Roxarsone
(rox ar' sone).
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263.04Arsonic acid, (4-hydroxy-3-nitrophenyl)-.
4-Hydroxy-3-nitrobenzenearsonic acid
[121-19-7].» Roxarsone contains not less than 98.0 percent and not more than 101.0 percent of C6H6AsNO6, calculated on the dried basis.
Packaging and storage—
Preserve in well-closed containers.
Labeling—
Label it to indicate that it is for veterinary use only.
USP Reference standards 
11
—
11—
USP Roxarsone RS 
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Identification—
Solution:
8 µg per mL.
Medium:
0.1 N hydrochloric acid in methanol.
Loss on drying 731—
Dry it at 100
for 6 hours: it loses not more than 1.0% of its weight.
731—
Dry it at 100 for 6 hours: it loses not more than 1.0% of its weight.
Residue on ignition 281:
not more than 0.5%.
281:
not more than 0.5%.
Limit of trivalent arsenic—
Transfer 2.50 g of Roxarsone to a 250-mL conical flask, add 5.0 mL of a solution containing 0.1237 mg of anhydrous arsenic trioxide per mL, 10 mL of water, and 4.0 mL of 5 N sodium hydroxide, and swirl to dissolve. Add 5.0 mL of glacial acetic acid, and a stirring bar, and titrate with 0.0025 N iodine VS, determining the endpoint potentiometrically. Perform the same procedure on a second 2.50-g portion of Roxarsone, except to replace the 5.0 mL of arsenic trioxide solution with 5.0 mL of water. Calculate the percentage of trivalent arsenic (As+++) in the Roxarsone taken by the formula:
(0.4623 / 25)[VB / (VA 
VB)]
in which 0.4623 is the arsenic equivalent of the 5.0 mL of arsenic trioxide solution, and VA and VB are the volumes, in mL, of 0.0025 N iodine consumed in the first and second titrations, respectively. Not more than 0.05% is found.
VB)]
Content of total arsenic—
Transfer about 200 mg of Roxarsone, accurately weighed, to a clean, dry 300-mL Kjeldahl flask, and clamp the flask at an angle of 45. Add 5 mL of sulfuric acid, 10 mL of nitric acid, 5 mL of a saturated solution of sodium sulfate, and several glass beads. Heat to boiling, heat strongly until dense white fumes are produced, and continue heating until the volume is reduced to a few mL. Allow to cool, and cautiously rinse the neck of the flask with about 5 mL of water. Boil again, and continue heating for 30 minutes after the water has boiled away. Allow to cool, add 100 mL of water and 4 mL of 50% potassium iodide solution, and boil to expel the iodine vapors. Continue boiling until the solution becomes colorless, occasionally adding water to maintain the volume at about 60 mL. Add 60 mL of water, and immediately cool the solution. Add 2 drops of phenolphthalein TS, neutralize with 5 N sodium hydroxide, and then make slightly acidic (pH 6.5 to 7.0) by adding a small quantity of 18 N sulfuric acid. Transfer this solution to a beaker with the aid of a water rinse, add 4 g of sodium bicarbonate, and stir with a stirring bar. Titrate with 0.05 N iodine VS, determining the endpoint potentiometrically. Each mL of 0.05 N iodine is equivalent to 1.873 mg of arsenic (As): between 28.0% and 28.8% is found, calculated on the dried basis.
. Add 5 mL of sulfuric acid, 10 mL of nitric acid, 5 mL of a saturated solution of sodium sulfate, and several glass beads. Heat to boiling, heat strongly until dense white fumes are produced, and continue heating until the volume is reduced to a few mL. Allow to cool, and cautiously rinse the neck of the flask with about 5 mL of water. Boil again, and continue heating for 30 minutes after the water has boiled away. Allow to cool, add 100 mL of water and 4 mL of 50% potassium iodide solution, and boil to expel the iodine vapors. Continue boiling until the solution becomes colorless, occasionally adding water to maintain the volume at about 60 mL. Add 60 mL of water, and immediately cool the solution. Add 2 drops of phenolphthalein TS, neutralize with 5 N sodium hydroxide, and then make slightly acidic (pH 6.5 to 7.0) by adding a small quantity of 18 N sulfuric acid. Transfer this solution to a beaker with the aid of a water rinse, add 4 g of sodium bicarbonate, and stir with a stirring bar. Titrate with 0.05 N iodine VS, determining the endpoint potentiometrically. Each mL of 0.05 N iodine is equivalent to 1.873 mg of arsenic (As): between 28.0% and 28.8% is found, calculated on the dried basis.
Assay—
Mobile phase—
Prepare a degassed mixture of water, methanol, and 0.17% (v/v) phosphoric acid (700:300:60). Make adjustments if necessary (see System Suitability under Chromatography 621).
621).
Standard preparation—
Transfer about 50 mg of USP Roxarsone RS, accurately weighed, to a 50-mL volumetric flask. Dissolve in and dilute with 1.2 N sodium hydroxide to volume, and mix. Transfer 10.0 mL of this stock solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. This solution contains about 0.1 mg of USP Roxarsone RS per mL.
Assay preparation—
Transfer about 50 mg of Roxarsone, accurately weighed, to a 50-mL volumetric flask. Dissolve in and dilute with 1.2 N sodium hydroxide to volume, and mix. Transfer 10.0 mL of this stock solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.
Chromatographic system
(see Chromatography 621)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.
621)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C6H6AsNO6 in the portion of Roxarsone taken by the formula:
500C(rU / rS)
in which C is the concentration, in mg per mL, of USP Roxarsone RS in the Standard preparation, and rU and rS are the roxarsone peak responses obtained from the Assay preparation and the Standard preparation, respectively.
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
|---|---|---|
| Monograph | Morgan Puderbaugh, B.S.
Associate Scientific Liaison 1-301-998-6833 |
(SM32010) Monographs - Small Molecules 3 |
| Reference Standards | RS Technical Services 1-301-816-8129 rstech@usp.org |
USP35–NF30 Page 4594