Ein NH 4 + -selektiv-enzymatisches Durchflußsystem. Verfahren zur kontinuierlichen enzymatischen Elektroanalyse von Harnstoff, II. Mitteilung

Abstract

Zusammenfassung: Es wird ein Durchflußsystem zur NH^-selektiv-enzymatischen Harnstoffbestimmung beschrieben, bei der mit löslicher Urease schwimmend eine Harnstoff Spaltung erfolgt und die NH 4 " h -Freisetzung sekundär mit einer ammoniumselektiven Disk-Elektrode erfaßt wird. Als aktive Komponente für die Elektrodenmembran wurde das Carrier-Antibiotikum Nonactin in eine Polyvinylchlorid-Matrix inkorporiert. A NH^-selective-enzymatic flow-through system. A method for the continuous enzymatic, electrochemical determination of urea, II.Summary: A flow-through system for the measurement of urea concentrations is described, using soluble urease and consecutive determination of liberated ammonium ions by a selective disc-electrode. The active component of the electrode membrane was the carrier-antibiotic nonactin which was incorporated in a Polyvinylchloride matrix. Einleitung

Why ammonium detection is particularly challenging but insightful with ionophore-based potentiometric sensors – an overview of the progress in the last 20 years

“…In particular, designing the tetrahedral symmetry of the binding site, with a coordination number of four, may play a key role in facilitating the binding of NH 4 + with respect to K + : indeed, K + is characterized by spherical symmetry and the preference for ionic bonds with coordination number of six or more. 26,27,80 One example of the described strategy was presented in the study by Graf et al 81 complex with electrostatic interactions. X-ray analysis revealed that NH 4 + was effectively placed at the center of a tetrahedron formed by the four nitrogen atoms of the receptor.…”

“…24,25 This preference could be attributed to the ad hoc properties of nonactin when binding with NH 4 + . [26][27][28][29] Nevertheless, both ionic size and monovalent charge of K + are competitively suitable with the receptor site features of nonactin. 26 Consequently, the presence of K + in the matrix in which NH 4 + needs to be measured represents an interference that sometimes-depending on the nature of the sampleimpedes the reliable detection of NH 4 + using ISEs based on nonactin.…”

“…18 The authors already discussed the possibility of incorporating nonactin as an NH 4 + ionophore in plasticized polyvinyl chloride (PVC) membranes (mainly with nitrophenyl octyl ether (NPOE)), silicone rubber polyurethane, and cellulose acetate membranes; however, all these electrodes reported similar K + interference levels. 27,[40][41][42][43][44] For overcoming this issue, the chemometric correction of K + interference using an array of inner-filling solution-type ISEs for NH 4 + , K + , Na + , and Ca 2+ in flow injection analysis (FIA) has been proposed by Diamond and co-workers in 1994. 45 Indeed, this approach was later used by the group of Del Valle with all-solid-state electrodes.…”

Fertilizers

“…Schindler et al (184) developed an ammonium ion-selective enzymatic flowthrough system for the measurement of urea concentrations. A selective disk electrode was used to measure the NH4+ liberated by urease.…”

Technologien für elektrochemische Festkontakt-Katheter-Sensoren und Teleskop-Katheter-Elektroden-Systeme zur Bestimmung von Ca ++ , K + , Na + , Cl - , Harnstoff, pH, O 2 und CO 2 - Technology of Electrochemical Solid-Contact Catheter Sensors and Telescope Catheter Electrode Systems for the Measurement of Ca++, K+, Na+, Cl-, Urea, pH, O2 and CO2

“…Bei NH 4 + -selektiv-enzymatischer Harnstoffanalyse muß der Substratumsatz durch die immobilisierte Urease im hydrophilen Membrananteil ausreichend hoch sein, so daß selbst bei physiologisch niedrigem Harnstoffpegel des Blutes die hohe Querempfindlichkeit für K* des Carrier-Antibiotikums Nonactin ausreichend kompensiert ist [37,38], Dies ist bei unserem Membranaufbau gegeben. Die geringen Unterschiede in den lonenradien von NK^r^n 1,48 · 10~1 0 m) und K + fron l,33-10~* 10 m) bedingen die für diese Ionen aufallend große Querempfindlichkeit von ionenselektiven Elektrodenmembranen mit den Carrier-Antibiotika Nonactin und Valinomycin.…”