What action should be taken when a contaminant is detected in the method blank?

• A. Investigate the source of contamination and take steps to minimize or eliminate
• B. Re-run the entire batch after cleaning
• C. Ignore if below detection limit
• D. Stop all testing for a month

Answer: (A)

A method blank is used to reveal contaminants that may be introduced during sample preparation or analysis, such as from reagents, glassware, or the lab environment. When a contaminant shows up in the blank, the priority is to identify the source and put corrective actions in place to minimize or eliminate it, then verify that the issue is resolved (for example, by cleaning components, replacing reagents, or changing workflow) and rechecking with blanks and affected samples. This protects the integrity of the entire batch because if the blank is contaminated, the measured signals in real samples could be biased or false.

Re-running the entire batch after cleaning might eventually be done, but only after the contamination source is found and corrected; doing it without addressing the cause could just reproduce the problem. Ignoring the contamination if it’s below the detection limit is unsafe, because even trace contamination in the blank can indicate a bias or carryover. Stopping testing for a month is not a targeted or practical remedy.