Salt/buffer systems

For ionic samples it is recommended that salt/buffer systems be used as eluants. The salts most commonly used are sodium sulfate, sodium nitrate, and sodium acetate because these cause little corrosion to stainless steel column hardware even at low pH. Ionic strength is varied according to sample type but generally does not exceed 1.0 M because increasing salt concentration promotes hydrophobic interaction. Often a buffer is used to allow pH to be controlled. 

Fig. 1. Purification of 2 dNAD+ by strong anion exchange-HPLC. Retention time of boronate-purified compounds before (A) and after (B) treatment with bacterid alkaline phosphatase. (C) Retention time of pure 2 dNAD+ on a PartisiHO SAX column of 250 mm x 4.6 mm I.D. utilizing a low salt buffer system at a flow rate of 1 ml/min. 

Al-Dabbas, M. M., K. Al-Ismail, K. Kitahara, N. Chishaki, F. Hashinaga, T. Suganuma, and K. Tadera. 2007. The effects of different inorganic salts, buffer systems, and desalting of Varthemia crude water extract on DPPH radical scavenging activity. Food Chemistry 104(2) 734-739. 

Na20 20 4H20 (60). Mixtures of B(OH)2 and B(OH) 4 appear to form classical buffer systems where the solution pH is governed primarily by the acid salt ratio, ie, [B(OH)3]/[B(OH) ]. This relationship is nearly correct for solutions of sodium or potassium (1 2) borates, eg, borax, where... 

Equilibrate the packed gel with at least 3 bed volumes at 1 ml/min of the desired buffer system. It is recommended to include 50-300 mM of salt in the buffer. 

An alternative way of eliminating water in the RPLC eluent is to introduce an SPE trapping column after the LC column (88, 99). After a post-column addition of water (to prevent breakthrough of the less retained compounds), the fraction that elutes from the RPLC column is trapped on to a short-column which is usually packed with polymeric sorbent. This system can use mobile phases containing salts, buffers or ion-pair reagents which can not be introduced directly into the GC unit. This system has been successfully applied, for example, to the analysis of polycyclic aromatic hydrocarbons (PAHs) in water samples (99). 

This very simple result makes it easy to make an initial choice of a buffer we just select an acid that has a pfC, close to the pH that we require and prepare an equimolar solution with its conjugate base. When we prepare a buffer for pH > 7 we have to remember that the acid is supplied by the salt, that the conjugate base is the base itself, and that the pKa is that of the conjugate acid of the base (and hence related to the pKh of the base by pR l + pKh = p/conjugate acid and base have unequal concentrations—such as those considered in Examples 11.1 and 11.2—are buffers, but they may be less effective than those in which the concentrations are nearly equal (see Section 11.3). Table 11.1 lists some typical buffer systems. 

A model of blending aqueous salt buffers for chromatography has been developed.1 The model assumed full miscibility, low mixing enthalpy and low volume change. It reproduced experimental S-curves of buffer strength produced by a Pharmacia P3500 dual piston system equipped with a model 24 V dynamic mixer with 0.6 mL internal volume as well as those produced by a BioSepra ProSys 4-piston system equipped with two dynamic mixers of 1.2 mL internal volume. 

Buffer systems for parenterals consist of either a weak base and the salt of a weak base or a weak acid and the salt of a weak acid. Buffer systems commonly used for injectable products are acetates, citrates, and phosphates (see Table 2). Amino acids are being increasingly used as buffers, especially for polypeptide injectables. 

The most common buffering system containing a weak base together with its salt formed with a strong acid is ammonia with ammonium sulphate. Some useful buffers are obtained from combinations of unrelated acids or bases with salts. The following combinations find occasional use in textile coloration processes, but the acetates and orthophosphates are most frequently used ... 

This is the most common route, the reagent being a metal compound/solvent combination. Typical conditions call for the metal salt (e.g., acetate) in a buffer system (e.g., NaOAc/AcOH) and a co-solvent such as chloroform. Generally the reaction mixture is refluxed until the metal complex spectrum (see Section 9.22.5.6 and Table 4) is fully developed. Metal acetylacetonates and metal phenoxides have also been employed. The topic has been reviewed in detail by Buchler,51 who has also summarized the history and classification of metal complexes of this series, and the mechanisms of metalation.52... 

Buffers contain mixtures of weak acids and their salts (i.e., the conjugate bases of acids), or mixtures of weak bases and their conjugate acids. Typical buffer systems used in pharmaceutical dosage forms include mixtures of boric acid and sodium borate, acetic acid and sodium acetate, and sodium acid phosphate and disodium phosphate. The reason for the buffering action of a weak acid, HA (e.g., acetic acid) and its ionized salt, A" (e.g., sodium acetate) is that A" ions from the salt combine with the added hydrogen ions, removing them from solution as undissociated weak acid. 

Phosphate buffer, pH6.0-7.7, 0.01-1.0M Table 7.4 gives the molar fraction x of the two basic salts of the buffer system H2 POj/HPOj for different pH and molarities M. The weighted portion g in grams of the salts Me2HP04 and MeH2P04 (Me sodium or potassium) per 1000 ml buffer is calculated by... 

A number of soluble oxymetal salts were screened, particularly those of Mo, W, V, Ti and Zr, which are known to act via peroxometal and/or oxometal mechanisms (8). Unfortunately, no alternative to the existing KBr based protocol was found, so it was decided to, at least, improve the aqueous buffer system to significantly reduce the volume of the aqueous phase. 

All these electrolytes are neutral in Bronsted acid-base properties. Although rather exceptional, an acid, a base, or a pH buffer may be added to the supporting electrolyte of neutral salts. The acid-base system to be selected depends on the purpose of the measurement. We often use trifluoromethanesulfonic acid (CF3S03F1) as a strong acid acetic acid, benzoic acid, or phenol as a weak acid an amine or pyridine as a weak base and tetraalkylammonium hydroxide (ILtNOH) as a strong base. Examples of buffer systems are the mixtures of picric acid and its R4N-salt and amines and their PlCl04-salts. Here, we should note that the acid-base reactions in aprotic solvents considerably differ from those in water, as discussed in Chapter 3. 

There are many different buffer systems useful for maintaining particular pH values. The acetic acid—sodium acetate system is good for maintaining a pH around 4.8. Buffer solutions containing equal mixtures of a weak base and a salt of that weak base maintain alkaline pH values. For example, a buffer solution of the weak base ammonia, NH3, and ammonium chloride, NH4C1, is useful for maintaining a pH about 9.3. 

Blood has several buffer systems that work together to maintain a narrow pH range between 7.35 and 7.45. A pH value above or below these levels can be lethal, primarily because cellular proteins become denatured, which is what happens to milk when vinegar is added to it. The primary buffer system of the blood is a combination of carbonic acid and its salt, sodium bicarbonate, shown in Figure 10.21. Any acid that builds up in the bloodstream is neutralized by the basic action of sodium bicarbonate, and any base that builds up is neutralized by the carbonic acid. 

Remove salt while exchanging the reaction mixture with an appropriate buffer system by dialysis or size-exclusion chromatography. 

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