Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2002

Testing for VOC, Exempt Solvents, PCBTF

Q. Question #1: A facility uses a 4 part primer that contains PCBTF. Our contracted lab says they cannot analyze for this compound since there is not an approved ASTM method. I heard there is a method in the works. Do you know anything about it? In the meantime, I cannot analyze this sample by Reference Method 24.

Question #2: The coating requires an 30 minute induction period before application. Is ASTM D-2369-81 an acceptable method for percentage solids by weight?

A. Answer #1 by Dave Salman: You can use D6133-00 Standard Test Method for Acetone, p-Chlorobenzotrifluoride (PCBTF), Methyl Acetate or t-Butyl Acetate Content of Solvent-Reducible and Water-Reducible Paints, Coatings, Resins, and Raw Materials by Direct Injection Into a Gas Chromatograph

Alternatively, you can follow D6438-99 Standard Test Method for Acetone, Methyl Acetate, and Parachlorobenzotrifluoride (PCBTF) Content of Paints, and Coatings by Solid Phase Microextraction-Gas Chromatography

Answer #2 by Dave Salman: There are special procedures in Method 24 and ASTM D-2369 for multi-component coatings which among other things say to leave the specimen in the dish (not the container) for an induction period of 1 hour in D2369 and 1 to 24 hours in Method 24. See section 7.3 in ASTM D-2369 and section 3.8 in Method 24.

This coating is a bit different from what I am used to if the induction time is pre-application. (The induction in ASTM D-2369 and Method 24 is to let the reaction that takes place in the coating on the surface of the part proceed before putting the dish in the oven.) There is nothing that says that the induction time can be in the container. Maybe the results would be the same if the induction is in the container or in the dish.

If the results would not be the same, then this is a new question. I can see some arguments for letting the induction take place in the container if the coating is never sprayed until at least half an hour after mixing, but it complicates the test to have to seal up the coating in the container while the induction takes place -- as opposed to getting the specimen in the dish as soon as possible.

Comment by Ron Joseph: Having read Dave Salman's answer, I would first mix the coating in the prescribed proportions in a container. Then, as is often the practice, I would keep a lid on the container for 30 minutes before transferring a sample of the coating to the aluminum dish. In the real world, painters often mix the epoxy in a pressure pot, or in a cup that is attached to the spray gun. During this period the pressure pot or cup are closed. After 30 minutes the painters start to apply the coating.

The only significant difference between the two alternatives is that the VOC content will be higher if the induction time takes place in a closed container.

I assume that in the situation mentioned by Dave Salman, in which the coating is mixed and then left in an open dish during the induction time, some of the volatiles actually react with the solid portion of the coating and are never emitted thereafter. This is probably not the case with the epoxy where all of the solvents will evaporate sooner or later.