pH

The pH of a sample is an indication of its acidity or alkalinity and pH determination is one of the most commonly conducted laboratory measurements. The term pH is defined as the negative logarithm (base 10) of the Hydrogen ion concentration (or, more accurately, Activity) expressed in molarity. The pH reference buffers listed here can be used for the standardization of pH meters or as media to check color development of pH indicators. For most routine pH measurements, a two-point standardization of a pH meter should be used; pH 4 and 7 buffers can be used for pH measurement of samples of pH 7 or below, while pH 7 and 10 buffers can be used for pH measurement of samples of pH 7 or higher. Other combinations of pH buffers may also be used, depending on the capability of the pH meter being used. For increased accuracy, buffers with pH values closer to that of the sample being measured can be used. Buffers of pH values much less than 1 or greater than 13 are not available due to instability and other limitations of actual pH measurement .

pH is somewhat dependent on temperature; the magnitude and direction of temperature dependence is determined by the chemical identity of the buffer system involved. RICCA CHEMICAL COMPANY standardizes all buffer solutions at 25°C. For use at other temperatures, pH-Temperature charts are available on the label and Certificate of Analysis for selected buffers. See Technical Reference Document TRD20, available at www.riccachemical.com, for more information.

Buffers of pH values greater than 7 are subject to increasing absorption of Carbon Dioxide from the air, which leads to a shorter shelf-life for higher pH buffers. Always keep buffer containers tightly capped when not in use and never return used or unused buffer to the container. The more commonly used buffers of pH 4, 7 and 10 are available as either clear solutions or as color-coded solutions that permit easy identification of these buffers whether in or out of the container. RICCA CHEMICAL COMPANY does not use Formaldehyde or Mercury salts as preservatives, or Chromium salts as colorants, thus eliminating some hazard and disposal problems that would be present if such chemicals were used.

The weakest link in a pH measurement is usually the pH and/or reference electrodes. Electrodes should always be handled carefully to avoid scratches, clogged liquid junctions, and improper filling of the internal electrodes. Electrodes should be immersed in an electrode storage solution, such as RICCA CHEMICAL COMPANY Group No. 2795, when not in use. Clean, rejuvenate, and fill electrodes according to the manufacturer’s directions. To prevent backflow and possible contamination of the internal electrolyte, always maintain the level of the filling solution in the reference electrode (or combination electrode) above the level of soaking, storage, standardizing buffer and sample solutions, and above the internal elements.