Which QA sample involves adding known concentrations to a sample to evaluate matrix effects?

• A. Matrix Spike.
• B. Blank spike.
• C. Reference sample.
• D. Proficiency testing sample.

Answer: (A)

Matrix effects happen when substances in a sample alter the signal of the analyte, which can bias results. To evaluate this for a specific sample, you add a known amount of the analyte directly to the sample and measure how much is recovered. This is a matrix spike. By comparing the spiked sample to the unspiked one, you can see if the sample’s components are suppressing or enhancing the signal and how accurately the method recovers the analyte in that matrix. Spiking a blank (solvent) tests the method without any matrix, so it doesn’t reveal matrix effects. A reference sample is a known standard for calibration or accuracy checks, not for assessing the sample’s matrix. Proficiency testing samples are external challenges to evaluate overall lab performance, not to study matrix interference. Therefore, the matrix spike is the appropriate choice for evaluating matrix effects.