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ing channel etched into both materials. It holds 50 uL of liquid, making it suitable for derivatization, and uses four Cr-Pt resistors of approximately 100 Ohms for a total power In HPLC, enhancing detector sensitivity usof 2 W. The temperature can be raised to ing pre- or postcolumn derivatization usually 90 °C at a rate of 2 °C/s and is controlled via requires healing the reaction mixture. But a feedback mechanism with two additional the typical heater, a piece of tubing in a waresistors. Calculations of the time constants ter reservoir, is bulky and slow to change temperature. The solution, as Andreas Manz for heat diffusion suggested that, in the worst case, the reaction mixture would be and colleagues at Imperial College and the heated to only 93% of the temperature on the Laboratory of the Government Chemist silicon chip. But for practical purposes, the (both in the United Kingdom) and at 3T BV researchers say, the reaction temperature (The Netherlands) have shown, is to fabrican be assumed to be the same as the temcate a heated silicon and glass microreactor. perature measured on the silicon. The reactor is made from a 0.5-mmthick glass chip sitting atop a 0.4-mm-thick The reactor was tested using precolumn silicon chip. The reactor chamber is a narderivatization and subsequent separation of row (width = 1 mm) 100-mm-long meander- five amino acids. The researchers saw the best results when the reaction mixture was heated at60°Cfor2min,andthe results were comparable to those achieved with a water bath. The researchers suggest that the exact timing oo fhe heattng process will lead to less variation between successive measurements and that such microreactors may later be integrated with other components in labThe heated chemical microreactor. The photograph hhows a on-a-chip devices (/. meandering reaction channel, Cr-Pt heattng resistors, ,nd Chromatoer A 1998 temperature-measuring resistors. (Adapted with permission. 815 26">-71) Copyright 1998 Elsevier Science.)
Heated chemical microreactor
Chiral differentiation of amino acids p-Cyclodextnn (CD) may be the key to c iiir ill dinerennaiton of amino acids. K^U reacts with amino acids in solution to form host-guest complexes, which can be separated by riPLC. But this is not new. Researchers have been quantifying enantiomeric mixtures of amino acids based on this approach for more than a decade. Carlito B. Lebrilla and co-workers at the University of California-Davis have now turned to the gas phase to explore what happens to these host-guest complexes when they are exposed to alkylamines. CD-amino acid complexes stay intact during electrospray ionization and when transferred to the analyzer cell of a Fourier transform mass spectrometer.
638 A
With a background pressure of 1—b x 10~ Torr of «-propylamine in the analyzer cell, an exchange reaction occurs such that the amino acici guest is replaced by M-propylamine. The exchange rates of various amino acids are measured and found to depend on the chirality of the amino acid. For all three amino acids tested (alanine, valine, and phenylalanine), the L-enantiomer is found to be more reactive than the Dform. IVCHe constants cire diso determined for niixtures of L- emu i-J-eiidniiomers
