A method blank must be analyzed at a minimum of how many per preparation batch?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (A)

A method blank checks for contamination that can be introduced during the sample preparation process. It goes through the same preparation steps as real samples, using all the same reagents and solvents, so any carryover or impurities become visible. Because its purpose is to represent the entire batch being prepared, you analyze at least one method blank for each batch. If the blank shows any analyte signals, that indicates contamination affecting that batch’s results and those results may need to be questioned or reworked. Running more than one blank in a batch isn’t necessary to fulfill this monitoring role; one blank per batch is the standard minimum.