Buffers and

Standardization—External standards, standard additions, and internal standards are a common feature of many quantitative analyses. Suggested experiments using these standardization methods are found in later chapters. A good project experiment for introducing external standardization, standard additions, and the importance of the sample s matrix is to explore the effect of pH on the quantitative analysis of an acid-base indicator. Using bromothymol blue as an example, external standards can be prepared in a pH 9 buffer and used to analyze samples buffered to different pHs in the range of 6-10. Results can be compared with those obtained using a standard addition. 

Adding as little as 0.1 mb of concentrated HCl to a liter of H2O shifts the pH from 7.0 to 3.0. The same addition of HCl to a liter solution that is 0.1 M in both a weak acid and its conjugate weak base, however, results in only a negligible change in pH. Such solutions are called buffers, and their buffering action is a consequence of the relationship between pH and the relative concentrations of the conjugate weak acid/weak base pair. 

The relationship between the pH of an acid-base buffer and the relative amounts of CH3COOH and CH3COO- is derived by taking the negative log of both sides of equation 6.43 and solving for the pH... 

As in Example 6.13, the Henderson-Hasselbalch equation provides a simple way to calculate the pH of a buffer and to determine the change in pH upon adding a strong acid or strong base. 

The procedure calls for placing a 100-pL aqueous sample containing the thiourea in a 60-mL separatory funnel along with 10 mL of a pH 7 buffer and 10 mL of a 12 pM solution of... 

A pH electrode is normally standardized using two buffers one near a pH of 7 and one that is more acidic or basic depending on the sample s expected pH. The pH electrode is immersed in the first buffer, and the standardize or calibrate control is adjusted until the meter reads the correct pH. The electrode is placed in the second buffer, and the slope or temperature control is adjusted to the-buffer s pH. Some pH meters are equipped with a temperature compensation feature, allowing the pH meter to correct the measured pH for any change in temperature. In this case a thermistor is placed in the sample and connected to the pH meter. The temperature control is set to the solution s temperature, and the pH meter is calibrated using the calibrate and slope controls. If a change in the sample s temperature is indicated by the thermistor, the pH meter adjusts the slope of the calibration based on an assumed Nerstian response of 2.303RT/F. 

The purity of a sample of Na2S203 was determined by a coulometric redox titration using as a mediator, and as the titrant. A sample weighing 0.1342 g is transferred to a 100-mL volumetric flask and diluted to volume with distilled water. A 10.00-mL portion is transferred to an electrochemical cell along with 25 mL of 1 M KI, 75 mL of a pH 7.0 phosphate buffer, and several drops of a starch indicator solution. Electrolysis at a constant current of 36.45 mA required 221.8 s to reach the starch indicator end point. Determine the purity of the sample. 

Antlblaze 19. Antiblaze 19 (Mobil), a flame retardant for polyester fibers (134), is a nontoxic mixture of cycHc phosphonate esters. Antiblaze 19 is 100% active, whereas Antiblaze 19T is a 93% active, low viscosity formulation for textile use. Both are miscible with water and are compatible with wetting agents, thickeners, buffers, and most disperse dye formulations. Antiblaze 19 or 19T can be diffused into 100% polyester fabrics by the Thermosol process for disperse dyeing and printing. This requires heating at 170—220°C for 30—60 s. 

Several aspects affect the extent and character of taste and smell. People differ considerably in sensitivity and appreciation of smell and taste, and there is lack of a common language to describe smell and taste experiences. A hereditary or genetic factor may cause a variation between individual reactions, eg, phenylthiourea causes a bitter taste sensation which may not be perceptible to certain people whose general abiUty to distinguish other tastes is not noticeably impaired (17). The variation of pH in saUva, which acts as a buffer and the charge carrier for the depolarization of the taste cell, may influence the perception of acidity differently in people (15,18). Enzymes in saUva can cause rapid chemical changes in basic food ingredients, such as proteins and carbohydrates, with variable effects on the individual. 

Basic Components. The principal components in emulsion polymerization are deionized water, monomer, initiator, emulsifier, buffer, and chain-transfer agent. A typical formula consists of 20—60% monomer, 2—10 wt % emulsifier on monomer, 0.1—1.0 wt % initiator on monomer, 0.1—1.0 wt % chain-transfer agent on monomer, various small amounts of buffers and bacteria control agents, and the balance deionized water. 

Indium-111. Kits for labeling using other radionucHdes include two indium-111 compounds. Indium-111 pentetreotide is used for the scintigraphic localization of primary and metastatic neuroendocrine tumors bearing somatostatin receptors. For octreotide DTP A, the active agent is suppHed in a lyopbilized kit with gentisic acid, citrate buffer, and inositol. 

The final vacciae coataHis the two toxoids, as weU as pertussis (whole ceU or aceUular), a buffer, and an adjuvant, ie, a substance that Hicreases the response to an antigen when combHied with the antigen, eg, aluminum. As noted above, the final vacciae can also contain a component that protects against Haemophilus disease. 

Milk and Milk Replacers. White pan bread was long made with about 3—4% nonfat dry milk (NEDM) in the United States, for reasons of enhanced nutrition, increased dough absorption, improved cmst color, fermentation buffering, and better flavor. Eor some years, however, sharply increased milk prices have led to a decline in its use in breadmaking. Many bakers have turned to the use of milk replacers to control the costs of their products, and these ingredients are now commonly utilized. Milk replacers were designed to dupHcate some of the functions and nutrition of milk. These blends may contain soy flour or cereals, with whey, buttermilk soHds, sodium or calcium caseinate, or NEDM. Milk replacers or NEDM used in bread dough amount to about 1—2%, based on flour. 

Hydrosulfite may be purchased as a proprietary formulation containing buffering and stabilizing agents, usually as a dry powder, but sometimes as a solution. The powder is pyrophoric and should be kept dry to avoid the possibiHty of fires. Alternatively, solutions of sodium hydrosulfite may be generated on-site by using a purchased solution of sodium borohydride and sodium hydroxide to reduce sulfur dioxide. 

In the presence of the chelating agent and the insoluble salt, MX, pM of the solution is subject to both the metal buffering and the solubiUty equiUbria. Equating the right-hand sides of the equations 26 and 29 and rearranging gives... 

Cosmetics and Toiletries. Citric acid and bicarbonate are used in effervescent type denture cleansers to provide agitation by reacting to form carbon dioxide gas. Citric acid is added to cosmetic formulations to adjust the pH, act as a buffer, and chelate metal ions preventing formulation discoloration and decomposition (213—218). 

There are several methods of buffer and capillary surface modification used to prevent electrostatic interactions. Two modes have been examined mn buffer with pH >10 in the uncoated capillary and anionic polymer coating capillary, developed in lAI. 

Figure 8.2. Target configuration for dynamic tensile fracture experiments on rock. PMMA buffers and windows were not used on those rocks with an acoustic impedance comparable to PMMA. Velocity for these tests was measured at the rock-free surface.

Figure 13-31. Restrictive ring seal system with both buffer and eduction cavities.

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