What is a Laboratory Control Sample (LCS)?

• A. A blank water sample.
• B. A sample from a controlled matrix known to be free of the analyte of interest, to which a known concentration of analyte has been added and that is taken through all preparation and analytical steps.
• C. A production sample.
• D. A matrix spike.

Answer: (B)

A Laboratory Control Sample is a fortified blank matrix used to verify that the analytical method is performing correctly. It starts with a matrix known to be free of the analyte, then a precise, known amount of the analyte is added, and this fortified sample is carried through all the same preparation and analytical steps as routine samples. Because the added amount is known and the matrix is controlled, the measured result shows how well the method recovers the analyte and how accurate the measurement is. This helps detect losses during extraction, instrument bias, or matrix effects, and the recovery percentage should align with expectations.

A blank water sample has no analyte to begin with, a production sample is an actual real sample from production, and a matrix spike involves adding analyte to a real sample to test matrix effects. Those concepts don’t provide the controlled, known-spike-through-the-entire-method setup that defines a Laboratory Control Sample.