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IntroductionFor more than 60 years, pH-glass electrodes have been widely used, and pH measurements in various samples are still made using these electrodes. They are very popular due to their high selectivity and dynamic pH range. However, in spite of the distinctive potential characteristic of pH-glass electrodes and their use in routine pH measurements for so many years, they have certain limitations, such as high resistance, brittleness, instability in hydrofluoric acid and fluoride-containing media. They also create problems in the construction of microelectrodes for biological applications and in vivo measurements. That is why studies related to the construction of nonglass pH electrodes have been gaining momentum. The construction of PVC pH electrodes based on neutral carriers will solve most of these problems. The facts that PVC electrodes have low electrical resistance and that they are easy to construct have increased interest in the implementation of these electrodes in place of glass membranes. These electrodes are of great practical importance, since they are solid and unbreakable. For example, there have been numerous studies about the use of pH-sensitive liquid membrane electrodes in clinical studies. 1 Le Blanc et al. prepared a liquid-membrane electrode with p-octadecyloxy-m-chlorophenylhydrazonemesoxalonitrile (OCPH) as a proton carrier. 2 Simon et al. developed different PVC membrane pH electrodes based upon tri-n-dodecylamine, which gave good response characteristics. [3][4][5][6][7][8] Wu and Yu prepared a pH-sensitive electrode using methyldioctadecylamine (MDODA) as a neutral carrier.9 Later, some authors continued similar research, and other compounds have been investigated as ionophores for hydrogen ions, many of which can be used for a very wide range of pH values. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] Calixarenes are metacylclophanes comprising phenolic and methylene units. They are very popular as attractive and excellent ionophores because they provide a platform for the attachment of convergent binding groups to create host molecules, mainly for the attraction of simple cations, anions and small molecules. [24][25][26][27][28][29][30][31] McKervey et al. first recognized that calixarenes with cations-complexing groups attached to the lower rim may possess the molecular requirements for the type of ionophore used in ion-selective electrodes (ISEs). 32,33 For example, the tetraesters of calix[4]arenes have been proved to be excellent ionophores for sodium in liquid membrane and PVC membrane electrodes. These types of electrodes based on such compounds were shown to be capable of measuring sodium in blood. 34,35 Some calixarenetetraesters are now commonly used in commercial blood electrolyte analyzers for sodium determination. The purpose of this study was to develop a hydrogen ionselective electrode using a macrocyclic compound of calix[4]arene as a neutral carrier and to determine its lifetime, response time, optimum working range and other response characteristics....