Evaluation study of an ion selective field effect transistor electrode for measuring quality parameters of fuel ethanol

Abstract

Um eletrodo íon seletivo baseado em transistor de efeito de campo (ISFET) foi avaliado na medição de pH e índice de acidez (IA) de etanol combustível e comparado a dois eletrodos de vidro contendo soluções de referência diferentes: solução aquosa de KCl (eletrodo glass-KCl) e solução etanólica de LiCl (eletrodo glass-LiCl). O pH foi determinado utilizando diferentes tempos de medição e AN foi determinado utilizando titulação potenciométrica automática. Para pH, o eletrodo glass-KCl apresentou as melhores precisão e estabilidade, com uma repetibilidade média cerca de quatro vezes melhor quando comparado ao eletrodo ISFET para o tempo de medição de 30 s (norma ASTM D6423). Para AN, os eletrodos glass-KCl e glass-LiCl apresentaram repetibilidades similares, as quais foram cerca de três vezes melhor do que a apresentada pelo eletrodo ISFET. Além disso, os resultados de um estudo de recuperação demonstraram a melhor exatidão do eletrodo glass-LiCl, com uma recuperação de 100,1%.An ion selective field effect transistor (ISFET) electrode was evaluated for measuring pH and acid number (AN) of fuel ethanol and compared to two glass electrodes with different reference filling solutions: KCl aqueous solution (glass-KCl electrode) and LiCl ethanolic solution (glass-LiCl electrode). pH was determined at different measurement times and AN was determined using automatic potentiometric titration. For pH, the glass-KCl electrode showed the best precision and stability, with an average repeatability about four times better when compared to the ISFET electrode for the measurement time of 30 s (as indicated in the ASTM D6423 standard). For AN, the glass-KCl and glass-LiCl electrodes showed similar repeatabilities, which were about three times better than that of the ISFET electrode. In addition, the results from a recovery study demonstrated better accuracy of the glass-LiCl electrode, with a recovery value of 100.1%.

Reconciling the pHe measurements of bioethanol: pHabs measurements of buffered 50-50 wt% water-ethanol mixtures

“…This method requires the use of a specific electrode, includes detailed measurement constraints, and suggests traceability is achieved through calibration of the specified electrode using aqueous buffer solutions. Reports on measurement of pHe in bioethanol originate with national metrology institutes (NMIs) in Brazil [ [11] , [12] , [13] , [14] , [15] ], the EU [ [16] , [17] , [18] ], and a national research center in the USA [ 19 ]. The significant issues with the ASTM method of measuring pHe have been discussed in Brown et al [ 17 ].…”

“…However, in low water content solvent mixtures, and generally in non-aqueous organic solvents, its applicability is restricted (often to the point of being useless) primarily due to: Poor performance of the commonly used glass electrodes in non-aqueous media. One of the major issues with the use of aqueous buffer calibrated glass electrodes, including those specifically marketed for the measurement of ethanol [ 11 , 14 , 15 , 23 ], is the unknown magnitude of the liquid junction potential (LJP) between the pH electrodes' reference electrode filling solution and the non-aqueous solution under test. Further, glass electrodes behave differently when in contact with aqueous solutions vs. mixed water-ethanol solutions.…”

Light‐addressable potentiometric sensor with the micro blind holes substrate

“…Light‐addressable potentiometric sensor (LAPS), which is similar to the ion‐sensitive field‐effect transistor [1–3], is one type of surface potential sensor based on semiconductor principle [4, 5]. LAPS can be used for many biochemical measurements [6–10].…”