Buffers endpoint

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. 

Pyridine was used in the beginning of the development of the method. The reaction was slow and the endpoint unstable because of weak basicity of pyridine. The pyridine system buffers at about pH 4. A stronger base, imidazole, has been used to replace pyridine since it gives a faster response and has the advantages of lower toxicity and decreased odor. The optimal pH range for the SO2 imidazole buffer is at pH 6. It is important that the pH of the Karl Fisher reaction be maintained within the range 5 to 7. Outside this recommended pH range, the endpoint may not be reached. 

The buffering capacity of milk is often estimated by determining its titratable acidity, which involves titrating a sample of milk, containing a suitable indicator (usually phenolphthalein), with NaOH and thus is a measure of the buffering capacity of the milk between its natural pH and the phenolphthalein endpoint (i.e. between about pH 6.6 and 8.3). Titratable acidity is normally used to estimate the freshness of milk and to monitor the production of lactic acid during fermentation. Fresh milk typically requires 1.3-2.0 milliequivalents OH to titrate 100ml from pH 6.6 to pH 8.3 (13-20 ml of 0.1 M NaOH), i.e. fresh milk has a titratable acidity of 0.14 to 0.16%, expressed as lactic acid. 

Visible spectra of Mg2 -Calmagite and free Calmagite at pH 10 in ammonia buffer. [From C. E. Dahm, J. W. Hal. and B. E. Mattioni, "A Laser Pointer-Based Spectrometer for Endpoint Detection of EDIA nrations. J. Chem. Ed. 2004,81. 1787.]... 

Fig. 56. Star electrophoresis. Buffer, Veronal-sodium Veronalate, pH 8.6 p 0.06 substrate, Whatman 3 MM, dimensions 22 x 30 cm electrical field constant current 26 ma starting point, 17 volts/cm endpoint, 11 volts/cm sample, 0.02 ml normal human serum duration, 3 hours.

Conductivity (Armitage et al, 1987 Pawlak, 1980 Larbre and Briant, 1960) TBN Mixture of toluene/2-propanol/H20/. HC1 in 2-propanol, or mixture of benzene/ alcohol. Sharp break at the endpoint. Eliminates contamination of electrode. Less time consuming. Buffer solution is eliminated. 

Assay Transfer about 4 g of sample, accurately weighed, into a 250-mL volumetric flask, dissolve in and dilute to volume with water, and mix. Transfer 25.0 mL of this solution into a 400-mL beaker, and add 10 mL of a 1 10 solution of hydroxylamine hydrochloride, 25 mL of 0.05 M disodium EDTA measured from a buret, 25 mL of ammonia-ammonium chloride buffer TS, and 5 drops of eriochrome black TS. Heat the solution to between 55° and 65°, and titrate from the buret to a blue endpoint. Each milliliter of 0.05 M disodium EDTA is equivalent to 9.896 mg of MnCl2-4H20. 

Titer Determination Pipet 50.0 mL of Magnesium Sulfate Solution into a 400-mL beaker, and add 200 mL of water, 2 mL of Buffer Solution Initial Preparation, 1.0 mL of a 1 20 potassium cyanide solution, and 5 drops of eriochrome black TS or another suitable indicator. While stirring with a magnetic stirrer, titrate with the Standard EDTA Solution to a true blue endpoint. Record the volume, / , in milliliters, of Standard EDTA Solution equivalent to 50.0 mL of Magnesium Sulfate Solution. 

Procedure Transfer 25.0 mL of the Substrate Solution to a 32- x 200-mm test tube. To a second 32- x 200-mm test tube transfer 25.0 mL of the Chloride-Acetate Buffer Solution (blank). Equilibrate both tubes in a 35° 0.1° water bath for 20 min. Add 3.0 mL of the Sample Preparation to each test tube, mix, and insert a glass sparger into each tube with a preadjusted air flow of 700 to 750 mL/min. If excessive foaming occurs, add 3 drops of the Octadecanol Solution to each tube. After exactly 15 min, remove the sparge and rinse any adhering reaction mixture back into the tube with water. Immediately add 10 mL of the Sodium Hydroxide Solution and 3 drops of the Phenolphthalein Solution to each tube. Insert a small magnetic stirrer bar, stir, and titrate to the phenolphthalein endpoint with the standardized 0.05 N Hydrochloric Acid Solution. 

Emulsion Capacity and Stability. A 0.5 g sample of the freeze-dried protein fraction was redissolved in a minimum of 0.3 M citrate-phosphate buffer at pH 7.0 and mixed thoroughly with 50 ml of 1 M NaCl for 1 min in a Sorvall Omnimixer at 1000 rpm in a one pint Mason jar set in a water bath (20°C). Crisco oil (50 ml) was added to the jar and an emulsion formed by mixing at 500 rpm with simultaneous addition of oil at the rate of 1 ml/min until the emulsion broke. The endpoint was determined by monitoring electrical resistance with an ohmeter. As the emulsion broke a sharp increase (l KS2 to 35- 0 KSi) was noted. Emulsion capacity was expressed as the total volume of oil required to reach the inversion point per mg protein. This method is similar to that used by Carpenter and Saffle (8) for sausage emulsions. To establish emulsion stability the same procedure was used except that 100 ml of oil was added and a stable emulsion formed by blending at 1000 rpm for 1 min. A 100 ml aliquot was transferred to a graduate cylinder and allowed to stand at room temperature. Observations were made of the volume of the oil, emulsion and water phases at 30, 60, 90 and 180 min. 

After the flocculation endpoint has been established and verified, the other components (preservative, colorant, flavor, buffer, etc.) are added, dissolved in the liquid vehicle, and the slurry is brought to final volume with liquid vehicle. 

MTT reduction is used to estimate cell numbers at the end of the assay. The validity of the endpoint depends on a linear relationship between MTT reduction and cell number. The absorption spectrum of MTT-formazan is pH dependent and the pH of the MTT-formazan solution in DMSO depends on the cell density in the well. Glycine buffer is added to shift the pH of all wells to pH 10.5. At this pH the spectrum shows a single peak with an absorption maximum at about 570 nm. In contrast, at pH 7 the spectrum shows two absorption maxima, at 500 nm and 570 nm and measurement at a single wavelength underestimated the amount of MTT-formazan present. 

Digestion is usually performed in a solution at specified conditions of pH, temperature, and buffer (see T able 1) and in a denaturing environment to ensure complete endpoint digestion. Volatile buffers such as ammonium carbonate and ammonium bicarbonate are preferred because they can be easily removed by lyophilization. A practical method for the removal of a nonvolatile buffer and salts is to use solid-phase extraction (SPE) cartridges prior to mass spectrometry analysis. One can also use immobilized trypsin packed into a small-diameter PEEK (polyetheretherketone) column or covalently attached to an activated MALDI probe for on-probe digestion.15... 

Acidity and alkalinity titrations determine the total capacity of natural waters to consume strong bases or acids as measured to specified pH values defined by the endpoints of titrations. Of more interest for many purposes is the ability of a water or water-rock system to resist pH change when mixed with a more acid or alkaline water or rock. This system property is called its buffer capacity. Buffer capacity is important in aqueous/environmental studies for reasons that include ... 

Figure 4. Absorbance difference at 233 nm between standard 10-6 M avidin solution in buffer (0.2 M ammonium carbonate at pH 8.9) and a 10"6 M avidin solution in which the protein is bound to varying amounts of biotin. The titration endpoint corresponds to a molar ratio of biotin to avidin of 3.89 1, in good agreement with the theoretical value for completely active avidin of 4 1.

The current human estimates for nerve agent vapor and aerosol toxicity are based upon data from animal models. Rodents are popular animal models in that they are readily available, cheap, and convenient to handle. Additionally, there is a great amount of background data on rodents available in the literature for comparison to many biological endpoints. However, nonrodent models are preferred for studies of prophylactic and therapeutic efficacy associated with nerve agent exposure due to the protective buffering impact of relatively high blood carboxylesterase levels in... 

Figure 13. FKBP12 titration spectra with FK506, rapamycin, and nonimmunosuppressive ligands, GPI 1046, 1456, and 1495. All titration data were collected at 30 °C on a 600 MHz GE NMR in PBS buffer, 5 mM DTT, 2 mM NaN3,10% D20, pH 7.4, and 15 N FKBP protein concentration of approximately 1 mM. Ligands were either dissolved in PBS or in combination with ethanol to increase solubility. (A) FK506 titration. (B) GP11046 titration. (C) Rapamycin titration. (D) Overlay of saturation endpoints for FK506, GPI 1046, and rapamycin. (E) GPI 1456 and 1495 overlay. (F) Overlay of all three nonimmunosuppressive ligands at saturation point.

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