Atomic absorption spectrometry (AAS) is an elemental quantification method in which free ground-state atoms in the gas phase absorb radiation at a wavelength characteristic of a given element, and the measured absorbance is related to that element’s concentration ^[1][2]. In analytical chemistry methods development the concept is bounded by absorption by free atoms—not by ions, molecules, or excited-state emission—as the analytical signal. Essential components are a source of element-specific radiation (commonly a hollow-cathode lamp), an atomizer that converts the sample into free atoms, and a detector that records the attenuation of the resonance line. Flame atomization introduces the sample into a combustion flame, whereas electrothermal (graphite-furnace) atomization uses a resistively heated tube, often with a L’vov platform and a matrix modifier, to produce a transient atomic vapor ^[2][3]. Preconcentration steps such as dispersive liquid–liquid microextraction or solid-phase extraction can be coupled to either atomizer so that the atoms presented to the beam represent a concentrated aliquot of the original sample ^[1][2][4]. The technique is distinguished from atomic emission spectrometry by the absorption rather than emission measurement, and from mass spectrometry by the optical rather than mass-to-charge signal. Conceptual limits exclude molecular absorption spectroscopies that do not atomize the analyte.