Procedures for Standardizing a pH Meter

Meters

• Common features to most pH meters are electrodes that sit in storage liquid, or the substance under test, and a computerized instrumentation panel, with control buttons and a readout screen. No standard protocol exists for all pH meters, as many different companies produce them. Some pH meter electrodes require special handling, in case of damage, such as internal electronic damage if a worker turns the electrode upside down, that can alter the meter readings.

Typical Method

• Generally, a procedure details how the meter's electrode should be stored, usually in a particular storage liquid to prevent damage. Each procedure tells the user how to wash the electrode, usually with distilled water, and how to dry it, typically with a patting motion. The control panel of each meter generally has a button for standardization mode, or calibration mode. Once the user presses this, and follows any other necessary steps on the panel, the meter is prepared to read a sequence of known pH liquids called buffers. The clean, dry electrode sits in each of the buffers, one after the other, until the meter value stabilizes, and the meter takes a reading. The procedure also generally calls for the analyst to wash and dry the electrode between each buffer. Information in procedures should also contain details on the necessary level of liquid in buffer beakers and storage solution containers, to ensure an accurate reading and a safe storage manner.

Buffers

• The pH scale runs from 0 to 14. Substances that have a value of seven are neutral, those below seven are acidic, and those above seven are alkaline. Commercial companies make buffers that have known pH values for a pH standardization procedure. When an analyst standardizes a pH meter, he typically calibrates the meter with buffers that are more acidic, neutral and more alkaline than the possible range of pH of his samples. For example, buffers with values of four, seven and ten span the possible range of many organic samples.

Required Protocols

• Some institutions or industries write procedures that relate specifically to each piece of technical equipment. These procedures are typically based on the user manual instructions, but can also contain additional steps, or directions as to which buffers to use. If a workplace has specific procedures, an employee typically has to follow these instead of the instructions present in the user manual.