normal plasma analytical zone

in inductively-coupled plasma optical emission spectroscopy
https://doi.org/10.1351/goldbook.08512
Inductively-coupled plasma volume mainly responsible for emission of analytically-useful light because processes leading to excited species, such as droplet desolvation, element vaporization, atomization (or ionization) and excitation have been completed.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 726 [Terms] [Paper]