Buffer strength

A model of blending aqueous salt buffers for chromatography has been developed.1 The model assumed full miscibility, low mixing enthalpy and low volume change. It reproduced experimental S-curves of buffer strength produced by a Pharmacia P3500 dual piston system equipped with a model 24 V dynamic mixer with 0.6 mL internal volume as well as those produced by a BioSepra ProSys 4-piston system equipped with two dynamic mixers of 1.2 mL internal volume. 

The development of biological tools to support DDI studies has paralleled the development of bioanalytical techniques. To better understand in vitro-in vivo (IVIV) correlations, the effects of differences in enzyme preparations and incubation conditions must be understood. Differences between enzyme preparations include nonspecific binding, the ratio of accessory proteins (cytochrome b5 and reductase) to CYPs and genetic variability differences in incubation conditions include buffer strength, the presence of inorganic cations and solvent effects. Understanding how biology influences enzymatic activity is crucial to accurate and consistent prediction of the inhibition potential. 

Acids and bases are used to increase ionisation by protonation or deprotonation of the analyte, and it is important to choose the buffer and buffer strength very carefully because both have a noticeable effect on sensitivity. In the positive mode, high PA additives such as triethylamine (TEA) will successfully compete with the analyte for available protons and show an intense ion at miz 102. Sensitivity can drop substantially when TEA is buffered with trifluroacetic acid (TFA). This is shown in Figure 6.3. The top diagram shows the mass spectrum of a compound analysed using acetonitrile/H20/TFA as the eluent and shows MH at mIz 511. The mass spectram of the same compound when analysed using... 

Buffer strength EOF decreases with increasing buffer strength... 

Equations 16-9 and 16-10 are analogous to the Henderson-Hasselbalch equation of acid-base buffers. Prior to the equivalence point, the redox titration is buffered to a potential near E+ = formal potential for Fc 1 Fe2+ by the presence of Fe 1 and Fe2+. After the equivalence point, the reaction is buffered to a potential near E+ = formal potential for Ce4+ Ce3+. [R. de Levie Redox Buffer Strength, J. Chem. Ed. 1999, 76, 574.]... 

Gadiraju, R. R., R. I. Poust, and H. S. Fluang. 1995. The effect of buffer species, pH and buffer strength on the CMC and solubility of amiodarone HCI, Poster presentation (AAPS annual meeting). 

Less than 1% of the applied coagulant activity is recovered in fraction Nos. 1, 2, 3, 4. Fraction 1 however possesses proteolytic activtity which in concentrated solutions would dissolve fibrin clots. The thrombin-like activity is eluted from these columns in significant amounts at a buffer strength of 0.04 M or greater. 

J L 11 4. Sample-column interaction. 4. Change buffer strength, pH, or... 

Standardized assay conditions across all CYP enzymes are recommended because buffer strength, composition, and pH can affect enzyme kinetics. 

Fig. 3. Effect of increasing concentrations of phosphate buffer, pH 7.0, on the adsorption of antibody-bound steroid. pH]Testosterone was incubated with antibody without added unlabeled testosterone. Hydroxyapatite suspensions in phosphate buffers of different molarities were added tubes were shaken and centrifuged, and the supernatants were counted. Phosphate buffer strengths recorded are the final concentrations after addition of the hydroxyapatite suspension.

Introduced in 1943, ED remains the most frequently used procedure. A membrane separates two compartments, and at equilibrium, one compartment contains the plasma or serum with protein and bound ligand, whereas free drug is sequestered to the buffer solution compartment. The unbound fraction is determined by the ratio of drug concentration on the buffer side [D] divided by that in the plasma P] -I- PP]. Results are influenced by drug properties, proteins (content and concentration), volume of compartments, buffer strength, and ionic composition as well as by the thickness and physicochemical characteristics of the membrane. Time and temperature are major environmental factors, and dialysis for 4h (or less) at 37°C has been found optimal for acidic and basic drugs. ... 

Subsequent to the selection of an appropriate column various characteristics of the buflFer were examined. Both pH and buffer strength were varied and retention time was measured. The results are presented in Table II. Generally it was found that a decrease in buffer strength or an... 

Lee RJ et al (1998) The effects of pH and intraliposomal buffer strength on the rate of liposome content release and intracellular drug delivery. Biosci Rep 18 69-78... 

Poochikian and Cradock used acetonitrile - aqueous phosphate buffers in combination with octadecyl columns for the analysis of heroin and its hydrolysis products. The retention times were found to be shorter with increasing percentages of acetonitrile and with more strongly buffered mobile phases. Also, the peak sharpness increased under such conditions. Optimum pH was between 5 and 8.7. The order of elution was not effected by changes in pH, buffer strength, or percentage of acetonitrile in the mobile phase. As well as mobile phases consisting of acetonitrile and aqueous buffers, phases in which acetonitrile has been replaced by methanol have been used in combination with octadecyl... 

If a separation is to be developed, a good starting buffer strength is 50 mM. It should not be lower than 20 ruM because otherwise an effective buffering is not guaranteed. The salts used should be of high purity. 

In general, the buffer species and the buffer strength will influence the rate of deamidation. High solvent dielectrics favor deamidation. 

There are large numbers of assay methods differing from one another in types of substrates employed, substrate concentrations, buffer types, buffer strengths, pH values, and temperatures of incubation. Some methods have been officially recommended by national institutes (Gll, S7) and the entire subject is reviewed in detail in a recent book (Mc3). 

The effect of buffer strength on the rate of hydrolysis was also examined. From the pH/selectivity determination, it was clear that pH control is essential to obtain good selectivity, especially during scale-up. The sensitivity of the process to deviations in pH could be decreased by the use of very concentrated buffers. From the results in Tab. 4, it is apparent that the rate of hydrolysis also decreases at very high buffer concentrations, possibly due to the decreased solubility of the substrate at high salt concentrations or inactivation of the enzyme. Based on these results, a buffer strength of 0.3 M was selected for scale-up of the process. 

As we have seen in section 4.3, the pH of a sample being titrated usually changes rapidly near the equivalence point, and much less so before and after that point. In section 4.5 we paid attention to the steep part of the curve, but we can also exploit its shallow parts, where the pH appears to resist change. A quantitative expression of such pH-stabilizing buffer action is the buffer strength, which is denoted by the symbol B, and is given by... 

The buffer strength for the aqueous solution of a single monoprotic acid and its conjugate base follows from (4.7-1) as... 

Fora mixture of monoprotic acids or bases, the buffer strength is... 

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