Chemiluminescence relative rate

The first detailed investigation of the reaction kinetics was reported in 1984 (68). The reaction of bis(pentachlorophenyl) oxalate [1173-75-7] (PCPO) and hydrogen peroxide cataly2ed by sodium saUcylate in chlorobenzene produced chemiluminescence from diphenylamine (DPA) as a simple time—intensity profile from which a chemiluminescence decay rate constant could be determined. These studies demonstrated a first-order dependence for both PCPO and hydrogen peroxide and a zero-order dependence on the fluorescer in accord with an earher study (9). Furthermore, the chemiluminescence quantum efficiencies Qc) are dependent on the ease of oxidation of the fluorescer, an unstable, short-hved intermediate (r = 0.5 /is) serves as the chemical activator, and such a short-hved species "is not consistent with attempts to identify a relatively stable dioxetane as the intermediate" (68). 

An indirect method has been used to determine relative rate constants for the excitation step in peroxyoxalate CL from the imidazole (IM-H)-catalyzed reaction of bis(2,4,6-trichlorophenyl) oxalate (TCPO) with hydrogen peroxide in the presence of various ACTs . In this case, the HEI is formed in slow reaction steps and its interaction with the ACT is not observed kinetically. However, application of the steady-state approximation to the reduced kinetic scheme for this transformation (Scheme 6) leads to a linear relationship of l/direct measure of the rate constant of the excitation step. 

DF-RF, discharge flow-resonance fluorescence LP-RF, laser photolysis-resonance fluorescence RRM, relative rate method LPC, laser photolysis-chemiluminescence. 

D24.5 Infrared chemiluminescence. Chemical reactions may yield products in excited states. The emission of radiation as the molecules decay to lower energy states is called chemiluminescence. If the emission is from vibrationally excited states, then it is infrared chemiluminescence. The vibrationally excited product molecule in the example of Figure 24.13 in the text is CO. By studying the intensities of the infrared emission spectrum, the populations of the vibrational states in the product CO may be determined and this information allows us to determine the relative rates of formation of CO in these excited states. 

Relative Rate Constants. A variety of new techniques have been developed for obtaining accurate measurements of relative rate constants for hydrogen abstraction reactions by atomic fluorine (t.i6.18.19.22.2i -27. 5-8q.87.88). Of principal present interest ai4 the HF chemiluminescence (81 85). H F product analysis (2 -26). and Indirect atom loss (87.88) procedures. 

A comparison of 300"K relative rate constants obtained using chemiluminescence and H F product analysis methods is presented in Table VIII. The (ka/ki) values listed in column three have been based upon the revised thermal reaction fraction (cf. Table v), upon new sample data in many instances, upon the modified data reduction procedures described above, and upon the Arrhenius parameters listed in Table XII. These updated results are intended to supplant the F-to-HF rate constants reported previously from this laboratory (25). 

The available chemiluminescence measurements (8 1.85) of F-to-HF relative rate constants have utilized CH4 as internal standard. 

Because they lend themselves to studies using both photochemical and chemical activation, bimolecular reactions of vibrationally excited hydrogen halides have been more throughly investigated than any other family of reactions. The rate constants in Table 1.3 have been obtained by the laser-induced vibrational fluorescence technique and correspond to the sum of rate constants for reactive and inelastic processes. The main problem is to establish the atomic concentrations accurately. This is usually accomplished by gas-phase titration in a discharge-flow system, although photolysis methods have also been employed. To find the ratio of reaction to non-reactlve relaxation, product concentrations have to be observed. This has been done in relatively few cases. Some systems have also been studied using the infrared chemiluminescence depletion technique (see Section 1.5.1). These experiments supply relative rate data for removal from several vibrational levels, and, in favorable cases, also provide some information about the rotational-state dependence of these rates. 

Solubility and stability of coelenterazine. Coelenterazine is very poorly soluble in neutral aqueous buffer solutions, and the solutions are unstable in air. It can be easily dissolved in water in the presence of alkali, but the resulting solution is extremely unstable under aerobic conditions. Coelenterazine is soluble in methanol, and the solution is relatively stable. The stability is enhanced by the addition of a trace of HCl. A methanolic solution of coelenterazine can be stored for several days at — 20°C, and a methanolic solution containing 1-2 mM HCl can be stored for several months at — 70°C under aerobic conditions without significant oxidation. In many other organic solvents, coelenterazine is less stable, and spontaneously auto-oxidized at significant rates. In dimethylformamide and DMSO, it is rapidly decomposed accompanied by the emission of chemiluminescence. e-Coelenterazines are generally less stable than coelenterazines. 

A kinetic analysis of the results, based on (17) and its O+OH analog, is in satisfactory agreement with observations on a wide variety of flames. These flames are relatively cool, and the concentrations of H and OH exceed their equilibrium values even in the burned gases, so that the observed sodium emission is definitely chemiluminescent. The third order rate coefficients for excitation by H+H and H+OH are estimated to be 8 x 109 and 2x 1010 l2.mole-2.sec-1, corresponding to an efficiency near unity per triple collision. The possible importance of mechanisms of the type (14,15) has not been carefully studied. 

A relatively new analytical technique, chemiluminescence (CL), is an ultrasensitive technique, and it has been reported that reaction rates as low as 10 mole/year can be measured (1-5). Thus, it could monitor the aging reactions on a real-time basis while the resins are exposed to a simulated service environment. If the method can be shown to be sufficiently sensitive and reliable, the errors inherent in extrapolating accelerated aging data to the actual conditions encountered can be eliminated (6-8). 

Figures 25—27 show the temperature and composition profiles calculated for the standard flame by the refined treatment using set 2 of the rate coefficients of Table 30. Figure 25 also includes for comparison a number of points representing the observed temperature profile. Agreement is excellent. The composition profiles for the stable species in the flame were measured by means of a mass spectrometric probe, using the unbumt gas ratios of each species concentration to that of nitrogen as calibration standards. Realistic comparison is then in terms of these ratios, and is shown in Fig. 28. The relative intensities of sodium chemiluminescence in the recombination region of the low temperature flames are proportional to the square of the H atom concentrations. A comparison between theory and experiment on this basis, with intensities normalized with respect to the maximum H atom concentration and the...

Sample Chemiluminescence Analysis Induction time Oxidation rate (relative units)(relative units) Oven life (days)... 

A given time interval is needed for the reagent to reach the region of the sample zone yielding the analytical signal. The mean available time for reaction development is then lower than the mean sample residence time in the flow manifold. This may limit sensitivity, especially in analytical procedures based on relatively slow chemical reactions or with detection techniques based on reaction rate measurements such as chemiluminescence and bioluminescence. 

In order to optimise the manifold design of the flow system, the lifetimes of the excited states of the molecules should be considered, because the processed sample is in motion. In the situation of too high a flow rate and too small a flow cell, a fraction of the excited molecules could exit the flow cell without emitting light. On the other hand, if the flow rate is too low, a significant fraction of the molecules may emit radiation before reaching the flow cell. Both situations can lead to a decrease in the analytical sensitivity. This feature can be considered as a "time window" in flow analysis and the effect is more pronounced in phosphorimetric methods where light emission is slow relative to fluorimetric methods [65]. This is also true for chemiluminescence and bioluminescence, as discussed in the next section. 

In the presence of oxygen, the chemiluminescence intensity (/CL) is significantly enhanced with respect to the emission produced under nitrogen. As the samples are highly oxidized in a diffusion-controlled reaction simultaneous to the emission, reaction (b) in Scheme 3.1 is very fast and the relative concentration of [POO ] will be larger in proportion to that of [P ]. The rate of oxidation (R,) in Equation 3.2 increases under these conditions, the bimolecular termination of peroxy radical, reactions (f) and (g) in Scheme 3.1, is, therefore, predominant. All these parameters can be used to evaluate the degradation in different materials and the effectiveness of antioxidants in the polymer stability. 

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