Ultrasound assisted extraction of A. paniculata was carried out
by indirect sonication in a dual frequency operated ultrasound bath
operating at 25 and 40 kHz (model no. 6.5l 250H/DTC/DF). A rectangular
tank having internal dimensions 300 × 150 × 150 mm, fitted
with five transducers at the bottom, arranged in a zigzag manner
was used. Fig. 1 shows a schematic representation of the top
view of ultrasound bath. The rated power of the bath was 222W.
All experiments were performed thrice and their average values
with standard deviations are reported. Ultrasound assisted extraction
was carried out in a cylindrical flat bottom glass vessel of
a specific height and diameter, at various positions and heights
to obtain maximum yield (Kulkarni and Rathod, 2014). Extraction
was carried out for 10 min at a temperature of 27 ± 4 ◦C. Effect of
parameters like choice of solvent, ultrasound exposure time, temperature,
solute to solvent ratio, position of the vessel in the bath,
depth of the vessel, frequency of sound waves, and power input, on
the extraction yield of andrographolide was investigated. A number
of solvents including water, various concentrations of ethanol,
methanol, and isopropyl alcohol were screened for extraction. Solid
to solvent ratio of 1:40 was maintained throughout the study. The
variation in cavitation activity at various positions in the bath was
then confirmed by aluminum foil test. A piece of accurately weighed
aluminum foil was taken in the glass vessel and sonicated in similar
conditions like A. paniculata, at same positions. The weight loss
of aluminum foil in the vessel at these positions was compared
with the extraction yield of andrographolide at identical positions
(Pugin, 1987). Also, power dissipation studies at these positions, to
estimate the amount of power actually being utilized for extracting
andrographolide, were done in detail. Calorimetric studies were
performed for the same purpose with 3.5 liters of water in the bath