At 12:55 PM 5/2/00 +1000, Gennette wrote: >Continuous pH is impossible. This is not quite true: it's done all the time in process control in industry. >If the special composition glass bulb is left in the unknown pH liquid for >an length of time it destroys the special oxides in the glass that pass the >voltage differences. To preserve the glass bulb you need to have the same >pH liquid on both sides of it (usually KOH). You store pH electrode in pH 4 buffer for long periods. The problems arise with keeping the electrode in alkaline solutions (pH > 7). The salt used in the interior is KCl, not KOH. Alkali dissolves glass slowly. However, nowadays there are solid state ISFET pH electrodes that don't have the membrane or shelf life probes. Of course, that means they are also expensive! ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: ral@lcfltd.com Least Cost Formulations, Ltd. URL: http://lcfltd.com/ 824 Timberlake Drive Tel: 757-467-0954 Virginia Beach, VA 23464-3239 Fax: 757-467-2947 "Vere scire est per causas scire" ================================================================