Analysis of the absorption kinetics for the detection of parathion using hybrid organic/inorganic coating on SH-SAW devices in aqueous solution

Abstract

Organophosphate pesticides (OPs) have been found as contaminants in surface and ground waters, soil, and agricultural products. Because OPs are toxic compounds, monitoring of OPs in groundwater is necessary to allow for real-time remediation. Various types of polymer-coated sensors are being investigated for the rapid detection/monitoring of OPs in groundwater. The focus of this paper is on analyzing the sensor response of an acoustic wave device for the detection of organophosphate pesticides in aqueous solutions to determine whether the analyte absorption is penetration limited or diffusion limited. In this work, kinetic studies for the absorption of organophosphates (parathion-methyl, parathion, and paraoxon) from aqueous solutions into a hybrid organic/inorganic chemically sensitive layer [bisphenol A–hexamethyltrisiloxane (BPA-HMTS)] coating are conducted using guided shear horizontal surface acoustic wave sensor platforms on 36° rotated Y-cut LiTaO3. The objective of the studies is to provide an understanding of the underlying physics of the sensor response. The sensor data are analyzed within the context of two absorption models: penetration-limited and diffusion-limited absorptions. It is shown that the absorption process is rate-limited by penetration with a concentration independent absorption time constant or mass transfer coefficient. The absorption time constants for parathion-methyl, parathion, and paraoxon are calculated. It is seen that even though paraoxon is only 3.8% smaller (by volume) than parathion, its absorption time constant (∼10.5±2.1min) is, for the same coating thickness, at least 50% faster than parathion (∼32.5±1.6min). On the other hand, parathion-methyl, which is 9.5% smaller than paraoxon, exhibited about the same absorption time (∼8.3±0.5min) as paraoxon. This difference in transient information can be used to improve analyte recognition (between parathion/paraoxon and parathion/parathion-methyl).