Cross-Sectional Profile of Flame in FAAS

The illustration below shows  a cross-section through a typical flame looking down the burner’s slot along the source radiation’s optical path. The primary combustion zone is usually rich in gas combustion products that emit radiation, limiting is usefulness for atomic absorption. The interzonal region generally is rich in free atoms and provides the best location for measuring atomic absorption. The hottest part of the flame is typically 2–3 cm above the primary combustion zone. As atoms approach the flame’s secondary combustion zone, the decrease in temperature allows for formation of stable molecular species. The relative size of each zone depends on many factors, including the choice of fuel and oxidant, and their relative proportions.