Reference solution—

Test solution— Transfer an accurately weighed quantity of Gadodiamide,equivalent to about 15g of anhydrous gadodiamide,to a 50-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Transfer 40mLof this solution to a 50-mLcolor comparison tube.

Blank— Transfer 40mLof water to a 50-mLcolor comparison tube.

Procedure— Five minutes after preparation of the Reference solution,view the Reference solution,the Test solution,and the Blankagainst a black background:the Test solutionis not more opalescent than the Reference solution.[NOTE—If the Test solutionis more opalescent than the Reference solution,heat the Test solutionto 60to 70for 2to 3minutes,cool to room temperature,and view again.]

A: Infrared Absorption á197Kñ.

B: It exhibits the maximum absorption at the relevant wavelength specified when tested as directed under the test for Content of gadolinium.

Arsenazo IIIindicator— Transfer 150mg of arsenazo IIIdisodium to a 100-mLvolumetric flask,dilute with water to volume,and mix.

MESbuffer— Transfer 48.8g of 2-(N-morpholino)ethanesulfonic acid (MES)to a 250-mLvolumetric flask.Add 180mLof water and 25mLof 2Nsodium hydroxide,and mix.Adjust with 2Nsodium hydroxide to a pHof 6.0,dilute with water to volume,and mix.

Edetate disodium titrant— Pipet 100mLof 0.02Medetate disodium VSinto a 1000-mLvolumetric flask,dilute with water to volume,and mix.

Test solution— Transfer about 1g of Gadodiamide,accurately weighed,to a 125-mLconical flask,add 25mLof MESbufferand 0.1mLof Arsenazo IIIindicator,and mix.Aturquoise color indicates the presence of excess gadolinium.

Procedure— Titrate the Test solutionwith Edetate disodium titrantto a violet-pink endpoint.Each mLof Edetate disodium titrantis equivalent to 0.3145mg of excess gadolinium:not more than 0.3%of free gadolinium is found,calculated on the anhydrous basis.

Arsenazo IIIindicator and MESbuffer— Proceed as directed for Limit of free gadolinium (III).

0.002Mgadolinium(III)titrant— Transfer 18.6g of gadolinium chloride to a 1000-mLvolumetric flask,dilute with 0.1Nhydrochloric acid to volume,and mix.Pipet 10mLof this solution into a conical flask,and add 25mLof MESbufferand 0.1mLof Arsenazo IIIindicator.Titrate with 0.02Medetate disodium VSto a violet-pink endpoint,and determine the molarity.Pipet 40mLof this solution into a 1000-mLvolumetric flask,dilute with water to volume,and mix.

Blank solution— Transfer 25mLof MESbufferand 0.1mLof Arsenazo IIIindicatorinto a suitable flask,and mix.

Test solution— Transfer about 1g of Gadodiamide,accurately weighed,to a 125-mLconical flask.Add 25mLof MESbufferand 0.1mLof Arsenazo IIIindicator,and mix.Aviolet-pink color indicates the presence of excess diethylenetriamine pentaacetic acid bismethylamide.

Procedure— Concomitantly titrate the Blank solutionand the Test solutionwith 0.002Mgadolinium(III)titrantto a turquoise endpoint.Calculate the percentage of free diethylenetriamine pentaacetic acid bismethylamide in the portion of Gadodiamide taken by the formula: in which VUis the volume of gadolinium (III)in the Test solution;VBis the volume of gadolinium (III)in the Blank solution;MTis the molarity of the 0.002Mgadolinium (III)titrant;419.43is the molecular weight of diethylenetriamine pentaacetic acid bismethylamide;and Wis the weight,in mg,of Gadodiamide taken to prepare the Test solution:not more than 0.7%of diethylenetriamine pentaacetic acid bismethylamide is found,calculated on the anhydrous basis.

Borate buffer— Transfer 12.4g of boric acid to a 500-mLvolumetric flask,and suspend it in 300mLof water.Add 100mLof 1Npotassium hydroxide,and mix.Adjust with 1Npotassium hydroxide to a pHof 10.0,dilute with water to volume,and mix.Store in a closed plastic container.

OPAreagent— Transfer 100mg of o-phthalaldehyde to an amber bottle,add 3mLof methanol,and mix.Add 220mLof Borate bufferand 0.1mLof mercaptoethanol,and mix.[NOTE—This solution must be freshly prepared.]

Standard solutions— Transfer about 110mg of methylamine hydrochloride,accurately weighed,to a 500-mLvolumetric flask,and dilute with water to volume to obtain a solution having a concentration of about 100µg of methylamine per mL.Pipet 1,5,10,and 20mLof this solution into separate 100-mLvolumetric flasks,dilute the contents of each flask with water to volume,and mix.

Test solution— Transfer about 1.5g of Gadodiamide,accurately weighed,to a 10-mLvolumetric flask,dilute with water to volume,and mix.

Procedure— Proceed as follows for each of the Standard solutions.Add 3.0mLof OPAreagent,mix,and within 1minute measure the absorbance at 335nm.Compare to a blank consisting of 3.0mLof water and 3.0mLof OPAreagent.Plot a calibration curve of absorbance versus standard concentration,in µg of methylamine per mL.Mix 3.0mLof the Test solutionwith 3.0mLof OPAreagent,and proceed as directed above.[NOTE—If the absorbance obtained with the Test solutionexceeds the absorbance of the highest Standard solution,perform an additional quantitative dilution of the Test solution,and repeat the analysis.]Determine the concentration,in µg per mL,of methylamine in the Test solutionby interpolation from the calibration curve.Calculate the amount of methylamine in the portion of Gadodiamide taken:not more than 0.05%of methylamine is found.

Internal standard solution— Transfer about 500mg of methyl ethyl ketone to a 100-mLvolumetric flask,dilute with water to volume,and mix.Pipet 5mLof this solution into a 100-mLvolumetric flask,dilute with water to volume,and mix.

Stock solution— Transfer about 1000mg each of acetone,ethyl alcohol,and isopropyl alcohol,accurately weighed,to a 100-mLvolumetric flask,dilute with water to volume,and mix.

Diluted stock solution A— Pipet 5mLof the Stock solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix.

Diluted stock solution B— Pipet 10mLof the Stock solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix.

System suitability solution— Pipet 10mLof the Internal standard solutionand 15mLof Diluted stock solution Ainto a 100-mLvolumetric flask,dilute with water to volume,and mix.

Test solution 1— Pipet 10mLof the Internal standard solutioninto a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 7.0mLof this solution to a 10-mLgas chromatographic headspace vial,add about 1300mg of Gadodiamide,accurately weighed,and cap immediately.Swirl to dissolve.

Test solution 2— Pipet 10mLof the Internal standard solutionand 2.5mLof Diluted stock solution Ainto a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 7.0mLof this solution to a 10-mLgas chromatographic headspace vial,add about 1300mg of Gadodiamide,accurately weighed,and cap immediately.Swirl to dissolve.

Test solution 3— Pipet 10mLof the Internal standard solutionand 15mLof Diluted stock solution Ainto a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 7.0mLof this solution to a 10-mLgas chromatographic headspace vial,add about 1300mg of Gadodiamide,accurately weighed,and cap immediately.Swirl to dissolve.

Test solution 4— Pipet 10mLof the Internal standard solutionand 25mLof Diluted stock solution Binto a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 7.0mLof this solution to a 10-mLgas chromatographic headspace vial,add about 1300mg of Gadodiamide,accurately weighed,and cap immediately.Swirl to dissolve.

Chromatographic system (see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 0.32-mm ×30-m capillary column coated with a 1.8-µm phase G43.The column temperature is maintained at 40.Helium is used as the carrier gas at a flow rate of about 1.5mLper minute,and the split ratio is 1:15.The injection port and detector block are maintained at about 250.Chromatograph the System suitability solutionas directed for Procedure:the order of elution is ethyl alcohol,acetone,isopropyl alcohol,and methyl ethyl ketone;the resolution,R,between the ethyl alcohol and acetone peaks is not less than 1.0and between the acetone and isopropyl alcohol peaks is not less than 1.0;and the relative standard deviation is not more than 3.0%for each of the three analytes.

Procedure— Separately inject equal volumes (about 1µL)of each of the four Test solutionsinto the chromatograph,record the chromatograms,and measure the areas for the major peaks relative to the area for the internal standard peak.Plot the responses of the Test solutionsversus the content,in µg per mL,of the relevant analyte in each vial,draw the straight line best fitting the four points,and calculate the correlation coefficient for the line.Asuitable system is one that yields a line having a correlation coefficient of not less than 0.99.Calculate the percentage of each analyte in the portion of Gadodiamide taken by the formula: in which ais the intercept and bis the slope of the straight line,evaluated by linear regression analysis.[NOTE—If ais negative,report the result as none detected.]Not more than 0.2%of acetone,ethyl alcohol,and isopropyl alcohol is found,calculated on the anhydrous basis;and the sum of all three analytes is not more than 0.2%,calculated on the anhydrous basis.

Mobile phase— Prepare as directed in the Assay.

Postcolumn reagent— Dissolve 120mg of arsenazo IIIacid in 400mLof water previously acidifed with 6.3mLof nitric acid.Add 650mg of urea,and mix to dissolve.Pass the solution through a 0.45-µm porosity filter,washing the filter with 600mLof water.Dilute with water to 1000mL,mix,and degas.

System suitability solution— Prepare an aqueous solution containing about 0.01mg of USP Gadodiamide Related Compound A RS,0.01mg of USP Gadodiamide Related Compound B RS,and 2mg of USP Gadodiamide RSin each mL.

Test solution— Transfer about 200mg of Gadodiamide,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— Proceed as directed in the Assay,except to use the Postcolumn reagentprepared as directed above.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the resolution,R,between the gadodiamide and gadodiamide related compound Apeaks is not less than 1.0,and between gadodiamide related compound Aand gadodiamide related compound Bpeaks is not less than 1.5;and the relative standard deviation for replicate injections is not more than 10%.

Procedure— Inject about 10µLof the Test solutioninto the chromatograph,record the chromatogram,and measure the peak responses.[NOTE—The tail of the gadodiamide peak may contain a small shoulder due to an isomer;the area of the shoulder should be included in the gadodiamide peak area.]Calculate the percentage of each impurity in the portion of Gadodiamide taken by the formula: in which riis the response of each impurity;and rsis the sum of all peaks having a percentage greater than 0.10%:not more than 2.0%of gadodiamide related compounds Aand Bis found;no individual impurity is more than 0.2%;and the sum of all impurities,other than gadodiamide related compounds Aand B,is not more than 0.5%.

Standard solutions— Prepare three separate solutions in 0.2Mnitric acid to obtain concentrations of 100,150,and 200µg of gadolinium per mL.

Test solution— Transfer about 600mg of Gadodiamide,accurately weighed,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Pipet 10mLof this solution into a 100-mLvolumetric flask,dilute with 0.2Mnitric acid to volume,and mix.

Procedure— Concomitantly determine the absorbances of the Standard solutionsand the Test solutionat the gadolinium resonance line of 342nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ),using 0.2Mnitric acid as the blank.Plot the absorbances of the Standard solutionsversus concentration,in µg per mL,of gadolinium,and draw the straight line best fitting the three plotted points.From the graph so obtained,determine the concentration,in µg per mL,of gadolinium in the Test solution:the content of gadolinium is between 26.0%and 29.0%,calculated on the anhydrous basis.

Mobile phase— Transfer 14.0mLof triethylamine,5.7mLof glacial acetic acid,and 5.7mLof water to a 1000-mLvolumetric flask,dilute with water to volume,and mix.Transfer 50mLof this solution to a 1000-mLvolumetric flask,add 900mLof water,and mix.Adjust with 1Nacetic acid or 1Nsodium hydroxide to a pHbetween 6.5and 7.0.Dilute with water to volume,mix,filter,and degas (see System Suitabilityunder Chromatography á621ñ).

Postcolumn reagent— Dissolve 325mg of urea in a solution of 60mg of arsenazo IIIacid in 550mLof water previously acidified with 3.2mLof nitric acid.Pass the solution through a 0.45-µm porosity filter,wash the filter with 400mLof water,dilute with water to 1000mL,mix,and degas.

Standard preparation— Prepare an aqueous solution of USP Gadodiamide RShaving a known concentration of about 0.6mg per mL.

Assay preparation— Transfer about 60mg of Gadodiamide,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 658-nm detector and a 4.6-mm ×25-cm column that contains 5-µm base-deactivated packing L1.Asecond pump mixes the Mobile phasewith the Postcolumn reagentprior to detection via a T-junction.The system is maintained at a constant temperature between 20and 35.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Separately inject equal volumes (about 10µL)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 C16H26GdN5O8in the portion of Gadodiamide taken by the formula: in which Cis the concentration,in mg per mL,of USP Gadodiamide RSin the Standard preparation;and rUand rSare the gadodiamide peak responses obtained from the Assay preparationand the Standard preparation,respectively.