[Dolphinsiu]

For internal addition method (INa/ILi), The result is that upward curvative of calibration graph is observed when ethanol concentration  at low concentration but downward curvature at high concentration.

But why?

I only know that self absorption or self quenching occurs at high concentration but how about upward curvature ? (really due to background radiation, as I remember that too much background will decreases the number of excitied atom, isn't it?)