Buffers Ammonium salts

For deliming, ammonium salts and acids are used. The proportion of ammonium salts to acids and the type of acids employed is a matter of the tanner s choice. The acid neutralizes the lime, Ca(OH)2, thereby adjusting the pH. The ammonium salts have two functions to buffer the solution to a pH required for bating, and to form calcium ammonium complexes. The acidity and the complex formation solubilize the calcium and serve to bring the hide to the desired pH. 

The peak capacity is not pertinent as the separation was developed by a solvent program. The expected efficiency of the column when operated at the optimum velocity would be about 5,500 theoretical plates. This is not a particularly high efficiency and so the separation depended heavily on the phases selected and the gradient employed. The separation was achieved by a complex mixture of ionic and dispersive interactions between the solutes and the stationary phase and ionic, polar and dispersive forces between the solutes and the mobile phase. The initial solvent was a 1% acetic acid and 1 mM tetrabutyl ammonium phosphate buffered to a pH of 2.8. Initially the tetrabutyl ammonium salt would be adsorbed strongly on the reverse phase and thus acted as an adsorbed ion exchanger. During the program, acetonitrile was added to the solvent and initially this increased the dispersive interactions between the solute and the mobile phase. 

Apparently, no bottles of aqueous ammonia are present in the laboratory, so the components of the buffer solution must come from the salts. The technician needs an ammonium salt with a counter anion that has no acid-base properties. Ammonium chloride (NH4 Cl) would be an appropriate choice. This salt contains the conjugate acid, NH4, and the technician can generate NH3 by adding strong base to the ammonium chloride solution NH4 ((2 q) + OH ((2 q) NH3((3 q) + H2 0(/)... 

The nitrile-hydrolyzing activity of Ar throb act er spp. NS SC 104 was shown to be resistant to the suppressing effect of a-hydroxy nitriles such as lactonitrile and HMTBN, and accumulated the corresponding a-hydroxy acid ammonium salt at a high concentration [77]. HMTBN (200 him) was added to a suspension of Ar throb act er spp. NSSC 104 cells (4% dew) in phosphate buffer (0.1 m, pH 7.5) and mixed at 30 °C seven more additions of the same amount of HMTBN were added at 1 h intervals, then a further eight additions made at 1.5 h intervals over a total reaction time of 19 h. At completion of the reaction, the concentration of 2-hydroxy-4-methylthiobutyrate... 

Lucifer Yellow CH is soluble in aqueous solution, and it should be stable for awhile if protected from light. The reagent is available as three different salts of the sulfonate groups. The ammonium salt of the fluorophore is soluble to a level of 9 percent in water, while the lithium and potassium salts have a solubility of 5 and 1 percent, respectively. A concentrated stock solution of the fluorophore may be prepared in water and an aliquot added to a buffered reaction medium to facilitate the transfer of small quantities. For aqueous reactions, a pH range of 5-9 will result in efficient hydrazone formation with aldehyde or ketone residues. 

Note also that ammonium sulfate is absent from the recommended binding buffer formulations despite its general popularity in the field. Ammonium ions become fully titrated at alkaline pH and convert to ammonia gas. Buffer pH may become unstable as a result and causticity of the free ammonia may partially hydrolyze the proteins in a sample, creating a source of assay variability.617 18 At small buffer volumes used for analytical applications, liberated ammonia gas may not be a significant health hazard, but precautions may still be necessary to meet regulations. For all these reasons, ammonium salts are best avoided at alkaline pH. 

The role of the ammonium salt anion is not the loading of the amphipathic weak base per se, but rather to control the stability of loading and the profile and rate of release of the amphipathic weak base from the liposome to the external aqueous phase. Two major factors that differentiate the different anions are, firstly, their ability to induce precipitation/crystallization/ gelation in the intraliposome aqueous phase (1,12), and secondly, their effect on the membrane/buffer and octanol/buffer partition coefficient of the amphipathic weak base (1). Regarding the precipitation, the higher the amount of precipitated amphipathic weak base, the more stable is the loading and the slower is its release rate (10-12,18,33,35) and (Wasserman et al.). There are also some risks involved in the precipitation which in some cases reduce the mechanical stability of the liposomes and change liposome shape (36). 

The solution pH influences a number of factors, and it is not always simple to predict its effect. Thus, thiourea decomposition (in alkaline solution) is generally faster at higher pH. The probability of the presence of a solid phase of Cd(OH)2 and its concentration in the solution are both increased at higher pH (higher OH concentration). The pH is determined, in the example given earlier, by the concentration of ammonia. However, it can be adjusted independent of the ammonia concentration. Addition of an ammonium salt, which with ammonia, acts as a buffer, will lower the pH through the following equilibrium ... 

To HEPES buffer (100 mL, 200 mM, pH 7.5) were added ManNAc 15 (1.44 g, 6 mmol), PEP sodium salt (1.88 g, 8 mmol), pyruvic acid sodium salt (1.32 g, 12 mmol), CMP (0.64 g, 2 mmol), ATP (11 mg, 0.02 mmol), pyruvate kinase (300 U), myokinase (750 U), inorganic pyrophosphatase (3 U), /V-acctylneuraminic acid aldolase (100 U), and CMP-sialic acid synthetase (1.6 U). The reaction mixture was stirred at room temperature for 2 days under argon, until CMP was consumed. The reaction mixture was concentrated by lyophilization and directly applied to a Bio-Gel P-2 column (200-400 mesh, 3 x 90 cm), and eluted with water at a flow rate of 9 mL/h at 4°C. The CMP-NeuAc fractions were pooled, applied to Dowex-1 (formate form), and eluted with an ammonium bicarbonate gradient (0.1-0.5 M). The CMP-NeuAc fractions free of the nucleotides were pooled and lyophilized. Excess ammonium bicarbonate was removed by addition of Dowex 50W-X8 (H+ form) to the stirred solution of the residual powder until pH 7.5. The resin was filtered off and the filtrate was lyophilized to yield the ammonium salt of CMP-NeuAc 17 (1.28 g, 88%). 

Buffer substances which occur in nature include phosphates, carbonates, and ammonium salts in the earth, proteins ol plant and animal (issues, and the carbonic-acid-bicaihonatc system in blood. Sec also Acid-Base Regulation (Blood). 

Mobile phase options are quite restricted, as only volatile buffers are suitable for LC-MS. In addition, ion-pairing agents traditionally used in LC to improve peak shape and retention time such as trifluoroacetic acid (TFA), have shown to produce ion suppression, and they are not recommended for LC-MS analysis [21]. Therefore, although few applications for specific antidepressants employ TFA or its ammonium salt due to sensitivity enhancement [48, 81-85], aqueous phases in most LC-MS analytical methods are composed by formic or acetic acid in water, or its ammonium buffers. Although acid mobile phases are by far the most common, basic aqueous mobile phases (pH ranging from 8 to 10) have been used for specific applications in order to increase antidepressant retention time or to couple the online SPE elution to chromatographic analysis [57, 72, 86, 87], Organic phase composition was typically ACN and/or MeOH. 

For strongly acidic samples (those that are completely ionized at pH 2), it is necessary to take advantage of the strongly ionic nature of the sample. By adding a buffer to control pH and to ensure that the sample maintains ionic character, and by adding a suitable compound (in this case a quaternary ammonium salt) as a paired-ion reagent, the retention of the acid will increase. 

Assay Dissolve about 1 g of sample, accurately weighed, in 50 mL of water, add 50.0 mL of 0.05 M disodium EDTA and 20 mL of pH 4.5 buffer solution (77.1 g of ammonium acetate and 57 mL of glacial acetic acid in 1000 mL of aqueous solution), and boil gently for 5 min. Cool, and add 50 mL of alcohol and 2 mL of dithizone TS. Back titrate with 0.05 M zinc sulfate to a bright rose-pink color. Perform a blank determination (see General Provisions), and make any necessary correction. The milliliters of 0.05 M disodium EDTA consumed is equivalent to 50 minus the milliliters of 0.05 M zinc sulfate used. Each milliliter of 0.05 M disodium EDTA is equivalent to 23.72 mg of A1K(S04)2T2H20. Ammonium Salts Add 1 g of sample to 10 mL of 1 N sodium hydroxide in a small beaker, and heat on a steam bath for 1 min. The odor of ammonia is not perceptible. Fluoride Determine as directed in Method V under Fluoride Limit Test, Appendix IIIB. 

Common surfactants that have been used in MEKC, are listed in Table 3.1 with the respective critical micelle concentrations the most popular are SDS, bile salts, and hydrophobic chain quaternary ammonium salts. Selectivity can also be modulated by the addition to the aqueous buffer of organic solvents (methanol, isopropanol, acetonitrile, tetrahydrofuran, up to a concentration of 50%). These agents will reduce the hydrophobic interactions between analytes and micelles in a way similar to reversed-phase chromatography. Organic modifiers also reduce the cohesion of the hydrophobic core of the micelles, increasing the mass transfer kinetics and, consequently, efficiency. Nonionic... 

A number of ketone catalysts have been developed. Crucial considerations are solubility and stability. As an example, catalytic amounts of ammonium salts such as Thexyl-l-methyl-4-oxopiperidinium triflate with Oxone in a buffered water-dichloromethane mixture are effective oxidation agents (Equation 69) <1995JOC1391>. Other... 

Another alternative and far more efficient procedure is to employ an organic buffer, such as methane sulfonic acid and a short length of reversed phase column subsequent to the analytical column. After the separation has been achieved and the individual ions are eluted from the column, the methyl sulfonate that is eluted with them is absorbed, virtually irreversibly, on to the revered phase leaving the ions of interest to enter the detector in the absence of any buffer ions. As the suppresser column is, itself, a high efficiency LC column, little or no dispersion occurs and consequently no loss of resolution. If a basic buffer is required, then a tertiary butyl ammonium salt can be used which would be removed equally effectively by the reversed phase suppresser column. 

Aromatic acids are reduced by metal-ammonia solutions very much more readily than simple hydrocarbons and ethers. In contrast to the normal requirements for the latter derivatives, it is often possible to achieve reduction with close to stoichiometric quantities of metal. The addition of aromatic carboxylic acids to liquid ammonia (or vice versa) results in the immediate precipitation of the ammonium salt. As the metal is added, however, the precipitate usually dissolves as reduction proceeds, especially if lithium is used. If reduction is carried out in carefully dried, redistilled ammonia, as little as 2.2 mol of lithium are consumed in some cAses, thereby demonstrating that the substrate is reduced much more readily than the ammonium ions, which instead react with the intermediates from reduction of the substrate. However, protonation by NH4 is not essential since reduction proceeds equally well on preformed metal car-boxylates (although low solubility is then often a problem). The addition of an alcohol is not necessary, but it may serve as a useful buffer and can often improve solubility. The presence of alcohol can nevertheless be deleterious, since it facilitates isomerization of the initially formed 1,4-dihydro isomer to the 3,4-isomer and in this way affords the possibility of further reduction. ... 

Ammonium Salt (ABTS). This method is modified from Saunders. The substrate buffer contains 1 mg of ABTS per milliliter and 0.003% H2O2 in 0.1 M citrate-phosphate buffer, pH 4.0. The enzyme reaction is stopped by addition of i volume of 37 mM NaCN. The green color is measured at 415 nm. 

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