Which quality-control sample is used to evaluate the effects of sample matrices on the performance of an analytical method?

• A. Matrix Duplicate
• B. Reagent Blank
• C. Matrix Spike
• D. Method Blank

Answer: (C)

Evaluating how a sample's matrix affects the analytical method's performance. To test this, a known amount of analyte is added to the actual sample matrix and processed through the method. The recovery observed from that spiked matrix reveals how the matrix influences detection or quantification—if the matrix suppresses or enhances the signal, the recovery will deviate from the expected value. This direct assessment of how the matrix impacts method performance is what a matrix spike provides. The other QC samples have different roles: a reagent blank checks for contaminants from reagents, a method blank checks for contamination introduced during the procedure, and a matrix duplicate is used mainly to examine precision within the same matrix but does not specifically quantify the matrix’s effect on recovery. So, the matrix spike is the best choice for evaluating matrix effects.