Nanoporous Organosilicas as Preconcentration Materials for the Electrochemical Detection of Trinitrotoluene

Abstract

We describe the use of nanoporous organosilicas for rapid preconcentration and extraction of trinitrotoluene (TNT) for electrochemical analysis and demonstrate the effect of template-directed molecular imprinting on TNT adsorption. The relative effects of the benzene (BENZ)- and diethylbenzene (DEB)-bridged organic-inorganic polymers, having narrow or broad pore size distributions, respectively, on electrochemical response and desorption behavior were examined. Sample volumes of 0.5-10 mL containing 5-1000 ppb TNT in a phosphate-buffered saline buffer were preconcentrated in-line before the detector using a microcolumn containing 10 mg of imprinted BENZ or DEB. Square-wave voltammetry was used to detect the first reduction peak of TNT in an electrochemical flow cell using a carbon working electrode and a Ag/AgCl reference electrode. Imprinted BENZ released TNT faster than imprinted DEB with considerably less peak tailing and displayed enhanced sensitivity and an improvement in the limit of detection (LOD) owing to more rapid elution of TNT from that material with increasing signal amplitude. For imprinted BENZ, the slope of signal versus concentration scaled linearly with increasing preconcentration volume, and for preconcentrating 10 mL of sample, the LOD for TNT was estimated to be 5 ppb. Template-directed molecularly imprinted DEB (TDMI-DEB) was 7-fold more efficient in adsorption of TNT from aqueous contaminated soil extract than nonimprinted DEB.

Molecularly Imprinted Electrochemical Sensors

“…In this, the transducer substrate was first dipped in 3-methacryloxypropyl-trimethoxy silane, followed by the monomer and the co-polymer was removed by simple washing after polymerization [23,27]. Other nanoporous silanes such as bis(trimethoxysilylethyl)benzene and 1,4bis(triethoxy)silylbenzene had also been used as inorganic and organic polymers [129]. In some cases, excess of benzophenone (initiator) and the monomer was made to adsorb on the sensing surface and after the photo polymerization, the excess initiator was removed simultaneously [53,59].…”

“…These analytes include 2,4-D [112] and sulfamethazine [40,140], glucose [141], salicylic acid [115], trinitrotoluene [129] and fenbendazole [37]. A combination of DPV and SWV was used for the trace determination of 1-hydroxy pyrecene using disposable MIP modified screen-printed electrode [142].…”

Recent advances of mesoporous materials in sample preparation

“…Because of the molecular affinity of the organic moieties on the skeleton of organic-inorganic hybrid mesoporous materials, these surface imprinted mesoporous materials have demonstrated the enhanced selectivity and sensitivity to the target analytes, which are analogous to the imprinted organic moieties. Trammell et al [44] realized the use of nanoporous organosilicas for the rapid preconcentration and extraction of trinitrotoluene (TNT) for electrochemical analysis and demonstrate the effect of template-directed molecular imprinting on TNT adsorption. They developed two types of TNT imprinted nanoporous organosilicas for the preconcentration of TNT prior to electrochemical analysis.…”

MCM41 functionalized with ethylenediaminetriacetic acid for ion-exchange chromatography

“…2,3 Mesoporous silica particles have been modified with 2-thiophene-carbaldehyde for separation and preconcentration of palladium (II) 4 and salicylaldehyde for uranium (VI) 5 Nanoporous organo-silicas have been synthesized using an imprinting method, with benzene-and diethylbenzene bridged polysilsesquioxane as precursors, for preconcentration and detection of trinitrotoluene adsorbed from soils. 8 Using similar strategies organo-silicas particles provided of chiral organo groups have been prepared and successfully tested for determining the enantiomeric purity of organo-silicas solids. 9 The interest of researchers in mesoporous materials for adsorption of analytes from gas and liquid phase is continuously growing.…”