Name:

Dr. Mercedes Vázquez

Contact details

Qualifications

Ph.D., Åbo Akademi University, Åbo-Turku, Finland, May 2005 

Ph.D. thesis: Potentiometric ion sensors based on conducting polymers― as ion-to-electron transducers and ion-selective membranes.

  Supervisors: Prof. Ari Ivaska and Dr. Johan Bobacka, Laboratory of Analytical Chemistry, Åbo Akademi University, Åbo-Turku, Finland.

  Opponent: Prof. Ernö Pretsch, ETH Hönggerberg, Zürich, Switzerland.

  Reviewer: Prof. Roland De Marco, Department of Applied Chemistry, Curtin University of Technology, Perth, Australia.

M.Sc.  (Analytical Chemistry), Faculty of Chemistry, University of Oviedo, Asturias-Spain, Sep 1998

Project Summary

This research project is focused on the development of rapid and robust analytical methods for drug development and quality control in the biopharmaceutical industry. Detailed information concerning the composition of the raw materials employed in the production of biologics is important for the efficient control and optimization of bioprocesses. The analytical methods used in these applications must be simple and fast as well as be easily transferable from one site to another.

Capillary Liquid Chromatography with Contactless Conductivity Detection

Conductimetric detection is a universal detection technique that involves the measurement of the differences in the conductivity of the electrolyte solution compared to that of the analyte zones. Therefore, it can be used as a very convenient detection mode for screening complex samples. Since its introduction in 1998, contactless conductivity detection has gained much popularity as an on-capillary detection mode for capillary electrophoresis (CE) and microcolumn liquid chromatography. The main reason for this is that there is no physical contact of the detection electrodes with the electrolyte solution. Therefore, the integration of this detection mode within the analytical system is rather simple (Fig. 1). Furthermore, the background noise is significantly reduced leading to lower detection limits than the conventional contact conductivity detection. The use of contactless conductivity as detection mode for capillary liquid chromatography (Cap LC) is being explored. Cap LC allows rather fast analysis of complex mixtures and, therefore, a reasonably fast characterization of the raw materials fed to the bioreactor. A commercially available contactless conductivity detector (TraceDec^®) is being used in this application.

 Fig. 1. Integration of the Cap LC system (with UV detection) with contactless conductivity detection.

Due to the complexity of biopharmaceutical samples, Solid Phase Extraction (SPE) methods are also being developed for sample clean-up prior to LC analysis.

Microfluidics

The current approach followed in the microfluidics area is based on the development of an electrophoresis microchip system that will allow a fast analysis (in the order of seconds or minutes) of complex mixtures. A typical channel configuration for an electrophoresis microchip is depicted in Fig. 2. Generally, gated injection (an specific type of electrokinetic injection) is used in these systems due to its flexibility regarding sample plug size. For gated injection (Fig. 2), a high voltage is applied to the buffer reservoir in order to fill the injection channel, and a fraction of that voltage is applied to the sample reservoir while sample and buffer waste reservoirs are at ground (Fig. 2A). Sample injection is then performed by floating the voltage at the buffer reservoir for a short time, e.g. 1-3 s, what drives the sample plug into the separation channel (Fig. 2B). The voltage at the buffer reservoir is then resumed to allow sample separation (Fig. 2C). The length of the sample plug can be easily controlled by varying the injection time (Fig. 2B). In-channel detection can then be done by using a contactless conductivity detector or UV-vis detection (click here for more details).

Fig. 2. Example of a gated injection: (A) filling the injection channel, (B) injection, (C) separation.

Different methodologies and materials can be used in the fabrication of an electrophoresis microchip. If you want to see more details about poly(dimethyl siloxane) (PDMS) chip fabrication, click here. In Fig. 3, a microchip fabricated in a polyester film (a common transparency) by laser printing can be seen. The basic instrumentation needed for this procedure includes a laser printer and a laminator. Therefore, this is a rather simple and cheap technique. A laser printer is used to selectively deposit a toner layer on a polyester film, which is subsequently laminated against another printed polyester film with mirrored images resulting in a chip with channels of aprox. 12 μm depth (Fig. 3).

Fig. 3. Toner-based microchip for capillary electrophoresis.

Publications

1. M. Vázquez, C. Frankenfeld, W. K. Tomazelli Coltro, E. Carrilho, D. Diamond, S. M. Lunte, Dual Contactless Conductivity and Amperometric Detection on Hybrid PDMS/Glass Electrophoresis Microchips, in preparation.

2. J. Bobacka, M. Vázquez, F. Sundfors, K. Mikhelson, A. Lewenstam, A. Ivaska, Determination of Ca(II) in wood pulp using a calcium-selective electrode with poly(3,4-ethylenedioxythiophene) as ion-to-electron transducer, in S. Alegret and A. Merkoçi (eds.), Electrochemical Sensor Analysis, Volume 2: Analytical Protocols, Potentiometric sensors, Procedure 4, in D. Barceló (ed.), Series: Comprehensive Analytical Chemistry, Vol. 49, Elsevier, Amsterdam, The Netherlands, 2007, pp e25-e28.

3. M. Vázquez, J. Bobacka, A. Ivaska, Potentiometic sensors for Ag⁺ based on poly(3-octylthiophene) (POT), J. Solid State Electrochem. 2005, 9, 865-873.

4. M. Vázquez, J. Bobacka, M. Luostarinen, K. Rissanen, A. Lewenstam, A. Ivaska, Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes, J. Solid State Electrochem. 2005, 9, 312-319.

5. M. Vázquez, J. Bobacka, A. Ivaska, A. Lewenstam, Small-volume radial flow cell for all-solid-state ion-selective electrodes, Talanta 2004, 62, 57-63.

6. M. Vázquez, P. Danielsson, J. Bobacka, A. Lewenstam, A. Ivaska, Solution-cast films of poly(3,4-ethylenedioxythiophene) as ion-to-electron transducers in all-solid-state ion-selective electrodes, Sens. Actuators B 2004, 97, 182-189.

7. M. Vázquez, J. Bobacka, A. Ivaska, A. Lewenstam, Influence of oxygen and carbon dioxide on the electrochemical stability of poly(3,4-ethylenedioxythiophene) used as ion-to-electron transducer in all-solid-state ion-selective electrodes, Sens. Actuators B 2002, 82, 7-13.

8. M. Vázquez, K. Mikhelson, S. Piepponen, J. Rämö, M. Sillanpää, A. Ivaska, A. Lewenstam, J. Bobacka, Determination of Na⁺, K⁺, Ca²⁺ and Cl^- ions in wood pulp suspension using ion-selective electrodes, Electroanalysis 2001, 13, 1119-1124.

Further Information

Scholarships

1. Research fellowship from Stiftelsens för Åbo Akademi Forskningsinstitut, 1 Jan- 30 Jun 2005

2. Erasmus international exchange program. Host University: Åbo Akademi University, Home University: University of Oviedo, 5 Jan- 5 Jul 1999

Awards

Award for the best oral presentation at the Spring Seminar of the Graduate School of Materials Research (GSMR), Åbo-Turku, Finland, May 2002