Detection comparison with chemiluminescence

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. 

The present study demonstrates the pH-dependent bimodal chemiluminescence of 6,8-diaryl-imidazopyrazinone la induced by superoxide. Despite its lower sensitivity to superoxide than CLA la showed enough sensitivity to superoxide in comparison with luminol and appears to be capable of superoxide detection. What the advantage of la over CLA is that it exhibits the pH-dependent bimodal chemiluminescence, and, therefore, the direct estimation of the local pH in a cell or a droplet is feasible based on the luminescence ratio, Iank /(la nii+Iaiiiai)- This property of la allows us to apply la for simultaneous detection of the two concurrent events, superoxide evolution and pH alteration, in biological systems. 

Table 1 Comparison of metal ion detection limits with different chemiluminescence systems. All ions have detection limits of lOnmoll" or lower. Ions in bold type have detection limits of lOnmoll" or lower. Only first-row transition-metal species are considered...

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

Flow injection methodology was used to estimate the total phenolic content of wine using acidic potassium permanganate chemiluminescence detection by Costin et al. (2003). Simple phenolic compounds such as quercetin, rutin, catechin, epicatechin, ferulic acid, caffeic acid, gallic acid, 4-hydroxycinnamic acid, and vanillin were examined analytically with chemiluminescence. Analysis of 12 different wines showed that detection limits were 2 x 10 M for caffeic acid, 3 x 10 M for ferulic acid, and 5 x 10 M for gallic acid. Comparison of the results of the chemiluminescence methodology and other total phenol/antioxidant assays showed that their correlation was good. Chemiluminescence... 

Hi. Lysine. Gamma radiolysis of aerated aqueous solution of lysine (94) has been shown, as inferred from iodometric measurements, to give rise to hydroperoxides in a similar yield to that observed for valine and leucine. However, attempts to isolate by HPLC the peroxidic derivatives using the post-column derivatization chemiluminescence detection approach were unsuccessful. This was assumed to be due to the instability of the lysine hydroperoxides under the conditions of HPLC analysis. Indirect evidence for the OH-mediated formation of hydroperoxides was provided by the isolation of four hydroxylated derivatives of lysine as 9-fluoromethyl chloroformate (FMOC) derivatives . Interestingly, NaBILj reduction of the irradiated lysine solutions before FMOC derivatization is accompanied by a notable increase in the yields of hydroxylysine isomers. Among the latter oxidized compounds, 3-hydroxy lysine was characterized by extensive H NMR and ESI-MS measurements whereas one diastereomer of 4-hydroxylysine and the two isomeric forms of 5-hydroxylysine were identified by comparison of their HPLC features as FMOC derivatives with those of authentic samples prepared by chemical synthesis. A reasonable mechanism for the formation of the four different hydroxylysines and, therefore, of related hydroperoxides 98-100, involves initial OH-mediated hydrogen abstraction followed by O2 addition to the carbon-centered radicals 95-97 thus formed and subsequent reduction of the resulting peroxyl radicals (equation 55). 

The extreme sensitivity of photon-detection techniques makes possible the measurement of chemiluminescent reactions whose quantum yields may be as low as 10 . Therefore it is essential, if these chemiluminescences are to be related to some physiological or biochemical processes, to be able to identify the nature of the reactions and the reactants. In many cases the yields of products are outside of the range of assay by microanalytical chemistry. In these cases, despite the uncertainties described in Section II above, the only remaining analytical technique is the comparison of the precise shapes of the chemiluminescence emission spectra with the photoexcited fluorescence emission spectra of proposed product molecules and the induction from these data of the substrate molecules and the mechanisms or pathways of the oxidation reactions. ... 

A comparison of the colorimetric and the chemiluminometric assay indicated that the sensitivity of the immunoassay was highly dependent on the antibody used. A prehminaiy comparison revealed that the detection hmit of the tube based chemiluminescent assay was 0.1 ng mL 2,4-D while the detection limit of the colorimetric assay was 22 ng mL This indicated the microformat imaging ELISA to be 20 times more sensitive than the luminometric assay and 4x10 times more sensitive than the colorimetric ELISA. The precision of the luminometric assay was 6% with a workable range between 0.1 and 10 ng mL Similarly for the colorimetric assay the precision was 33% with a workable range between 10 10 ng mL". ... 

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