Water Content: Karl Fisher versus ASTM D95

We are getting phone calls asking why we do not use ASTM D 95 to measure the water content of penetrants and emulsifiers. ASTM E 1417 & NADCAP PRI AC7114/1 revision A, allow the use of ASTM D 95 or the modified Karl Fischer method. This latter method was introduced to ASTM E 1417 some years ago by Met-L-Chek®. The reasons for this are simple. ASTM D 95 requires the use of Xylene and boiling it in a special apparatus. The method is not particularly safe, takes more time than the Karl Fischer method, is more expensive to perform, and is not as accurate. But a second reason is that the ASTM D 95 method cannot measure the water content in formulations that contain azeotropes, and there are formulations that do include these. Consequently, if you are using a penetrant product that contains an azeotrope, the ASTM D 95 method will report that the product is 100% water, something that will immediately be obvious as false. Any specification that only lists

ASTM D 95 as the acceptable method for measuring water content is probably out of date, since the Karl Fischer method has been included in ASTM E 1417 since the early 2000’s.