Buffer solutions useful mixtures

This paper reports the results so far on tests of the usefulness of the programme imder more realistic conditions. The first phase involved spiking aqueous buffer solutions with mixtures of different activities of Sr-85, Sr-89 and Sr-90+Y-90. Y(OH)3 was then precipitated from these solutions to remove Y-90. The Sr nuclides were then concentrated by precipitating SrCOs. The SrCOs was dissolved and transferred to a scintillation vial, mixed with the usual cocktail and tracers then measured by LSC. Here, Sr losses are expected, spurious cross-contaminations in the laboratory are possible, and Y-90 grows in during the analysis and measurement procedure. In a second test phase, the laboratory participated in an interlaboratory comparison with raw milk spiked with Sr-89 and Sr-90 as well as potentially interfering nuclides 1-131, Ba-133, Cs-134 and Cs-137. A known activity of Sr-85 tracer was added directly to aliquots of sub-samples of the raw milk prior to radiochemical separation and preparation for LSC by a rapid method ll... 

The elution order for neutral species in MEKC depends on the extent to which they partition into the micelles. Hydrophilic neutrals are insoluble in the micelle s hydrophobic inner environment and elute as a single band as they would in CZE. Neutral solutes that are extremely hydrophobic are completely soluble in the micelle, eluting with the micelles as a single band. Those neutral species that exist in a partition equilibrium between the buffer solution and the micelles elute between the completely hydrophilic and completely hydrophobic neutrals. Those neutral species favoring the buffer solution elute before those favoring the micelles. Micellar electrokinetic chromatography has been used to separate a wide variety of samples, including mixtures of pharmaceutical compounds, vitamins, and explosives. 

Calcium Chloride [25]. Calcium chloride estimation is based on calcium titration. To 20 ml of 1 1 mixture of toluene (xylene) isopropyl alcohol, add a 1-ml (or 0.1-ml, if calcium is high) sample of oil-base mud, while stirring. Dilute the mixture with 75 to 100 ml of distilled water. Add 2 ml of hardness buffer solution and 10 to 15 drops of hardness indicator solution. Titrate mixture with standard versenate solution until the color changes from wine-red to blue. If common standard versenate solution (1 ml = 20 g calcium ions) is used, then... 

Buffer solution. Add 55 mL of concentrated hydrochloric acid to 400 mL de-ionised water and mix thoroughly. Slowly pour 310 mL of redistilled monoethanolamine with stirring into the mixture and cool to room temperature (Note 2). Titrate 50.0 mL of the standard magnesium chloride solution with standard (0.01M) EDTA solution using 1 mL of the monoethanolamine-hydrochloric acid solution as the buffer and solochrome black as the indicator. Add 50.0 mL of the magnesium chloride solution to the volume of EDTA solution required to complex the magnesium exactly (as determined in the last titration), pour the mixture into the monoethanolamine-hydrochloric acid solution, and mix well. Dilute to 1 litre (Note 3). 

Reduction by sodium dithionite. A small amount of sodium dithionite, solid or in solution, is added to a luciferase solution made with 50 mM phosphate, pH 7.0, containing 50 pM FMN. The amount of dithionite used should be minimal but sufficient to remove oxygen in the solution and to fully reduce the flavin. The solution made is injected into an air-equilibrated buffer solution containing a long-chain aldehyde and luciferase to initiate the luminescence reaction. With this method, the reaction mixture will be contaminated by bisulfite and bisulfate ions derived from dithionite. 

The mobile phase is interesting in that the water is buffered appropriately to complement the dissociation constants of the solutes. A mixture of methanol and acetonitrile is employed, the acetonitrile being used to increase the dispersive interactions in the mobile phase. The reason for the particular solvent mixture is not clear and it would appear that the separation might be achieved equally well by using a stronger solution of methanol alone or a more dilute solution acetonitrile alone. There is no particular advantage to one solvent mixture over another except for the fact that waste acetonitrile produces greater solvent disposal problems than methanol. 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

IC-0 residue is cleaned up with a mixture of dichloromethane and acetone by liquid-liquid partitioning under neutral conditions and then extracted into diethyl ether under acidic conditions. The diethyl ether in the extract is removed by rotary evaporation and the residue is dissolved in buffer solution, which is subjected to a cleanup procedure using a Sep-Pak Cig Env. column. 

A 10 mM ionic strength universal buffer mixture, consisting of Good zwitterio-nic buffers, [174] and other components (but free of phosphate and boric acid), is used in the pION apparatus [116,556], The 5-pKa mixture produces a linear response to the addition of base titrant in the pH 3-10 interval, as indicated in Fig. 7.53. The robotic system uses the universal buffer solution for all applications, automatically adjusting the pH with the addition of a standardized KOH solution. The robotic system uses a built-in titrator to standardize the pH mapping operation. 

Gelsema, W. J. de Ligny, C. L. Remijnse, A. G. Blijleven, H. A., pH-measurements in alcohol-water mixtures, using aqueous standard buffer solutions for calibration, Reel. Trav. Chim. Pays-Bas 85, 647-660 (1966). 

Catalytic hydrogenations were performed generally under 500 psig of H2 at 25 or 80 °C in H20 or 1 1 H20/EtOH media, typically with a total volume of 5 mL the substrates were essentially insoluble in water, but dissolved readily in the mixed medium. H20/NaOH and H20/buffer imply, respectively, use of a 1 1 mixture of the Ru catalyst solution with either 5.0 mM aq. NaOH or a pH 10 buffer solution (made from 44 mM NaHC03 and 17.6 mM NaOH (19)). Catalyst concentrations were either 4.1 or 2.05 mM, while the substrate (S) concentration was always 100 mM. The reaction mixture was placed into a glass sleeve equipped with a magnetic stir bar in air. The sleeve was placed in a steel... 

It is difficult in practice to use ec reduction as a method of detection in hplc. Oxygen is very easily reduced, and if it is present in the mobile phase it will create a background current thousands of times larger than the current due to the solutes. To prevent this, oxygen would have to be very carefully removed. This can be done, but it certainly is not easy in practice. So most of the ec applications are oxidations. Another important consideration with ec detectors is that the mobile phase used must have fairly high conductance, so they are used with aqueous-organic mixtures containing added salts, or with buffer solutions. 

Byeon et al. [23] described a fluorimetric method for (z>)-penicillamine using 9-fluorenylmethyl pentafluorophenyl carbonate and acetonitrile. Capsules containing penicillamine were extracted with water and then filtered. The solution was incubated at 70 °C for 40 min with borate buffer solution. After cooling, the mixture was extracted with diethyl ether and the fluorescence of the aqueous phase measured at (excitation = 260 nm, emission = 313 nm). The calibration graph was linear for 0.4-5.0 pM of penicillamine with a coefficient of variation of 0.4%. 

Merino-Merino et al. [32] used the OPA reagent (o-phthaldehyde condensed with 2-mercaptoethanol) to separate penicillamine enantiomers after their derivatization. Racemic and (/q-penicillamine were dissolved in aqueous 0.5 M NaOH, and treated with the derivatizing solution (methanolic o-phthaldehyde and 2-mercaptoethanol in 0.4 M potassium borate buffer solution of pH 10). The reaction mixture was set aside for 2 min at room temperture, whereupon a portion of solution was analyzed by HPLC. The method used a Cyclobond column (25 cm x 4.6 mm) maintained at 5 °C, a mobile phase of ethanol/1% triethylammonium acetate (1 1 pH 4.5) eluted at... 

As mentioned previously for KLH, DMSO may be used to solubilize hapten molecules that are rather insoluble in aqueous environments. Conjugation reactions may be done in solvent/ aqueous phase mixtures to maintain some solubility of the hapten once it is added to a buffered solution. BSA remains soluble in the presence of up to 35 percent DMSO, becomes slightly cloudy at 40 percent, and precipitates at 45 percent (v/v). 

Various chromogenic reagents have been used for the spectrophotometric determination of boron in seawater. These include curcumin [108,109], nile blue [110], and more recently 3,5 di-tert butylcatechol and ethyl violet [111]. Uppstroem [108] added anhydrous acetic acid (1 ml) and propionic anhydride (3 ml) to the aqueous sample (0.5 ml) containing up to 5 mg of boron per litre as H3BO3 in a polyethylene beaker. After mixing and the dropwise addition of oxalyl chloride (0.25 ml) to catalyse the removal of water, the mixture is set aside for 15-30 minutes and cooled to room temperature. Subsequently, concentrated sulfuric-anhydrous acetic acid (1 1) (3 ml) and curcumin reagent (125 mg curcumin in 100 ml anhydrous acetic acid) (3 ml) are added, and the mixed solution is set aside for at least 30 minutes. Finally 20 ml standard buffer solution (90 ml of 96% ethanol, 180 g ammonium acetate - to destroy excess of protonated curcumin - and 135 ml anhydrous acetic acid diluted to 1 litre... 

Pilnik and coworkers163 used the value of specific viscosity rjs expressed as i)s = (t — tb)ltb, where t is the flow time of the reaction mixture, and tb, the flow time of the buffer solution. The activity is determined graphically, by plotting reciprocal specific viscosities against reaction time. The slopes of the straight lines resulting provide the values of the activity. 

Liposphere formulations are prepared by solvent or melt processes. In the melt method, the active agent is dissolved or dispersed in the melted solid carrier (i.e., tristearin or polycaprolactone) and a hot buffer solution is added at once, along with the phospholipid powder. The hot mixture is homogenized for about 2 to 5 min, using a homogenizer or ultrasound probe, after which a uniform emulsion is obtained. The milky formulation is then rapidly cooled down to about 20°C by immersing the formulation flask in a dry ice-acetone bath, while homogenization is continued to yield a uniform dispersion of lipospheres. 

Mixtures of methanol or acetonitrile with either phosphate, TRIS or MES (Table 4.23) buffer solutions are the most frequently used, but many others are being investigated. The higher above 4 the buffer pH is, the greater the EOF generated and the faster the separation. The composition of the mobile phase can have dramatic effects on both the EOF and the selectivity of the separation via the sorption processes with the stationary phase. 

Talsma et al. [1.34] described the freezing behavior of certain liposomes by DSC measurements. Besides the expected influences of freezing and rewarming speeds, and of the CPAs (mannitol and mannitol in Tris-buffer solutions) it was shown, that the heterogeneous and homogeneous crystallization in mannitol solutions exists and the nucleation of ice depends also on the liposome size In small liposomes (e. g. 0.14 pm) mannitol suppressed the heterogeneous crystallization more effectively than in large (0.87 pm) liposomes. If in certain substances no crystallization or eutectic mixtures can be found by DSC (cephalosporin, Williams [1.35]) with the used experimental conditions, one has to seek different conditions [1.32]. 

The tetracyclines are well known for their ability to form complexes with polyvalent cations. This property changes their solubility characteristics in the mobile solvents and often results in troublesome streaking. To overcome this difficulty, Selzer and Wright used paper dipped in Mcllvaine s buffer (pH 3.5) which contains citrate ions capable of binding the metallic ions. The chromatograms were developed with a mixture of nitromethane, chloroform, and pyridine (20 10 3) on paper still damp from the treatment with the buffer solution. 

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