Diffusion coefficient measurement in a microfluidic analyzer using dual-beam microscale-refractive index gradient

Colin D Costin¹, Roy K Olund, Bethany A Staggemeier

¹Center for Process Analytical Chemistry (CPAC), Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195-1700, USA.

|November 8, 2003

Summary

This study introduces a microchip sensor that measures refractive index gradients to determine analyte diffusion coefficients and molecular mass. The microscale molecular mass sensor (micro-MMS) offers high resolution for distinguishing small molecules.

Area of Science:

Analytical Chemistry
Microfluidics
Biophysics

Background:

Accurate determination of molecular mass and diffusion coefficients is crucial for characterizing analytes.
Existing methods may have limitations in resolution, speed, or sample volume.
Microfluidic devices offer miniaturization and precise control over fluid dynamics.

Purpose of the Study:

To develop and validate a microchip-based detection scheme for determining analyte diffusion coefficients and molecular mass.
To utilize refractive index gradients (RIG) within laminar flows for quantitative analysis.
To establish a microscale molecular mass sensor (micro-MMS) for real-time molecular characterization.

Main Methods:

Simultaneous measurement of RIG at two positions along a microchannel using dual-beam laser deflection.
Exploiting laminar flow conditions for diffusion-driven mixing of sample and mobile phase streams.
Correlating the ratio of downstream-to-upstream RIG signals to analyte molecular mass.

Main Results:

The micro-MMS successfully determined diffusion coefficients and molecular masses of polyethylene glycols (PEGs) and sugars.
Achieved a molecular mass resolution of 9% for PEGs (106-22,800 g/mol).
Demonstrated a limit of detection of 0.9 ppm for PEG (11,840 g/mol) with a refractive index LOD of 7x10⁻⁸ RI.

Conclusions:

The micro-MMS provides a sensitive and high-resolution method for characterizing analytes.
The sensor is effective for distinguishing small molecules and assessing peak purity in size-exclusion chromatography (SEC).
This technology enables real-time determination of diffusion coefficients and molecular mass in a microfluidic format.

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Diffusion coefficient measurement in a microfluidic analyzer using dual-beam microscale-refractive index gradient

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Diffusion coefficient measurement in a microfluidic analyzer using dual-beam microscale-refractive index gradient...

Area of Science:

Background:

Purpose of the Study:

Main Methods:

Main Results:

Conclusions:

Related Concept Videos

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Diffusion coefficient measurement in a microfluidic analyzer using dual-beam microscale-refractive index gradient