Acids buffer solutions

Fig. 2.12 Potential-time curves on mild steel in sodium borate/hydrochloric acid buffer solutions, pH 7-60, oxygen-saturated solution (after Ashworth )...

Reagents. In view of the sensitivity of the method, the reagents employed for preparing the ground solutions must be very pure, and the water used should be re-distilled in an all-glass, or better, an all-silica apparatus the traces of organic material sometimes encountered in demineralised water (Section 3.17) make such water unsuitable for this technique unless it is distilled. The common supporting electrolytes include potassium chloride, sodium acetate-acetic acid buffer solutions, ammonia-ammonium chloride buffer solutions, hydrochloric acid and potassium nitrate. 

C18-0004. An acidic buffer solution can be prepared from phosphoric acid and dihydrogen phosphate. What is the pH of solution prepared by mixing 23.5 g NaH2 PO4 and 15.0 mL concentrated phosphoric acid (14.7 M) in enough water to give 1.25 L of solution ... 

The PG activity was measured [10] by detecting the increase of reducing groups during the depolymerisation of 1 % (w/v) polygalacturonic acid buffered solutions, by a colorimetric method based on the 3,5-dinitrosalicylic acid. 

Reverse phase HPLC describes methods that utilize a polar mobile phase in combination with a nonpolar stationary phase. As stated above, the nonpolar stationary phase structure is a bonded phase—a structure that is chemically bonded to the silica particles. Here, typical column names often have the carbon number designation indicating the length of a carbon chain to which the nonpolar nature is attributed. Typical designations are C8, C18 (or ODS, meaning octadecyl silane), etc. Common mobile phase liquids are water, methanol, acetonitrile (CH3CN), and acetic acid buffered solutions. 

You must be able to calculate the pH of an acid buffer solution. 

An acidic buffer solution consists of a weak acid with a salt of the acid - its conjugate base. 

Aizawa and Suzuki (83,84,85,86) utilized, as an ordered system, liquid crystals in which Chi was immobilized. Electrodes were prepared by solvent-evaporating a solution consisting of Chi and a typical nematic liquid crystal, such as n-(p-methoxybenzyl-idene)-p -butylaniline, onto a platinum surface. Chl-liquid crystal electrodes in acidic buffer solutions gave cathodic photocurrents accompanied by the evolution of hydrogen gas (83). This was the first demonstration of photoelectrochemical splitting of water using in vitro Chi. Of particular interest in these studies is the effect of substituting the central metal in the Chi molecule. 

DNA films grown in acid buffer solutions presented greater DNA surface coverage, due to overlaying and superposition of DNA molecules, in relation to films formed in neutral buffer solutions [26]. The DNA network patterns define nanoelectrode systems with different active surface areas on the graphite substrate and form a biomaterial matrix to attach and study interactions with molecules such as drugs [27]. 

As in the SETFICS and TALSPEAK processes, the DIAMEX-SANEX/HDEHP process involves selectively back-extracting the trivalent actinides by a hydrophilic polyamino-carboxylate complexing agent, HEDTA, in a citric acid buffered solution (pH 3). However, the combination of HDEHP and DMDOHEMA at high acidity promotes the coextraction of some block transition metals, such as Pd(II), Fe(III), Zr(IV), and Mo(VI), which must be dealt with by specific stripping steps (as described on Figure 3.26) that increase the total volume of the output streams ... 

The An(III) are selectively stripped by HEDTA in a citric acid buffered solution (pH 3), while the Ln(III) are maintained extracted in the organic phase by HDEHP. 

Dianilino-l,T-binaphthyl-5,5 -disulfonate (bis-ANS) is a probe that has been shown to increase in fluorescence with soluble Ap in acidic buffer solutions.24 Briefly, Ap 42 was incubated for 30 minutes at room temperature in the presence of different polyphenols. Bis-ANS fluorescence (excitation = 360 nm, emission = 485 nm) was then measured by dilution of 100-pl aliquots in a final volume of 300 pi of citrate buffer (30 mM, pH 2.4) containing bis-ANS (25 pM), using a fluorescence multiwell plate reader (Bio-Tek Instruments , Inc.). To determine amyloid fibril formation, the thioflavin T (Th-T) fluorescence method was performed as previously described.24 Briefly, a fresh solution of Ap 42 was incubated at 37°C for 24 hours in phosphate-buffered saline (pH 7.4). After incubation, a 100-pl aliquot of solution was added in a final volume of 300 pi of phosphate buffer (50 mM, pH 6.0) containing 5 pM Th-T in the presence of different drugs. Fluorescence was then monitored at excitation and emission wavelengths of 450 and 485 nm, respectively. 

Parkash and Bansal reported the detection and determination of microgram quantities of ethylenediaminetetraacetic acid with molybdophosphoric acid by a spectrophotometric method [25]. For the detection of EDTA, 5 to 10 Amberlite IRA-400 resin beads (hydroxide form) were placed on a white spot-plate and blotted dry. One drop of sample solution was added, followed by one drop of 4% molybdophosphoric acid solution. A blue color develops if EDTA is present. For the determination, the sample solution (2 mL, containing 18.6 to 186 pg of EDTA) and 4% molybdophosphoric acid solution (3 mL) are mixed for 5 minutes and diluted to 10 mL with water or sodium acetate-acetic acid buffer solution of pH 2. The absorbance is measured at room temperature at 690 nm against a reagent blank. 

Buffer solutions are created by pairing a weak acid with a salt of its conjugate base or a base with a salt of its conjugate acid. Buffer solutions maintain a relatively stable pH when small amounts of acids or bases are added. 

Figure 6.3 Schematic of anodic polarization curve of iron,10 showing active-passive behavior of iron in sodium borate-boric acid buffer solution at pH 8.4...

The study of the chromatographic behavior of natural indole alkaloids on cyclodextrin polymers was different, and unexpectedly high retentions were observed in mildly acidic buffer solutions at room temperature, which permitted their separation by inclusion chromatography (25) (Table IV). Figure 7 shows the separation of two Vinca-alkaloids of very similar structure, the (+)-vincamine and (+)-apovincamine. 

If similar calculations are carried out for a number of other metal sulphide precipitates it is easy to classify these metals into two distinct groups. Metal ions like Ag+, Pb2+, Hg3+, Bi3+, Cu2+, Cd2+, Sn2+, As3+ and Sb3+ form sulphides under virtually any circumstances e.g. they can be precipitated from strongly acid (pH = 0) solutions. Other metal ions, like Fe2+, Fe3+, Ni2+, Co2+, Mn2+, and Zn2+ cannot be precipitated from acid solutions, but they will form sulphides in neutral or even slightly acid (buffered) solutions. The difference is used in the analytical classification of these ions the first set of ions mentioned form the so-called first and second groups of cations, while the second set are members of the third group. The separation of these ions is based on the same phenomenon. 

An acidic buffer solution has an excess of all the reactants and products, except for H30. Thus, when we try to change the concentration of H30 by adding strong acid or base, the equilibrium shifts, in accordance with LeChatelier s principle, to resist that change. The pH changes very little. (We will do calculations to show quantitatively how little the pH changes in such systems later in this section.)... 

There are also a number of wet chemical approaches used to isolate NH4 including precipitation with mercuric chloride (Fisher and Morrisey, 1985). This method, however, is problematic with marine samples and generates particularly toxic waste. A newer method converts NH4 in natural waters to N02, via hypobromite, and then to N2O using a sodium azide/acetic acid buffer solution the N2O produced is than analyzed using a mass spectrometer (Zhang et ah 2007). 

Nitrate can also be converted to N02 using cadmium reduction (columns or spongy cadmium) as described above. Once the NOa" is in the form of N02, the N02 can be isolated via organic extraction (e.g., Olson, 1981) or with SPE after the N02 is converted to an azo dye (Kator et al, 1992). Nitrate can be isolated by conversion to N2O via sodium azide in an acetic acid buffer solution (Mcllvin and Altabet, 2005). Another approaches uses a genetically engineered denitrifier to convert N03 to N2O (Sigman et al, 2001) the bacteria wiU denitrify NOa" in a sample to N2O, but lacking nitrous oxide reductase the bacteria cannot take the reaction to completion and form N2. The N2O produced by either approach can then be analyzed on a mass spectrometer. A more detailed discussion of these methods is presented in Chapter 31 by Lipschultz, this volume. 

Shapiro R, Klein RS. The deamination of cytidine and cytosine by acidic buffer solutions. Mutagenic imphcations. Biochemistry 1966 5 2358-2362. 

Nicotinamide (118) forms the 1,6-dihydropyridine (119) and the 6,6 -dimer (120) upon polarography in aqueous solution. The 4-isomer (121 Scheme 24) generates the aldehyde (122) when reduced in 0.8 M hydrochloric acid and the alcohol (123) in an alcoholic citric acid buffer solution. The thioamides produce the 4-aminomethyl- or 4-cyano-pyridines under related conditions. The isomeric cyanopyridines... 

D-Glucose and D-fructose, when heated in a phosphate-citric acid buffer solution of pH 7 in the presence of asparagine, produce considerable amounts of unfermentable reducing substances. n-Glucose, in the... 

The electrolytic method is an indirect oxidation, as the small amount of bromide present is constantly converted to bromine, the actual oxidant. Essentially the reaction is the same as the action of bromine in weakly acidic buffered solution. The presence of only a small amount of extraneous salts is of advantage in processing the reaction mixture. The... 

An acidic buffer solution is made up of a weak acid HA and its salt (M+A ), where H denotes the presence in the molecule of hydrogen atoms which can form ions, and M+ refers to a (usually) metal ion ... 

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