chemical interference
/ KEM-ih-kul in-ter-FEER-ence /
Chemical interference is when something in the sample grips your analyte so tightly that it refuses to break apart into free atoms — like trying to count guests who never leave their coats at the door. The element is there, but bound in a stubborn compound, so the source cannot free it and your reading falls short.
More precisely, another substance in the matrix forms a heat-resistant (refractory) compound with the analyte, lowering how completely it atomizes. The classic case is phosphate locking up calcium. Because fewer free atoms form, the absorption or emission signal drops, and the loss changes with how much interferent the sample happens to hold.
It matters because it biases results low in a way that plain calibration misses, since standards usually lack the troublesome companion. Honest fixes are a hotter source that forces atomization, a releasing agent that grabs the interferent instead (lanthanum for phosphate), a protective agent, or matrix-matching the standards to the sample.
In a cool flame, phosphate ties up calcium as a refractory compound, so calcium reads low. Adding lanthanum, which preferentially binds the phosphate, releases the calcium to atomize and the signal returns to its true value.
Bound in a stubborn compound, the analyte never fully atomizes and reads low.
Keep the three apart: chemical interference changes how many atoms form (in the chemistry), ionization interference turns atoms into ions, and spectral interference is unwanted light at the wavelength. Chemical interference is a kind of matrix effect, since it springs from the sample's other contents.