Apparatus 2 - Running the Test
Running the Paddle Test
The actual paddle test follows exactly the same procedure as Running the Basket Test, except for the sample introduction.
Sample introduction for the paddle test is often the cause of errors. Once again, the sample should not be left out on the open bench for any length of time before it is used.
Unlike the basket test, the paddles will already be in position in the vessels at the time the test starts. With this test however, the sample is introduced with the paddle stationary - i.e. not rotating. For a system where manual sampling is employed, with a staggered time start, this can present some challenges with some dissolution testers since the paddles will need to be stopped one at a time.
If automated sampling is to be employed then the paddles can be switched off, the samples introduced, and the paddles re-started. Or an automated tablet dropping device can be used to drop the tablets simultaneously.
So, why is it so important to have the paddles stationary? There are two main reasons, both simply a point of practicality.
#1 If the tablet drops and the paddle is rotating, there is a good chance that it will collide with the blade. If that happens, then the tablet will probably be chipped, and the test will be invalidated before it has even started.
#2 If the paddle and media is rotating, there is a good chance that the tablet will not fall to the bottom of the vessel, but to one side. This is particularly a problem with coated or sticky tablets (and can happen without the media rotating also), but having everything stationary reduces the risk.
In all other respects the test is the same as with baskets, with the same sampling position requirements (discussed later). The only other variation that the paddle test might employ, is the use of capsule sinkers.