Topic No.7.4, 2.2 Oral Paper ID No: 0012 INTEGRATING INDEPENDENT SILICA MONOLITH ELECTROOSMOTIC PUMPS FOR REAGENT DELIVERY AND SAMPLE PRECONCENTRATION IN A -TAS DEVICE Fu-Qiang Nie, Brett Paull and Mirek Macka National Centre for Sensor Research and School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland, mirek.macka@dcu.ie A microfluidic chip-based total analysis system ( -TAS) integrating two independent monolithic electroosmotic pumps (EOPs) [1] for sample preconcentration [2] and reagent delivery has been developed. Based on our previous work on EOPs and a microchip-based flow injection analysis system ( -FIA) using monolithic EOPs [3, 4], the novelty of the -TAS reported here (Fig. 1) rests in the integration of two independent EOPs, one as the reagent -FIA pump (EOP-a), and a second (EOP-b) for analyte preconcentration by micro-solid phase extraction ( -SPE); both using silica monolithic capillary columns embedded in the chip, and applying light emitting diode (LED) based photometric and capacitively coupled contactless conductometric (C4D) detections. The chip was designed so that the -FIA reagent was placed in a reagent reservoir (Fig. 1) propelled indirectly by the EOP-a pumping water. In this way, the composition of the reagent can be independent from the propellant liquid, which is kept constant (water). The -SPE preconcentration step is followed by elution of the analyte from the EOP-b and injection of the zone of preconcentrated analyte in a -FIA stream of reagent. This is visualised in Fig. 2 where eluted Ca2+ as a test analyte is seen exiting the EOP-b as blue zone as it reacts with o-cresolphthalein complexone (o-CPC). EOP-a and EOP-b contain 3 parallel pieces and 1 piece of 100 m i.d. monolith containing fused silica capillary columns, respectively, each 10 mm in length. The advantage of using commercial silica-based monolithic fused silica capillary columns (Caprod, Merck) is in significant simplification of the process of making the -TAS chip. The monolith fused silica capillary columns were embedded in 400 x 400 m channels micromilled in PMMA bonded with the top plate using a double-sided adhesive polypropylene layer and the fused silica capillaries were sealed with epoxy glue through access holes in the top plate. The green LED detector (576 nm) and the C4D are used in an off-chip-configuration on the fused silica capillary (oncapillary detection) exiting the chip (Fig. 1). The advantages are flexibility of the design, the well as approved robustness of on-capillary detection and relatively better sensitivity and S/N ration compared to onchip photometric and C4D detection methods. The silica C18 EOP-b monolith is semi-permanently coated with dioctylsulphosuccinnate (DOSS) for on-chip cation-exchange -SPE preconcentration [5]. The coating process and column capacity are well controlled and characterized using the C4D detector (Fig. 3). Ethylenediamine/phthalate eluent pH=4.5 was chosen due to its elution strength and low conductivity background [6]. An elution time of 60 s (Fig. 4) leads to band broadening and a longer analysis time, so 10 s elution was chosen as optimal. Fig. 5 shows the -TAS -SPE achieving preconcentration factor of approx. 10x judged by the LED-detection peak height. It is estimated that only 20 L volume of sample and 7 nL eluent volume are consumed. The potential of the approach has been demonstrated by trace analysis of calcium achieving concentration limit of detection (LOD) of 0.01 mol/L which is an improvement in LOD by 100 times (Fig. 6). REFERENCES: 1. “A review of micropumps”, D. J. Laser, J. G Santiago, Journal of Micromechanics and Microengineering, 14(6), R35-R64 (2004). 2. “Less common applications of monoliths: Preconcentration and solid-phase extraction”, F. Svec, Journal of Chromatography B - Analytical Technologies in the Biomedical and Life Sciences, 841(1-2), 52-64 (2006). 3. “Robust Monolithic Silica Based On-Chip Electro-Osmotic Micro-Pump,” F. Q. Nie, M. Macka, L. Barron, D. Connolly, N. Kent, B. Paull, The Analyst, in press (2007). 4. “Miniaturisation and integration of sample injecting and dispensing silica monolithic electroosmotic pumps on a microfluidic chip”, F. Q. Nie, M. Macka, B. Paull, Proc. NanoTech 2006, Montreux, 12-14 November 2006. 5. “Rapid, low pressure, and simultaneous ion chromatography of common inorganic anions and cations on short permanently coated monolithic columns”, D. Connolly, D. Victory, B. Paull, Journal of Separation Science, 27, 912 (2004). 6. “Improved sensitivity and characterization of high-speed ion chromatography of inorganic anions,” P. Hatsis, C. A. Lucy, Analytical Chemistry, 75, 995 (2003). 1 Fig. 1. Schematic diagram of the -TAS device: EOPa= injecting pump; EOPb= dispensing pump; Detector= LED-based optical detector and C4D. Fig. 2. Visible images of the intersection of microchip during the elution and delivery processes (a-f) of Ca2+ visualized as a Ca2+-o-CPC complex. 0.20 1200 Absorbance (AU) Conductivity response (mV) 1400 1000 800 600 400 0.16 0.01 mM CaCl2 with preconcentration 0.12 0.08 0.04 0.00 200 0 0 0 10 20 30 40 50 60 500 10 s Eluent= 3mM Phthalate/ 2 mM Ethylenediamine solution 400 350 20 s 30 s 300 40 s 50 s 250 60 s 6 9 12 8 10 Fig. 5. Absorbance (εmax=576 nm for 0.01 mM Ca2+ without and with preconcentration. 500 450 Injection voltage: 1.2 KV Delivery voltage: 1.2 KV Injection time: 10 s 400 350 Preconcentration of CaCl2 300 Sample: CaCl 2 Eluent: 3 mM Phthalate/ 2 mM Ethylenediamine 250 0 3 6 200 200 0 4 Time (min) Detector Response (mV) Fig. 3. Conductivity response to the DOSS coating as a function of time demonstrating the saturation point. 450 2 70 Time (min) Detector Response (mV) 0.01 mM CaCl2 15 Time (min) Fig. 4. Conductivity signal as a function of elution time. 3 6 9 12 15 Time (min) Fig. 6. Conductivity signal for 0.01mM Ca2+ without and with preconcentration. 2