Fiber optical fluorosensor for determination of halothane and or oxygen

Abstract

A flber optical fluoroescence sensor for measurlng concentrations of the wldeiy used lnhalatlon narcotic halothane In the presence of varying concentratlons of oxygen is presented. I t Is based on dynamlc fluorescence quenching and consists of a highly halothane-sensltive indlcator layer exposed to the sample. Interferences by molecular oxygen are taken Into account by a second, polytetrafluoroethylene-covered fluorescent indlcator layer highly sensltlve toward oxygen. Haiothane concentrations can be calculated wlth the help of an extended Stern-Volmer relation (eq 10). The two-sensor technlque presented here allows the determination of halothane, or oxygen, or both wlth a preclslon of 1 5 % for halothane and 13.5% for oxygen In the concentration range encountered in practlce. The probe Is practlcally speclflc for the two anaiytes, since other gases present in inhalatlon gases or blood including carbon monoxlde, dlnltrogen monoxlde, or fluorans do not interfere. The method is thought to be applicable to various other quenching analyte couples as well.Halothane (2-bromo-2-chloro-l,l,l-trifluoroethane) is the inhalation narcotic most frequently used in anesthetics (1). Numerous methods for its determination in breath gas and blood have been described. They are based on quite different analytical techniques such as gas chromatography (2,3), UV (4, 5 ) , mass (6, 71, or NMR spectrometry (81, and surface plasmon resonance (9). A commercially available monitor for anesthetic gases ("EMMA") is based on the absorption of, e.g., halothane, by a thin oil film. The physical parameter measured in this case is the mass of the film which is monitored with a piezoelectric crystal (10). The Datex anesthetic agent monitor measures halothane (or other anesthetic gases) in air via their characteristic IR absorption.Unfortunately, all of these methods either do not allow continuous determination of halothane or are not suitable for use in probes or catheters. We have taken advantage of the observation that halothane is able to quench the fluorescence of polycyclic aromatic hydrocarbons and have devised a fiber-optical sensor suitable for ita continuous monitoring. Since all indicators were also quenched by molecular oxygen-a process that is frequently observed and can be used for sensing oxygen (1 l-l6)-the Stern-Volmer equation has to be modified to take into account multiple quenching. Fluorescence quenching of oxygen-sensitive indicators by halothane has already been noticed (16), a fact that makes all oxygen sensors based on dynamic fluorescence quenching halothane-sensitive and can lead to considerable bias in clinical routine.We report here on the first sensor that is able to probe both oxygen and halothane with practically no mutual interference. Its fiber optical design can be quite similar to that reported by Peterson et al. (16), except that two fibers are required and the mathematics is slightly more complicated. THEORY Halothane in Air. Dynamic fluorescence quenching is known to obey the Stern-Volmer equation (eq l), whi...

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