| Abstract
| - An electrospray microchip for mass spectrometry comprising an integrated passive mixer to carry out on-chipchemical derivatizations is described. The microchipfabricated using UV-photoablation is composed of twomicrochannels linked together by a liquid junction. Downstream of this liquid junction, a mixing unit made ofparallel oblique grooves is integrated to the microchannelin order to create flow perturbations. Several mixerdesigns are evaluated. The mixer efficiency is investigatedboth by fluorescence study and mass spectrometricmonitoring of the tagging reaction of cysteinyl peptideswith 1,4-benzoquinone. The comparisons with a microchip without a mixing unit and a kinetic model are usedto assess the efficiency of the mixer showing taggingkinetics close to that of bulk reactions in an ideally mixedreactor. As an ultimate application, the electrospraymicromixer is implemented in a LC−MS workflow. On-line derivatization of albumin tryptic peptides after areversed-phase separation and counting of their cysteinesdrastically enhance the protein identification.
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