The procedure used to prepare the blank varies from older to newer versions of method 10132 for Trihalomethanes (THM). Is there a rational for the change?
Blank preparation for the THM methods.
In old versions of method 10132 for THM, the blank was prepared by adding the reagents to the sample, but omitting the heating step. In newer versions, the blank is prepared using deionized water and treating it like the sample.
The newer procedure is better for customers testing multiple samples as it would save them money on reagents. Furthermore, with the old blank procedure the heating step was removed. As a result, turbidity from the reagents may not be adequately removed. Ultimately, the United States Environmental Protection Agency (USEPA) tested both methods and found no significant difference between the two procedures.