ABSTRACT
Technology........................................................... 368 10.2.2 Filtering by Diffusion .......................................................... 370 10.2.3 Cell Lysis ............................................................................. 370 10.2.4 Dialysis................................................................................. 373
10.2.4.1 The Dialysis Process ............................................ 374 10.2.4.2 Microdialysis Probe Designs ............................... 376 10.2.4.3 Factors Influencing the Performance
of Microdialysis ................................................... 376 10.2.4.4 Examples of Microdialysis on a Chip ................. 379
10.3 Analyte Extraction/Preconcentration................................................ 383 10.3.1 Liquid-Liquid Extraction .................................................... 383
10.3.1.1 Factors Influencing Extraction Efficiency and Selectivity.................................... 384
10.3.1.2 Examples on Chip ................................................ 384 10.3.2 Solid-Phase Extraction......................................................... 385
10.3.2.1 Adsorption Mechanisms ...................................... 386 10.3.2.2 Practical Considerations for SPE
on Chip ................................................................. 389 10.3.2.3 Examples of SPE on a Chip ................................ 391
10.3.3 Electrokinetic-Mobility-Based Sample Preconcentration .................................................................. 395
10.3.4 Creating Electrokinetic Velocity Gradients ........................ 395 10.3.4.1 Molecular Transport at an Electrokinetic
Velocity Gradient ................................................. 398 10.3.4.2 Effects of Induced, Pressure-Driven Flow .......... 401
10.3.5 Techniques for Electrokinetic Sample Preconcentration for Microchip Devices............................. 401 10.3.5.1 Field-Amplified Sample Stacking ....................... 401 10.3.5.2 Field-Amplified Injection .................................... 404 10.3.5.3 Thermal Gradient Focusing ................................. 405 10.3.5.4 Stacking of Neutral Analytes............................... 405
10.3.6 Isotachophoresis for Sample Preconcentration and Clean-Up ....................................................................... 406
10.4 Biochemical Sample Pretreatment ................................................... 408 10.4.1 DNA Purification................................................................. 408 10.4.2 Nucleic Acid Amplification ................................................ 413 10.4.3 Biomolecule Fragmentation ................................................ 419
10.4.3.1 Enzymatic Digestion of DNA.............................. 419 10.4.3.2 Enzymatic Digestion of Proteins ......................... 420 10.4.3.3 Physical Biomolecule Fragmentation .................. 421
10.5 Conclusion ........................................................................................ 423 Acknowledgments ....................................................................................... 424 References.................................................................................................... 424
Both qualitative and quantitative chemical information about a sample can be
obtained using separation techniques such as high-performance liquid chro-
matography or capillary electrophoresis (CE). As in all branches of analysis,
however, the quality of that information will very much depend on the matrix
in which the analyte of interest is determined. In laboratory standards, the
composition of the matrix is very well defined and generally kept very simple,
allowing the measured response of the detector to be directly related back to
the original concentration of the analyte. With real samples, of course, the
situation very rapidly becomes more complicated. Components in the matrix
can often mask the presence of an analyte through complexation or other
chemical interactions. Alternatively, there may be components present that
induce an additional detector response, making it difficult to attribute results
solely to the analyte(s) of interest. Matrix components may also affect the
analysis in nonspecific ways. For instance, particulate matter may clog a
column, or matrix components may foul surfaces in the separation system.
