Dissolution testing determines the rate (how fast) and the extent (how much) that the active pharmaceutical ingredient(s) of a product dissolve(s) in a medium of pH range of 1 – 8.

A dissolution apparatus consists of a water bath where the water can be heated to the required temperature 37.0 ±0.5^oC , 8 glass vessels with hemispherical bottoms and lids (6 for the product to be tested, one for the medium (blank) and one for control, typically of a 1000mL capacity, that are immersed in the water bath, a mechanically raised/lowered platform holding 8 metal drive shafts that rotate at specified speeds, onto which a paddle or a cylindrical basket (constructed of sieve mesh) can be fitted. This being an automated dissolution tester also has a peristaltic pump, a spectrophotometer and a computer with a suitable software.

Once the vessels have been filled with the required quantity of the specified medium (normally from 500 to 1000 mL), the platform is lowered so that the rotating rods are immersed in the medium. When that has reached the specified temperature, six tablets or capsules to be tested are simultaneously dropped ,one in each vessel if the paddle apparatus is used, leaving the other two without product: the one with medium (which serves as a blank) and the control (which serves as a check).If the basket apparatus is used the product is placed in the basket and inserted in the medium.

The automatic sampling is carried out through a cannula with fixed, manually adjustable depth, while the sample filtering is done with the filter placed in the sample probe in each vessel. Each probe is connected to a tube that runs all the way into the spectrophotometer and back, so that a continuous closed circuit (loop) is attained. This means there is no sample volume loss over the time of the dissolution test. At pre-programmed time points, the sample circulation is stopped and either a single point absorbance reading or a full UV spectrum of each vessel is collected. Calculations are done through the software and the final results are printed out.