The evaluation of the factorial design demonstrated that the factors:
RF power (Effect = +985), hydrochloric acid concentration (Effect
= −774) and the interaction (nebulizer gas flow rate) × (RF
power) are significant.
The curvature with value of ( −475) demonstrates that there is a
maximum condition of emission intensity in the point central region.
Considering the result of the curvature test, a Box–Behnken design
was performed being that the experimental conditions for these three
factors and the response are shown in Table 4.
The evaluation of the data obtained in this design results in a quadratic
model, which presents a maximum condition of emission intensity
for the critical values of the factors studied. These coded and
real values are shown in Table 5.
Considering these results, the experimental conditions established
for the procedure are: hydrochloric acid concentration = 0.53 M, nebulizer
gas flow rate = 0.40 mL min−1 and RF power = 1.1 kW.