Chemiluminescence detection efficiency

The efficient recovery of volatile nitrosamines from frankfurters, followed by gc with chemiluminescence detection, has been described (133). Recoveries ranged from 84.3 to 104.8% for samples spiked at the 20 ppb level. Methods for herbicide residues and other contaminants that may also relate to food have been discussed. Inorganic elements in food can be deterrnined by atomic absorption (AA) methods. These methods have been extensively reviewed. Table 8 Hsts methods for the analysis of elements in foods (134). 

The potential for improved chemiluminescent detection is large, since the efficiency for activation of the acceptor is less than 0.01%. A thousand-fold increase in signal could be anticipated from this reaction. 

In the HPLC mode, most solvent vapors and pyrolysis products are similarly trapped in a series of two cold traps (dry ice + ethanol). This has been found to be quite efficient in removing most organic solvent vapors, but is unworkable with aqueous mobile phases because of freeze-up and blockage of the cold traps. Also, traces of moisture entering the detection chamber interfere with the chemiluminescence detection. Furthermore, mobile phases containing in-... 

The intensity (I) of chemiluminescence will depend on the rate of the luminescent reaction (R), the overall efficiency of the formation and emission of excited species (O) and a geometrical factor (G), which is a product of the fraction of emitted photons that are detected and the detection efficiency [24] ... 

Kim, D.J., Cho, W.H., Ro, K.W., Hahn, J.H., Microchip-based simultaneous online monitoring for Cr(III) and Cr(VI) using highly efficient chemiluminescence detection. Micro Total Analysis Systems, Proceedings 5th pZAS Symposium, Monterey, CA, Oct. 21-25, 2001, 525-526. 

Hayakawa and co-workers have intensively developed HPLC techniques with on-line reduction of NPAC to aminoPAC (APAC) and chemiluminescence detection of APAC for trace analysis of NPAC, particularly of nitropyrenes. In this study, we examined the HPLC method for the analysis of novel NPAC, 3-NBA and 2-NTP in airborne particles including the interference of coexisting NPAC in the sample in separation and the efficiency of the on-line reduction to selective conversion of 3-nitrobenzanthrone, which has one carbonyl group, to detectable 3-aminobenzanthrone in the HPLC system. 

Lab-on-a-Chip Devices for Chemical Analysis, Fig. 12 (a) Microchip layout. The inlets are 400 pm wide, 800 pm deep, and 10 mm long. The mixing channel is 800 pm wide, 800 pm deep, and 520 mm long. The active area of the photodiode used for chemiluminescence detection is 1 x 1 mm. The photodiode is located at a position 10 mm downstream from the point of confluence of the two inlet streams, (b) Quantum efficiency spectrum of the organic photodiode and the normalized emission spectra for the two chemiluminescent dyes used in the work (cyalume blue and cyalume green). The emission spectra of both dyes overlap the spectral response of the photodiode (Reprinted with permission from [20])... 

The liquid method utilised a direct analysis technique to measure the activity of oils of various grades and wears, however no accurate account could be taken for the effect of chemiluminescence and high count rate responses on the accuracy of the true sample activity. Further the use of an aqueous standard due to the unavailability of an appropriate organic simulant could not accurately model the detection efficiency. 

Chemiluminescence has been studied extensively (2) for several reasons (/) chemiexcitation relates to fundamental molecular interactions and transformations and its study provides access to basic elements of reaction mechanisms and molecular properties (2) efficient chemiluminescence can provide an emergency or portable light source (J) chemiluminescence provides means to detect and measure trace elements and pollutants for environmental control, or clinically important substances (eg, metaboHtes, specific proteins, cancer markers, hormones, DNA) and (4) classification of the hioluminescent relationship between different organisms defines their biological relationship and pattern of evolution. 

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

Chemiluminescent reactions must proceed at a sufficiently fast rate to provide the minimum number of quanta per time unit, as determined by the sensitivity of the detector used. According to Hercules 4> a chemiluminescence reaction with 100% efficiency emitting only one photon per fortnight would not be detected . 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

HTAC cationic micelles also markedly enhance the CL intensity of fluorescein (FL) in the oxidation of hydrogen peroxide catalyzed by horseradish peroxidase (HRP) [39], However, no CL enhancement was observed when anionic micelles of sodium dodecyl sulphate (SDS) or nonionic micelles of polyoxyethylene (23) dodecanol (Brij-35) were used (Fig. 9). CL enhancement is attributed to the electrostatic interaction of the anionic fluorescein with the HTAC micelles. The local concentration of fluorescein on the surface of the micelle increases the efficiency of the energy transferred from the singlet oxygen (which is produced in the peroxidation catalyzed by the HRP) to fluorescein. This chemiluminescent enhancement was applied to the determination of traces of hydrogen peroxide. The detection limit was three times smaller than that obtained in aqueous solution. 

The analytical detectability applying a CL method should, in principle, be comparable to that obtained using radioactive labels, without all the disadvantages related to the use of isotopic labeling. In fact, assuming reasonable values for the quantum efficiency of the chemiluminescent reaction (Cl 0.01), for the overall photon collection efficiency of the optical system-CCD camera assembly (T) 0.01%), and for the intensity of the lowest detectable CL signal (about... 

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