The IUPAC Recommendations for the Nomenclature of Ion-Selective Electrodes (1994) aim to standardize terminology in the field of ion-selective electrodes (ISEs), which are electrochemical sensors based on potentiometric, amperometric, and conductometric principles. The previous IUPAC Recommendations from 1975 have been revised using recent experimental and theoretical findings. The recommendations define key terms such as activity, activity coefficient, concentration, calibration plot, combination electrode, detection limit, drift, standard deviation, hysteresis, reproducibility, interfering substances, ionic-strength adjustment solutions, ion-selective electrode (ISE), ion-selective electrode cell, isopotential point, membrane, membrane sites, Donnan exclusion, Nernstian response, potentiometric selectivity coefficient, range and span, reference electrode, internal reference electrode, response time, standard addition or known addition method, standard subtraction or known subtraction method, and the "suspension effect" or Pallmann effect. The recommendations also classify ISEs into primary ion-selective electrodes, compound or multiple membrane electrodes, and metal contact or all-solid-state electrodes. They provide equations for the emf responses of ISE cells and define the potentiometric selectivity coefficient, which measures an ISE's ability to distinguish a particular ion from others. The recommendations also describe methods for determining the selectivity coefficient, including the fixed interference method and the separate solution method. The document emphasizes the importance of standardized terminology and procedures for the accurate and reliable use of ISEs in various applications, including clinical and environmental measurements. It also highlights the need for proper calibration, detection limit determination, and the interpretation of response characteristics such as response time and drift. The recommendations aim to improve the standardization of nomenclature and ensure the consistency and accuracy of ISE measurements.The IUPAC Recommendations for the Nomenclature of Ion-Selective Electrodes (1994) aim to standardize terminology in the field of ion-selective electrodes (ISEs), which are electrochemical sensors based on potentiometric, amperometric, and conductometric principles. The previous IUPAC Recommendations from 1975 have been revised using recent experimental and theoretical findings. The recommendations define key terms such as activity, activity coefficient, concentration, calibration plot, combination electrode, detection limit, drift, standard deviation, hysteresis, reproducibility, interfering substances, ionic-strength adjustment solutions, ion-selective electrode (ISE), ion-selective electrode cell, isopotential point, membrane, membrane sites, Donnan exclusion, Nernstian response, potentiometric selectivity coefficient, range and span, reference electrode, internal reference electrode, response time, standard addition or known addition method, standard subtraction or known subtraction method, and the "suspension effect" or Pallmann effect. The recommendations also classify ISEs into primary ion-selective electrodes, compound or multiple membrane electrodes, and metal contact or all-solid-state electrodes. They provide equations for the emf responses of ISE cells and define the potentiometric selectivity coefficient, which measures an ISE's ability to distinguish a particular ion from others. The recommendations also describe methods for determining the selectivity coefficient, including the fixed interference method and the separate solution method. The document emphasizes the importance of standardized terminology and procedures for the accurate and reliable use of ISEs in various applications, including clinical and environmental measurements. It also highlights the need for proper calibration, detection limit determination, and the interpretation of response characteristics such as response time and drift. The recommendations aim to improve the standardization of nomenclature and ensure the consistency and accuracy of ISE measurements.