Borate buffer titration

At room temperature, the pH of a sodium borate solution is 9.3. The buffering capacity of boric acid-borate solutions was evaluated at 350°C and 3500 psia by measuring the pH change during titrations with sodium hydroxide and hydrochloric acid[13]. The borate buffer titration experiments were conducted at 350°C and 24.1 MPa (3500 psia) where the water density is 0.622 g/mL and the pKa of boric acid is approximately 9.6. The concentration of sodium borate in the feed solutions was fixed at 6.25 X 10 m, which corresponded to a total boron concentration of 0.025 m. At 350°C, the measurable pH ranges of the various optical indicators are 9.0-11.0 for 2-naphthol, 7.0-9.0 for 2-naphthoic acid, 3.0-5.0 for collidine, and 2.0-4.0 for acridine. The indicator 2-naphthol was used to measure pH for the titration of the borate buffer with NaOH which began at pH of 9.5 and ended at 10.5. For the titration with HCl, 2-naphthol, 2-naphthoic acid, and collidine were used in series to measure pH values between 9.5 and 3.0. 

The sample was mixed with an equal volume of borate buffer (pH 9.2). Titration with 0.01 M EDTA gave two breaks corresponding to the concentration of each cation. 

Coordination of flexible amidic structures to the palladium ion resulted in the formation of a rigid hydrophobic cavity of 61 [82]. This self-assembly takes place in water, and aromatic carboxylates are recognized in it. It was found using NMR titration in D20 (pD=8.5, borate buffer). The structure of the complex formed is shown schematically in Fig. 4. It is apparent that cooperative binding of both carboxylates is essential for the stability of the complex formed nevertheless, the enantioselection of carboxylates is only very weak (Table 5). 

Store the solutions at 0-5°C. Warm 1 mL of each solution to about 25°C over 15 min and use 50 xL of each solution for each titration. Carry out the titration in an atmosphere of nitrogen. Transfer 10.0 mL of borate buffer solution pH 8.0 (0.0015 M) R to the reaction vessel and, while stirring, add 1.0 mL, of a freshly prepared 0.686% m/V solution of benzoylarginine ethyl ester hydrochloride R. 

The tweezer-type receptor 43 that was developed by Kilbum and coworkers contains a disnbstitnted guanidinium group in the middle of the chain which was expected to bind to the terminal carboxylate gronp of peptidic guests (Scheme 22). The two peptide arms that are arranged in a parallel fashion serve to induce substrate selectivity. To test this idea, 43 was incubated in aqueous sodium borate buffer (pH 9.2, 16.7% DMSO) with a 1000-member library of tripeptides attached to a TentaGel resin via the amino terminus. Mainly hydrophobic amino acid residues were incorporated into these tripeptides to ensure that receptor substrate interactions are largely due to hydrophobic interactions. Receptor 43 was found to bind to about 3% of the library members and showed 95% selectivity for Val at the carboxylate terminus of the tripeptides and 40% selectivity for Glu(OfBu) at the amino terminus. A stability constant of 4 x lO M- was determined for the complex between 43 and Z-Glu(OrBu)-Ser(OfBu)-Val-0 in 16.7% DMSO/water (1 mM sodium borate buffer, pH 9.2) by means of isothermal titration microcalorimetry. 

Additionally, PEDOT-SSA films stabilized by conditioning in alkaline or acidic solutions were successfully used in classical Me-EDTA titration. Titration of Ca was performed in borate buffer of pH = 9.2, and Cu titration was performed in acetate buffer of pH = 5. 

Usability of such miniature galvanic cells equipped with CP-based reference membrane was confirmed experimentally [21]. One of such microcells, with a solid-contact type Ca-sensitive electrode and the PEDOT-SSA reference membrane, was used for end-point detection in the course of calcium titration with EDTA in a borate buffer (pH 9.2). The potential changes were measured against an external Ag/AgCl electrode and potential change for the PEDOT-SSA membrane was negligible during the whole titration. 

In the sodium borate solution containing bromide, when the pH 4 buffer is added before the potassium iodate solution, titrations give low total residual chlorine concentrations. This loss increases with the amount of stirring time between the addition of the reagents. Even for a stirring time of 10 seconds, there is a loss of about 17% of the total residual chlorine. If the solution were stirred for 30 min, 85% of the chlorine would have disappeared. The concentration of total residual chlorine determined by the reference methods does not change throughout the experiment. This implies that this loss of chlorine does not occur in the reaction vessel, but in the titration cell as a result of the analytical procedure. 

A mixture consisting of 25 mL of an aqueous (0.2 to 1.0 mM) solution of chlorpromazine hydrochloride and 5 mL of 0.1 M acetate buffer (pH 3.3) was titrated to a potentiometric endpoint with 0.0 IM sodium tetraphenyl-borate [77]. The titrant was added at a rate of 0.36 mL/min with continuous stirring, and the temperature of the medium was maintained at 22 2°C. The end point was detected by a tetraphenylborate-selective electrode. 

Although B(0H)3 and B(OH)4 are monomeric in dilute solutions, at concentrations above about O.lmolL, condensed borate species that are often referred to as polyborates form. Titration of a boric acid solution with one molar equivalent of a strong base leads to formation of the tetrahydroxyborate anion, B(OH)4, as the principal species in solution. Mixtures of boric acid and its conjugate base, the tetrahydroxyborate anion, form what appears to be a classical buffer system where the pH is determined primarily by the acid salt ratio with [H+] = K[B(OH)3]/[B(OH)4 ]. This relationship is approximately correct for sodium and potassium borates with a sodium boron ratio of 1 2. Here the B(0H)3 B(0H)4 ratio equals one, and the solution pH remains near 9 over a wide range. However, for borate solutions with pH values significantly above or below 9,... 

The use of buffer solutions is usually advisable for accurate control of the pH of solutions used in spectrophotometric titrations, since the solutions will usually be so dilute (because of the relatively high protein or peptide absorptivity) as to offer little self-buffering. The usual buffers for the pH range from 9 to 13, i.e., borate, glycinate, phosphate, lysine, -aminocaproic acid, etc., are generally transparent through the 2950 A phenolate band. Buffer systems composed of piperidine (pK, 11) and its hydrochloride have been used to avoid the use of multivalent anions in the spectrophotometric titration of ribonuclease (Klee and Richards, 1957), but no other advantage is apparent for this system. 

Capillary Electrophoresis (CE) and Micellar Electrokinetic Chromatography (MEKC). - Di(2-ethylhexyl) thiophosphoric acid (DEHTPA) has been earlier characterised by potentiometric titration, and quantified by capillary zone electrophoresis with carbonate buffer, operating at —20 kV, and using UV detection at 210 nm. ° Also, a comparison has been made of capillary electrophoresis (CE) and liquid chromatography (LC) for the enantiomeric separation of a-phosphonosulfonic acids, where CE used 3-cyclodextrin as chiral selector in a borate electrolyte. Alkylphosphonic acids, at trace levels in water, have been determined by CE coupled online with flame photomeric detection, and alkylphosphonic acid esters have been separated and determined by CE using indirect UV detection. 

Figure 9-11. (A) Structure of 3-nitrotyrosine. Bond distances (A) are taken from the crystallographic structure of free NT [103]. (B-C) Spectrophotometric titration of Y3NT by UV/Vis absorption spectroscopy. Absorption spectra (B) and plot of the absorbance values at 430nm of Y3NT (2mL, 48(xM) as a function of pH (C). Measurements were carried out in 2-mM citrate-borate-phosphate buffer, at the indicated pH. Fitting data points yields a pKa value of 6.74 + 0.02 for NT.

Alkalinity A measure of the buffer capacity to resist drop in pH when acid is added, i.e. it is the measure of the chemical constituents of water that react with hydrogen ions, and thus resist a decrease in pH. The major portion of alkalinity is due to hydroxide, carbonate andbicarbonate. Other contributors include salts of weak acids such as borates, silicates, phosphates, and organic acids such as humic acid. Alkanitiy can be expressed as M alk. to a methyl orange titration end point (pH 4.2) or P alk. to a phenolphthalein end point (pH>8.2). 

In the mercurimetric titration of thiol compounds in proteins( the flat titration curves became steep after the addition of chloride ions. The titration can be carried out in acetate pH 5-6 buffer with 0-5 M potassium chloride, phosphate pH 7-3 buffer with 0-5 M potassium chloride or borate pH 8-8 buffer with 0-5 M ammonium nitrate. In the presence of ammonia the curves were steep, even in the absence of chlorides. It has been suggested< > that ammonia prevents the bonding of mercury to groups other than the thiol grouping. 

When the titration is complete, the elect] odes aie at once washed, and placed in either phthalate, borate, or tiisodium phosphate buffer (choosing the buffer which is neatest to the pK found). If its pH is not repiodticed to 0 02 without adjustment of the set, the titration lesults must be discarded. 

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