This work presents the results of the studies on the operating characteristics of ISFET sensors, which had a silicon nitride membrane, using glacial acetic acid as solvent. The stability periods found were between five and seven minutes with response time in the range of 50 to 70 seconds. Pyridine was determined quantitatively and the results were compared with those obtained with a commercial glass electrode; the analysis of variance (ANOVA) demonstrated that there were no significant differences for the results from either type of sensor. The Biederman and Sille ¬ n calibration method was applied to the potentiometric system: the linear response range found was 4.3 < pH < 10.4. The ISFET presented different sensitivities for the acid and basic regions, such that with usage the sensitivity increased toward the acetate ion while that for the solvated proton decreased, and so did the reproducibility as well. The initial analytical properties of the sensor are restored upon regeneration of the silicon nitride membrane. The equilibrium constants for the protonated pyridine and diethylamine perchlorates were determined: the values found do not differ statistically in respect to those reported in the literature. Also, it was found that upon regeneration of the selective membrane, the ISFET can be used in aqueous and glacial acetic media.

<span>Se propone un reactivo para un curso de licenciatura de métodos de análisis instrumental para evaluar el conocimiento de curvas de adiciones patrón y curvas de calibración, considerando el tratamiento estadístico de los datos.</span>

<span>En el número anterior de la revista (vol. 16, núm. 2, pp. 114-115) se presentó un reactivo constituido por dos problemas de examen para un curso de la licenciatura en Química de la UAM-Iztapalapa. A continuación se presentan las respuestas que consideramos correctas, junto con algunos comentarios. En las tablas 1 y 2 se reproducen las que se presentaron en el Reactivo, por si el lector no lo tiene a la mano.</span>