Chemiluminescence factors determining

C is the concentration of limiting reactant in mol/L, c is the chemiluminescence quantum yield in ein/mol, and P is a photopic factor that is determined by the sensitivity of the human eye to the spectral distribution of the light. Because the human eye is most responsive to yellow light, where the photopic factor for a yellow fluorescer such as fluorescein can be as high as 0.85, blue or red formulations have inherently lower light capacities. 

Another rather striking example demonstrates that the fluorescence efficiency of the respective dicarboxylates is not the most important factor in determining the chemiluminescence efficiencies of the hydrazides 9.10-diphenylanthracene-2.3-dicarbonic acid 25 has a fluorescence efficiency of about 0.9 (as has the parent compound 9.10-di-phenylanthracene) 94>. The corresponding hydrazide 26, however, gives a quantum yield of 48% that of luminol only (in DMSO/t-BuOK/ O2) 95) although 3-aminophtalic acid has a fluorescence efficiency of about 0.3 only. 

Finally, Yamada and Suzuki made a comparative study of the use of DDAB, HTAB, STAC, and CEDAB to improve the sensitivity and selectivity of the determination of ultratraces of Cu(II) by means of the CL reaction of 1,10-phenanthroline with hydrogen peroxide and sodium hydroxide, used as detection in a flow injection system [46]. Of the four cited surfactants it was found that CEDAB causes the greatest enhancement of the chemiluminescent signal (Fig. 12) (an enhancement factor of 140 with respect to the absence of surfactant). 

In this case, chemiluminescence was monitored using a red-sensitive PMT to detect emissions from HFf. A factor-of-six enhancement in sensitivity to 1.1 parts per billion (ppbv) DMS was obtained. This is consistent with the fact that, based on the rate constant for the H + F2 rate determining step [Reaction (28)], the reaction can cycle approximately 7 times during the cell residence time and confirms the observation by Turnipseed and Birks [7] that F atoms are produced in the F2 + DMS reaction. 

The manual procedure for determination of total nitrogen by chemiluminescence involves preparing the standards from a stock solution, diluting the samples, injecting the standards into the combustion furnace for analysis, and calculation of the nitrogen content of the samples. The calculation is based on the signal from the diluted sample compared to the standard curve and the dilution factor for the sample. 

Nussbaum MA, Baertschi SW, Jansen PJ. Determination of relative UV response factors for HPLC by use of a chemiluminescent nitrogen-specific detector. J Pharm Biomed Anal 2002 27 983-993. 

As mentioned above, the formation of excited states in chemical reactions may be understood in the context of an electron transfer model for chemiluminescence, first proposed by Marcus [2]. According to this model the formation of excited states is competitive with the formation of the ground state, even though the latter is strongly favored thermodynamically. Thus, understanding the factors that determine the electron transfer rate is of considerable importance. The theory of electron transfer reactions in solution has been summarized and reviewed in many reviews (e.g., [30-36]). Therefore, in this chapter the relevant ideas and equations are only briefly summarized, to serve as a basis for description of the ECL experiments. 

While compendial standards are available for some monographed article impurities, it may be difficult at times to obtain pure standards of impurities. Manufacturers of pharmaceuticals function as a potential source for obtaining reference standards of impurities, which may be synthesis precursors, process intermediates, or degradation products. The characterization and evaluation of these impurities reference standards should be constant with their intended use. In many cases, analytical procedures are developed and validated, where the response of an impurity is compared to that of the new drug substance itself. Response factor evaluation of impurities at the chosen detection wavelength is necessary to determine if a correction factor is needed (when the responses differ). Potentiometric detection, fluorescence/ chemiluminescence detection, and refractive index detection are some examples of detection modes available for compounds that may not be suitable for UV detection. 

Methods in which some property related to substrate concentration (such as absorbance, fluorescence, chemiluminescence, etc.) is measured at two fixed times during the course of the reaction are known as two-point kinetic methods. They are theoreticahy the most accurate for the enzymatic determination of substrates. However, these methods are technically more demanding than equifibrium methods and all the factors that affect reaction rate, such as pH, temperature, and amount of enzyme, must be kept constant from one assay to the next, as must the timing of the two measurements. These conditions can readily be achieved in automatic analyzers. A reference solution of the analyte (substrate) must be used for calibration. To ensure first-order reaction conditions, the substrate concentration must be low compared to the K, (i.e., in the order of less than 0.2 X K, . Enzymes with high K , values are therefore preferred for kinetic analysis to give a wider usable range of substrate concentration. 

Titrimetric luminescence methods record changes in the indicator emission of radiation during titration. This change is noted visually or by instruments normally used in luminescence analysis. Most luminescence indicators are complex organic compounds which are classified into fluorescent and chemiluminescent, compounds according to the type of emission of radiation. As in titrimetry with adsorption of colored indicators, luminescence titration makes use of acid-base, precipitation, redox, and complexation reactions. Unlike color reactions, luminescence indicators enable the determination of ions in turbid or colored media and permit the detection limit to be lowered by a factor of nearly one thousand. In comparison with direct luminescence determination, the luminescence titrimetric method is more precise. 

Most chemiluminescence reactions are reported to have low efficiencies, less than 10%, which has restricted their usefulness for analyses. The duration of the reactions is influenced by the reaction conditions and may occur rapidly, within 1 s, or last longer than 24 h. In the development of chemiluminescent assay methods the two basic factors that influence the intensity of chemiluminescence (i.e., efficiency and rate) should be considered. The efficiency of the reaction influences both analytical sensitivity and detection limits, while the reaction kinetics determine both the precision and sample throughput. 

Experimental determination of the excitation factor shows that with chemical luminescence excitation (chemiluminescence) in flames the f value is, as a rule, much higher than the thermal emission factor. This stems from the non-equilibrium nature of this kind of emission, directly related to the energy liberated by some or other elementary chemical process. This shows the high importance of chemiluminescence both for the identification of labile intermediates and for the elucidation of certain fine details of the chemical reaction mechanism. 

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