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Flow-injection gradient dilution for obtaining UV spectra of concentrated solutions

Image Number 4 for United States Patent #5801820.

The invention relates to methods and apparatus for precise dilution of concentrated samples enabling their spectra to be obtained. The spectra thus obtained may then be used for calculation of the aromatic hydrocarbon content in the concentrated samples. This invention comprises an arrangement of computer-controlled pumps, an injection valve, a mixing chamber, a flow cell (these components are known as "the manifold") and a scanning spectrophotometer, with a sophisticated computational software program. The arrangement generates a reproducible, well-defined gradient from a concentrated sample which is continuously scanned and, using the computational software, allows the spectrum of the sample to be derived, even where the majority of the spectrum for the undiluted sample has an absorbance greater than the upper measurable limit of the spectrophotometer. All of the methods described in prior art publications differ from the present invention by their reliance on calibration (the adjustment of factors used, by comparing spectral data for a standard with its reference data) or characterization (measurement of the characteristics of the system, e.g., flowrate and mixing volume, and inclusion of these values in the calculation) of the systems for defining dilution factors, due to measurement of a single species/wavelength. The present invention requires no calibration/characterization for single species measurement since multiparameters (absorbance at many wavelengths) are monitored or conversely, can be used to obtain spectra of highly concentrated samples and therefore determine multiple species. None of the previous systems were used to obtain spectra per se.

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