Gas dissolved in the dissolution medium may interfere with the reproducibility of the dissolution results. Therefore, before making up the dissolution medium, the purified water should be degassed, the specific methods of which include: ultrasonic, boiling, and vacuum degassing after heating to 41°C, etc. If the method of heating and degassing is used, the dissolution medium can only be made up when the water temperature is reduced to indoor temperature after the end of degassing. That is to avoid evaporation of the dissolution medium by heating after the addition of hydrochloric acid or acetic acid, affecting the pH value of the dissolution medium. Purified water from different sources have different pH values. When using purified water as a dissolution medium, it is advisable to first determine the pH value of the water before the preparation, for fear that the data of dissolving should fluctuate because of different PH value of the water.
Installation of stirring paddle(basket)
Mechanical verification is needed when the dissolution tester is shipped or installed (or every 6 months). In the process of using after verification, if the installation position of the stirring paddle (basket) is not the same as that in the verification, the coaxiality of the stirring paddle(basket) and the dissolving cup will be affected, and then the flow state of the dissolution medium in the dissolving cup will be affected too, thereby affecting the dissolution data of the sample.
In addition, the stirring paddle (basket) of some dissolution testers require adjustment to the mounting height. Frequently, for the convenience of the next use, we, however, do not remove the stirring paddle(basket) when cleaning the equipment. It is assumed that once we adjust the height of the stirring paddle (basket), there is no need to adjust it again. However, the fixed paddle (basket) is likely to loosen due to the shaking of the stirring paddle (basket) during use. After a long period of use, the height of the stirring paddle (basket) may descend, which will ultimately cause a change in the dissolution rate of the sample or deterioration to the parallelism of dissolution medium within the group. When using the basket-stirring method to test, one should pay attention to the cleanliness of the basket and observe whether the basket gap is blocked or not. If it is blocked, one should use ultrasonic treatment or put it in dilute nitric acid to boil and then clean it by boiling it in water. Or, the accuracy of the dissolution data will be impacted. At the same time, whether the shape of the basket is complete needs to be noticed. If distortion occurs, one should replace it with a new basket promptly.
Installation of Dissolution Cup
As the stirring paddle (basket), the dissolution cups have different serial numbers, so they also need to be installed to the corresponding locations. Not only the installation position of the dissolving cup needs to correspond to the serial No. , but also the upper edge of the dissolution cup connecting the fixed equipment, after the verticality and coaxiality verification, should be marked with vertical lines or arrowheads, etc. For this reason, in the process of the dissolution rate test, the basket, the paddle and the dissolution cup should be placed in the originally verified position to keep the relative position between each dissolution cup and fixed device unchanged.
But everybody when installing a dissolution tester tend to ignore this, that the dissolution of cup of shaft and stirring paddle shaft misalignment, and then change the dissolution cup of dissolution medium flow state, and make the change dissolution data. People,however, often ignores this when installing a dissolution equipment. As a result, the coaxiality of the dissolution cup does not coincide with that of the stirring paddle, which then leads to a change in the flow state of the dissolution medium in the dissolution cup, eventually resulting in changes in the dissolution data.
Installation of Filter
Currently, dissolution testers are generally equipped with fully automatic or semi-automatic devices. At the sampling end of them, a filter must be installed. Without it, undissolved sample particles will enter the instrument pipeline with the sampling solution. On one hand, undissolved particles may clog the pipeline, ending up with inaccurate sample volume; on the other hand, as it generally takes 2-5 minutes (fluctuating according to the sample volume) for the sample to be transferred from the sampling end to the test tube, undissolved particles continue to dissolve in the pipeline in this process, thus affecting the accuracy of the measurement or the final dissolution rate. For the filter used, ultrasonic treatment for 20-30 min in the medium and ultrasonic cleaning with purified water are preferred at the end of the test, rather than just soak it in the dissolution medium, and then clean it with clean water. Because the latter method can not clean the filter head, but affect the next use.
Position of Sample
In the process of sample feeding in the dissolution test, the position of sample should be in the specific location of the dissolving cup. Taking paddle-stirring method as an example, the sample should all be at the bottom of the dissolution cup, right underneath the paddle. If some of the tablets are adhered to the pipe wall after sample feeding, the RSD of the dissolution test results will be larger than usual, and the dissolution velocity of the sample will rise up. Therefore,one should also see to it whether the position of the sample in the dissolution cup is normal (or identical) after each sample feeding during the test.
Phenomenon of Dissolution
Dissolution test results are not just about dissolution data. When examining or comparing the dissolution curve, one usually only pays attention to the dissolution data but ignores the observation of the dissolution phenomena. In fact, the dissolution phenomenon is of guiding significance to the prescription analysis of the original preparation and the adjustment to the procedures of the self-made preparation.
For example, the disintegration phenomena of the original preparations include: dissolution type (high content of lactose in the prescription), dilatation type disintegration and "smoke" phenomenon (high content of Microcrystalline Cellulose in the prescription) and tablet disintegration; whether or not the tablets are piled up into in a sand dune at the bottom of the cup after the disintegration. Another examples are whether the original preparation is disintegrated into particles or powder, whether the coating film of the pellet bursts or dissolves, and whether the pellet expands during the dissolution process.
Water height
The water in the external tank of the dissolution tester will also volatilize due to heat, causing the liquid level in the tank to drop. If the external water height of the dissolution tester is lower than the liquid level of the dissolution medium in the dissolution cup, the temperature of the dissolution liquid will be affected, which leads to a change in the dissolution rate of the sample, resulting in affecting the dissolution results. Therefore, attention should be paid to the height of the water outside the dissolution tester during the dissolution test.
Surroundings
The shaking of the stirring paddle (basket) of the dissolution tester can affect the coaxiality between the paddle (basket) and the dissolution cup. On one hand, the shaking of the stirring paddle (basket) comes from the shaking caused by the instrument itself. On the other hand, the surroundings around the equipment, such as the vibration produced by the centrifuges, the vortex machines, the vacuum pumps, and so on, will also cause the shaking of the stirring paddle (basket). Therefore, during the dissolution experiment, we should minimize the impact of other devices on the dissolution meter.
Conclusion
Beyond that, other factors such as the height of the sampling needle, the rotation speed of the stirring paddle (basket), the actual temperature of the dissolution medium, and so on should also be taken into account in the dissolution test. In comparison with the dissolution curves of the original preparation and the self-made product, the inconsistency of the curves lies not only in the difference of the prescription process, so attention should be paid to the influence of various factors in the experiment on the dissolution results.
