pH Electrodes ST270 (0.00 – 14.00 pH)

pH Electrodes

Basic Theory of pH

pH is a one of the most commonly measured parameters in chemical and life sciences research, as well as is many different industries, including water and wastewater treatment, food technology, environmental protection, production and agriculture. pH is defined as the negative logarithm of the hydrogen ions concentration in the sample: pH = -log [H+ ] pH provides a convenient way to compare the relative acidity or alkalinity of a sample at a given temperature. pH electrodes produce different mV values in solutions with different pH. Ideally, at 25°C, a pH electrode should produce a slope of 59.16mV per 1 pH unit

Electrodes for pH Measurement

pH measurement is usually conducted using a combination electrode that consists of a pH-sensitive glass electrode that is sensitive to hydrogen ions present in the sample as well as a reference electrode that has a constant potential value. A potential is developed on the membrane surface when a pH electrode comes into contact with a sample. pH meters measure variations in the potential and convert it directly to a corrsponding pH value, according to the Nernst equation: E = E0 + (2.303RT/nF)log[H+ ] pH measurement is sensitive to temperature changes. However, at a pH of 7, temperature will not have an effect on the potential of the system.This is known as the isopotential point. OHAUS' 3-in-1 electrodes are convenient tools that contain a built-in temperature probe that can be used together with a meter to compensate temperature changes without application of any extrernal temperature probe.

Maintenance and Storage of pH Electrodes

pH electrodes are delicate measuring instruments that require proper care and maintenance to produce accurate and reliable results as well as to ensure a long usable life. If an electrode is not in use always keep it moist by placing the electrode's glass bulb in the storage solution (3M KCl). Do not store the electrode in distilled or deionized water as this will cause ions to leak out of the glass bulb and reference electrolyte, which can cause a slow response and damage the electrode. Electrodes may be shipped with either protective caps or in electrode soaking bottles to prevent cracking or scratching and to keep the glass bulbs moist. Gently remove the electrode from the storage bottle and rinse it with distilled water before use. For long-term storage, always keep the electrode in the bottle in enough storage solution to cover the bulb. Replenish the bottle as needed.