Hydrolysis alkalinity titration

The pH-stat technique monitors the course of a reaction in which each peptide bond is hydrolyzed by one or several enzymes. pH-stat evaluates the progress of hydrolysis by titrating the released amino groups with an alkaline solution. Enzymes work at constant pH and temperature during the entire process, so that no buffering is needed. 

Discussion. Iodine (or tri-iodide ion Ij" = I2 +1-) is readily generated with 100 per cent efficiency by the oxidation of iodide ion at a platinum anode, and can be used for the coulometric titration of antimony (III). The optimum pH is between 7.5 and 8.5, and a complexing agent (e.g. tartrate ion) must be present to prevent hydrolysis and precipitation of the antimony. In solutions more alkaline than pH of about 8.5, disproportionation of iodine to iodide and iodate(I) (hypoiodite) occurs. The reversible character of the iodine-iodide complex renders equivalence point detection easy by both potentiometric and amperometric techniques for macro titrations, the usual visual detection of the end point with starch is possible. 

In a study of the alkaline hydrolysis of ethyl 2-methylpropenoate in 84.7% ethanol, Thomas Watson (JACS 77 3962, 1956) obtained the data of the first two columns of the table, t in sec, NaOH titre/cc. The initial concentrations of both ester (A) and alkali (B) were 0.058 mol/liter. 10 cc of the reaction mixture were removed from the vessel at the time stated, pipetted into 10 cc of 0.0668 mol/liter HC1 and the excess titrated with 0.0511 nol/liter NaOH. Find the mean value of the second order specific rate. 

Singhal et al. [78, 79] have described a titrimetric method for the determination of low levels of Oxamyl residues in soils. Their investigations revealed that after hydrolysis Oxamyl gave a brown precipitate with carbon disulphide and an alkaline solution of copper(II) sulphate. This reaction suggested a procedure for the determination of Oxamyl by titration with ethylene diamine tetracetic acid of the copper remaining unreacted to the 1-(2 pyridylazo)-2-naphthol end-point indicator). The following stoichiometric reaction appeared to occur between Oxamyl and the reagents ... 

Thioetherification of PECH is feasibly performed in DA-solvents as already described in the patent (20J. For example, the highest substitution was obtained by the reaction of P(ECH-EO)(1 1 copolymer of epichloro-hydrin and ethylene oxide) and equimolar thiophenoxide in HMPA at 100°C for 10 h as DS 83% for sodium and 93% for potassium salts. The DS in our nucleophilic substitution was estimated by the elemental analysis as well as the titration of liberated chloride ion with mercuric nitrate (21). In the latter method, reacted medium was pretreated with hydrogen peroxide when the reductive nucleophiles which can react with mercuric ion were used. As described before for PVC, thiolation was also achieved conveniently with iso-thiuronium salt followed by alkaline hydrolysis without the direct use of ill-smelling thiolate. The thiolated PECH obtained are rubbery solids, soluble in toluene, methylene chloride, ethyl methyl ketone and DMF and insoluble in water, acetone, dioxane and methanol. 

Chlorpromazine was determined by precipitation with an excess of 0.2% ammonium reineckate solution, and titration of the unconsumed reagent bromatometrically after alkaline hydrolysis [67]. Excess hexathiocyanato-chromate was used as a precipitating reagent for chlorpromazine, whereupon the unconsumed reagent was determined with KBr03 in the filtrate [68]. 

The ester function was determined by alkaline hydrolysis followed by precipitating the liberated acids as calcium salts. In the present work, samples of 1-1.5 grams were added to 50 ml. of 0.2N aqueous sodium hydroxide and refluxed with continuous stirring under nitrogen for 18-24 hours. After hydrolysis the samples were titrated to a pH of 9 with hydrochloric acid. Then 15 ml. of IN calcium acetate was added, and the sample was stirred rapidly under a stream of nitrogen for 1 hour. The suspension of calcium salt was filtered, washed with dilute base until free of excess calcium acetate as determined by titration with ethylenediaminetetraacetic acid (EDTA), and dried under a stream of nitrogen. Calcium was determined on the dried product. 

Titration of the products of alkaline hydrolysis of the teichoic acid from L. arabinoms showed that 7-8% of the phosphate groups remain as phos-... 

Schultz, T.H. 1965a. Determination of acetyle in pectin. Determination of acetate ester content by alkaline hydrolysis followed by distillation and titration of the liberated acetic acid. In Methods in Carboydrate Chemistry, Vol. 5 (R.L. Whistler, ed.) pp. 187-189. Academic Press, New York. 

The 3-4 Cals, here represent the heat of admixture of a mol of ammonia with water, and this is much greater than the heat of admixture of ammonia with other liquids which do not react chemically with the ammonia. There is also a possibility that ammonia hydrates. NH3.nH20, are formed, vide infra and a possibility that the ammonium hydroxide is ionized NH OH NH +OH. In agreement with the assumption that ammonium hydroxide is formed which acts as a weak base, the liquid tastes alkaline it reddens turmeric colours the juice of violets green and colours litmus, etc., the same as do soln. of the alkali hydroxides. These changes of colour disappear on exposure to air owing to the volatilization of the ammonia— the volatile alkali of the early chemists. The feeble character of ammonium hydroxide as a base is evidenced by its heat of neutralization with acids which is about 1-5 Cals, less than is the case with potassium or sodium hydroxides like other weak bases, the soln. cannot be satisfactorily titrated with phenolphthalein S. Arrhenius found that its effect on the hydrolysis of ethyl acetate is about 40 times leBS than that of sodium hydroxide and the electrical conductivity of aq. soln. of... 

Assessment of indomethacin powder had been specified in the U.J5. XIX and the British Pharmacopeia, 1980 as a back titration with hydrochloric acid after alkaline hydrolysis(13,14). This method can attain a precision of + 0.8%(62). A direct titration for tablets and capsules is described using sodium hydroxide. If performed rapidly with phenolphthalein indicator, a precision of +0.3% is attainable. 8 The latter procedure serves to differentiate ester formation as well as hydrolysis products from intact material. The presence of parachlorobenzoic acid and 5-methoxy-2-methylindole-3-acetic acid are cause for positive error. 

Titration with silver nitrate is used both to confirm the lack of chloride ions in the sample and, after alkaline hydrolysis, as an assay for the drug. The compendial assays are performed potentiometrically using silver and calomel electrodes, the latter modified to contain saturated potassium sulfate solution [25—27]. 

The assay is performed by potentiometric titration of the chloride ions liberated by alkaline hydrolysis, as described under 9.1 Assay (a). 

Generally speaking the classical alkaline hydrolysis reaction followed by back-titration could be used to determine steroid esters. The results for 21-acyloxycortico-steroids (where R = H, OH) are however quite unsatisfactory. The reason behind the unacceptable result is the auto-oxidation of the a-ketol side-chain in an alkaline medium. Because of the formation of acidic products in side reactions, there is an over consumption of base in the titration and a corresponding over determination of the amount of steroid. 

The initial acidity or alkalinity of paper is measured conventionally by the pH of the water extract or by the total titratable acidity or alkalinity of the water extract (TAPPI T428 and ASTM D548). The extract for measurement of pH may be prepared as the cold water extract (TAPPI T509) or as the hot water extract (TAPPI T435 and ASTM D778). In the absence of hydrolyzable salts, it may be expected that hot and cold extraction methods will give approximately the same results. If hydrolyzable acid salts (particularly alum) are present, the hot extraction method yields a lower pH because of hydrolysis promoted at the higher temperature to yield free acids. 

At the equivalence-point, which represents the other extreme of the titration, a and h are equal, and cn may be neglected in comparison with CoH , since the solution is alkaline owing to hydrolysis of the salt of the weak acid and strong base. It is seen, from equation (42), therefore, that B is now equivalent to a — coh , and, neglecting the activity coefficients, equation (39) becomes... 

The iodometric method was then modified (G23, G24) by changing the final concentration of trichloroacetic acid from 8% to 3.3%, leaving more proteose-like substances in the filtrate, and quantitating the mucosubstances in the filtrate colorimetrically by the Folin-Ciocalteu reaction with the phenol reagent, instead of iodometric titration. This colorimetric reaction determines the tyrosine and tryptophan content after alkaline hydrolysis of the total dissolved mucin. 

Now, Gulland and coworkers have found, by electrometric titration, that yeast ribosenucleic acid possesses four acid dissociations per tetranucleotide unit, three of which are primary dissociations, and one a secondary dissociation of phosphoric acid. (It was verified that de-aminated yeast ribosenucleic acid is constituted similarly, thus eliminating the possibility of phosphoamide links.) In addition, they found that mild alkaline hydrolysis diminishes the molecular weight of the poly-tetranucleotide, and the titration results for the product suggested that a further secondary dissociation of phosphoric acid is set free that is, that if it were possible to isolate the fundamental tetranucleotide, the penta-basic product should have three primary and two secondary phosphoric acid dissociations. 

---