Talanta 51 (2000) 1205 – 1212 Development of a positive pressure driven micro-fabricated liquid chromatographic analyzer through rapid-prototyping with poly(dimethylsiloxane) Optimizing chromatographic efficiency with sub-nanoliter injections Paul G. Vahey, Sang Hyun Park, Brian J. Marquardt, Younan Xia, Lloyd W. Burgess, Robert E. Synovec * Department of Chemistry, Center for Process Analytical Chemistry, Box 351700, Uniersity of Washington, Seattle, WA 98195, USA Received 8 November 1999; received in revised form 21 January 2000; accepted 21 January 2000 Abstract A rapid and low-cost means of developing a working prototype for a positive-displacement driven open tubular liquid chromatography (OTLC) analyzer is demonstrated. A novel flow programming and injection strategy was developed and implemented using soft lithography, and evaluated in terms of chromatographic band broadening and efficiency. A separation of two food dyes served as the model sample system. Sample and mobile phase flowed continuously by positive displacement through the OTLC analyzer. Rectangular channels, of dimensions 10 m deep by 100 m wide, were micro-fabricated in poly-dimethylsiloxane (PDMS), with the separation portion 6.6 cm long. Using a novel flow programming method, in contrast to electroosmotic flow, sample injection volumes from 0.5 to 10 nl were made in real-time. Band broadening increased substantially for injection volumes over 1 nl. Although underivatized PDMS proved to be a sub-optimal stationary phase, plate heights, H, of 12 m were experimentally achieved for an unretained analyte with the rectangular channel resulting in a reduced plate height, h, of 1.2. Chromatographic efficiency of the unretained analyte followed the model of an OTLC system limited by mass-trans- fer in the mobile phase. Flow rates from 6 nl min -1 up to 200 nl min -1 were tested, and van Deemter plots confirmed plate heights were optimum at 6 nl min -1 over the tested flow rate range. Thus, the best separation efficiency, N of 5500 for the 6.6 cm length separation channel, was achieved at the minimum flow rate through the column of 6 nl min -1 , or 3 ml year -1 . This analyzer is a low-cost sampling and chemical analysis tool that is intended to complement micro-fabricated electrophoretic and related separation devices. © 2000 Elsevier Science B.V. All rights reserved. www.elsevier.com/locate/talanta * Corresponding author. Fax: +1-206-6858665. E-mail address: synovec@chem.washington.edu (R.E. Synovec) 0039-9140/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0039-9140(00)00311-8