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.

This invention provides an apparatus and method for the complete fractionation of submicron particles according to size by capillary hydrodynamic fractionation. This objective is achieved by using small diameter capillaries; introducing a minor fraction of a liquid dispersion of particles to be separated into at least one capillary fraction; passing the minor fraction through the capillary; and, at the exit of the capillary, diluting the minor fraction with the same liquid as is carrying the fractionated sample. These modifications in the flow patterns are essential to the use of capillaries with diameters smaller than 60 microns. This invention is especially adapted for rapid analytical separation of not only rigid colloidal particles but also of soft latexes.

In a trap flow path, two diluents are supplied by solvent pumps that can respectively determine the flow rates independently. One of the diluents is allowed to pass through a fraction loop so as to direct a fractioned component(s) held in the fraction loop to a trap column together with a mobile phase. The other diluent is allowed to join with a flow path that has passed through the fraction loop on the downstream side of the fraction loop, and flows to the trap column while diluting the mobile phase from the flow path. In the trap column, the sample component(s) is condensed while being trapped therein.

A high pressure liquid chromatography injection system with two independently controlled valves and a pump is provided which permits the simultaneous and independent concentration and analysis of trace components using two different solvent systems.

The present invention relates to a method for the processing of molecules by determining one or more selection parameters for a plurality of molecules; selecting a compatible grouping of molecules based on the selection parameters to form a set; forming a mixture of molecules of interest from the set; and resolving the mixture to fractionate the molecules of interest. The preferred method utilizes HPLC chromatography column to resolve and purify molecules which have different retention times.