Ammonium, buffer capacity

The monoethanolamine-hydrochloric acid buffer has a buffering capacity equal to the ammonia-ammonium chloride buffer commonly employed for the titration of calcium and magnesium with EDTA and solochrome black (compare Section 10.54). The buffer has excellent keeping qualities, sharp end points are obtainable, and the strong ammonia solution is completely eliminated. 

During the lifetime of a root, considerable depletion of the available mineral nutrients (MN) in the rhizosphere is to be expected. This, in turn, will affect the equilibrium between available and unavailable forms of MN. For example, dissolution of insoluble calcium or iron phosphates may occur, clay-fixed ammonium or potassium may be released, and nonlabile forms of P associated with clay and sesquioxide surfaces may enter soil solution (10). Any or all of these conversions to available forms will act to buffer the soil solution concentrations and reduce the intensity of the depletion curves around the root. However, because they occur relatively slowly (e.g., over hours, days, or weeks), they cannot be accounted for in the buffer capacity term and have to be included as separate source (dCldl) terms in Eq. (8). Such source terms are likely to be highly soil specific and difficult to measure (11). Many rhizosphere modelers have chosen to ignore them altogether, either by dealing with soils in which they are of limited importance or by growing plants for relatively short periods of time, where their contribution is small. Where such terms have been included, it is common to find first-order kinetic equations being used to describe the rate of interconversion (12). 

At a suitable concentration of ammonium ions and ammonia, providing the electrolyte with an adequate buffer capacity, the height of the protein double-wave increases with the increasing concentration of the cobalt in the shape of a parabola. In solutions containing cobalt(III) ions the... 

A buffer is frequently used in reversed-phase LC to reduce the piotolysis of ionogenic analytes, which in ionic form show little retention. Phosphate buffers are widely applied for that purpose, since they span a wide pH range and show good buffer capacity. The use of buffers is obhgatory in real world applications, e.g., quantitative bioanalysis, where many of the matrix components are ionogenic. LC-MS puts constraints to the type of buffers that can be used in practice. Phosphate buffers must be replaced by volatile alternatives, e.g., ammonium formate, acetate or carbonate. 

Despite these considerations, the first approach in method development for ESl-MS is the formation of preformed ions in solution, i.e., protonation of basic analytes or deprotonation of acidic analytes. Thus, for basic analytes, mixtures of ammonium salts and volatile acids like formic and acetic acid are applied. Alternatively, formic or acetic acid may be added to the mobile phase, just to set a low pH for the generation of preformed ions in solution. The latter approach is successful if sufficient hydrophobic interaction between preformed aiialyte ions and the reversed-phase material remains. The concentration of buffer is kept as low as possible, i.e., at or below 10 nunol/1 in ESl-MS. The buffer concentration is obviously determined by the buffer capacity needed to achieve stable pH conditions upon repetitive injection of the samples. Constantopoulos et al. [99] derived an equilibrium partitioning model to predict the effect of the salt concentration on the analyte response in ESI. If the salt concentration is below 10 moFl, the analyte response is proportional to its concentration. The response is found to decrease with increasing salt concentration. 

Dead organic matter undergoes decomposition by a host of different bacteria. Thereby, organic nitrogen is mineralized to ammonium unless it is assimilated. NH4 and NH3 are in aqueous equilibrium, and if environmental factors like pH, temperature, buffer capacity of the soil, etc. are favorable, ammonia can be released to the atmosphere. Another important source of ammonia is urea arising from animal excreta. 

Because of its good buffering capacity and the high pH (9.0) at which hydroxyl (OH ) and carbonate (COa ) ions are exchanged for adsorbed Mo, the method of ammonium carbonate extraction should be suitable for alkaline soils, but this needs to be tested under field conditions. 

Alkalinity and buffer capacity Dissociation of ammonium ions to ammonia results in the production of hydrogen ions. Unless the water column or soils are well buffered, the medium can be acidified and the rate of ammonia volatilization can decrease. Thus, a water column with high alkalinity and calcium carbonate content can buffer the system and maintain high-pH conditions. Alkalinity is affected by the balance between photosynthesis and respiration by algae and submersed macrophytes in the water column. Ammonia volatilization losses are directly proportional to the alkalinity of the system. 

Which buffer system will have the greatest buffer capacity at pH 9.0 (i) dimethylamine/dimethylammonium ion, (ii) ammonia/ammonium ion, (iii) hydroxylamine/ hydroxylammonium ion, (iv) 4-nitrophenol/4-nitrophenolate ion ... 

If only white plaques but no clearing zones appear on the overlay gel, the buffering capacity of the overlay gel may be insufficient. In this case, transfer the overlay gel briefly into a buffer optimal for the protease under investigation. Shortly, the white zones will turn into clearing zones. Stop the reaction by returning the gel to the saturated ammonium sulfate solution. An intermediate acid bath may be necessary to accelerate the quenching process. 

Pro 5 True, effects of phenolic acids on seedlings occur most readily under acidic conditions. However, soils have substantial buffering capacity, and thus pH changes due to root and microbial activity are unlikely to occur at the bulk-soil levels over short time intervals. Changes in pH resulting from root and microbial activity do occur within the rhizosphere and on the rhizoplane (Heckman and Strick 1996 Rao et al. 2002 Ortas and Rowell 2004). Alkalization or acidification of the rhizosphere occurs for many species because of changing cation-anion uptake ratios, particularly uptake of nitrate or ammonium, respectively. In cowpea, for example, the rhizosphere is alkalinized in the dark and acidified wifh lighf exposure of fhe shoofs even when supplied with nitrate (Marschner and Romheld 1983 Rao et al. 2002). 

This implies that the pH is changed if the solution is not buffered, especially in the vicinity of the metal surfaces. Because the buffer capacity of seawater is not suMdent ammonium chloride is added both as a complexant and as a buffer ... 

Currently, the preferred buffer for enzymatic decontamination systems under development by the U.S. Army is anunonium carbonate. The addition of solid ammonium carbonate to wat results in a pH of 8.5 to 9.0 with no adjustment needed, and the ammonium ions are known to stimulate the activity of OPAA (Cheng and Calomiris, 1996). Ammonium carbonate, however, does not have a high buffering capacity, thus making it impractical for use in large-scale decontamination. 

LC/MS applications in the alkaline pH range. The reason for this is the overlapping and additive buffer capacities of the ammonium cation and the hydrogencarbonate anion. Above 60 °C, ammonium hydrogencarbonate decomposes into water, ammonia, and carbon dioxide. 

We have already mentioned some of the commonly used mobile phase additives for MS-compatible pH control. The most important attribute is the volatility of all buffer components. The most frequently used mobile phase additives are formic acid and acetic acid, together vhth the true buffers formic acid/ammonium formate and acetic acid/ammonium acetate. In the alkaline pH range, the preferred additive is ammonia, and the buffer of choice is ammonium hydrogencarbonate. One can also use the ammonium ion with volatile counterions such as formate or acetate to establish a true buffer at the pfQ of the ammonium ion (pKj = 9.24). One finds sometimes in the literature the reported use of ammonium formate or acetate at neutral pH. It needs to be pointed out that this has little to do with pH control, since these salt solutions have no buffer capacity at pH 7 ... 

Buffer systems for high-pH chromatography in the ESI mode include ammonium bicarbonate (1—10 mM, pH 10), ammonium hydroxide (0.1—1% pH 10), and ammonium formate adjusted to pH 9 with ammonium hydroxide. In the last case, the buffering capacity is due to the ammonia/ammonium equilibrium rather than the organic acid components and, as alluded to already, are thought to play an important part in gas-phase ionization at high pH. 

The buffer capacity is purely and simply the sum of the buffer components mixture. This property is true regardless of the couple s number and the electrical charge of the acidic form. In order to illustrate this point, let s consider a 0.1 mol/L ammonium acetate solution [pKg (acetic acid) = 4.75) and (pK (ammonium ion) = 9.24]. The preceding relation permits us to calculate P as a function of the pH value (Fig. 6.4). The latter is adjusted by adding a strong acid or a strong base. 

For this purpose the effect of the concentration of potassium chloride added to a borate buffer solution (total concentration of boric acid and potassium borate 0,10 mole/liter, pH 8,4) on polaro-gp ams for the Co (II) - cysteine system, with constant cobalt chloride (1,74 mmole/liter) and cysteine (0,08 mmole/liter) concentrations, was investigated. The borate buffer solution was used in place of the traditional ammoniacal buffer solution in order to avoid a number of complications and, primarily, decrease in the buffer capacity of the ammoniacal solution near the electrode when potassium chloride is added, since ammonium ions (being proton donors) also participate in the formation of the outer layer of the electric double layer. The pH value of the solution was selected so that the solution would contain approximately equal amounts of anions and cysteine zwitterions (pl am 8.33). 

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