Image: Courtesy of R.E. Synovec ©2002 American Chemical Society
MEASUREMENT of a refractive index gradient by deflection of a diode laser beam on a position- sensitive detector. (Reprinted with permission from Analytical Chemistry, 74:4558-65, 2002).

Determining the molecular mass of polymers, including natural biopolymers such as proteins and nucleic acids, or synthetic plastics, is critical to quality control and to understanding the effects of processing technology on these products.

A microscale, lab-on-a-chip device, recently developed by analytical chemists at the University of Washington in Seattle, uses a change in refractive index as a solution flows through its tiny channels to determine the molecular mass of macromolecular samples.

The microfluidic channel contains two parallel streams, one containing the analyte in a mobile-phase solvent, the other containing only the solvent. Mixing occurs by diffusion at the interface between these two streams, producing a polymer gradient transverse to the sample flow; the...

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