The optimized US-assisted extraction procedure consisted of adding
4.0 mL of 30% (v/v) hydrochloric acid, equivalent to 3.6 mol L−1, to treat
150 mg of samples in glass tubes with capacity of 15 mL, for 5 min of
sonication in ultrasound bath without heating. The tubes were placed
in the region of higher cavitation intensity, previously mapped according
to literature. After US-assisted extraction, extractswere centrifuged
to separate aliquots free of particulates and were diluted to
10.0 mL with deionized water. The final extracts were analyzed by CV
AAS in the univariate selection of the best extraction conditions and
by both CV AAS and MIP OES when analyzing all the inorganic fertilizer
samples using the best extraction conditions.