Optrode Methods

Marcel Dekkbr, Inc. 270 Madison Avenue, New York, New Yoik 10016 

Gerlache, M., J. M. Kauffmann, G. Quarin, J. C. Vire, G. A. Bryant, J. M. Talbot, Electrochemical analysis of surfactants an overview, Talanta, 1996,43, 507-519. 

Linhart, K., Polarographic determination of surface active materials in water and wastewater, and the determination of their degradibility (in German), Tenside, 1972, 9, 241-259. Bednarkiewicz, E., Z. Kublik, Surfactants by suppression of the polarographic maximum of the first kind, J. Electroanal. Chem. Interfacial Electrochem., 1987,218,93-106. Bednarkiewicz, E., Surfactants in fresh waters based on suppression of polarographic oxygen maximum. Electroanalysis (N.Y.), 1991, i, 839-845. 

Cosovic, B., V. Vojvodic, Surface active substances in natural waters. Mar. Chem., 1987,22, 363-373. 

Batina, N., B. Cosovic, D. Tezak, Surface-active compounds in precipitation studies by AC polarography. Ana/. C/t/m. Acto, 1987,199,177-180. 

---

Figure 5.25 — Flow-through ion-selective optrode based on a multilayer lipidic membrane prepared by the Langmuir-Blodgett method. (A) Cross-sectional view of the composite six-layer membrane (four layers of arachidic acid/ valinomycin covered by an arachidic acid and rhodamine dye bilayer). (B) Optical arrangement integrated with the sensor, which is connected to a flow system. LS light source Ml and M2 excitation and emission monochromator, respectively FI and F2 primary filters M mirror LB lipid-sensitive membrane in a glass platelet FC flow-cell A amplifier D display P peristaltic pump. (Reproduced from [107] with permission of the Royal Society of Chemistry).

In the last decade, fiber-optic chemical sensors (FOCS), also known as optrodes, have emerged as alternatives to conventional methods of analysis. FOCS development for a particular analyte depends on the availability of reversible indicating schemes to detect the analyte of interest. Typically, the indicating schemes use commercially available colorimetric or fluorometric indicators (e.g. fluorescein to measure pH (1)). However, the utility of these indicators is limited. Furthermore, indicators may not exist for many analytes. Several reviews discuss the scope of this approach (2,3,4). 

Indirect measurement Gas-phase detection Use of nucleophilic species Simultaneous determination of nitrate using a Cu-Cd column/standard method EN/ISO 13395 Solid-phase optrode... 

Enzyme/indicator optrodes for registration of enzyme reactions and their inhibitors, such as heavy metal ions and pesticides, can be produced by PESA technique. Composite films containing the enzyme urease and cyclo-tetra-chromotropylene as indicator molecules show some characteristic spectral transformations caused by urea decomposition. The reaction of inhibition of urease by heavy metal ions can be also registered with this method. Further development of the enzyme sensors and sensor arrays lies in finding suitable pairs of enzyme/indicator, their deposition by PESA method and studying the enzyme reactions (including inhibition) with UV-vis spectroscopy. 

In order to quantitate the amount of drug released by the dosage form in our biorelevant method, we need an accurate analytical technique. The ideal technique for this analysis is in situ UV analysis, facilitated with a fiberoptic optrode. Fiberoptic dissolution has been applied to the analysis of solid dosage forms for over 15 years.The technique has been applied successfully to a whole host of dosage forms, and has been shown as a fast and effective technique, when applied to single component dosage forms, which contain an active ingredient... 

---