Size exclusion chromatography with dual-beam refractive index gradient detection of polystyrene samples.

Non-aqueous size exclusion chromatography (SEC) of polystyrenes (as model analytes) is examined using the microscale molar mass sensor (mu-MMS) for detection. The mu-MMS is combined with SEC to demonstrate this simultaneously universal and molar mass selective detection method for polymer characterization. The mu-MMS is based on measuring the refractive index gradient (RIG) at two positions (upstream and downstream) within a T-shaped microfluidic channel.

An absorbance-based micro-fluidic sensor for diffusion coefficient and molar mass determinations.

The H-Sensor reported herein is a micro-fluidic device compatible with flow injection analysis (FIA) and high performance liquid chromatography (HPLC). The device detects analytes at two separate off-chip absorbance flow cells, providing two simultaneous absorbance measurements. The ratio of these two absorbance signals contains analyte diffusion coefficient information.

Investigation of high-speed gas chromatography using synchronized dual-valve injection and resistively heated temperature programming.

High-speed temperature programming is implemented via the direct resistive heating of the separation column (2.3m MXT-5 Silicosteel column with a 180 microm I.D.

Ultrafast gas chromatography on single-wall carbon nanotube stationary phases in microfabricated channels.

The key to rapid temperature programmed separations with gas chromatography are a fast, low-volume injection and a short microbore separation column with fast resistive heating. One of the major problems with the reduction of column dimensions for micro gas chromatography is the availability of a stationary phase that provides good separation performance. In this report, we present the first integration of single-wall carbon nanotubes (SWNTs) as a stationary phase into 100 mum x 100 mum square and 50-cm-long microfabricated channels.

Microfabricated refractive index gradient based detector for reversed-phase liquid chromatography with mobile phase gradient elution.

Typical refractive index (RI) detectors for liquid chromatography (LC) are not well suited to application with mobile phase gradient elution, due to the difficulty in correcting for the detected baseline shift during the gradient. We report a sensitive, highly reproducible, microfabricated refractive index gradient (micro-RIG) detector that performs well with mobile phase gradient elution LC. Since the micro-RIG signal remains on-scale throughout the mobile phase gradient, one can apply a baseline correction procedure.

Theoretical modeling and experimental evaluation of a microscale molecular mass sensor.

A theoretical model for a recently developed microscale molecular mass sensor (micro-MMS) is presented. The micro-MMS employs a widely applicable technique of measuring the refractive index gradient (RIG) in a microchannel created after two adjacent streams merge: a "sample stream" containing analyte(s) of interest in a host solvent and a "mobile-phase" stream containing only the host solvent. Because the flow in the microchannel is laminar, the analytes in the sample stream mix with the mobile-phase stream primarily by diffusion.