Thymol phthalein

Reactions are quenched by the addition of ethanol, which not only attenuates enzyme action but also facilitates solubilization of the fatty acids during subsequent titration to yield sodium salts (the presence of Ca2+ or Mg2+ can interfere in the assay by forming fatty acid soaps recalcitrant to titration). One will note a clearing of the titration vessel as titration progresses, even though the ethanol-quenched subsample may initially be turbid because of insoluble fatty acids. The choice of a thymol-phthalein end-point (pH 9.3 to 10.5) indicator is essential to ensure the complete titration of all fatty acids, in view of the relative high pKa values for oleic acid noted earlier. 

Figure 15-3 compares the performance of a thymol-phthalein acid phosphatase assay with that of the PSA assay for discrimination between BPH and prostatic carcinoma stages A through D. Although each has been claimed to be... 

Urea is tested for the content of nitrogen using H,SO and formaldehyde. The indicator used is a mixed indicator containing 0.5 g phenolphthalein and 0.5 g thymol phthalein dissolved in 100 ml ethanol. A 25% formaldehyde solution used should be neutralised before use. The procedures of the method is briefly described below. 

Volume % Alcohol S R FOR Thymol- PHTHALEIN S R. FOR Phenol- PHTHALEIN S R. FOR Thymol Blue S R FOR CURCUMIN... 

Fig. 12. I, tropeolin 0 II, thymol-phthalein III, phenolphthalein IV, thymol blue.

Finely divided particles in suspension can also interfere with colorimetric mea.surements if one of the indicator forms happens to be preferentially adsorbed. Lanthanum hydroxide is a very striking example of such interference. This compound is a strong base which is very slightly soluble in water. A saturated solution in water at 25° has a pH of 9.0. If the pH of a suspension (turbid solution) of the solid hydroxide is measured with thymol-phthalein, the result obtained is 10.5. The suspension is colored a dark blue, although thymolphthalein is colorless at pH 9.0. The precipitate settles after a time, leaving a colorless supernatant solution although the solid itself is dark blue. Because of the strong basic properties of solid lanthanum hydroxide, it forms on its surface a salt with the indicator acid. In other words, the adsorption of the colored indicator anion predominates, and the presence of the solid phase favors a displacement of the indicator equilibrium towards the alkaline form. Phenol-... 

After hydrolysis, Glick suggested that the sample be neutralized to the thymol-phthalein end point (pH 9-10) with acetic acid. A 2% solution of methanolic... 

Irreversible reaction of [18] iodine with acetylsalicylic acid, aethaverine, amidopyrine, ascorbic acid, benzo-caine, quinine, dihydrocodeine, fluorescein, glycine, hydrocortisone acetate, isoni-azid, metamizole, papaverine, paracetamol, phenacetin, phenol-phthalein, piperazine, resorcinol, salicylic acid, salicylamide, sulfaguanidine, thymol, triethanolamine, tris buffer detection by reaction chromatography... 

Thymol blue (acid) Thymol-sulphone-phthalein Red Yellow 1-2-2-8... 

The measurements were carried out with thymol blue and phenol-phthalein as indicators. 

Indicator papers frequently aid in the identification of chemicals. Strong mineral acids are acid towards methyl violet or thymol blue papers, moderately strong acids react acid towards Congo paper, and very weak acids are acid towards htmus and azolitmin paper. Strong bases show an alkaline reaction with turmeric or tropeolin 0 paper, medium strong bases with phenol-phthalein, and very weak bases with litmus or azolitmin paper. These papers are not recommended for use in quantitative analysis. ... 

Chloroform and Bromoform are formed if the chloride or bromide of the alkalies is used (comp. Elbs and Herz, who deny this ). Analogous to these substitution reactions is the formation of aristol, a di-thymol-di-iodide, as made by Messinger and Vortmann, by the electrolysis of thymol with the addition of potassium iodide. Similar to this also is the preparation of nosophene, a tetra-iodo-phenol-phthalein (Classen and L6b ). 

TropceoUrt-phthalein, or t.p. indicator is prepared by miring equal volumes of 0 1 per cent, tropaeolin 00 and phenol phthalein. Like thymol blue, it has a triple change red below pH 2, yellow from pH 3 to pH 8 3, and red above pH 9. 

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