Investigación

Designing the measurement cell of a swept–field differential aspiration condenser

A.A. Solis and E. Sacristán

Departamento de Ingeniería Eléctrica, Universidad Autónoma Metropolitana, Michoacán y Purísima, Col. Vicentina, Iztapalapa, México D.F., 09340, México.

Recibido el 25 de noviembre de 2005
Aceptado el 22 de marzo de 2006

Abstract

We present the description of a small–size and low–cost sensor based on the aspiration method that can be used as an ion–mobility spectrometer: the planar swept–field first–order differential aspiration condenser. A mathematical model for the measurement cell of the condenser has been developed, and in this paper a design strategy based on the model is described. A measurement cell has been constructed following this strategy and was used in a prototype aspiration condenser device. Some collector–plate ion–current curves have been measured for gas samples with several different anesthetic gases in different concentrations in order to evaluate the model and the design of the measurement cell. The inverse transform via the truncated singular value decomposition (TSVD) has been applied to the data to obtain ion–mobility spectra. The results suggest that, although the model simplifies the actual physical behavior of the ions, thereby causing some inconsistencies in the mobility spectra, it is still useful in the aspiration condenser's design process. The proposed device is an attractive small–size, cost–effective alternative for ion–mobility gas analysis applications.

Keywords: Aspiration condenser; gas monitoring; ionization; ionic mobility; spectrometry; Tammet transform.

Resumen

Presentamos la descripción de un nuevo sensor basado en el método de aspiración, pequeño y de bajo costo, que puede ser utilizado como un espectrómetro de movilidad iónica: el condensador de aspiración plano de primer orden con barrido de campo. Se ha desarrollado un modelo matemático de la celda de medición del sensor, y basado en éste se describe en este artículo un metodo estructurado para su diseño. Aplicando el método propuesto se ha construido una nueva celda de medición y se ha empleado en un condensador de aspiración prototipo. Se presentan a modo de evaluación del modelo y del diseño algunos espectros de movilidad iónica obtenidos por medio de la transformación inversa por truncamiento de la descomposición en valores singulares (TSVD) del modelo matemático, aplicada a las curvas de voltaje obtenidas mediante el sensor para una mezcla gaseosa con diferentes concentraciones de agentes anestésicos. Los resultados sugieren que, aunque el modelo simplifica el comportamiento físico de los iones, causando algunas inconsistencias en el espectro de movilidad, es de una gran utilidad en el proceso de diseno de un condensador. El dispositivo propuesto se perfila como una alternativa atractiva de bajo costo y tamaño pequeño para aplicaciones de análisis de gases por movilidad iónica.

Descriptores: Condensador de aspiración; monitoreo de gases; ionización; movilidad iónica; espectrometría; transformada de Tammet.

PACS: 02.30.Rz; 02.30.Zz; 07.81.+a; 51.50.+v

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