A flow spoiler or an impact bead is positioned at the exit of the nebulizer stream in the spray chamber and it serves to remove the large droplets in the aerosol stream to the burner head and eventually into the flame.
In Flame Atomic Absorption Spectroscopy the sample solution is never introduced as a stream direct into the flame as it can destabilize the fame or even extinguish it. The sample is first reduced to an aerosol with the help of a nebulizer. The liquid drops vary in size depending on the efficiency of the nebulizers under the given set of operating conditions. Larger size droplets condense on the walls of the spray chamber and the impact device and get drained out into the waste reservoir. Only small droplets are permitted to enter the flame.
Atomic Absorption Spectroscopy flow spoiler is a multi- vane fan shaped device made of chemically inert material and is more efficient at removing large droplets then the impact bead. This results in reduction in sensitivity as lesser amount of sample enters the flame. However, its benefit is that the interference from sample matrix also get reduced proportionately due to reduction in sample amount.
An Atomic Absorption Spectroscopy impact bead is made of glass or ceramic and has lower efficiency for removal of large droplets. It thereby contributes to sensitivity improvement making it possible to analyze samples at lower detection levels. However, glass or ceramic beads can introduce memory effects of previous analysis and lead to more interferences.
Several physical variables control the droplet size such as velocity of the nebulizer stream, sample liquid density and its viscosity. In essence the choice of the intercepting device – flow spoiler or impact is based on the Atomic Absorption Spectroscopy analysis requirements. When you require to determine low concentrations use an impact bead and when interference is an issue then flow spoiler is preferable.
Please share your experiences on the choice of the impacting device and do forward your comments.