A: Infrared Absorption á197Kñ:undried.

B: To 5mLof water in a test tube add 2drops of ammonium thiocyanate TSand 2drops of ferric chloride TS,and mix.To the deep red solution add about 50mg of Edetate Disodium,and mix:the red color is discharged,leaving a yellowish solution.

C: It responds to the flame test forSodium á191ñ.

Mobile phase— Add 10mLof 1.0Mtetrabutylammonium hydroxide in methanol to 200mLof water,and adjust with 1Mphosphoric acid to a pHof 7.5±0.1.Transfer the solution so obtained to a 1000-mLvolumetric flask,add 90mLof methanol,dilute with water to volume,mix,pass through a filter having a 0.5-µm or finer porosity,and degas.

Cupric nitrate solution— Prepare a solution containing about 10mg of cupric nitrate (Cu(NO3)2)per mL.

Standard stock solution— Transfer about 100mg of nitrilotriacetic acid,accurately weighed,to a 10-mLvolumetric flask,add 0.5mLof ammonium hydroxide,and mix.Dilute with water to volume,and mix.

Resolution solution— Transfer 10mg of Edetate Disodium to a 100-mLvolumetric flask,add 100µLofStandard stock solution,dilute withCupric nitrate solutionto volume,and mix.Sonicate,if necessary,to dissolve.

Standard solution— Transfer 1.0g of Edetate Disodium to a 100-mLvolumetric flask,add 100µLofStandard stock solution,dilute withCupric nitrate solutionto volume,and mix.Sonicate,if necessary,to dissolve.

Test solution— Transfer 1.0g of Edetate Disodium to a 100-mLvolumetric flask,dilute withCupric nitrate solutionto volume,and mix.Sonicate,if necessary,to dissolve.

Chromatographic system(see Chromatography á621ñ)— The chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains packing L7.The flow rate is about 2mLper minute.Chromatograph theResolution solution,and record the peak responses as directed forProcedure:the relative retention times are about 0.35for nitrilotriacetic acid,0.65for copper,and 1.0for edetate;and the resolution,R,between nitrilotriacetic acid and copper is not less than 3.Chromatograph theStandard solution,and record the peak responses as directed forProcedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50µL)of theStandard solutionand theTest solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The response of the nitrilotriacetic acid peak obtained from theTest solutiondoes not exceed the difference between the nitrilotriacetic acid peak responses obtained from theStandard solutionand theTest solution:not more than 0.1%of nitrilotriacetic acid is found.

Assay preparation— Dissolve about 5g of Edetate Disodium,accurately weighed,in about 100mLof water contained in a 250-mLvolumetric flask,add water to volume,and mix.

Procedure— Place about 200mg of chelometric standard calcium carbonate,previously dried at 110for 2hours,cooled in a desiccator,and accurately weighed,in a 400-mLbeaker,add 10mLof water,and swirl to form a slurry.Cover the beaker with a watch glass,and without removing the latter,add 2mLof 3Nhydrochloric acid from a pipet.Swirl the contents of the beaker,and dissolve the calcium carbonate.Wash down the sides of the beaker,the outer surface of the pipet,and the watch glass with water,and dilute with water to about 100mL.While stirring the solution,preferably with a magnetic stirrer,add about 30mLof theAssay preparationfrom a 50-mLburet.Add 15mLof 1Nsodium hydroxide and 0.30g of hydroxy naphthol blue,and continue the titration with theAssay preparationto a blue endpoint.Calculate the weight,in mg,of C10H14N2Na2O8in the portion of Edetate Disodium taken by the formula: in whichWis the weight,in mg,of calcium carbonate;andVis the volume,in mL,of theAssay preparationconsumed in the titration.