VERSATILITY in
ANALYTICAL INSTRUMENTATION ORIEL'S modular design enables a DO-IT-YOURSELF component approach for SPECTROFLUORIMETRY ABSORPTION MEASUREMENTS TRANSMISSION MEASUREMENTS SCATTERING MEASUREMENTS MONOCHROMATIC ILLUMINATION SPECTRORADIOMETRY BROADBAND GENERAL ILLUMINAHQffe
Figure 6. N o n r e v e r s i b l e 0 2 sensor 0 2 diffuses through Teflon membrane, M, into reagent phase, R, where it reacts to yield chemiluminescence measured by detection system, D
steady-state mass transfer to get a constant signal. Any processes that perturb mass transfer are potential sources of error. The difference between reversible and nonreversible optical sensors is similar to the difference between potentiometric and amperometric electrodes. Amperometric electrodes, like nonreversible optical sensors, involve a reaction and require mass transfer to an electrode surface. The use of tetrakis(dimethylaminoethylene) (TMAE) to measure oxygen serves as an example of a nonreversible sensor (13). The device is illustrated in Figure 6. Oxygen in the sample diffuses through a hydrophobic 02-permeable membrane into a reservoir of TMAE. There it reacts with TMAE yielding chemiluminescence, which is measured by a light detection system. (No probe radiation is required for this device.) Steadystate chemiluminescence is proportional to the partial pressure of oxygen. Both the flow rate of O2 past the membrane and the temperature affect response because they affect the steady-state supply of 0 2 into the reagent phase. The lifetime of the sensor is determined by the rate of TMAE consumption relative to the total TMAE available. The lifetime can be quite long—months and even years— if a large TMAE reservoir is used with a low rate of oxygen permeation. Again, it should be noted that this particular reagent was not combined with a fiber optic but readily could be. Other nonreversible sensors include U 0 2 + and halide sensors (1). These devices differ from the O2 sensor in
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 1, JANUARY 1984 · 33 A
