Performance of a portable biosensor for the analysis of ethion residues.

Sensitive disposable potentiometric sensors for determination of the organophosphorus pesticide (OPs), ethion and its degradation residues have been constructed. The fabricated screen printed sensors are based on multi-walled carbon nanotube-polyvinyl chloride (MWNT-PVC) composite incorporated with α-cyclodextrin (α-CD) ionophore for butyrylcholine (BuCh) determination. Butyrylcholinesterase (BuChE) activity was measured through monitoring the BuCh hydrolysis using the fabricated sensors. The electrode potential changes linearly with BuChE concentration over the range from 0.04 to 0.4 U in phosphate buffer solution. This approach can also be used to analyze ethion and its degradation products in the concentration range from 0 to 330 ng mL(-1) by measuring the relative inhibition percentage of BuChE. From different ethion degradation products, inhibition by dioxon and monooxon were more potent than the parent pesticide. The proposed method was applied for determination of ethion in different samples with good accuracy and precision. The relative simple fabrication protocol of biosensor, high sensitivity and stability represents a promising approach for determination of environmental pollutants in field conditions.

Miniaturized ionophore-based potentiometric sensors for the flow-injection determination of metformin in pharmaceutical formulations and biological fluids.

Miniaturized potentiometric sensors based on ß-cyclodextrins (ß-CDs) are described for determination of metformin (Mf) in pharmaceutical preparations and biological fluids. Electrode matrix compositions are optimized on the basis of the nature and content of sensing ionophore, ionic sites and plasticizers. Coated wire electrodes (CWEs) modified with heptakis(2,3,6-tri-O-methyl)-ß-CD, sodium tetrakis(4-fluorophenyl)borate (NaTFPB) and 2-fluorophenyl 2-nitrophenyl ether (f-NPE), work satisfactorily in the concentration range from 10(-6) to 10(-1) mol L(-1) with Nernstian compliance (55.7 ± 0.4 mV per decade activity) and a detection limit of 8 × 10(-7) mol L(-1). Incorporation of ß-CD as a molecular recognition element improved the electrode sensitivity and selectivity due to encapsulation of Mf into the ß-CD cavity (host-guest interaction). The developed electrodes have been successfully applied for the potentiometric determination of Mf under batch and flow injection analysis (FIA). FIA allows analysis of 90 samples per h offering the advantages of simplicity, accuracy and automation feasibility. The dissolution profile for metformin pharmaceutical samples (Cidophage®) was monitored using the proposed electrode in comparison with the official spectrophotometric methods. Characterization of the formed Mf-ß-CD inclusion complexes is discussed in detail.

Novel multi walled carbon nanotubes/ß-cyclodextrin based carbon paste electrode for flow injection potentiometric determination of piroxicam.

A novel carbon paste electrode based on functionlized multi-walled carbon nanotubes/ß-cyclodextrin composite (FMWCNTs/ß-CD-CPE) is described for potentiometric determination of piroxicam (PXM). Improved sensitivity and selectivity was achieved by application of CDs as molecular host-guest recognition elements and MWCNTs. The electrochemical performance of carbon paste electrodes incroporated with FMWCNTs/ß-CD composite was compared to those incroporated with MWCNTs and free CDs. Matrices compositions of each electrode are optimized on the basis of nature and content of the modifier, ionic sites and selected plasticizer. CPEs containing FMWCNTs/ß-CD composite, hyamine (Hy) and 2-fluorophenyl 2-nitrophenyl ether (f-NPE) as electrode plasticizer, work satisfactory in the concentration range from 10(-6) to 10(-2) mol L(-1) with Nernstain compliance (58.7±0.9 mV decade(-1) activity) with fast response time of about 2s and exhibit adequate operational lifetime (16 weeks). The developed electrodes have been applied for the potentiometric determination of PXM in pharmaceutical formulation under batch and flow injection analysis (FIA). FIA allows the analysis of 120 samples h(-1) with the advantage of simplicity, accuracy and automation feasibility.