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Abstract

There is disclosed herein an apparatus and method for performing liquid chromatography analysis with a stable baseline. The apparatus utilizes positive displacement means on each of two flow paths and a control system to regulate the flow such that the flow in both flow paths is identical. Only one flow path has sample injected therein. Each flow path is passed through a separate liquid chromatography column and a common detector at the output end of each column. Since one flow path contains solvent only and the other flow path contains both solvent and sample, any changes in the characteristics of the output streams of the liquid chromatography columns caused by changes in the solvent composition itself have a common mode. Therefore, only the difference signal is output from the detector which indicates changes in the characteristics of the output stream of the sample flow path caused solely by the presence of the sample components. By outputting the signal from the detector, a stable baseline may be achieved which takes into account only changes caused by the sample components and not changes caused by alteration of the solvent composition. This allows refractive index detectors to be used with gradient solvent analysis for the first time.

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