Borax-sodium hydroxide buffer

The diazotization of amino derivatives of six-membered heteroaromatic ring systems, particularly that of aminopyridines and aminopyridine oxides, was studied in detail by Kalatzis and coworkers. Diazotization of 3-aminopyridine and its derivatives is similar to that of aromatic amines because of the formation of rather stable diazonium ions. 2- and 4-aminopyridines were considered to resist diazotization or to form mainly the corresponding hydroxy compounds. However, Kalatzis (1967 a) showed that true diazotization of these compounds proceeds in a similar way to that of the aromatic amines in 0,5-4.0 m hydrochloric, sulfuric, or perchloric acid, by mixing the solutions with aqueous sodium nitrite at 0 °C. However, the rapidly formed diazonium ion is hydrolyzed very easily within a few minutes (hydroxy-de-diazonia-tion). The diazonium ion must be used immediately after formation, e. g., for a diazo coupling reaction, or must be stabilized as the diazoate by prompt neutralization (after 45 s) to pH 10-11 with sodium hydroxide-borax buffer. All isomeric aminopyridine-1-oxides can be diazotized in the usual way (Kalatzis and Mastrokalos, 1977). The diazotization of 5-aminopyrimidines results in a complex ring opening and conversion into other heterocyclic systems (see Nemeryuk et al., 1985). 

Carbonate and sodium metaborate are the most stable alkalis. Borax does not buffer well against a rise in pH, and hydroxide loses its alkalinity rapidly as the solution is diluted. 

Borax Buffer Dissolve 47.63 g of sodium borate decahy-drate in warm water. Cool to room temperature. Add 20 mL of 4 N sodium hydroxide solution, adjust the pH of the solution to 9.7 with 4 N sodium hydroxide, and dilute to 2 L with water. 

Fig. 2. Effect of pH on the ultraviolet spectrum of phenobarb-itone. A, non-ionised barbiturate in 0.1 M hydrochloric acid B, mono-anion in 0.05M borax buffer (pH 9.2) C, di-anion in 0.5M sodium hydroxide (pH 13).

Buffers hitherto proposed have not exceeded a pH of 10.0. Accordingly the same authors have prepared a series of mixtures for strongly alkaline media. Sodium carbonate-borax mixtures are used for the range 9.20-11.0, whereas between 11.0 and 12.2 mixtures of disodium phosphate and sodium hydroxide are employed. When buffers with a still higher pH are needed, they may be obtained conveniently by diluting 0.1 N NaOH with carbonate free water. 

Equal vols. of amyl alcohol containing 1% (v/v) di-2-ethyl hexyl phosphate and 0.5% sodium chloride in borate buffer (0.62 g boric acid, 0.21 g borax) are mixed. Adjust pH to 8.0 with sodium hydroxide while stirring for 30 min. Separate phases dip paper in lower phase, blot, apply samples and dry several minutes. While still wet develop with organic phase either ascending or descending Detection... 

A similar quantitative analysis of six water-soluble vitamins (B, B2, Bg, C, nicotinamide, and pantothenic acid) in a pharmaceutical formulation using CZE in uncoated fused silica capillaries with UV detection was described by Fotsing et al. (91). Eor the B-group vitamins, a good compromise among resolution, analysis time, and analyte stability was obtained by use of 50 mM borax buffer pH 8.5. A capillary wash with sodium hydroxide was necessary between successive runs to minimize absorption of excipients from the pharmaceutical formulation to the capillary surface, otherwise giving rise to a progressive decrease of the electro-osmotic flow. 

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