Roxarsone
;)
Arsonic acid,(4-hydroxy-3-nitrophenyl)-.
4-Hydroxy-3-nitrobenzenearsonic acid [121-19-7].
»Roxarsone contains not less than 98.0percent and not more than 101.0percent 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.
Identification—
A:
Infrared Absorption á197Kñ.
Solution:
8µg per mL.
Medium:
0.1Nhydrochloric acid in methanol.
Loss on drying á731ñ—
Dry it at 100
for 6hours:it loses not more than 1.0%of its weight.
for 6hours:it loses not more than 1.0%of its weight.
Residue on ignition á281ñ:
not more than 0.5%.
Limit of trivalent arsenic—
Transfer 2.50g of Roxarsone to a 250-mLconical flask,add 5.0mLof a solution containing 0.1237mg of anhydrous arsenic trioxide per mL,10mLof water,and 4.0mLof 5Nsodium hydroxide,and swirl to dissolve.Add 5.0mLof glacial acetic acid,and a stirring bar,and titrate with 0.0025Niodine VS,determining the endpoint potentiometrically.Perform the same procedure on a second 2.50-g portion of Roxarsone,except to replace the 5.0mLof arsenic trioxide solution with 5.0mLof water.Calculate the percentage of trivalent arsenic (As+++)in the Roxarsone taken by the formula:
(0.4623/25)[VB/(VA-VB)],
in which 0.4623is the arsenic equivalent of the 5.0mLof arsenic trioxide solution,and VAand VBare the volumes,in mL,of 0.0025Niodine consumed in the first and second titrations,respectively.Not more than 0.05%is found.
Content of total arsenic—
Transfer about 200mg of Roxarsone,accurately weighed,to a clean,dry 300-mL Kjeldahl flask,and clamp the flask at an angle of 45.Add 5mLof sulfuric acid,10mLof nitric acid,5mLof 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 5mLof water.Boil again,and continue heating for 30minutes after the water has boiled away.Allow to cool,add 100mLof water and 4mLof 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 60mL.Add 60mLof water,and immediately cool the solution.Add 2drops of phenolphthalein TS,neutralize with 5Nsodium hydroxide,and then make slightly acidic (pH6.5to 7.0)by adding a small quantity of 18Nsulfuric acid.Transfer this solution to a beaker with the aid of a water rinse,add 4g of sodium bicarbonate,and stir with a stirring bar.Titrate with 0.05Niodine VS,determining the endpoint potentiometrically.Each mLof 0.05Niodine is equivalent to 1.873mg of arsenic (As):between 28.0%and 28.8%is found,calculated on the dried basis.
.Add 5mLof sulfuric acid,10mLof nitric acid,5mLof 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 5mLof water.Boil again,and continue heating for 30minutes after the water has boiled away.Allow to cool,add 100mLof water and 4mLof 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 60mL.Add 60mLof water,and immediately cool the solution.Add 2drops of phenolphthalein TS,neutralize with 5Nsodium hydroxide,and then make slightly acidic (pH6.5to 7.0)by adding a small quantity of 18Nsulfuric acid.Transfer this solution to a beaker with the aid of a water rinse,add 4g of sodium bicarbonate,and stir with a stirring bar.Titrate with 0.05Niodine VS,determining the endpoint potentiometrically.Each mLof 0.05Niodine is equivalent to 1.873mg 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 Suitabilityunder Chromatography á621ñ).
Standard preparation—
Transfer about 50mg of USP Roxarsone RS,accurately weighed,to a 50-mLvolumetric flask.Dissolve in and dilute with 1.2Nsodium hydroxide to volume,and mix.Transfer 10.0mLof this stock solution to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.This solution contains about 0.1mg of USP Roxarsone RSper mL.
Assay preparation—
Transfer about 50mg of Roxarsone,accurately weighed,to a 50-mLvolumetric flask.Dissolve in and dilute with 1.2Nsodium hydroxide to volume,and mix.Transfer 10.0mLof this stock solution to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.
Chromatographic system
(see Chromatography á621ñ)—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 1mLper 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 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C6H6AsNO6in the portion of Roxarsone taken by the formula:
500C(rU/rS),
in which Cis the concentration,in mg per mL,of USP Roxarsone RSin the Standard preparation,and rUand rSare the roxarsone peak responses obtained from the Assay preparationand the Standard preparation,respectively.
Auxiliary Information—
Staff Liaison:Ian DeVeau,Ph.D.,Senior Scientist
Expert Committee:(VET)Veterinary Drugs
USP28–NF23Page 1742
Phone Number:1-301-816-8178