Buffer adjusting agents

Acidity regulator/acid, alkali, base, buffer, buffering agent, pH adjusting agent... 

Among the polymers used in lens comfort solutions are polyvinyl alcohol, polyvinylpyrrolidone, dextran, and various cellulose derivatives such as hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methylcellulose. Surfactants include certain poloxamer and poloxamine compounds. Other normal components comprise appropriate preservative(s) as well as buffering and tonicity-adjusting agents. 

Other additives such as antimicrobial agents, antioxidants, buffers and tonicity-adjusting agents can be included in injection formulations and it is the responsibility of the pharmacist to check that all excipients and adjuvants are suitable (benzyl alcohol, ethanol, sulfites, sodium content, etc.). Nevertheless, one is left with a difficult choice over excipients, either those for which toxicity is known and therefore predictable, or those with safety profiles that have not been established in children (see under Critical excipients, page 55). The pH and osmo-larity of the preparation must also be checked before administration by another route. 

Direct Titrations. The most convenient and simplest manner is the measured addition of a standard chelon solution to the sample solution (brought to the proper conditions of pH, buffer, etc.) until the metal ion is stoichiometrically chelated. Auxiliary complexing agents such as citrate, tartrate, or triethanolamine are added, if necessary, to prevent the precipitation of metal hydroxides or basic salts at the optimum pH for titration. Eor example, tartrate is added in the direct titration of lead. If a pH range of 9 to 10 is suitable, a buffer of ammonia and ammonium chloride is often added in relatively concentrated form, both to adjust the pH and to supply ammonia as an auxiliary complexing agent for those metal ions which form ammine complexes. A few metals, notably iron(III), bismuth, and thorium, are titrated in acid solution. 

Complexing agents, which act as buffers to help control the pH and maintain control over the free metal—salt ions available to the solution and hence the ion concentration, include citric acid, sodium citrate, and sodium acetate potassium tartrate ammonium chloride. Stabilizers, which act as catalytic inhibitors that retard the spontaneous decomposition of the bath, include fluoride compounds thiourea, sodium cyanide, and urea. Stabilizers are typically not present in amounts exceeding 10 ppm. The pH of the bath is adjusted. 

Wa.terBa.la.nce Chemicals. Water balance chemicals include muriatic acid, sodium bisulfate, and soda ash for pH control, sodium bicarbonate for alkalinity adjustment, and calcium chloride for hardness adjustment. A recent development is use of buffering agents for pH control. One of these products, sodium tetraborate, hydrolyzes to boric acid and a small amount of orthoborate (50) which provides significantly less buffering than carbonate and cyanurate alkalinity in the recommended pool pH range of 7.2—7.8 even at 100 ppm. 

Citric acid is utilized in a large variety of food and industrial appHcations because of its unique combination of properties. It is used as an acid to adjust pH, a buffer to control or maintain pH, a chelator to form stable complexes with multivalent metal ions, and a dispersing agent to stabilize emulsions and other multiphase systems (see Dispersants). In addition, it has a pleasant, clean, tart taste making it useful in food and beverage products. 

Textiles. Citric acid acts as a buffer in the manufacture of glyoxal resins which are used to give textiles a high quaUty durable-press finish (see Amino resins). It has been reported to increase the soil-release property of cotton with wrinkle-resistant finishes and is used as a buffer, a chelating agent, and a non-volatile acid to adjust pH in disperse dying operations (182—193). 

Sodium bicarbonate is used as a leavening in breads, as a stomach antacid, as a buffering agent to adjust the acidity or alkalinity of a product, as a mild abrasive in toothpaste, and as an odor absorber. Sodium bicarbonate reacts with acids to release carbon dioxide gas. 

Buffers are necessary to adjust and maintain the pH. Buffering agents can be salts of a weak acid and a weak base. Examples are ammonium, potassium, sodium carbonates (caustic soda), bicarbonates, and hydrogen phosphates [1345]. Weak acids such as formic acid, fumaric acid, and sulfamic acid also are recommended. Common aqueous buffer ingredients are shown in Table 17-8. 

Taste is only one of several qualities of a process or product that is affected by an excess of either of these 10ns. Some raw materials are naturally too acidic, others too alkaline—so that neutralizers must be added to adjust the pH within an acceptable range. In die dairy industry, for example, the acid in sour cream must be adjusted by the addition of alkaline compounds in order that satisfactory butter can be churned. Quite often, the pH may be difficult to adjust or to maintain after adjustment. Stability of pH can be accomplished by the addition of buffering agents that, within limits, effectively maintain the desired pH even when additional acid or alkali is added. For example, orange-flavored instant breakfast drink has just... 

Since APCI and ESI interfaces operate at atmospheric pressure and do not depend upon vacuum pumps to remove solvent vapor, they are compatible with a wide range of HPLC flow rates. HPLC methods that have been developed using conventional detectors such as UV/VIS, IR, or fluorescence are usually transferable to LC/MS systems without adjustment. However, the solvent system should contain only volatile solvents, buffers, or ion-pair agents to reduce fouling of the mass spectrometer ion source. In the case of chlorophyll solvent systems, isocratic and gradient combinations of methanol, acetonitrile, water, acetone, and/or ethyl acetate have been used for APCI or ESI LC/MS. Unlike continuous-flow FAB/LSIMS, no sample matrix is necessary. 

Ethoxyquin, a synthetic antioxidant, is not generally allowed for human consumption in foods, but it is being added to animal feed and to fruits as an antiscald agent (94,143). Ethoxyquin is also used in the spice industry to prevent carotenoid loss during postharvest handling. However, ethoxyquin-treated paprika is unacceptable for some markets and some consumers (129). Perfetti et al. (130) described a method for determination of ethoxyquin in paprika and chili powder. Ethoxyquin was extracted from the spice with hexane and partitioned into 0.3 N HC1. After adjusting the solution to pH 13-14, ethoxyquin was extracted into hexane, and the hexane layer was evaporated to dryness. An acetonitrile solution of the residue was then analyzed by reversed-phase HPLC, with detection at 254 nm. The mobile phase was water/acetonitrile with ammonium acetate buffer. Recoveries from samples fortified at 50, 100, and 200 ppm averaged 92%, with a coefficient of variation of 2.3%. The method was applied to a number of commercial samples of paprika and chili powder. Ethoxyquin was found in paprika samples at levels up to 63 ppm and in chili powder samples at levels up to 20 ppm. 

Electroless solutions contain a metal salt, a reducing agent, a pH adjuster or buffer, a complexing agent, and one or more additives to control stability, film properties, deposition rates, etc. 

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