What is a Method Blank?

• A. A blank water sample.
• B. A sample with analyte added.
• C. A sample of a known matrix, similar to the samples, free of analyte and taken through all steps.
• D. A production sample.

Answer: (C)

The main idea here is using a control that reveals anything introduced during the lab process itself. A method blank is created from a known matrix that matches the samples, but it contains no analyte, and it goes through every step of the preparation and analysis just like the real samples. This setup makes it possible to see any background signal, contamination from reagents, glassware, or the environment, or matrix-related interferences that could falsely appear as the target analyte. Because the blank shares the same matrix as the samples, it reflects how the method behaves in reality, not just in pure solvent, so you can distinguish true sample signals from processing artifacts.

A plain blank water sample wouldn’t reproduce the same matrix effects, so it might miss contamination or interferences that only appear with the sample matrix. A sample with analyte added is used for spike or recovery testing, to assess how well the method detects analyte when it’s present. A production sample is something different altogether and isn’t used to assess method carryover or blank contamination.