Low buffering capacity

Microbial activity, which is often stimulated during bioremediation projects, can alter the external pH. For instance, the anaerobic degradation of chlorinated compounds produces organic acids and HC1 and the pH may drop to acidic values if the soil has a low buffering capacity. In this case, control of the external pH will be required in order to maintain biodegradation activity at... 

To test the robustness of the formulation to variations in gastric pH, dissolution results should be obtained in both the pH 2 medium described in Table 3 and a model which reflects the conditions in the hypochlohydric stomach. A good choice would be acetate buffer adjusted to pH 5 and having a very low buffer capacity, since hypochlorhydria is generated by a reduction in HCl secretion rather than the addition of buffer species. 

Under semidry electrotransfer conditions, some low-molecular weight proteins are driven through the membranes, and because low buffer capacity limits run times, some high-molecular weight proteins are poorly transferred. 

The difference in the conductivity of the calibration buffers and sample can cause a very large error on the sample measurement, due to junction potentials in different environments. Solid samples should be dissolved in purified water. It is necessary that the water be carbon dioxide-free. The presence of dissolved carbon dioxide will cause significant bias in the measurement of samples with low buffering capacity. For pH measurements with an accuracy of 0.01 to 0.1 pH unit, the limiting factor is often the electrochemical system (i.e., the characteristics of the electrodes and the solution in which they are immersed). 

The low buffer capacities of the KHPh solution in solvents of aptotic nature is caused by the increase in the (pKa2-pKai) value of phthalic acid. In H20-DMF and H20-DMS0 mixtures, the buffer capacity of 0.05 mol kg-1 KHPh is not enough if the water content is less than 30v/v% [18]. 

Streams flowing over soil with low buffering capacity are equally as susceptible to damage from acid rain as lakes are. Approximately 580 of the streams m the Mid-Atlantic Coastal Plain are acidic primarily due to acidic deposition. The New Jersey Pine Barrens area endures the highest rate of acidic streams in the nation with over 90 percent of the streams acidic. Over 1,350 of the streams in the Mid-Atlantic Highlands (mid-Appalachia) are acidic, primarily due to acidic deposition. Many streams in that area have already experienced trout losses due to the rising acidity. 

Buffer Capacity and pH The normal pH of the tear fluid is 7.4. Ocular formulations should ideally be formulated between pH 7.0 and 7.7 to avoid irritation of the eye [31], However, in most cases the pH necessary for maximal solubility or stability of the drug is well outside this range. The tear fluid has only a limited buffering capacity, which is mainly due to the dissolved carbon dioxide and bicarbonate. It is therefore recommended to formulate using buffers with a low buffering capacity to allow the tears to regain their normal pH more rapidly [31],... 

Preparing the sol is basically a matter beyond electrokinetics, but it should be noted that, particularly for microelectrophoresis (see below), the sols have to be stable and very dilute. Strong dilution implies a low area to liquid volume ratio and hence a low buffering capacity against Impurities that may be introduced inadvertently upon diluting the sol. Obviously, pH and electrolyte concentration should be controlled. The pH may not only affect the surface... 

Furosemide injection may be administered by slow IV injection or by intermittent or continuous IV infusion at a rate not exceeding 4 mL/min. Therefore, the question arises whether photoprotection of the drug reservoir is necessary during parenteral administration. Furosemide injection contains the sodium salt of furosemide formed in situ by the addition of sodium hydroxide during the manufacturing process. The injection solution has a pH of 8 to 9.3. In use, it can be mixed with weakly alkaline and neutral infusion solutions (e.g., 0.9% sodium chloride or Ringer s solution) or with some weakly acidic solutions having a low buffer capacity (e.g., dextrose 5% in water). 

As discussed earlier, the pH of the rectal fluid can have a marked effect on the absorption of drugs from the rectum. Since the rectal fluid has a relatively low buffering capacity and the volume of the rectal fluid is small, it might be expected that the contents of the rectal dosage form largely control the pH of the rectum during administration. On this basis, one may be able to utilize the pH characteristics of the drug and incorporate suitable buffers and other excipients in the... 

Voltammetry has also been made in (toluene)3tetrabutylammonium tetrafluorobo-rate the resistance of the solution is between that of DMF and THF [435] but closer to that of DMF. On addition of proton donors, a low "buffer capacity of the solvent is observed. 

Folic acid [LXVII R = NHC6H4CONHCH(COOH)(CH2)2COOH] is in the first step reduced as LXVII (R = H) in acidic solution 7,8-dihydrofolic acid is reduced with cleavage of the C-9/N-10 bond to LXIX (R = H) [365]. Besides the electrochemical cleavage, a nonelectrochemical cleavage with loss of the 4-aminobenzoylglutamate side chain from the 5,8-dihydrofolic acid has been observed [368]. In neutral medium with low buffer capacity, it is possible to reduce 7,8-dihydrofolic acid to the 5,6,7,8-tetrahydrofolic acid [369]. 

Buffer solutions are widely used in pharmacy to adjust the pH of aqueous solutions to that required for maximum stability or that needed for optimum physiological effect. Solutions for application to delicate tissues, particularly the eye, should also be formulated at a pH not too far removed from that of the appropriate tissue fluid, as otherwise irritation may be caused on administration. The pH of tears lies between 7 and 8, with an average value of 7.4. Fortunately, the buffer capacity of tears is high and, provided that the solutions to be administered have a low buffer capacity, a reasonably wide range of pH may be tolerated, although there is a difference in the... 

Tears have some buffering capacity so, as we noted before, the pH-partition hypothesis has to be applied with some circumspection. The acid neutralising power of the tears when 0.1 cm of a 1% solution of a dmg is instilled into the eye is approximately equivalent to 10 fjL of a 0.01 mol dm strong base. The pH for either maximum solubility (see Chapter 5) or maximum stability (see Chapter 4) of a dmg may well be below the optimum in relation to acceptability and activity. Under these conditions it is possible to use a buffer with a low buffering capacity to maintain a low pH adequate to prevent change in pH due to alkalinity of glass or carbon dioxide ingress from the air. When such drops are instilled into the eye the tears will participate in a fairly rapid remm to normal pH. 

The first studies of carrier ampholytes were conducted using amino acids and dipeptides, but these species did not work well because their pK values for the amino and carboxylate groups are too far removed from their pi values. After they were prefocused, these species had very low buffering capacity. Good... 

Pyridine, followed by water, extracted more humic substances than did the DMF, DMSO, or sulfolane systems (Table 4). The enhanced solubilization by pyridine could be attributed partially to a pH effect. When pyridine (eight parts) was diluted with water (one part) to simulate the composition of the solvent in the air-dried soil, the pH of the mixture was 11.6. Because of the low buffering capacity of the solvent system, the pH of the extract was only 4.2 (Swift, 1968). Theory suggests that substantially more humic materials can be brought into solution by pyridine if the pH of the medium is maintained at 9.0 (the pAT for pyridine is 8.96). 

For assaying the pH-dependent activity of subtilisin crystals as mentioned above, low buffer capacities were used [6,102]. Thus, the formation of a dynamic pH-gradient during hydrolysis may explain the observed pH-shift in activity. Also carrier-fixed a-chymotrypsin reveals exactly the same phenomena [86, 97], which is discussed in more detail elsewhere [103]. 

Application of P amendments affected the pH of the sandy soil with a low buffering capacity at the contaminated site (Melamed et al., 2003). At the surface soil, TI, H3PO4, promoted the highest decrease in soil pH, while T3, H3PO4 5% PR, promoted the least decrease. The range of pH values at the surface during the sampling period varied from 6.5 to 7.0 in TO to 4.4 to 5.0 in TI, 5.0 to 5.5 in T2, and 5.5 to 5.7 in T3. These data indicate that phosphoric acid should be applied with caution to avoid enhanced mobility of nonimmobilized Pb and other heavy metals (e.g., Zn, Cd, and Cu) (Cao et al., 2003). 

The Sudan-Guinean geographical region is located in the North Hemisphere. In accordance with annual P PF ratio changing in the limits 0.6-1.0, low buffering capacity of Ferrasols, low pH values and very intensive type of biogeochemical cycling, the sustainability of these ecosystems to pollutant input is moderate. 

Figure 5.10. The titration curve of soil A, with a low buffer capacity, and soil B, with a high buffer capacity. The lime requirements of these soils are indicated (in units of centimoles of base per kilogram of soil) assuming that they are to be limed to pH 6.0.

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