High chip-based

Buetow, K.H., Edmondson, M., MacDonald, R., Clifford, R., Yip, P., Kelley, ]., Little, D.P, Strausberg, R., Koester, H., Cantor, C.R., and Braun, A., High-throughput development and characterization of a genome-wide collection of gene-based single nucleotide polymorphism markers by chip-based matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, Proc. Natl. Acad. Sci. USA, 98, 581-584, 2001. 

Although this section provides a brief description of most commonly nsed detectors for HPLC, most of the focus is on a few detection modes. Optical absorbance detectors remain the most widely nsed for HPLC, and are discnssed in some detail. We also focns on flnorescence, condnctivity, and electrochemical detection, as these methods were not widely nsed for HPLC in the past, bnt are especially well suited to micro- and nano-flow instrnments becanse of their high sensitivity in small sample volumes. Mass spectrometry has also come into wide and rontine nse in the last decade, but as it is the subject of another chapter, it will not be fnrther discnssed here. Miniaturization has been particularly important for capillary and chip-based electrophoresis, which often employs sub-nanoliter detection volnmes [36,37]. 

Another class of readout measures RNA expression levels, with the three most common methods being chip-based hybridization/fluorescence techniques, realtime polymerase chain reaction (RT-PCR) and quantitative nuclease protection assays (QNPA) [48, 49]. Chip-based methods are widely used for whole-genome scans (discussed in more detail below), but have a disadvantage that they are relatively expensive and so are not really high throughput. The quantitative reproducibility and dynamic range of these chip-based methods are also lower than for the other RNA readout techniques. RT-PCR is a more quantitative technique for measuring transcript levels, and is typically run for up to 40 transcripts at a time. QNPA is another... 

The most common types of MS/MS instruments available to researchers in food chemistry include triple quadrupole mass spectrometers and ion traps. Less common but commercially produced tandem mass spectrometers include magnetic sector instruments, Fourier transform ion cyclotron resonance (FTICR) mass spectrometers, and quadrupole time-of-flight (QTOF) hybrid instruments (Table A.3A.1). Beginning in 2001, TOF-TOF tandem mass spectrometers became available from instrument manufacturers. These instruments have the potential to deliver high-resolution tandem mass spectra with high speed and should be compatible with the chip-based chromatography systems now under development. 

The first two points represent a general motivation for miniaturization in separation science independent of the actual fabrication technology. The benefit of a reduction of the consumption of sample, reagents, and mobile phase in chemical and biochemical analysis is self-evident and does not need to be discussed further (reduced consumption of precious samples and reagents, reduced amounts of waste, environmental aspects). This advantage is, however, sharply contrasted by its severe implications on the detection side, as discussed elsewhere in this volume in detail. The detection of the separated zones of very small sample volumes critically depends on the availability of highly sensitive detection methods. It is not surprising that extremely sensitive laser-induced-fluorescence (LIF) has been the mostly used detection principle for chip-based separation systems so far. 

Fang, Q., Xu, G.-M., Fang, Z.-L., High throughput continuous sample introduction interfacing for microfluidic chip-based capillary electrophoresis systems. Micro Total Analysis Systems, Proceedings 5th XTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 373-374. 

Yun, K.S., Yoon, E., A micro/nano-fluidic chip-based micro-well array for high-throughput cell analysis and drug screening. Micro Total Analysis Systems 2003, Proceedings 7th pTAS Symposium, Squaw Valley, CA, Oct. 5-9, 2003, 861-864. 

Electrochemical detection offers also great promise for CZE microchips, and for other chip-based analytical microsystems (e.g., Lab-on-a-Chip) discussed in Section 6.3 (77-83). Particularly attractive for such microfluidic devices are the high sensitivity of electrochemical detection, its inherent miniaturization of both the detector and control instrumentation, low cost, low power demands, and compatibility with micromachining technologies. Various detector configurations, based on different capillary/working-electrode... 

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