Fluorescence stabilization

Similar fluorescence-stabilization has been reported for polyethylene glycol 4000 by Wintersteiger [291]. 

Further examples pf fluorescence stabilization and intensity augmentation as a result of treatment of the chromatogram with viscous, lipophilic liquids are listed in Table 22. The alteration of the pH [293] or the addition of organic acids or bases [292] have also been found to be effective. Wintersteiger [291] has also described the effect that the TLC layer itself (binder) can influence the fluorescence intensity. 

Reagents. Perylene was obtained from Sigma Chemical Company (St. Louis, Missouri). All other PAHs were supplied by Aldrich Chemical Company (Milwaukee, Wisconsin) and were reported to contain less that 3% impurities. All PAHs were used without further purification. Isopropyl ether (99%) for extraction work was also purchased from Aldrich. Hydroquinone, a fluorescent stabilizer present in the ether, was removed prior to solution preparation by rotary evaporation. Fluorometric-grade 1-butanol was supplied by Fisher Scientific Company (Fair Lawn, New Jersey). All solutions for extractions of PAHs were prepared by evaporating portions of a stock cyclohexane solution and diluting to the appropriate volume with isopropyl ether. Fluorescence measurements were performed on 1 10 dilutions of the stock and final organic phase solutions. The effect of dissolved CDx on the fluorescence intensity of the organic phase PAH was minimized by dilution with isopropyl ether. 

Fluorescence stabilization, porphyrins la 100-101 Fluorophors la 57 Flupentixol lb 354 Fluphenazine la 104 lb 354-356 Fluspirilen lb 354 Fluvalinates lb 86 Foam bath, brominated la 64 Folic acid la 223,225 Folin-Ciocalteu s reagent lb 180 Folin s reagent lb 321 Formaldehyde la 299,351 -, vapor la 86 Formazan lb 65... 

Parsons, D.L. (1982). Fluorescence stability of human albumin solutions. J. Pharm. Sci., 71, 349-351. 

The observed fluorescence stabilizes after a few seconds and then begins to drop as the chamber warms. 

Phosphazene substituted with glycine has been prepared as a passivation agent for CdSe (green emission) and CdSe/ZnS (red emission) quantum dots. The polymer was prepared by the reaction of ethylglycinate with poly(di-chlorophosphazene), which was then de-esterified by base to reveal the active material. Quantum dots were prepared for passivation by initial treatment with mercaptoethanol, followed by treatment with the phosphazene. Fluorescent CdSe/ZnS quantum dots were found to be encapsulated in the polymer, which acted as a multidentate pendant group. It was found to passivate the dots and provided colloidal stability. Encapulated ZnS exhibited fluorescence stability. 

The fluorescence stability of coatings on different membrane types was monitored over a year and the results showed that stability was dependent on both the monomer tail structure, headgroup and the membrane material (9). Typically the emission of coatings would rise slightly over the first few days after deposition and then stabilize. Mixed cellulose ester (MCE), hydrophilic polyvinylidene floride (e.g., Durapore) and hydrophilic polypropylene... 

In principle at least, CO isotope lasers can most conveniently serve as reference lasers in the 4.9 to 8.0 pm wavelength domain. In terms of spectral purity, sealed-off operation ) a d abundance of readily available lasing transitions CO isotope lasers are at least as good as their COi counterparts. Lamb-dip stabilization of CO lasers was also accomplished 3) nearly 15 years ago. However, the resettability of the Lamb-dip stabilization method is at least 100 times less accurate than the 4.3 pm fluorescence stabilization of CO2 lasers. The absolute accuracy of presently available CO laser transition frequencies is also only good to within about one or two MHz. If one MHz or so accuracy is not sufficient, a direct comparison of a CO reference laser line with an appropriately selected frequency doubled line-center stabilized CO2 laser transition is always possible and was so demonstrated several years ago. ... 

Precision When the analyte s concentration is well above the detection limit, the relative standard deviation for fluorescence is usually 0.5-2%. The limiting instrumental factor affecting precision is the stability of the excitation source. The precision for phosphorescence is often limited by reproducibility in preparing samples for analysis, with relative standard deviations of 5-10% being common. 

Many hydrazones and azines are colored and useful as dyestuffs. Examples are 2-hydroxynaphthazine, a yellow fluorescent dye (Lumogen LT Bright Yellow), and the pyridon—azino—quinone class of red-violet dyes. Numerous hydrazine derivatives are antioxidants and stabilizers by virtue of their reducing and chelating powers. 

Fluorescent Pigments. The first patents for daylight fluorescent products were issued in 1947 (9,10), describing fluorescent dyed cellulose acetate fabrics with several barrier coats to improve long-term stability. These fabrics were brilliantly fluorescent and were widely used during World War II as signal panels. 

In 1967 spraying with a solution of paraffin wax allowed the recording of the fluorescence spectrum of anthracene directly on the TLC plate without any difficulties [228]. Hellmann too was able to stabilize emissions by the addition of 2% paraffin to the solvent [229]. Low concentrations evidently serve primarily to stabilize the fluorescence — this stabilization concentration extends up to ca... 

Figure 49 shows that porphynns are decomposed in the layer within a few hours if no special measures are taken, but that they can be stabilized for more than 24 hours if the layers are dipped m 50% paraffin solution and stored in the dark. This was true of all six porphynns investigated (Fig. 52). Quantitation should not be undertaken less than an hour after dipping the chromatograms, because it takes so long for the fluorescence emission to stabilize [230].

Fluorescence intensifier Substances Sensitivity increase/ stabilization Remarks/references... 

Hydrophilic liquids can also cause stabilization and amplification of fluorescence Thus, Dunphy et al employed water or ethanol vapor to intensify the emissions of their chromatograms after treatment with 2, 7 dichlorofluorescein [260] Some groups of workers have pointed out that the layer matenal itself can affect the yield of fluorescent energy [261 —263] Thus, polyamide and cellulose layers were employed m addition to silica gel ones [245] The fluorescence yield was generally increased by a factor of 5 to 10 [264], but the increase can reach 100-fold [234, 265]... 

Triton X-100 ethoxyquin (antioxidant in spices) > 200-fold, stabilization > 15 h spray solution, 33% in benzene the fluorescence of aflatoxin Bi is reduced by 10 to 15% [292]. 

Detection and result The chromatogram was freed from mobile phase and dipped for 1 s in solution I and after drying for 1 min in a stream of cold air it was dipped in a solution of liquid paraffin — -hexane (1 + 2) in order to stabilize and increase the intensity of fluorescence by a factor of 1.5—2.5. The derivatives which were pale yellow in daylight after drying fluoresce pale blue to turquoise in long-wave... 

The fluorescence intensity of the chromatogram zones could be stabilized and increased by a factor of 2.5 to 3.5 by subsequent immersion in liquid paraffin — -hexane (1 + 2). 

The chromatogram was then immersed for 1 s in reagent solution II to increase sensitivity and stabilize the fluorescence and then dried in a stream of hot air. 

The chromatogram was then immersed for 1 s in a mixture of liquid paraffin and -hexane (1 -I- 2) to stabilize and enhance the fluorescence (by a factor of ca. 1.5). The detection limits were then ca. 1 ng substance per chromatogram zone. 

Note A 5% solution of polyethylene glycol 4000 in ethanol can be sprayed onto the chromatogram [2, 4] for the purpose of increasing and stabilizing the fluorescence instead of dipping it in liquid paraffin - -hexane (1 - - 2). If this alternative is chosen the plate should not be analyzed for a further 30 min since it is only then that the full intensity of the fluorescence develops [6]. 

The chromatogram is freed from mobile phase (stream of warm air, 15 min), immersed for 2 s in the reagent solution after cooling to room temperature and heated to 110— 120°C for 10—20 min. The chromatogram is then briefly immersed in liquid paraffin — n-hexane (1 + 6) in order to enhance and stabilize the fluorescence. 

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