Citrate, buffer salt

An alternative sample preparation is based on the QuEChERS (Quick Easy Cheap Effective Rugged Safe) technique [14]. In this the sample is extracted into acetonitrile and magnesium sulfate, sodium chloride and citrate buffer salts at pH 5-5.5 are added, the mixture is shaken and then centrifuged to separate the phases. When applied to honey [15] the samples, containing isoproturon-d6 as an internal standard, were diluted with water and homogenized before addition of the QuEChERS salts described above, and acetonitrile. After extraction, centrifugation... 

Buffer salts also can exert a secondary salt effect on drug stability. From Table 5 and Fig. 5 it is clear that the rate constant for an ionizable drug is dependent on its pKa. Increasing salt concentrations, particularly from polyelectrolytes such as citrate and phosphate, can substantially affect the magnitude of the pKa, causing a change in the rate constant. (For a review of salt effects, containing many examples from the pharmaceutical literature see Ref. 116.)... 

For the hydrosilylation reaction various rhodium, platinum, and cobalt catalysts were employed. For the further chain extension the OH-functionalities were deprotected by KCN in methanol. The final step involved the enzymatic polymerization from the maltoheptaose-modified polystyrene using a-D-glucose-l-phosphalc dipotassium salt dihydrate in a citrate buffer (pH = 6.2) and potato phosphorylase (Scheme 59). The characterization of the block copolymers was problematic in the case of high amylose contents, due to the insolubility of the copolymers in THF. 

It had been shown that 50 mM Tris-citrate buffer with 1 M NaCl was a suitable incubation buffer for the binding to GATl [95], The high salt concentration in this incubation buffer caused no problems in the new MS binding assays, since most of the incubation buffer was removed before the liberation step. The separation of the bound from the nonbound marker was conducted by filtration over glass fiber filters as common in radioligand binding assays. 

Amino acids can be separated without prior derivatization on a cation-exchange resin column. The elution buffers are classically lithium citrate buffers with different pH values and salt concentrations, which are applied stepwise. There is usually a programmed increase in column temperature. Consequently, there are numerous variables affecting the separation of the individual amino acids [6]. For the detection of the amino acids, the column effluent is mixed with the ninhydrin reagent. Nowadays there are only very few manufacturers of AAAs left. The considerable cost of purchase and the operation costs are a potential threat to the widespread application of this technique, although it is still considered to be the definitive method for diagnosing disorders of amino acid metabolism. 

Besides the swelling transitions, the swelling behaviors below the critical pH have been considered. In Fig. 1, we see that swelling continues to increase as pH is lowered below the transition point. This behavior is seen when the gels are immersed in citrate buffered saline, and is due to the shift in the charge on the citrate counterions. Citrate buffer has three ionizable carboxylic acid groups, with pK values in water pKj = 3.15, pK2 = 4.78 and pK3 - 6.40. (These values are somewhat lower in salt solutions.) Thus as pH is lowered, the citrate passes... 

Avicel was first incubated with Cx at 50 °C for 30 min liquids were removed by centrifugation. Pretreated Avicels were then washed with high-salt buffer (0.5 Af NaCl) followed by sodium citrate buffer. The Avicels were then digested by enzymes as indicated. 

If one chooses PI for DNA staining, the following procedure may be used.7 After the nuclei are pelleted, they are resuspended in staining solution, which consists of 3% (w/v) polyethylene glycol (PEG) 6000, 50 pig/ml PI, 180 units/ml RNase, 0.1% Triton X-100 in 4 mM citrate buffer. The pH of the staining solution is 7.2. The nuclei are then incubated at 37° for 20 min. After incubation, an equal volume of salt solution is added. The... 

Ferrimagnetic nanoparticles of magnetite (Fc304) in diamagnetic matrices have been studied. Nanoparticles have been obtained by alkaline precipitation of the mixture of Fe(II) and F(III) salts in a water medium [10]. Concentration of nanoparticles was 50 mg/ml (1 vol.%). The particles were stabilized by phosphate-citrate buffer (pH = 4.0) (method of electrostatic stabilization). Nanoparticle sizes have been determined by photon correlation spectrometry. Measurements were carried out at real time correlator (Photocor-SP). The viscosity of ferrofluids was 1.01 cP, and average diffusion coefficient of nanoparticles was 2.5 10 cm /s. The size distribution of nanoparticles was found to be log-normal with mean diameter of nanoparticles 17 nm and standard deviation 11 nm. 

Newly formed collagen extracted with cold, aqueous NaCl solutions consists of three equal-sized chains (a-components) of two different composition types ( -l and -2). The two chains of similar composition are the a-1 chains. The a-2 chain differs from the a-1 in a number of amino acids, particularly hydroxyproline, proline, lysine, and histidine (26). As the collagen molecule matures, the a-chains crosslink intramo-lecularly in pairs this older protein can be readily extracted with acidic solutions such as dilute acetate and citrate buffer, but not with salt solutions. The crosslinked chains are called /3 components the crosslinks are probably covalent bonds (26) that arise by condensation of the side chains of strategic lysyl residues after enzymatic oxidative deamination. Older collageil also forms intermolecular bonds, but the nature of this crosslink has not yet been determined (27). 

Fig. 2 Shifts in pH during freezing arising from buffer salt crystallization. Near-equilibrium conditions were achieved by seeding with ice and salt, circles sodium phosphate squares potassium phosphate triangles citrate. (Data from RefP l)...

The effects of sulphonate salt concentration and chain length on the retention factor k ) were studied by measuring k using only berenil as the diamidine, with a mobile phase consisting of 25.0 mM citrate buffer, pH=3.25, 45.0% methanol, T=30.0°C, with pentane sulphonate, hexane sulphonate, heptane sulphonate, octane sulphonate, and decane sulphonate sodium salts at concentrations of 0.00, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 9.00, and 12.00 mM. The resultant data are shown in Fig. 4, where it may be observed that retention times and hence k increase as the concentration of the ion pairforming agent increases. This increase is much more... 

Elution buffer was 0.125% citrate, trisodium salt, pH 7.3. All other conditions used are stated in text. Values are the average of three trials. 

The dissociation constants of most acids used in buffer mixtures vary but little with temperature. This leads us to expect that the pH of most acid-sodium salt buffer solutions will be independent of temperature within wide limits. The measurements of Walpum (cf. table on page 249) show this to be true of the citrate buffers. I. M. Kolthoff and F. Tekelenbukg have determined the temperature coefficient of the pH of a great number of buffer mixtures. Their results are summarized in the following table. 

Conversely, the addition of some other ions can promote solubility by the indifferent electrolyte effect. The use of hydrophilic molecules such as the hydroxyacids (e.g. citrate, tartaric) or aromatic carboxylic acids (e.g. benzoic) can create cavities in the water structure thereby promoting solubilization. Many salt formers increase drug solubility by this type of mechaiusm. Citrate buffers and sodium benzoate, the latter often used in formulations as an antimicrobial preservative, are known to enhance the solubility of a number of drugs. 

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