Luminescence detection concentration

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

Luminol (3-aminophthalhydrazide) reacts with hydrogen peroxide in the presence of a metal catalyst in basic solution to produce luminescence. This reaction is extremely sensitive and may be used to detect concentrations of parts per 1012 of metals separated by liquid chromatography [199-202]. 

In this assay, the minimum detectable concentration (MDC) of TSH was estimated to be less than 0.001 pIU/mL TSH. The MDC is defined as that concentration of TSH which corresponds to the relative luminescent unit that is two standard deviations from the mean relative luminescent unit of a zero calibrator. 

Analytical Applications. Chemiluminescence and bioluminescence are useful in analysis for several reasons. (/) Modem low noise phototubes when properly instmmented can detect light fluxes as weak as 100 photons/s (1.7 x 10 eins/s). Thus luminescent reactions in which intensity depends on the concentration of a reactant of analytical interest can be used to determine attomole—2eptomole amounts (10 to 10 mol). This is especially useful for biochemical, trace metal, and pollution control analyses (93,260—266) (see Trace and residue analysis). (2) Light measurement is easily automated for routine measurements as, for example, in clinical analysis. 

Tungsten is usually identified by atomic spectroscopy. Using optical emission spectroscopy, tungsten in ores can be detected at concentrations of 0.05—0.1%, whereas x-ray spectroscopy detects 0.5—1.0%. ScheeHte in rock formations can be identified by its luminescence under ultraviolet excitation. In a wet-chemical identification method, the ore is fired with sodium carbonate and then treated with hydrochloric acid addition of 2inc, aluminum, or tin produces a beautiful blue color if tungsten is present. 

In summary, CL can provide contactless and nondestructive analysis of a wide range of electronic properties of a variety of luminescent materials. Spatial resolution of less than 1 pm in the CL-SEM mode and detection limits of impurity concentrations down to 10 at/cm can be attained. CL depth profiling can be performed by varying the range of electron penetration that depends on the electron-beam energy the excitation depth can be varied from about 10 nm to several pm for electron-beam energies ranging between about 1 keV and 40 keV. 

The HS2 radical was detected by its infrared absorption spectrum and the S2 molecule by luminescence spectroscopy. In addition, infrared bands assigned to dimers of disulfane molecules were observed at higher H2S2 concentrations. The HS2- radicals may further be split into hydrogen atoms and S2 molecules during the photolysis since the concentration of HS2- first increases and then decreases while that of S2 steadily increases. No evidence for the thiosulfoxide H2S=S was found, and the probably formed HS- radicals are assumed to be unable to leave their cage in the matrix and either recombine to H2S2 or form H2+S2 [69]. 

Definition and Uses of Standards. In the context of this paper, the term "standard" denotes a well-characterized material for which a physical parameter or concentration of chemical constituent has been determined with a known precision and accuracy. These standards can be used to check or determine (a) instrumental parameters such as wavelength accuracy, detection-system spectral responsivity, and stability (b) the instrument response to specific fluorescent species and (c) the accuracy of measurements made by specific Instruments or measurement procedures (assess whether the analytical measurement process is in statistical control and whether it exhibits bias). Once the luminescence instrumentation has been calibrated, it can be used to measure the luminescence characteristics of chemical systems, including corrected excitation and emission spectra, quantum yields, decay times, emission anisotropies, energy transfer, and, with appropriate standards, the concentrations of chemical constituents in complex S2unples. 

It is important to model a correlation spectroscopy system, firstly to predict performance, and also to aid the very important choice of optical filter (or choose the best LED or super-luminescent optical fibre source to give the optimal spectral output), in order to achieve the best detection performance or best selectivity possible. The length of the cells and the pressure of gas (or gas concentration) are also important parameters (although all simulated results described below are based on use of lm long cells). 

Alcohol oxidase was used to generate H202 followed by its reaction with luminol in the presence of K3[Fe(CN)6] as a catalyst [53], The luminescence was transmitted from the flow cell to the detector via optical fibers. Ethanol can be determined in the 3-750-pmol/L concentration range, with a detection limit of 3 pmol/L. Also, using an immobilized alcohol dehydrogenase reactor in glass beads, a FIA sensor for a reduced form of NADH was constructed by the ECL using the above-mentioned ruthenium tris(2,2 -biryridine) complex. The sensor was satisfactorily applied to the determination of ethanol concentration [54],... 

Hermann (2000) described a rapid automated method involving generation of a known amount of free radicals and the detection of the excess by photochemiluminescence. Test kits are available for determination of total water-soluble antioxidants, fat-soluble antioxidants and ascorbic acid. A luminometric method was developed for the determination of antioxidative activity and was subsequently applied to anthocyanin and betalaine colour concentrates (Kuchta et al., 1999). The method involved quantification of the interruption in luminescence from the hydrogen peroxide-horse radish peroxidase-luminol system in the presence of antioxidants. 

In the [Zn(2)2]2+ species, a single Zn2+ ion is able to revive the luminescence of all the 32 naphthyl units present in the two dendritic structures. This result shows that dendrimers can be profitably used as supramolecular fluorescent sensors for metal ions, as shown in Fig. 2. In this case, the sensor fluorescence is switched on upon metal ion coordination, and low Zn2+ concentrations (ca. 1 pM) can be easily detected. 

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