved in recent years, the basic manner in which ion-selective membranes are used has not fundamentally changed. The potential readings are directly co-dependent on the potential at the reference electrode, which requires maintenance and for which very few accepted alternatives have been proposed. Fouling or clogging of the exposed electrode surfaces will lead to changes in the observed potential. At the same time, the Nernst equation predicts quite small potential changes, on the order of millivolts for concentration changes on the order of a factor two, making frequent recalibration, accurate temperature control and electrode maintenance key requirements of routine analytical measurements. While the relatively advanced selective materials developed for ion-selective sensors would be highly attractive for low power remote sensing application, one should consider solutions beyond classical potentiometry to make this technology practically feasible. This paper evaluates some recent examples that may be attractive solutions to the stated problems that face potentiometric measurements. These include high-amplitude sensing approaches, with sensitivities that are an order of magnitude larger than predicted by the Nernst equation; backside calibration potentiometry, where knowledge of the magnitude of the potential is irrelevant and the system is evaluated from the backside of the membrane; controlled current coulometry with ion-selective membranes, an attractive technique for calibration-free reagent delivery without the need for standards or volumetry; localized electrochemical titrations at ion-selective membranes, making it possible to design sensors that directly monitor parameters such as total acidity for which volumetric techniques were traditionally used; and controlled potential coulometry, where all ions of interest are selectively transferred into the ion-selective organic phase, forming a calibration-free technique that would be exquisitely suitable for remote sensing applications.

Validación de una técnica potenciométrica para determinar el grado de desacetilación de la quitosana / Validation of potentiometric method to determine the degree of deacetylation of chitosan

Un método potenciométrico para la determinación del grado de desacetilación de muestras de quitosanas derivadas dequitina de langosta se validó según las exigencias internacionales actuales. Para garantizar que ocurriera la reaccióncompleta entre el analito y la disolución de HCl se aplicó calentamiento de las muestras a temperatura inferior a60ºC. Auxiliarmente a los cambios de pH, para la detección del primer punto de infl exión, se utilizó el anaranjadode metilo como indicador visual cuyo intervalo de transición está en un rango estrecho de pH ácido, entre 2 a 4. Nose registraron interferencias desde el punto de vista analítico en la zona de interés de la curva potenciométrica enausencia del analito, por lo que el método fue selectivo. Se demostró que el método fue lineal en el rango de 10.0a 15.0 mg/mL, además fue preciso y exacto para la determinación del porcentaje de grupos aminos libres

The purpose of this study was to validate, in accordance with international standards, a potentiometric method todetermine the degree of deacetylation of chitosan samples derived from lobster chitin. To ensure a complete reactionbetween the analyte and the HCl solution, the samples were heated to temperatures of up to 60ºC. The change in pHand the methyl orange method, as a visual indicator were used to detect the fi rst infl ection point. The transition intervalfell within the narrow pH acid range of 2 to 4. From an analytical point of view, no interference was observed onthe potentiometric curve in the absence of the analyte, thus showing that the method was suffi ciently selective. For thedetermination of the percentage of free amino groups, the method proved to be linear within the 10.0 to 15.0 mg/mL range, as well as precise and exact (AU)