Stern-Volmer, oxygen

Fig. 2. a) Transient absorption spectra of RF (35 pM) in N2-saturated MeOH-Water (1 1) solution observed after 60 ps of the laser pulse as a function of the concentration of GA. b) Effect of dissolved molecular oxygen ( 2) on the decay of the 3RF at 700 nm. Inset Stern-Volmer plot for the quenching of 3RF by 3O2. 

We focus on luminescence quenching based sensors, but many of the principles are generic. Quenching-based oxygen detectors are probably the most mature. In homogeneous media with only a single component exponential decay the intensity and lifetime forms of the Stern-Volmer equations are ... 

Significant curvature may be observed in the case of lifetime- (and intensity-) based sensors, mainly when the relation knri [Parameter]) is not linear. Figure 9.4 shows this type of nonlinear behavior for a fiberoptic oxygen sensor. The figure shows Stern-Volmer-type plots (r l versus [02]) at four different temperatures. The curvature is caused by the inability of the carrier to transport oxygen proportionally to the equilibrium partial pressure of oxygen. 

As in the former cases, k2 was calculated from the integrated extinction coefficients,149 k3 + kt was derived from fluorescence quantum yields,149 while k3 and k4 were separately estimated from the maximum quantum yields of photooxygenations at high oxygen concentrations.150 Flash spectroscopy techniques were used in order to determine k5 and k7, while kB was obtained from the Stern-Volmer quenching constant of oxygen.149 The ratio ke/kg was determined from the variation of AOz with the concentration of the anthracene.71 When photodimerization occurred, k13l(kia + k13) was calculated from the maximum yield of... 

Depending on the number of these cycles the final oxygen concentration is determined by the residual pressure of the pump. Quantitative analysis of traces of oxygen in liquids can be done by the measurements of long-lived luminescence lifetimes (e.g. pyrene fluorescence) and applying the Stern-Volmer equation. 

Figure 13.7 Stern-Volmer plot of the reciprocal of biacetyl triplet lifetime vs. the pressure of added oxygen. Reprinted with permission of H. W. Sidebottom, C. C. Badcock, J. G. Calvert, B. R. Rabe, and E. K. Damon, J. Amer. Chem. Soc., 94, 13 (1972). Copyright by the American Chemical Society.

If the Stern-Volmer constants for oxygen for both sensors are the same, simplifies to... 

The overall oxygen sensitivity exhibited by an optical sensor is basically predefined by the Stern-Volmer constant Ksv. The sensitivity of the final optical oxygen sensor increases with Ksv [65]. Generally, high Ksv values are provided by the Pd- and Pt-porphyrin complexes, by Ru(dpp)3, and by pyrene. Fluorescence quenching by oxygen not only affects the fluorescence intensity of the dye, but also has an influence on its lifetime r (Fig. 6) ... 

Figure 10.2 shows a Stern-Volmer plot for the fluorescence intensity quenching by oxygen of zinc protoporphyrin IX embedded in the heme pocket of apomyoglobin (Mbdes Fe). The slope of the plot yields Ksv and A q values of 15.96 M-1 s-1 and 7.6 x 109 M-1 s-1,... 

Figure 10.3 Stern-Volmer plot of quenching with oxygen of intensity and lifetime of protoporphyrin IX embedded in the heme pocket of myoglobin. Experiments performed at20°C.

Figure 10.9 Stern-Volmer plots of the fluorescence intensity quenching of by oxygen. The Arg...

As the slopes of the Stern-Volmer plots are equal to kto, and since the fluorescence lifetimes, to, of both porphyrins do not change with temperature, the slope variation reflects a change that occurs in oxygen diffusion with the temperature. From the slopes at low quencher concentrations, we have found values of k equal to 8.4 0.4 x 108 M-1 s-1 and 13 0.4 x 108 M-1 s 1 at 20° and 35°C, respectively. 

Once polymer encapsulated, several emissive metal complexes can be used to measure oxygen in the gas phase as well as in aqueous or biomedia (29, 43, 44, 49-64). Oxygen concentrations can be determined using emission intensity by adapting the Stern-Volmer... 

Time-resolved fluorescence spectra can be obtained without recourse to sophisticated equipment by the use of an electronic quencher, (invariably molecular oxygen), wdiich will quench preferentidly those mdecules with the longest decay times, as is illustrated by the Stern-Volmer Eq. (61). Addition of increasing amounts of quencher to a system under continuous illumination thus progressively... 

The amount of fluorescence intensity quenching can be quantitatively related to the partial pressure of oxygen in a sample from the simplified Stern-Volmer equation ... 

An expanded version of the Stern-Volmer equation containing a factorial expansion of these same terms can also be employed to relate /q to oxygen levels in a more exact manner. Standard operation includes, at minimum, a daily calibration at a number of oxygen concentrations (at a fixed pressure and temperature) and use of the measured calibration coefficients to determine the concentration of oxygen in an unknown sample. 

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