A 15-crown-5-functionalized carbosilane dendrimer as ionophore for ammonium selective electrodes

The synthesis of CH2=CHCH2OCH2[15-crown-5] (III) is achieved by the treatment of HOCH2-[15-crown-5] (I) with equimolar amounts of CH2=CHCH2Br (II) in the presence of KOH. The hydrosilylation of III with Si(CH2CH2CH2SiMe2H)(4) (IV) in the presence of the Karstedt catalyst affords the crown ether end-capped carbosilane dendrimer Si(CH2CH2CH2Si-Me2CH2CH2CH2OCH2[15-crown-5,])(4) (V). PVC-based membranes of V as ionophore with sodium tetraphenyl borate (NaTPB) as anion excluder and dioctyl phthalate (DOP), diphenyl ether (DPE), dibutyl amine (DBA) and dibutyl phthalate (DBP) as plasticizing solvent mediators were prepared and investigated as NH4+-selective electrode. The response of the electrode was linear with a Nernstian slope of 53.3 mV/decade over an NH4+ ion concentration range of 7.60 x 10(-6) to 1.0 x 10(-1) M and a detection limit of 3.9 x 10(-6) M. The response time to achieve a steady potential for NH4+ ions was between 6 and 10s, and the electrode is suitable for use within the pH range of 2.2-8.5. The selectivity relative to alkali, alkaline earth. and transition heavy metal ions is good. The newly developed ionophore showed higher NH4+ selectivity over K+ (log K-NH4 '+K+(Pot) = - 1.801) and Na+ (log K-NH4 '+Na+(Pot) = - 2.850). The electrode could be used for at least 45 days without considerable alteration in its potential. The electrode also shows a better working concentration range and slope in comparison to other NH4+-selective electrodes reported in literature. (c) 2006 Elsevier B.V. All rights reserved.