| Abstract
| - Polymer membrane-based potentiometric sensors havebeen developed earlier to provide a rapid and directmethod of analysis for polyions such as heparin, a naturalanticoagulant administered to prevent thrombus formation during cardiovascular surgery. These heparin sensorsare irreversible, requiring a membrane renewal procedurebetween measurements which currently prevents thesensors from being used for continuous monitoring ofblood heparin. A newly developed heparin sensor isshown here to allow an alternate and more practicalmethod of membrane renewal. The electrically chargedH+ ionophore 5-(octadecanoyloxy)-2-(4-nitrophenylazo)phenol (ETH 2412) is incorporated as an additionalionophore into a heparin-sensing membrane. This membrane will respond to pH only at low H+ concentrations,while sample anions are coextracted with H+ ions into themembrane at physiological pH. In buffered samples atphysiological pH, the sensors will therefore respond toheparin via an ion-exchange mechanism with chlorideanions. The pH cross-sensitive heparin-sensing membranes are shown to give an excellent potentiometricresponse toward heparin in aqueous samples at physiological pH and Cl- levels as well as in undiluted wholeblood with no loss of heparin response. The membranerenewal is accomplished by moderately increasing the pHof the sample, causing heparin to diffuse out of themembrane with H+ ions. Reproducibilities are, with lessthan 1 mV standard deviation, improved over the classicalsystem. Unlike the high NaCl concentration used to stripheparin from the previously established heparin sensor,the pH change used here could ultimately be performedlocally at the sample−membrane interface, allowing thesensor to be used for automated long-term monitoring ofheparin in blood. A theoretical model is presented toexplain the experimental results.
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