A: Infrared Absorption 197K.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Mobile phase— Prepare a filtered and degassed solution containing about 0.94 g of sodium bicarbonate, 0.952 g of sodium carbonate, 0.38 g of 4-cyanophenol, and 80 mL of acetonitrile in 4 L of water. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard stock solution— Transfer about 118.1 mg of sodium iodide, accurately weighed, to a 1000-mL volumetric flask. Dissolve in and dilute with water to volume, and mix to obtain a solution containing the equivalent of 100 µg of iodide per mL.

Standard solutions— Pipet 2.0 mL, 4.0 mL, 6.0 mL, and 8.0 mL of the Standard stock solution into separate 100-mL volumetric flasks, dilute with water to volume, and mix to obtain solutions having known concentrations of about 2 µg, 4 µg, 6 µg, and 8 µg of iodide per mL.

Test solution— Transfer about 300 mg of Fenoldopam Mesylate, accurately weighed, to a 100-mL volumetric flask. Dissolve in and dilute with water to volume, and mix.

Chromatographic system— The ion chromatograph is equipped with a conductivity detector, a 4-mm × 3.5-cm anion-exchange guard column, a 4-mm × 15-cm anion-exchange analytical column, and a micromembrane anion suppressor column. The flow rate is about 2.0 mL per minute. The regeneration solution for the suppressor column is a 0.050 M sulfuric acid solution, flowing at a rate of 5 mL per minute. Chromatograph the 6 µg per mL Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Separately inject equal volumes (about 100 µL) of each of the Standard solutions and the Test solution into the chromatograph, record the chromatograms, and measure the heights of peak responses. Plot the response of each of the Standard solutions versus the concentration, and draw the straight line best fitting the plotted points. From the graph so obtained, determine the quantity of iodide in the portion of Fenoldopam Mesylate taken: not more than 0.2% is found.

Buffer solution, System suitability stock solution, and System suitability solution— Proceed as directed in the Assay.

Solution A— Use Mobile phase as prepared in the Assay.

Solution B— Use filtered and degassed methanol.

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Test solution— Use the System suitability stock solution.

Chromatographic system— Proceed as directed in the Assay, except to program the chromatograph as follows.

Procedure— Inject a volume (about 20 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the peak responses. Calculate the percentage of each impurity in the portion of Fenoldopam Mesylate taken by the formula: in which ri is the peak response for each impurity; and rs is the sum of the responses of all the peaks: not more than 0.3% of fenoldopam related compound A is found; not more than 0.1% of any other individual impurity is found; and not more than 1.0% of total impurities is found.

Internal standard solution— Prepare a solution, in organic-free water, containing 10 mg of n-butanol per mL. Transfer 100 µL of this solution to a 10-mL volumetric flask, dilute with dimethylsulfoxide to volume, and mix.

Standard solution— Prepare a solution, in organic-free water, containing 10 mg each of n-propanol, isopropyl alcohol, and dimethylformamide per mL. Transfer 100 µL of this solution to a 10-mL volumetric flask, dilute with Internal standard solution to volume, and mix.

Test solution— Transfer about 50 mg of Fenoldopam Mesylate, accurately weighed, to a 1-mL volumetric flask. Dilute with Internal standard solution to volume, and sonicate to dissolve completely.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector, a 0.32-mm × 30-m fused-silica capillary column coated with a 1.8-µm film of stationary phase G43, and a split injection system. The carrier gas is helium, flowing at a rate of about 1 mL per minute through the column and a split ratio of about 50:1. The injection port and the detector temperatures are maintained at 140 and 260, respectively. The column temperature is programmed as follows. It is maintained for 12 minutes at 40, then increased at a rate of 8 per minute to 120, held for 0.1 minute, then increased at a rate of 25 per minute to 180, and maintained at that temperature for 8 minutes.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard solution, dimethylsulfoxide, and the Test solution into the chromatograph, record the chromatograms, and measure the peak areas. Identify, based on retention time, any peaks present in the chromatogram of the Test solution. Calculate the response factor, F, for each solvent in the Standard solution by the formula: in which WR is the weight, in mg, of the solvent of interest; WI is the weight, in mg, of the internal standard taken to prepare the Internal standard solution; and rI and rR are the peak responses for the internal standard and the solvent of interest, respectively, obtained from the Standard solution. Calculate the percentage, by weight, of each solvent found in the Test solution by the formula: in which F is the average response factor for the solvent of interest obtained from all injections of the Standard solution; D is the dilution factor for the internal standard in the Test solution (i.e., 0.0001); rI and rS are the peak responses for the solvent of interest and the internal standard, respectively, obtained from the Test solution; WI is the weight, in mg, of the internal standard taken to prepare the Internal standard solution; and WD is the weight, in mg, of Fenoldopam Mesylate taken to prepare the Test solution: not more than 0.2% of total residual solvents is found.

Buffer solution— Transfer about 16.33 g of monobasic potassium phosphate and 2 mL of triethylamine to a 2-L volumetric flask, and dissolve in 1800 mL of water. Adjust with phosphoric acid to a pH of 2.5, dilute with water to volume, and mix.

Mobile phase— Prepare a filtered and degassed mixture of Buffer solution and methanol (19:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability stock solution— Transfer about 50 mg of Fenoldopam Mesylate, accurately weighed, to a 50-mL volumetric flask. With the aid of an ultrasonic bath, dissolve in and dilute with Mobile phase to volume, and mix.

System suitability solution— Transfer about 5 mg of USP Fenoldopam Related Compound A RS, accurately weighed, to a 50-mL volumetric flask. Add about 25 mL of Mobile phase, and sonicate to dissolve. Add 5 mL of the System suitability stock solution, dilute with Mobile phase to volume, and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Fenoldopam Mesylate RS in Mobile phase to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Transfer 5.0 mL of the System suitability stock solution, accurately measured, to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 225-nm detector and a 3.9-mm × 30-cm column that contains packing L11. The flow rate is about 1.7 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between fenoldopam and fenoldopam related compound A is not less than 1.5; the column efficiency is not less than 2000 theoretical plates; the tailing factor is not more than 1.3; 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 peak responses. Calculate the quantity, in mg, of C16H16ClNO3·CH4SO3 in the portion of Fenoldopam Mesylate taken by the formula: in which C is the concentration, in mg per mL, of USP Fenoldopam Mesylate RS in the Standard preparation; and rU and rS are the peak responses for fenoldopam obtained from the Assay preparation and the Standard preparation, respectively.