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Sampling BIAS at channel junctions in gated flow injection on chips
Benjamin E Slentz1, Natalia A Penner, Fred Regnier
1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Analytical Chemistry
|September 28, 2002
Summary
A new microchip injection method overcomes sampling bias found in older gated injection techniques. This diffusion-based method improves accuracy for complex samples like peptide mixtures.
Area of Science:
- Analytical Chemistry
- Microfluidics
- Separation Science
Background:
- Gated injection schemes in microchip devices can introduce electrokinetic sampling bias.
- A newly identified bias, transradial electrokinetic selection (TREKS), affects analytes with different electrophoretic mobilities.
- This bias is time-dependent and disproportionately affects negatively charged analytes.
Purpose of the Study:
- To investigate the electrokinetic sampling bias in gated injection methods.
- To introduce and validate a novel microchip injection technique.
- To demonstrate the improved performance for complex sample analysis.
Main Methods:
- Examination of the commonly used gated injection scheme.
- Identification and characterization of transradial electrokinetic selection (TREKS).
- Development and application of a new interstream diffusion injection method at zero potential.
Main Results:
- Gated injection exhibits significant, time-dependent electrokinetic sampling bias, particularly against negatively mobile analytes.
- The new diffusion-based injection method effectively minimizes bias for complex samples, including peptide mixtures.
- The proposed method achieves precise sample volumes (12-45 pL) with high reproducibility (retention times RSD < 1.5%, peak areas RSD < 2.3%).
Conclusions:
- The conventional gated injection method is prone to electrokinetic sampling bias, including TREKS.
- Interstream diffusion at zero potential offers a superior alternative for microchip sample injection.
- This novel method enhances accuracy and reproducibility for analyzing complex mixtures in microfluidic devices.