Dissolve 12.0 g in 37 mL of acetone, and add 3 mL of water. Titrate potentiometrically with 0.02 M lead perchlorate, prepared by dissolving 9.20 g of lead perchlorate in water to make 1000 mL of solution, using a pH meter capable of a minimum reproducibility of ±0.1 mV (see pH 791
) equipped with an electrode system consisting of a lead-specific electrode and a silver-silver chloride reference glass-sleeved electrode containing a solution of tetraethylammonium perchlorate in glacial acetic acid (1 in 44): not more than 1.25 mL of 0.02 M lead perchlorate is consumed (0.02%).
Dissolve 1 g in 25 mL of acetone, and add 2 mL of water. Add 1.2 mL of thioacetamide-glycerin base TS and 2 mL of pH 3.5 Acetate Buffer
, and allow to stand for 5 minutes: any color produced is not darker than that of a control made with 25 mL of acetone and 2 mL of Standard Lead Solution
(see Heavy Metals 231
) and treated in the same manner. The limit is 20 µg per g.
Prepare a mixture of water, methanol, and glacial acetic acid (60:40:1). Make adjustments if necessary (see System Suitability
under Chromatography 621
Prepare a mixture of methanol, water, and glacial acetic acid (70:30:4).
Prepare a solution in Diluent containing about 0.05 mg of 4-hydroxybenzoic acid and 0.025 mg of 4-hydroxyisophthalic acid per mL, and a second solution in Diluent containing about 0.05 mg of 4-hydroxybenzoic acid and 0.01 mg of phenol per mL.
Dissolve accurately weighed quantities of 4-hydroxybenzoic acid, 4-hydroxyisophthalic acid, phenol, and the Salicylic Acid under test in Diluent to obtain a solution having known concentrations of about 0.05 mg per mL, 0.025 mg per mL, 0.01 mg per mL, and 50 mg per mL, respectively.
Prepare a solution of Salicylic Acid in Diluent containing 50 mg per mL. Sonicate until completely dissolved.
(see Chromatography 621
)The liquid chromatograph is equipped with a 270-nm detector and a 4.6-mm × 10-cm column containing 5-µm packing L1. The flow rate is about 0.5 mL per minute. Chromatograph the Reference solutions
, record the chromatograms, and note the retention times of the peaks. Chromatograph the Standard solution
, and record the peak responses as directed for Procedure:
the relative retention times are about 0.35, 0.45, 0.5, and 1.0 for 4-hydroxybenzoic acid, 4-hydroxyisophthalic acid, phenol, and salicylic acid, respectively, and the peaks are all baseline-resolved from each other. Changes in the composition of the Mobile phase
made to optimize resolution may change the elution order of impurities. Use the chromatograms obtained from the Reference solutions
to determine the elution order of the specified impurities.
Separately inject equal volumes (about 2 µL) of the Standard solution
and the Test solution
into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of each relevant related compound taken by the formula:
/ (rSi ri
in which Ci
is the concentration, in mg per mL, of the relevant related compound in the Standard solution;
are the peak responses for the relevant related compound obtained from the Test solution
and the Standard solution
, respectively: not more than 0.1% of 4-hydroxybenzoic acid, 0.05% of 4-hydroxyisophthalic acid, and 0.02% of phenol is found. Calculate the percentage of any other impurity, other than the solvent peak, observed in the chromatogram of the Test solution
by the same formula, except to use the concentration of 4-hydroxyisophthalic acid in the Standard solution
the response of the peak of 4-hydroxyisophthalic acid in the chromatogram obtained from the Standard solution
and the response of any other impurity as ri:
not more than 0.05% of any other impurity is found; and the sum of all of the related compounds and other impurities found is not more than 0.2%.
Dissolve about 500 mg of Salicylic Acid, accurately weighed, in 25 mL of diluted alcohol that previously has been neutralized with 0.1 N sodium hydroxide, add phenolphthalein TS
, and titrate with 0.1 N sodium hydroxide VS. Each mL of 0.1 N sodium hydroxide is equivalent to 13.81 mg of C7