Apera Instruments 201-C Combination pH Electrode is an economical choice for a reliable combination pH electrode, designed for general water solutions' pH measurement in scientific research, environmental monitoring, and quality control. Not suitable for testing in low-ion concentration solutions (e.g.: deionized water or distilled water), strong base and strong acid solutions, highly corrosive liquid, or for continuous testing in high-temperature solutions (>140°F). Compatible with any pH meters that use BNC connectors. Temperature sensor is not built-in. Users need to have a separate temperature probe to enable ATC or manually input temperature to complete temperature compensation. (1 per EA )