Limit of o-arsanilic acid—
Mobile phase—
Dissolve 4.04 g of monobasic potassium phosphate in 985 mL of water, add 2 mL of phosphoric acid, and mix. Add 10 mL of methanol, mix, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard solution—
Transfer about 67 mg of
o-arsanilic acid, accurately weighed, to a 100-mL volumetric flask, add about 65 mg of warm (about 70
to 80
) water, and shake or sonicate to dissolve. Allow to cool, dilute with water to volume, and mix. Dilute a portion of this solution quantitatively and stepwise with water to obtain a solution having a known concentration of about 0.0012 mg of
o-arsanilic acid per mL.
Test solution—
Transfer about 50 mg of Arsanilic Acid, accurately weighed, to a 50-mL volumetric flask, add about 30 mL of warm water, and shake or sonicate to dissolve. Allow to cool, dilute with water to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 242-nm detector and a 4.6-mm × 15-cm column that contains 5-µm base-deactivated packing L1 and is maintained at a constant temperature of about 30
. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard solution, and record the peak responses as directed for
Procedure: the capacity factor,
k¢, for the
o-arsanilic acid peak is between 2.8 and 3.8; and the relative standard deviation for replicate injections is not more than 2.5%.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the areas of the responses for the
o-arsanilic acid peaks. Calculate the percentage of
o-arsanilic acid in the portion of Arsanilic Acid taken by the formula:
5000(C / W)(rU / rS),
in which
C is the concentration, in mg per mL, of
o-arsanilic acid in the
Standard solution; W is the weight, in mg, of Arsanilic Acid taken to prepare the
Test solution; and
rU and
rS are the responses of the
o-arsanilic acid peaks obtained from the
Test solution and the
Standard solution, respectively: not more than 0.12% is found.
Limit of aniline—
Mobile phase—
Dissolve 7.76 g of monobasic potassium phosphate in 950 mL of water, add 50 mL of methanol, mix, and degas. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard solution—
Transfer about 176 mg of aniline, accurately weighed, to a 25-mL volumetric flask, add about 1 mL of methanol, swirl, then add about 15 mL of water, and shake to dissolve. Dilute with water to volume, and mix. Dilute a portion of this solution quantitatively and stepwise with water to obtain a solution having a known concentration of about 0.00045 mg of aniline per mL.
Test solution—
Transfer about 50 mg of Arsanilic Acid, accurately weighed, to a 50-mL volumetric flask, add about 30 mL of warm (about 70
to 80
) water, and shake or sonicate to dissolve. Allow to cool, dilute with water to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 235-nm detector and a 4.6-mm × 15-cm column that contains 5-µm base-deactivated packing L1 and is maintained at a constant temperature of about 30
. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard solution, and record the peak responses as directed for
Procedure: the capacity factor,
k¢, for the aniline peak is between 2.3 and 3.3; and the relative standard deviation for replicate injections is not more than 3.0%.
Procedure—
Separately inject equal volumes (about 50 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the areas of the responses for the aniline peaks. Calculate the percentage of aniline in the portion of Arsanilic Acid taken by the formula:
5000(C / W)(rU / rS),
in which
C is the concentration, in mg per mL, of aniline in the
Standard solution; W is the weight, in mg, of Arsanilic Acid taken to prepare the
Test solution; and
rU and
rS are the responses of the aniline peaks obtained from the
Test solution and the
Standard solution, respectively: not more than 0.045% is found.
Assay—
Transfer about 125 mg of Arsanilic Acid, accurately weighed, to a 50-mL conical flask, and add 10.0 mL of a mixture of sulfuric acid, nitric acid, and perchloric acid (1000:50:50) and several glass beads. Digest on a hot plate for about 1 hour, increasing the temperature of the hot plate in steps until a ring of sulfuric acid rises into the neck of the flask. Allow to cool, to the colorless solution add about 400 mg of hydrazine sulfate, and heat the flask vigorously on a hot plate until a ring of sulfuric acid rises into the neck of the flask. Allow to cool, and wash down the rim, neck, and insides of the flask with about 1 mL of water. Heat the flask again until a ring of sulfuric acid rises into the neck of the flask. Allow to cool, and transfer the colorless solution, with the aid of about 80 mL of water, to a 125-mL conical flask. Add 10 mL of hydrochloric acid and several drops of 0.002 M potassium iodide, cool to between 0
and 5
, and titrate with 0.1 N potassium permanganate VS to a pale pink endpoint, maintaining the temperature between 0
and 5
during the titration. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N potassium permanganate is equivalent to 10.852 mg of C
6H
8AsNO
3.
;)
