Sampling and Analytical Instrumentation

As a single dissolution test generally requires the sampling and analysis of several samples (usually six per sampling interval), it is necessary to have efficient sampling systems and rapid analytical systems in place. Sampling can be performed manually or by using automated sampling systems. Manual sampling can be quite labor intensive and tedious. The manual sampling from six vessels for a single time point in a dissolution test can take several minutes making the establishment of dissolution profiles for rapidly dissolving dosage forms quite difficult at early time points. Several automated sampling systems are commercially available in today's market. The automated sampling systems are typically microprocessor or computer controlled allowing for precisely timed sampling at frequent intervals, if necessary. Some automated sampling systems transfer the samples to collection tubes for manual transfer to the analytical instrument while other sampling systems transfer the samples directly into the analytical instrument for analysis. It is important to note that all sampling systems should be evaluated for absorption to tubing or filters. Carry-over between samples should also be determined, especially when common sampling pathways are used. Errors associated with automated sampling systems are usually related to partial or complete blockage of the sampling lines. Therefore, it is recommended that the appropriate flow rate be determined and used prior to each use of an automated sampling system.

Because of the large number of samples normally generated in a dissolution test, the analytical system should be relatively rapid, allowing for a high throughput of samples. The most common analytical instruments used for dissolution testing are UV-Visible spectroscopy and liquid chromatography with UV detection (LC-UV).

UV-Visible spectroscopy allows for rapid analysis of samples. Diode array based instruments with sophisticated computer generated data analysis have improved the quality and speed of single component as well as multicomponent analysis by UV-Visible spectroscopy. When this mode of analysis is used, the accuracy should be confirmed by a selective mode of analysis such as LC. LC analysis is a more discriminating and selective means of analysis. When LC analysis is required, a rapid chromatographic method is desirable for the assay. It is important to note that the analytical instrumentation should be checked for wavelength accuracy and repeatability as well as photometric accuracy and repeatability.

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