Matrix Effect
When the overall sample composition changes measured intensities for target elements.
Matrix effects occur because X-rays are absorbed and scattered by all elements in the sample, not just the analyte of interest. A high-Z matrix can suppress fluorescence from lighter elements and vice versa.
Modern portable XRF uses FP correction, Compton normalization, and grade-specific libraries to compensate. Understanding matrix effects is key to interpreting PMI results correctly.