MULTINUCLEAR NMR AND POTENTIOMETRIC STUDIES ON THE INTERACTION OF ZINC AND CADMIUM WITH CYTIDINE AND GLYCYLGLYCINE - THE EFFECT OF THE ANION

The stability constants for binary complexes formed between Zn2+ and Cd2+ With cytidine and glycylglycine and for the ternary complexes with the same ligands were determined by spectroscopic (H-1 and C-13 NMR) and, except those involving Zn2+ and cytidine, by potentiometric pH titrations in aqueous solution. The calculated values show that cadmium binds much more strongly to cytidine than zinc, and that a small but significant increase in the stability of zinc/cytidine interaction, but not for cadmium/cytidine, is observed in the presence of glycylglycine. The chemical shifts observed for cytidine with zinc show a marked dependence on the anion, being much larger for the chloride salt than for the nitrate and increase upon addition of glycylglycine, although the calculated stability constants are identical for both salts. Finally, the choice of reference chemical shifts used in the spectroscopic titrations and the effect of charged species on the values of die acidity constants are discussed

Construction and evaluation of an ammonium tubular ion-selective electrode with ionophore nonactin.

This paper describes the construction of an ammonium tubular potentiometric detector for flow injection analisys (FIA) in which the high molecular weight polyvinyl chloride (PVC) membrane is applied directly on a conducting support consisting of a mixture of an epoxy resin and graphite. The tubular ammonium ion-selective electrode, without internal reference solution, is based on nonactin as the ionophore and bis-(2-ethylhexyl)-adipate as plasticiser solvent, supported upon a PVC membrane, The electrode exhibited a response of 55.6 mV per concentration decade within the 5.0x10(-5) to 1.0x10(-1) mol/L NH4+ range in TRIS-HCl 0.2 mol/L (pH=6.7) buffer. Potassium ions constituted the greatest analytical interference; the electrode response time was 10 seconds, at 25.0 degrees C.19554955

Potentiometric FIA system with reactor based on natural urease source and tubular detector of ammonium ions. Determination of urea in fertilizers

An FIA system was developed to analyze urea by monitoring ammonium ions generated by enzymatic degradation with a tubular ion-selective electrode containing nonactin on polyvinyl chloride (PVC) membrane. As an urease source, 120 mg of the leguminous canavalia brasiliensis were immobilized in an enzymatic reactor with glutaraldehyde. Ammonium ions are converted to ammonia by an alkaline solution, 1 mol l(-1) NaOH, and permeates through a polytetrafluoroethylene membrane until the detector. The method can be used in an urea concentration range of 2.5X10(-4) to 2.5X10(-3) mol l(-1) (25.0 degrees C). Analysis of 25 mu l commercial samples of fertilizers, showed a relative error of 0.2% with a high selectivity to the species present.13458959