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Evaluation of an Organic Semiconductor as a Sensor of Volatilized Herbicides

Servicio de Investigación, Desarrollo y Tecnología Agraria, Junta de Castilla y León, Apdo 172, 47080 Valladolid, Spain;

J. Souto and J. A. De Saja

Dep. de Física de la Materia Condensada, Cristalografía y Mineralogía, Univ. de Valladolid, Spain;

S. Bolado

Dep. de Ingeniería Química, Univ. de Valladolid, Spain.

^* Corresponding author (javier{at}iq.cie.uva.es).

ABSTRACT

The use of a ytterbium bisphthalocyanine Langmuir-Blodgett film sensor for the study of the volatilization of the herbicides imazamethabenz-methyl, tri-allate, and terbutryn is evaluated. The dynamic response of the sensor to the herbicides is analyzed using a model that relates the response of an isotropic sensor to the total immobilized amount of a particular herbicide, accounting for the diffusion through the sensor and the adsorption of each herbicide in the sensor's film. Three model parameters are analyzed in the response of the sensor to a pulse in the concentration of herbicide, analyzing separately the sorption and desorption stages: the response time (), the adsorption isotherm linearity (1/n), and the linearity of the variation of the electrical conductivity of the sensor with the amount of sorbed herbicide (B). In the sorption stage, ranged from 174 to 341 s, 1/n ranged from 0.57 to 1.04, and B was within the interval from 1.54 to 2.4. The desorption stage required a longer time to be accomplished and thus is less useful for practical purposes. The model parameters are compared with semiqualitative analysis of the response curves in the sorption stage and the capabilities of these sensors in qualitative and quantitative analysis of volatilized herbicides are discussed. Based on the differences in the model parameters, the sensors offered promising results for identification purposes. The results also suggest applications in quantitative analysis, although further improvements in the methodology are required for that purpose.