Abstract: An automated sample changing chemical analysis system for sequentially analyzing a series of samples such as pharmaceutical chemical samples, the system being particularly useful for dissolution rate testing. A pressure/vacuum source provides motivation for withdrawing each sample from its respective source in sequence through a sample selector valve and transporting the sample to the flow cell of a chemical analyzer such as an U.V. Spectrophotometer, and then returning all or part of the sample to its source through the same selector valve and purging the flow cell and conduits back to the sample source. In one form each sample is simply drawn by vacuum from its source through the selector valve into the flow cell and then the entire sample is returned after analysis, by air pressure, back through the selector valve to the source, while in another form a diluent or reagent is mixed with the sample in an intermediate step to bring the sample within the testing range of the analyzer.