Rhodamine concentration

At low rhodamine concentrations, the rate of diffusion into the hair shaft was sufficiently slow to monitor. A cross section of Caucasian hair exposed to rhodamine at 1 pg/mL is shown in Figure 16. As exposure time was increased, more rhodamine reached the interior of the hair. At 120 min, even though the surface was much brighter than the interior, substantial fluorescence was observed in the interior when compared with unexposed hair or to the 30-min exposure. At a rhodamine exposure of 10 pg/mL for 2 h the rhodamine had penetrated throughout the hair sample (Figure 16). 

In Figure 5, observed (31) and computed Rhodamine concentration profiles are compared for a lateral discharge. The agreement bet>veen these data is satisfactory and shovv s the validity of the model for conservative constituents (Equations 1-3). 

Figure 5 Fluorescence signal from cuvettes with constant concentration of gold nanopaiticles but altering concentration of tetramethyl-Rhodamine. Assuming that one Rhodamine molecule occupies an area of-1 nm one can calculate the surface coverage for each concentration. Below 100 % surhice coverage the fluorescence is quenched, while above the fluorescence intensity increases linearly with Rhodamine concentration.

Organic Dye Lasers. Organic dye lasers represent the only weU-developed laser type in which the active medium is a Hquid (39,40). The laser materials are dyestuffs, of which a common example is rhodamine 6G [989-38-8]. The dye is dissolved in very low concentration in a solvent such as methyl alcohol [67-56-17, CH OH. Only small amounts of dye are needed to produce a considerable effect on the optical properties of the solution. 

A high concentration of the fluorescent dye itself in a solvent or matrix causes concentration quenching. Rhodamine dyes exhibit appreciable concentration quenching above 1.0%. Yellow dyes, on the other hand, can be carried to 5 or even 10% in a suitable matrix before an excessive dulling effect, characteristic of this type of quenching, occurs. Dimerization of some dyes, particularly those with ionic charges on the molecules, can produce nonfluorescent species. 

Dissolve the purified SPDP-modified dendrimer of step 5 in 50 mM sodium phosphate, 0.15M NaCl, pH 7.5, or in DMSO at a concentration of at least lOmg/ml. Add a 10-20 X molar excess of an amine-reactive fluorescent molecule (i.e., NHS-rhodamine or a hydrophilic NHS-Cy5 derivative see section on fluorescent probes). React with mixing for 1 hour at room temperature. Purify the fluorescently labeled SPDP-modified dendrimer using gel filtration or ultrafiltration. Follow the method of either step 7 or 8 to conjugate the dendrimer to another protein or molecule. 

NHS-rhodamine is insoluble directly in aqueous solution and should be dissolved in organic solvent prior to addition of a small aliquot to a buffered reaction medium. Concentrated stock solutions may be prepared in DMSO or DMF. Such solutions are relatively stable for short... 

Dissolve NHS-rhodamine at a concentration of 1 mg/ml in DMSO. Protect from light. 

Dissolve Lissamine rhodamine B sulfonyl chloride (Invitrogen) in DMF at a concentration of l-2mg/ml. Protect from light and use immediately. 

Lissamine rhodamine B sulfonyl hydrazine is soluble in DMF. The reagent may be dissolved in this solvent as a concentrated stock solution before adding a small aliquot to an aqueous reaction medium. The compound itself and all solutions made with it should be protected from light to avoid decomposition of its fluorescent properties. 

Leung et al. [ 104] and Kim and Zeitlin [105] described a method for the separation and determination of uranium in seawater. Thoric hydroxide (Th(OH)4) was used as a collector. The final uranium concentration was measured via the fluorescence (at 575 nm) of its Rhodamine B complex. The detection limit was about 200 jLg/l. 

Fig. 18.8 SERS detection in LC ARROW, (a) Top view of experimental beam geometry excitat ing rhodamine 6G molecules bound to silver nanoparticles (leyLC) excitation beam, 1R Raman signals) (b) R6G concentration dependent SERS power for three representative Raman peaks PI P3, inset spectra at various excitation powers...

To evaluate linearity, limits of detection (LOD), limits of quantitation (LOQ), and sensitivity, an experiment assessed the responses for different concentrations of two analytes of interest. The analytes employed were methyl paraben and rhodamine 110 chloride. Consecutive 5.0 /jL injections of a series of serial dilutions (four replicates) of this standard mixture containing the analytes described were carried out via a cartridge packed with C18 stationary phase and per-column dimensions of 0.5 mm circular cross section and 80 mm length. 

LOD is defined as the lowest concentration of an analyte that produces a signal above the background signal. LOQ is defined as the minimum amount of analyte that can be reported through quantitation. For these evaluations, a 3 x signal-to-noise ratio (S/N) value was employed for the LOD and a 10 x S/N was used to evaluate LOQ. The %RSD for the LOD had to be less than 20% and for LOQ had to be less than 10%. Table 6.2 lists the parameters for the LOD and LOQ for methyl paraben and rhodamine 110 chloride under the conditions employed. It is important to note that the LOD and LOQ values were dependent upon the physicochemical properties of the analytes (molar absorptivity, quantum yield, etc.), methods employed (wavelengths employed for detection, mobile phases, etc.), and instrumental parameters. For example, the molar absorptivity of methyl paraben at 254 nm was determined to be approximately 9000 mol/L/cm and a similar result could be expected for analytes with similar molar absorptivity values when the exact methods and instrumental parameters were used. In the case of fluorescence detection, for most applications in which the analytes of interest have been tagged with tetramethylrhodamine (TAMRA), the LOD is usually about 1 nM. 

FIGURE 6.23 Standard calibration curve obtained for rhodamine 110 chloride. Peak area values represent average value for four replicates. Error bars represent + one standard deviation (%RSD is very small error bars may not be visible at all concentration values). 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

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