title: Highly selective electrode for potentiometric analysis of methadone in biological fluids and pharmaceutical formulations.
abstract: In order to develop a fast and simple procedure for methadone analysis in biological fluids, a graphite paste electrode (GPE) was modified with the ion-pair of methadone-phosphotungstic acid, and multiwalled carbon nanotubes (MWCNTs). Optimized composition of the electrode with respect to graphite powder:paraffin oil:MWCNTs:ion pair, was 58:30:8:4 (w/w%). The electrode showed a near-Nernstian slope of 58.9 ± 0.3 mV/decade for methadone in a wide linear range of 1.0 × 10(-8)-4.6 × 10(-3)M, with a detection limit of 1.0 × 10(-8)M. The electrode response was independent of pH in the range of 5-11, with a fast response time (~4s) at 25 °C. The sensor showed high selectivity and was successfully applied to the determination of sub-micromolar concentrations of methadone in human blood serum and urine samples, with recoveries in the range of 95-99.8%. The average recovery of methadone from tablets (5 mg/tablet) by using the proposed method was 98%. The life time of the modified electrode was more than 5 months, due to the characteristic of GPE which can be cut off and fresh electrode surface be available. A titration procedure was performed for methadone analysis by using phosphotungstic acid, as titrating agent, which showed an accurate end point and 1:1 stoichiometry for the ion-pair formed (methadone:phosphotungstic acid). The simple and rapid procedure as well as excellent detection limit and selectivity are some of the advantages of the proposed sensor for methadone.
authors.affiliation: Department of Chemistry, Razi University, Kermanshah 67149, Iran.
authors.forename: Moslem
authors.initials: M
authors.lastname: Ardeshiri
authors.affiliation: Department of Chemistry, Razi University, Kermanshah 67149, Iran. Electronic address: fjalali@razi.ac.ir.
authors.forename: Fahimeh
authors.initials: F
authors.lastname: Jalali
mesh_terms: D004339:Drug Compounding; D004566:Electrodes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057230:Limit of Detection; D008691:Methadone / Q000032:analysis* / Q000097:blood / Q000652:urine; D037742:Nanotubes, Carbon / Q000737:chemistry; D010772:Phosphotungstic Acid / Q000737:chemistry; D011199:Potentiometry; D013607:Tablets / Q000737:chemistry
chemical_list: D037742:Nanotubes, Carbon; D013607:Tablets; D010772:Phosphotungstic Acid; D008691:Methadone
keywords: Biological fluids; Graphite paste electrode; Methadone; Multi-walled carbon nanotubes; Potentiometry