Standard hydrochloric acid-salt mixture

The pH of the mixture was adjusted to 7.5 by adding a saturated sodium bicarbonate solution. After being washed twice with diethyl ether, the reaction solution was acidified to pH 2 with dilute hydrochloric acid and extracted with ether. The ether solution containing the free penicillin was washed twice with water and then extracted with 50 ml of N potassium bicarbonate solution. After freeze drying of the obtained neutral solution, the potassium salt of o-azidobenzylpenicillin was obtained as a slightly colored powder (11.2 grams, 54% yield) with a purity of 55% as determined by the hydroxylamine method (the potassium salt of penicillin G being used as a standard). 

Procedure (indirect method). Weigh out accurately 0.1-0.2 g of the ammonium salt into a 500 mL Pyrex conical flask, and add 100 mL of standard 0.1M sodium hydroxide. Place a small funnel in the neck of the flask in order to prevent mechanical loss, and boil the mixture until a piece of filter paper moistened with mercury(I) nitrate solution and held in the escaping steam is no longer turned black. Cool the solution, add a few drops of methyl red, and titrate with standard 0.1M hydrochloric acid. Repeat the determination. 

Three methods for determining mineral carbon dioxide in coal were investigated using bituminous coal. The titrimetric method is claimed to be superior to either of the then-used British standard gravimetric or manometric methods (BS 1016). The procedure involves the decomposition of carbonate minerals with hydrochloric acid and absorption of the evolved carbon dioxide in a mixture of benzylamine, ethanol, and dioxan. This mixture forms a stable salt of benzylcar-bamic acid, which is then titrated with sodium methoxide. The method was said to be suitable for all concentrations of carbon dioxide. It is especially accurate for low concentrations, and it is much more rapid than other methods tested. 

The separation of cimetidine and its metabolites is usually carried out by extraction of the biological medium with 1-octanol fran an aqueous alkaline pH solution followed by mixing, addition of an internal standard and centrifugation. The extraction with octanol is repeated and the combined extracts are re-extracted with dilute hydrochloric acid. The aqueous acid solution is then separated, ethanol is added and mixed. This is then followed by saturating the mixture with a large amount of potassium or sodium carbonate to "salt out" the ethanol layer which contains the cimetidine and its metabolite, the sulfoxide. Several different internal standards have been used Metiamide, 1-methyl-3-[2-[[(5-methyl-imidazole-4-yl) -methyl] thio]ethyl]-2-thiourea,19 31 39 (N-cyano-N1-methy1-N"-(3-(4-imidazolyl)-propyl)guanidine32, and 13-hydroxy-theophylline. 0 After extraction the samples are either evaporated to dryness and reconstituted with a known amount of ethanol, injected directly or dissolved in the mobile phase for the HPLC analysis. 

Indirect Titration (Method B). A weighed sample of salt was added to a flask containing methanol and a known excess of aqueous sodium hydroxide solution. The mixture was stirred and warmed on a hot plate for 1 h. After cooling, the amount of excess hydroxide present was determined by titration with standard aqueous hydrochloric acid. The titration was monitored using a pH electrode and meter, and the end point was determined from the resulting titration curve. 

Procedure Pifty cc of a molal solution of pure sodium sulfite (prepared dissolving 252 g of hydrated sodium sulfite or 126 g of the anhydrous salt in sufficient distilled water to make one liter of solution) and three drops of thymolphthalein indicator solution (0.1 per cent in alcohol) are placed in a 500-cc Erlenmeyer flask and carefully neutralised by titration vith normal sulfuric or hydrochloric acid until the blue color of the indicator has disappeared (one or two drops is sufficient). An accurately measured and substantially neutral formaldehyde sample is then added to the sodium sulfite and the resulting mixture titrated with the standard add to complete decoloration. One cc of normal acid is equivalent to 0.03002 g formaldehyde and the per cent formaldehyde in the sample is determined "by the following equation ... 

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