Fluorescein indicator

Fluorescein indicator. Dissolve 0.2 g in 250 ml ethanol. It is not satisfactory for solns of chloride content of less than 0.005 (such as in drinking water). Solutions 0.025N in chloride may be titrated with dich loro fluorescein as indicator... 

Figure l6-5 Contact lens fluorescein pattern in eye with keratoconus. Central dark area reflects the absence of fluorescein, indicating central contact lens bearing (touch). There is also bearing in the intermediate area, surrounded by peripheral clearance indicated by the pooling of fluorescein. (Courtesy A. Christopher Snyder, O.D.)... 

Figure 9.2 Sequence of fluorescence microscope images describing the mixing dynamics in the 50 pm wide by 20 pm deep channels. Quenching of the fluorescence of a solution of fluorescein indicates complete mixing of the reagents injected at total flow rates ranging between 0.2 and 2pLmin 1 (from a to h). The double amount of fluorescein in the 40 pm deep channel (first 100 pm) compared to that in the 20 pm deep channel is clearly visible in the images, due to the higher fluorescence intensity.

Chloride was done by titration with AgN03 using starch-fluorescein indicator. AgNOj was initially gravimetrically standardized and intercalibration between sample sets checked by titration of standard Long Island Sound sea water that had been sealed in glass ampules (courtesy L. K. Benninger). 

Prepare a 0.1 M silver nitrate solution and a solution which is O.OS M in NaCl and O.OS M in Nal. Pipette 25.0 cm of the mixed halide solution into a conical flask, add 10 drops of fluorescein indicator. Titrate with the silver nitrate solution while rotating the flask in diffuse daylight until the silver halides coagulate and a pink colour develops locally on the addition of the silver solution. Continue the titration until the precipitate suddenly assumes a permanent pink colour. Repeat to obtain concordant results. The titre gives the total halide concentration. Repeat the titration using diiododimethyl-fluorescein as indicator, when the precipitated compound assumes a permanent blue red colour. Repeat to obtain concordant results. The average titre in this case is equivalent to the iodide alone. Work out the difference between the titres using the two indicators, which corresponds to the chloride. Calculate [NaCl] and [Nal] in mol dm. ... 

Fajans method The titration of Cl" with Ag using fluorescein as an adsorption indicator. At the end point the precipitate becomes red. 

Addition of silver nitrate to a solution of a chloride in dilute nitric acid gives a white precipitate of silver chloride, AgCl, soluble in ammonia solution. This test may be used for gravimetric or volumetric estimation of chloride the silver chloride can be filtered off, dried and weighed, or the chloride titrated with standard silver nitrate using potassium chromate(VI) or fluorescein as indicator. 

Silver nitrate is used volumetrically to estimate chloride, bromide, cyanide and thiocyanate ions. Potassium chromate or fluorescein is used as an indicator. 

Analysis. The abiUty of silver ion to form sparingly soluble precipitates with many anions has been appHed to their quantitative deterrnination. Bromide, chloride, iodide, thiocyanate, and borate are determined by the titration of solutions containing these anions using standardized silver nitrate solutions in the presence of a suitable indicator. These titrations use fluorescein, tartrazine, rhodamine 6-G, and phenosafranine as indicators (50). 

Eosin [15086-94-9] (tetrabromofluorescein), C2QHgBi40, made by the bromination of fluorescein, is both a dye and an adsorption indicator. Eosin Y /7 7372-87-17, C2QH Br40 2Na, the disodium salt, is a biological stain. 475 -Dibromofluorescein [596-03-2], C2QH2QBr20, is used in D C Orange No. 

For the titration of chlorides, fluorescein may be used. This indicator is a very weak acid (Ka = ca lx 10-8) hence even a small amount of other acids reduces the already minute ionisation, thus rendering the detection of the end point (which depends essentially upon the adsorption of the free anion) either impossible or difficult to observe. The optimum pH range is between 7 and 10. Dichlorofluorescein is a stronger acid and may be utilised in slightly acid solutions of pH greater than 4.4 this indicator has the further advantage that it is applicable in more dilute solutions. 

Procedure. Pipette 25 mL of the standard OAM sodium chloride into a 250 mL conical flask. Add 10 drops of either fluorescein or dichlorofluorescein indicator, and titrate with the silver nitrate solution in a diffuse light, while rotating the flask constantly. As the end point is approached, the silver chloride coagulates appreciably, and the local development of a pink colour upon the addition of a drop of the silver nitrate solution becomes more and more pronounced. Continue the addition of the silver nitrate solution until the precipitate suddenly assumes a pronounced pink or red colour. Repeat the titration with two other 25 mL portions of the chloride solution. Individual titrations should agree within 0.1 mL. 

Similar remarks apply to the determination of bromides the Mohr titration can be used, and the most suitable adsorption indicator is eosin which can be used in dilute solutions and even in the presence of 0.1 M nitric acid, but in general, acetic (ethanoic) acid solutions are preferred. Fluorescein may be used but is subject to the same limitations as experienced with chlorides [Section 10.77(b)], With eosin indicator, the silver bromide flocculates approximately 1 per cent before the equivalence point and the local development of a red colour becomes more and more pronounced with the addition of silver nitrate solution at the end point the precipitate assumes a magenta colour. 

Figure 5. Guanine-nucleotide-dependent receptor interconversion from LRG" to LR. Penneabilized cells (10 /mL) (no GTPyS 1 ml Mg " ) were allowed to bind FLPEP for 1 min. Data analysis begins with the addition of antibody to fluorescein (after 60 s, but not indicated). At 90 s (indicated), GTPyS is added to induce interconversion to the rapidly dissociating state. The guanine nucleotide concentrations are shown (saturated at 10" If). The solid lines are the fit to the onestep model shown in the inset, and the k for the fit is shown at the end of each solid line. Data...

Labelling Na,K-ATPase with ATP analogues provides evidence for contribution from charged residues that are widely separated in the sequence of a subunit of Na,K-ATPase. The first indication came from ATP sensitive covalent insertion of fluorescein-isothiocyanate (FITC) into Lys ° in the a subunit [90], The strong fluorescence signal provides a convenient probe for monitoring conformational transitions in the proteins. Site-directed mutagenesis of Lys reduces the activity of... 

This observation is supported by experiments carried out with a phosphate buffer and a fluorescein solution for visualization of the mixing process. However, in the experiments there are indications that the critical Reynolds number where the mass transfer enhancement sets in is lower (-7) than predicted by the simulations, a fact which is not well understood. 

Samples used in this work are the binary polymer mixtures with the characteristics illustrated in Table 10.1. Here, PSA and PSAF stand, respectively, for polystyrene labeled with anthracene and polystyrene doubly labeled with anthracene and fluorescein used as a fluorescent marker. On the other hand, PSC and PVME stands respectively for polystyrene labeled with trans-cirmamic acid and poly(vinyl methyl ether). The factor a in Table 10.1 indicates the label content of anthracene in the polystyrene chain in the unit of number of labels per one chain. For PSC, the label content is 1 cinnamic acid per 28 styrene monomers. 

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