Good buffers

FIGURE 2.18 The pAT,values and pH range of some good buffers. 

Presume that a yield of 20 g F1 of L-phenylalanine can be obtained. This is more realistic, based on patent literature, than the low yields in the example considered previously (section 8.6). This automatically means that more glucose will be needed. Let us again presume that instead of 35 g P glucose we now need 150 g l 1 to achieve this overall yield. The concentrations of the mineral salt are kept fire same to maintain good buffering capadty, whilst the concentration of tyrosine and tryptophan are also increased by a factor 4.3 (tyrosine 0.21 g F1 and tryptophan 0.11 g F1)... 

Borax is a good buffer, helping to stabilize the acidity or alkalinity of a solution. 

Fig. 3.3 Solubility profiles of sparingly soluble drugs, based on data taken from Avdeef et al. [20]. The solutions consisted of robotically adjusted universal buffers, based on a mixture of Good buffers (see text), and contained 0.2 M KCl. The dashed lines were calculated by the Henderson-Hasselbalch equation and, as can be seen, did not accurately describe the solubility profiles. The solid curves were...

Mash, H., Chin, Y., Sigg, L., Hari, R., and Xue, H., Complexation of copper by zwitterionic aminosul-fonic (good) buffers, Anal Chem, 75 (3), 671-677, 2003. 

Because standardization is an essential component of soil pH measurement, care must be taken to have good buffers. If the buffers show any indication of contamination, such as material floating in them, soil, or microbial growth, they... 

The silanol induced peak tailing is also a function of the pH of the mobile phase. It is much less pronounced at acidic pH than at neutral pH. Therefore many of the older HPLC methods use acidified mobile phases. However, pH is an important and very valuable tool in methods development. The selectivity of a separation of ionizable compounds is best adjusted by a manipulation of the pH value. The retention factor of the non-ionized form of an analyte is often by a factor of 30 larger than the one of the ionized form, and it can be adjusted to any value in between by careful control of the mobile phase pH. This control must include a good buffering capacity of the buffer to avoid random fluctuations of retention times. 

The pK value indicates the pH range in which the dissociation of the H" occurs. More specifically, the pK is the pH at which the group is 50% dissociated, or half of it is in the acid form and half in the base form. These values of pK are used in determining the net charge a substance (amino acid, protein, drug) will have in the body and which ones will act as good buffers to keep the pH constant, and to understand pathologic states of acidosis and alkalosis. 

BBS is a good buffer for storing antibodies because of its bacteriostatic qualities. Care must, however, be taken when adding antibodies in BBS to living cells so that the final volume of BBS added does not exceed 10%. 

Figure I-I. Weak acids act as buffers in a pH range near their pK s. According to the Henderson-Hasselbalch equation, when the ratio of conjugate base to conjugate acid, [A ]/[HA] is plotted versus pH, a titration curve is generated that indicates a region of good buffering at pH = pK I pH unit.

Titration curves of PAA rise only slowly with increasing neutralization. Because of this, partial salts of PAA are good buffers in the pH range of 4 to 6.4. PAA is difficult to titrate because equilibrium is only slowly established (4). 

Regarding the UV assay, excessive absorption may be encountered in certain cases. For example, the Good buffers PIPES and HEPES absorb substantially at 234 nm. The optional use of a 9-mm optically transparent quartz spacer inserted into a 1-cm cuvette gives a 10-fold advantage with solutions of high UV absorbance. The spacer also serves as a convenient mixer, whereas mixing is difficult with specialized 1-mm cuvettes. 

In the range of pH exhibited by most natural water and in the concentration range greater than millimolar few metal ions exist as simple hydrated cations, and relatively few oxyanions exist as simple monomeric species. The hydrated cations are good buffers toward bases, the metallate ions toward acids. As pH is raised in solutions of many hydrated cations, isopolycations are produced, and ultimately, hydrous metal oxides precipitate. As pH is lowered in solutions of many metallate ions, isopolyanions are produced, and ultimately, hydrous oxides precipitate. Salts of the intermediate isopolyions precipitate in some cases. Where the results are unambiguous, the nature of the intermediate species can be described. Kinetics are thought to have been neglected in studies of such solutions up to the present time. 

In this way, the running buffer solution plays an important role for electrophoresis separations in microchips. The main properties that have to be taken into account are a good buffering capacity in the pH range of choice and low mobility, which means minimally charged ions and low ionic strength in order to minimise current generation. 

As substrate, rather thick and rapid paper is required, such as Whatman 3 MM, because such paper compensates easily for evaporation due to heating, thanks to a relatively small surface combined with a good buffer speed. 

Several polycations with a good buffering capacity below physiological pH, such as lipopolyamines and polyamidoamine polymers, have proved to be efficient transfection agents (Boussif et al., 1995). Two of the most popular methods based on polycations are discussed below diethylami-noethyl-dextran (DEAE-dextran) and polyethylenimine (PEI). 

At what pH values would glutamate be a good buffer ... 

They maintain the pH control for all systems. This is particularly true for the amino acid and protein molecules or zwitter ions which are good buffers . 

The effectiveness of a sand wall was not unique it varied with the source of the explosion and its direction, but it was generally a good buffer except in the direction of the door. Of the horizontal and vertically receiving room, the former was higher in noise and sonic pressure and was the highest by about 5dB in the direction of the door. 

Lysozyme shows a high buffer capacity in the acidic region around pH 5 and has almost no buffer function above pH 10. It appears that this lowest point is around the isoelectric point of lysozyme, which is reported to be about pH 11 (22], Ribonuclease has a good buffer function in the acidic region around pH 5... 

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