Water Content

ASTM E-1417 requires that the water content of in-use water washable penetrants and lipophilic emulsifiers be less than 5 percent. The listed analytical methods for measuring this percentage are ASTM D-95 and a modified Karl Fischer method described in ASTM E-1417 Annex 1. We recently received an inquiry as to whether the standard Karl Fischer method is also an acceptable alternative to the modified method. The standard Karl Fischer method is described in ASTM D 6304-04a.

Reviewing the wording of ASTM E-1417, paragraph reads as follows:

Water content — shall be checked at the intervals specified in Table 1 in accordance with Test Method D-95 or the Karl Fischer method as described in Annex A1.

The text of Annex A1 then reads:

A1.1 Scope and Application—This modified Karl Fischer volumetric procedure is a practical alternative to Test Method D-95 for undiluted hydrophilic emulsifiers and water contamination of in-use lipophilic emulsifiers and Method A penetrants.

One could play word games with the wording of the specification and arrive at the conclusion that the intent of the specification was to include both the regular automated Karl Fischer method and the modified manual method, but this was probably not in the minds of those who wrote the specification. However, in reviewing the regular method, it appears obvious that it is equal in accuracy to the modified method, and that the only significant difference is that the modified method does not require the purchase and use of the automated equipment. In our opinion, there is no reason why the regular Karl Fischer method cannot be used to satisfy the requirements of ASTM E-1417, and that only a small text revision needs to be made to include this. We have made this suggestion to Committee E-07 and presume that the necessary change will be made in due time in accordance with ASTM procedures.

More on Water Content

ASTM E-1417, and perhaps other specifications, require the periodic analysis of used water washable penetrant for water content. The analysis is to be performed by using either the method of ASTM D-95 or the Karl Fischer method described in Annex A1 of ASTM E-1417. We recently received the question of whether the results were in volume percent or in weight percent. The answers to this are found in the specification documents. The Annex A1 calculation (paragraph A1.5) is made by dividing the weight of the titrant used by the weight of the sample, thus giving the weight percentage of water. The weight of the titrant is calculated in the final equation by multiplying the volume of titrant used by a factor that converts the volume into weight. This “titer” constant is provided with the titrant.

The equation is as follows: Weight % water = 100 X volume of titrant X titer value, in grams per ml, divided by the weight of the sample.

The ASTM D-95 method calculates either weight percent or volume percent, depending upon whether the sample was taken by weight or by volume.