Concentrated buffers

Buffer solution, dilute. To one volume of concentrated buffer solution, add five volumes water and adjust the pH to 6.1 by adding acetic acid or sodium hydroxide solution. 

The capacity of a buffer is determined by its concentration and pH. A more concentrated buffer can react with more added acid or base than can a less concentrated one. A buffer solution is generally most effective in the range... 

Before releasing a process column for chromatography, it is advisable to perform some test to measure efficiency, such as calculating height equivalent theoretical plates (HETP), both to forestall any problems in the column bed and to provide a benchmark by which to measure column reproducibility and predict degradation of the bed or material. Examples of compounds that are relatively innocuous for use in pharmaceutical applications are 1% NaCl (for gel filtration), concentrated buffer solutions (for ion exchange), and benzyl alcohol and parabens for reverse phase LC.10... 

Even for experimentally simple systems, a quantitative understanding of the dissolution of ionizable drugs is possible only if drug solubility, drug ionization constant, buffer concentration, buffer species, and buffer pH are known. 

Talsma shows that peak 2 changes only from -39.8 °C to —40.4 °C (liposomes, liposomes concentration, buffer and cooling speed as in (I), but no mannitol) if the liposomes size is decreased from 0.87 pm to 0.14 pm. With small liposomes, the start of the homogeneous crystallization is delayed. This can also be deduced from the weakly performed crystallization (Fig. 3.19 (d), peak 3), if mannitol is only within the liposome. 

As mentioned earlier, the response of each protein will vary. This is especially apparent with colorimetric assays or derivatization methods requiring a chemical reaction. These protein-to-protein reactivity differences mean that a protein assay suitable for one protein may not be suitable for another. Even for a given protein and a specific protein determination method, results may still vary based on limitations of the assay. Methods requiring extensive sample preparation including protein concentration, buffer exchange, and time-sensitive reactions are liable to be less reproducible than direct measurement techniques, which have fewer variable parameters. The application will determine the suitability of the method. 

Examined factors were buffer or electrolyte concentration,buffer or electrolyte pH,7i,73,74 Q). electrolyte ionic strength, " rinse times,capillary temperature,... 

Examined factors were organic solvent concentration, buffer or electrolyte concentration, - - buffer or electrolyte pH,7 7 - T83,85,86 voltage,chiral selector concentration " and supplier, active pharmaceutical ingredient (API) concentration, internal standard concentration, injection time - and pressure, ... 

Examined factors were voltage, buffer or electrolyte concentration, " buffer or electrolyte pH, chiral selector concentration, capillary temperature, detection wavelength and its bandwidth, reference wavelength and its bandwidth, peak width, threshold, data acquisition rate, filter and its peak width, and surfactant... 

An acceptable method quite frequently used in practice depends on the cell whose EMF is being measured having a liquid junction with a constant potential value. Such a situation is attained in the determination of the activity of fluoride ions, by adding a constant amount of quite concentrated buffer, for example TISAB, to the studied solution this buffer also fulfills other functions in the analysis (see p. 146). Then the liquid junction potential is a function of the composition of the reference electrode electrolyte and of the buffer composition alone, and not of the concentrations of the other components of the studied solution. 

The sample-preparation technique may depend on a number of variables, for example the molecular weight of sample and interferences, the sample volume and analyte concentration, buffer salt (anion and cation) content and metal concentration and type. Other than filtration for particulate removal, most of the approaches are based on the use of chromatographic media for cleaning up samples before analysis. 

Fig. 3 Electrophoretic ionic mobilities fj, of propranolol as influenced by BS concentration buffer x mM BS, 20 mM phosphate, pH = 7.4, detection 220 nm m— electrophoretic ionic mobility /r, GC—glycocholic acid, GDC—glycodeoxycholic acid, GCDC—glycochenodeoxycholic acid.

Elemental composition Cr 52.00%, 0 48.00%. The compound may he identified from its dark red color. Other color phases are noted above. Chromium may he measured in the aqueous phase hy AA, ICP or x-ray techniques, or in the solid phase hy x-ray methods. Hexavalent chromium (Cr6+) may he analyzed hy ion chromatography. For this, the aqueous sample is adjusted to pH 9 to 9.5 with a concentrated buffer (ammonium sulfate and ammonium hydroxide mixture) and mixed into the eluent stream of the buffer. Cr " is separated from Cr + on a column, and derivatized with an azide dye as a colored product measured at 530 nm, which is identified from its retention time. (APHA, AWWA, and WEF. 1999. Standard Methods for The Examination of Water and Wastewater, 20th ed., Washington, DC American Public Health Association.)... 

X SSC means the tenfold concentrated buffer. If 10 x SSC was adjusted to pH 7.0, after dilution to working concentration the pH is different to 7.0, but this difference is negligible in most cases. 

TABLE 2. Effects of Polymer Concentration, Buffer Solution pH, and Incubation Temperature on Gel Formation... 

Another key feature of redox thermodynamic cycles is that the free energy change in solution is still defined to involve a gas-phase electron, that is, the solvation free energy of the electron is happily not an issue. And, once again, redox potentials in soludon typically assume 1 M standard states for ad species (but not always in this chapter s case study, for instance, all redox potentials were measured and computed for chloride ion concentrations buffered to 0.001 M). So, free energy changes associated with concentration adjustments must also be properly taken into account. 

A more comprehensive approach was reported in 1975 by Brabander and Verbeke (612). In this method, tissue samples were extracted with methanol and the acidified extract defatted with petroleum ether to be loaded onto a Dowex 50W-X8 anion-exchange resin. Following elution with aqueous methanol, the concentrated buffered extract was further defatted with diethyl ether. The sample was derivatized with 7-chloro-4-nitrobenzo-2-oxa-l,3-diazole (NBD-Cl) to be further spotted on a silica high-performance thin-layer chromatographic plate developed in two dimensions using chloroform/ethanol and chloroform/propionic acid consecutively as eluents. Detection of the propylthiouracil, phenylthiouracil, and tapazole residues was carried out on the basis of the fluorescence induction of the NBD derivatives of the drugs with an alkaline cysteine solution. 

Organic solvents cannot be used to conduct the separation of fragile water soluble compounds such as proteins, because of denaturation. A reversed phase column is equilibrated with a concentrated buffer. Under these conditions, the compounds retained by the stationary phase can be eluted in decreasing order of their hydrophilic character by reducing the concentration of salt in the mobile phase. 

If you use a buffer in the eluent, it must be volatile or else it will evaporate down to solid particles that scatter light and obscure the analyte. Low-concentration buffers made from acetic, formic, or trifluoroacetic acid, ammonium acetate, diammonium phosphate, ammonia, or triethylamine are suitable. Buffers for evaporative light scattering are the same as for mass spectrometric detection. 

A concentrated buffer has a greater capacity than the same volume of a more dilute buffer. 

The reaction of barbiturate and 1,3 -dimethylbarbiturate ions with 2- and 4-nitrobenzaldehyde and 2,4-dinitrobenzaldehyde represented generally in Scheme 5 involves a diffusion-controlled (viscosity effects on rates) proton transfer from hydronium ion to an addition intermediate T in the slow step.14 The addition of water and ring-opening reactions of the protonated benzoxazines (14) involves the cyclic intermediate (15). At low buffer concentrations buffer-catalysed collapse of the intermediate is rate limiting but, at high buffer concentrations, the addition of water is the rate-limiting step.15 The anionic tetrahedral intermediate (16) is involved in the hydrolysis of the 2, 2, 2,-trifluoroethyl monoester of 1,8-naphthalic acid (17).16... 

Sometimes, the use of high-concentration buffers in the reversed-phase mode decreases column life and efficiency. Therefore, the use of an alternative mobile phase (i.e., normal phase) is an advantage in chiral resolution with these buffers. The most commonly used solvents in the normal phase mode are hexane, cyclohexane, and heptane. However, dichloromethane, acetone, propanol, ethyl-acetate, ethanol, and chloroform also have been used as mobile phase solvents. Hargitai and Okamoto [110] used hexane-2-propanol (in different ratios) as the mobile phase in the chiral resolution of several drugs. These authors also studied... 

The concentration of buffer is also a very important aspect in the optimization of the chiral resolution on these CSPs. It has been reported that an increase in buffer concentration caused a decrease in the retention and selectivity for all amino acids except for the basic amino acids. Therefore, the separation of basic amino acids is possible only with the most concentrated buffers. The buffers of concentrations in the 25-50-mM range were used for the chiral resolutions with some exceptions. In spite of this, few reports are available for the optimization of the chiral resolution by varying the ionic strength of the mobile phase. The effect of ionic strength of phosphate buffer on the chiral resolution of serine was carried out by Gubitz and Jellen [18] and the best resolution was achieved at 0.01 M concentration (Fig. 7). In another study, the concentration of ammonium acetate (0.001-0.01 M) was varied to optimize the chiral resolution of amino acids [19]. The effect of the concentration of ammonium acetate on the chiral resolution of amino... 

Berzas Nevado et al. [138] developed a new capillary zone electrophoresis method for the separation of omeprazole enantiomers. Methyl-/ -cyclodextrin was chosen as the chiral selector, and several parameters, such as cyclodextrin structure and concentration, buffer concentration, pH, and capillary temperature were investigated to optimize separation and run times. Analysis time, shorter than 8 min was found using a background electrolyte solution consisting of 40 mM phosphate buffer adjusted to pH 2.2, 30 mM /1-cyclodextrin and 5 mM sodium disulfide, hydrodynamic injection, and 15 kV separation voltage. Detection limits were evaluated on the basis of baseline noise and were established 0.31 mg/1 for the omeprazole enantiomers. The method was applied to pharmaceutical preparations with recoveries between 84% and 104% of the labeled contents. 

The key operational parameter in free-solution capillary electrophoresis is the pH of the running buffer, as the electroosmotic flow and ionization of the analyte can be regulated by this variable. The role of buffers in capillary electrophoresis has been discussed in detail, with emphasis on buffer concentration, buffer type, and pH effects [10]. The effect of organic solvents on separation and migration behavior has been studied for dipeptides [11] and somatostatin analog peptides [12]. The order of migration as well as the selectivity may be manipulated by organic modifiers in... 

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