spectral interference
/ SPEK-trul in-ter-FEER-ence /
Spectral interference is what happens when two voices speak at almost the same pitch and you cannot tell them apart. In atomic spectroscopy, an element you are not interested in emits or absorbs light so close to your analyte's line that the instrument lumps them together, and the reading swells with light that does not belong to your element.
More precisely, it is an interference at the measurement wavelength itself: another element's line falls within the slit's view of the analyte line, or a broad background — molecular emission, scattered light, or a recombination glow — sits under the line. Either way, the detector cannot separate the wanted signal from the unwanted light at that wavelength.
It matters because, unlike a chemical interference that changes how many atoms form, this one fools the eye at the detector itself. Honest defences are choosing a cleaner, well-resolved line, narrowing the slit, using a higher-resolution instrument, or applying background correction to subtract the intruding light.
In ICP-OES, an arsenic line at 228.812 nm sits right beside a cadmium line at 228.802 nm. In a cadmium-rich sample, arsenic can read falsely high unless you pick a different arsenic line or use a higher-resolution spectrometer.
Two lines too close to resolve: the intruder's light inflates the reading.
Spectral interference (overlapping light at the wavelength) is distinct from chemical and ionization interferences, which change how many free atoms or ions actually form. Background correction targets the broadband part of spectral interference, but a true line overlap usually needs a different line or higher resolution.