Influence of flame atomic absorption on measurement of K using laser-induced breakdown spectroscopy

When the measurement of alkali metals is performed using laserinduced breakdown spectroscopy (LIBS) in flame，the emission of the alkali atoms in the plasma can be absorbed by the alkali atoms outside the plasma in the flame，influencing the LIBS measurement accuracy. Based on the BeerLambert law and the thermodynamic equilibrium calculation，a flame atomic absorption model covering the concentration range of K released during practical biomass combustion was developed，and the influences of the atmosphere of the flame，the K distribution and the total K concentration on the flame atomic absorption efficiency were analyzed. It is found that，with the increase of the O2/CH4 ratio，the equilibrium molar fraction of atomic K in all Kcontaining species decreases from approximate 25%，leading to the decrease of the flame atomic absorption efficiency from 86.8%. When the O2/CH4 molar ratio ratio exceeds 2，excess O2 exists in the flame, and the flame atomic absorption efficiency is always less than 13%. Meanwhile，by proper adjustment of K distribution and the total K concentration，the flame atomic absorption efficiency can also be reduced. Based on this，it is proposed that to reduce the flame atomic absorption efficiency and facilitate the K LIBS measurement accuracy in flame，an oxidizing flame atmosphere and a proper K distribution profile should be created.