title: New selenite ion-selective electrodes based on 5,10,15,20-tetrakis-(4-methoxyphenyl)-21H,23H-porphyrin-Co(II).
abstract: New polymeric membrane (PME), modified carbon paste (MCPE), and coated wire (CWE) selenite ion-selective electrodes based on 5,10,15,20-tetrakis-(4-methoxyphenyl)-21H,23H-porphyrin-Co(II) (CoTMeOPP) are reported. The best composition was the electrode containing 2% CoTMeOPP as the active material and 49% TCP as plasticizer. The electrodes reveal a Nernstian behavior over a concentration range of 5.5x10(-5) to 1.1x10(-2) M for PME, 5.2x10(-5) to 1.2x10(-2) M for MCPE and 1.2x10(-4) to 4.4x10(-3) M for CWE. The potentiometric response is pH dependent, since selenous acid is a diprotic acid. The slope of the selenite PVC electrode was -57.0 mV for the monovalent anion at pH 6.47, and -26.0 mV for the divalent anion at pH 11.00. The detection limits were 3.4x10(-5) and 4.7x10(-5) M at pH values 6.47 and 11.00, respectively. The electrodes manifest advantages of low resistance, very short response time (15 s), and most importantly good selectivities relative to a wide variety of other anions. In fact, the proposed selenite ion-selective electrodes show a great improvement compared to previously reported electrodes for selenite ion. The electrode was used for the determination of selenite in selenite/selenate mixture, in sodium selenite raw material powder, and in VitaFit Selenium ACE antioxidant tablets with recovery ranges of 90.0-103.3%.
authors.affiliation: Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt.
authors.forename: H
authors.initials: H
authors.lastname: Ibrahim
authors.forename: Y M
authors.initials: YM
authors.lastname: Issa
authors.forename: Ola R
authors.initials: OR
authors.lastname: Shehab
mesh_terms: D003035:Cobalt; D006863:Hydrogen-Ion Concentration; D017736:Ion-Selective Electrodes / Q000592:standards*; D011166:Porphyrins; D018038:Sodium Selenite / Q000032:analysis*
chemical_list: C445706:5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin; D011166:Porphyrins; D003035:Cobalt; D018038:Sodium Selenite