Phenolsulfonphthalein
354.38Phenol Red
Phenol, 4,4¢-(3H-2,l-benzoxathiol-3-ylidene)bis-,(S,S-dioxide).
3,3-bis(4-hydroxyphenyl)-3H-2,l-benzoxathiole 1,1-dioxide
[143-74-8].» Phenolsulfonphthalein contains not less than 98.0 percent and not more than 102.0 percent of C19H14O5S, calculated on the dried basis.
Packaging and storage—
Preserve in well-closed containers. No storage requirements specified.
Identification—
A:
Transfer 5 mg of Phenolsulfonphthalein to a 100-mL volumetric flask, dissolve in and dilute with sodium carbonate solution (1 in 100) to volume, and mix. Dilute 5.0 mL of the solution so obtained to 100.0 mL with sodium carbonate solution (1 in 100). Examined between 400 and 630 nm, the solution exhibits an absorption maximum at 558 nm. The specific absorbance at the maximum is between 1900 and 2100.
B:
Dissolve about 10 mg of Phenolsulfonphthalein in 2 mL of 1 N sodium hydroxide, and add 8 mL of water. To 5 mL of the solution so obtained add 1 mL of 0.1 N potassium bromide–bromate and 1 mL of diluted hydrochloric acid, shake, and allow to stand for 15 minutes. Render the solution alkaline with 1 N sodium hydroxide: an intense violet-blue color is produced.
Visual transition interval—
Dissolve 1.0 g of potassium chloride in 100 mL of water, and adjust with 0.01 N hydrochloric acid or sodium hydroxide to a pH of 6.8. Dissolve 0.1 g of Phenolsulfonphthalein in 100 mL of alcohol, and add 0.15 mL of this solution to the potassium chloride solution. The color of the resulting solution is yellow, with not more than a faint trace of green color. Titrate the solution with 0.01 N sodium hydroxide to a pH of 7.0: the color of the solution becomes orange. Continue the titration to pH 8.2: the color of the solution becomes red. Not more than 0.20 mL of 0.01 N sodium hydroxide is consumed in the entire titration.
Microbial enumeration tests 
61
and Tests for specified microorganisms 62—
The total aerobic microbial count does not exceed 1000 cfu per g, and the total combined molds and yeasts count does not exceed 100 cfu per g.
61 and Tests for specified microorganisms 62—
The total aerobic microbial count does not exceed 1000 cfu per g, and the total combined molds and yeasts count does not exceed 100 cfu per g.
Loss on drying 731—
Dry 1 g of the powdered Phenolsulfonphthalein at 105
to constant weight: it loses not more than 1.0% of its weight.
731—
Dry 1 g of the powdered Phenolsulfonphthalein at 105 to constant weight: it loses not more than 1.0% of its weight.
Residue on ignition 281:
not more than 0.2%, determined on a 0.5-g portion.
281:
not more than 0.2%, determined on a 0.5-g portion.
Insoluble substances—
To about 1 g of the finely powdered Phenolsulfonphthalein, accurately weighed, add a solution of 0.5 g of sodium bicarbonate in 12 mL of water. Allow to stand for 1 hour, shaking frequently. Dilute with sufficient water to make 100 mL, and allow to stand for 15 hours. Centrifuge at 2000 to 3000 g for 30 minutes, and decant the supernatant. Wash the residue first with 25 mL of sodium bicarbonate solution (1 in 100), then with 25 mL of water, and dry at 105: the weight of the insoluble residue does not exceed 0.5% of the weight of Phenolsulfonphthalein taken.
: the weight of the insoluble residue does not exceed 0.5% of the weight of Phenolsulfonphthalein taken.
Chromatographic purity—
Adsorbent:
0.25-mm layer of chromatographic silica gel mixture.
Application volume:
10 µL.
Developing solvent system:
a mixture of tert-amyl alcohol, glacial acetic acid, and water (100:25:25).
Test solution—
Transfer about 100 mg of Phenolsulfonphthalein to a 5-mL volumetric flask, dissolve in and dilute with 0.1 N sodium hydroxide to volume, and mix.
Diluted test solution—
Transfer 0.5 mL of the Test solution to a 100-mL volumetric flask, dilute with 0.1 N sodium hydroxide to volume, and mix.
Procedure—
Proceed as directed for Thin-Layer Chromatography under Chromatography 621. Allow the plate to air-dry until the solvent has evaporated, and expose the plate to ammonia vapor. Examine the plate under short-wavelength UV light. Not more than one spot, apart from the principal spot, appears in the chromatogram obtained from the Test solution. This spot is not more intense than the spot in the chromatogram obtained from the Diluted test solution: not more than 0.5% is found.
621. Allow the plate to air-dry until the solvent has evaporated, and expose the plate to ammonia vapor. Examine the plate under short-wavelength UV light. Not more than one spot, apart from the principal spot, appears in the chromatogram obtained from the Test solution. This spot is not more intense than the spot in the chromatogram obtained from the Diluted test solution: not more than 0.5% is found.
Assay—
Transfer about 0.9 g of Phenolsulfonphthalein, accurately weighed, to a 250-mL volumetric flask, dissolve in 15 mL of 1 N sodium hydroxide, dilute with water to volume, and mix. Transfer 10.0 mL of the solution so obtained to a glass-stoppered flask; add 25 mL of glacial acetic acid, 20.0 mL of 0.1 N potassium bromate VS, 5 mL of potassium bromide solution (1 in 10), and 5 mL of hydrochloric acid; and immediately insert the stopper into the flask. Allow to stand protected from light for 15 minutes. Quickly add 10 mL of potassium iodide solution (1 in 10), taking care to avoid the escape of bromine vapor; immediately insert the stopper into the flask; and shake vigorously. Rinse the stopper and the neck of the flask with a small quantity of water, and titrate the liberated iodine with 0.1 N sodium thiosulfate VS, using starch TS as the indicator. Perform a blank determination (see Residual Titrations under Titrimetry 541), and note the difference in volumes required. Each mL of the difference in volumes of 0.1 N sodium thiosulfate is equivalent to 4.43 mg of C19H14O5S.
541), and note the difference in volumes required. Each mL of the difference in volumes of 0.1 N sodium thiosulfate is equivalent to 4.43 mg of C19H14O5S.
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
| Monograph | Robert H. Lafaver, B.A.
Scientist 1-301-816-8335 |
(EM105) Excipient Monographs 1 |
| 61 |
Radhakrishna S Tirumalai, Ph.D.
Senior Scientist 1-301-816-8339 |
(MSA05) Microbiology and Sterility Assurance |
| 62 |
Radhakrishna S Tirumalai, Ph.D.
Senior Scientist 1-301-816-8339 |
(MSA05) Microbiology and Sterility Assurance |
USP32–NF27 Page 1299
Pharmacopeial Forum: Volume No. 31(1) Page 94