Bromothymol blue reagent

Bromothymol blue reagent 45 Brucine 60, 67, 315, 316 Bufotenine 380 Bunitrolol 429... 

PHOTOMETRIC DETERMINATION OF ACIDIC IMPURITIES IN OILS AND ORGANIC LIQUIDS WITH THE USE OF THE ION PAIR OF TRINONYLOCTADECYLAMMONIUM AND BROMOTHYMOL BLUE AS THE COLORED REAGENT... 

Al-Bromosuccinimide (NBS), 13 116 brominated butyl rubber from, 4 434 bromination reagent, 4 344 Bromothymol blue, 4 362t Bromotrichloroethane, 6 269 Bromotrifluoromethane, 4 348, 348t Bromous acid, 4 333... 

A fiber optic sensor for the determination of sodium was reported by Burgess.<52) A bifurcated fiber with a reference fiber 5 mm apart from the tip was used to observe the changes of bromothymol blue (Amax = 620 nm) attached to Nafion in the presence of sodium ions. As the tip was saturated, the probe was renewed with fresh reagent. However, the epoxy holding the fibers was prone to damage from high sodium concentrations of around 2.5 M and the sensitivity of analysis was low. 

The pH of the solution therefore decreases. Hence if the solution is initially almost neutral to, say, bromothymol blue (green), then upon the addition of mannitol the colour becomes yellow. It is advisable when testing for minute quantities of borates to recrystallize the mannitol from a solution neutralized to bromothymol blue, wash with pure acetone and dry at 100°. The reagent (a 10 per cent aqueous solution of mannitol) may also be neutralized with 0 01m potassium hydroxide solution, using bromothymol blue (a 0 04 per cent solution in 96 per cent ethanol) as indicator. Only periodate interferes with the test it can be decomposed by heating on charcoal. 

Render the test solution almost neutral to bromothymol blue by treating it with dilute acid or alkali (as necessary) until the indicator turns green. Place a few drops of the test solution in a micro test-tube, and add a few drops of the reagent solution. A yellow colouration is obtained in the presence of a borate. It is advisable to carry out a blank test with distilled water simultaneously. 

An interesting example is die assay of clonidine hydrochloride in injections and tablets (British Pharmacopoeia, 1980). In 0.01 Mhydrochloric acid, clonidine exhibits two sharp maxima ne - 272 nm and 279 nm, which are not suitable for precise measurement. However, clonidine forms an ion pair with bromothymol blue, and this can be readily extracted into chloroform for subsequent measurement of the broad maximum near 420 nm. Because of the intiinsic variabihty of reagents used in such methods, a pharmacopoeial reference standard is employed for cahbration. A similar policy is adopted for assays involving chemical modification of the drug, as in the tetrazolium assay for corticosteroids, the assay for folic acid involving hydrolysis, diazotisation, and coupling with N-(l-naphthyl)ethylenediamine, and the reaction of penicillins with imidazole and mercuric salts. 

The indicators were obtained from Kodak Laboratory Chemicals, Aldrich Chemical Company, and J.T. Baker and were used without further purification. The indicators employed in the majority of the titrations were bromocresol green and bromothymol blue each of which exhibits two acid-base transitions at Pka = -3.7, +4.6, and -1.5, +6.8, respectively(20, 22, 26) The medium for the titration and electrophoretic mobility experiments was benzene (Burdick and Jackson Laboratories) having a water content of less than 0.03 percent. The base used as titrant was n-butylamine, Baker analyzed reagent grade. 

Test strips, 10 mL of bromothymol blue solution + 10 mL of urease solution. Dip paper strips into the reagent, let dry naturally. The strips should be orange. Store in a dark bottle. 15/S Urease, 0.2 g urease powder to a few drops of water to make a paste then dilute to 10 mL with water. 

Reagent The carrier stream (1.0 x 10" M NaOH, carbonate free) is prepared by mixing 5 mL of 0.1 M sodium hydroxide (it is convenient to use, for example, Titrisol standard solution Merck, Germany) with 50 mL of 96% ethanol and 2 mL bromothymol blue indicator stock solution (see Section 6.3), making the final volume up to 500 mL with distilled water. 

Total acidity in must or wine, also known as titratable acidity , is determined by neutralization, using a sodium hydroxide solution of known normality. The end point of the assay is still often determined by means of a colored reagent, such as bromothymol blue, which changes color at pH 7, or phenolphthalein, which changes color at pH 9. Using one colored reagent to define the end point of the assay rather than the other is a matter of choice. It is also perfectly conventional to use a pH meter and stop the total acidity assay of a wine... 

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