A: Dissolve about 500mg of Maleic Acid in 10mLof water:the pHof the solution is not less than 2.

B: The principal spot in the chromatogram obtained from Test solution 2corresponds in color,size,and RFvalue to that in the chromatogram obtained from the Maleic acid standard solution,as obtained in the test for Limit of fumaric acid.

C: Dissolve about 35mg of resorcinol in 10mLof sulfuric acid(Resorcinol solution).Dissolve about 100mg of Maleic Acid in 10mLof water(Test solution).To 0.3mLof the Test solutionadd 3mLof the Resorcinol solution,and heat in a water bath for 15minutes:no color develops.To 3mLof the Test solutionadd 1mLof bromine TS,heat in a water bath for 15minutes to remove the bromine,then heat to boiling,and cool.To 0.2mLof this solution,add 3mLof the Resorcinol solution,and heat in a water bath for 15minutes:a violet-pink color develops.

Dilute hydrochloric acid solution— Mix 27.5mLof hydrochloric acid with sufficient water to make 1000mL.

Test solution— Transfer 1.0g of Maleic Acid to a quartz crucible,add 0.5g of magnesium oxide,and mix.Ignite the crucible to dull redness until a homogeneous white or grayish-white mass is obtained.Ignite at 800for 1hour,cool,and dissolve the residue by adding two 5-mLportions of diluted hydrochloric acid.Add 0.1mLof phenolphthalein TS,and then add ammonium hydroxide until a pink color is obtained.Cool,add glacial acetic acid until the solution is decolorized,then add 0.5mLof glacial acetic acid in excess,and dilute with water to 20.0mL.

Standard solution— To 0.5g of magnesium oxide,add 1.0mLof Standard Lead Solution,and evaporate to dryness at 105for 1hour.Following the procedure described above for preparation of the Test solution,ignite,dissolve in diluted hydrochloric acid,add ammonia and then acetic acid,and dilute with water to 20.0mL.

Procedure— To 12mLof the Test solution,add 2.0mLof pH3.5Acetate Buffer,mix,add to 1.2mLof thioacetamide–glycerin base TS,and mix immediately.To 10mLof the Standard solution,add 2.0mLof the Test solutionand 2.0mLof pH3.5Acetate Buffer,mix,add 1.2mLof thioacetamide–glycerin base TS,and mix immediately.Prepare a blank,using a mixture of 10mLof water and 2.0mLof the Test solution.Compared to the blank,the solution obtained from the Standard solutionshows a light brown color.Dilute each of the solutions obtained from the Test solutionand the Standard solutionwith water to 50mL,allow to stand for 2minutes,and view downward over a white surface.The color of the solution obtained from the Test solutionis not darker than that of the solution obtained from the Standard solution:not more than 10µg per g.

Adsorbent: 0.25-mm layer of chromatographic silica gel mixture.

Test solution 1— Dissolve an accurately weighed quantity of Maleic Acid in acetone to obtain a solution having a concentration of about 100mg per mL.

Test solution 2— Transfer about 1.0mLof Test solution 1to a 50-mLvolumetric flask,dilute with acetone to volume,and mix.

Maleic acid standard solution— Dissolve an accurately weighed quantity of USP Maleic Acid RSin acetone to obtain a solution having a known concentration of about 2mg per mL.

Fumaric acid standard solution— Dissolve an accurately weighed quantity of USP Fumaric Acid RSin acetone to obtain a solution having a known concentration of about 1.5mg per mL.

Resolution solution— Prepare a mixture of Maleic acid standard solutionand the Fumaric acid standard solution(1:1).

Developing solvent system— Prepare a mixture of heptane,butanol,chloroform,and anhydrous formic acid (44:36:16:16).

Procedure— Proceed as directed for Thin-Layer Chromatography under Chromatography á621ñ,using an unsaturated chamber.Separately apply 10µLof the Resolution solutionand 5µLeach of Test solution 1,Test solution 2,the Maleic acid standard solution,and the Fumaric acid standard solution.Dry the plate at 100for 15minutes,and examine the plate under short-wavelength UVlight at 254nm.The chromatogram obtained from the Resolution solutionexhibits two clearly separated spots,and any spot corresponding to fumaric acid in the chromatogram of Test solution 1does not exceed,in size or intensity,the principal spot obtained in the chromatogram of the Fumaric acid standard solution:not more than 1.5%of fumaric acid is found.

Diluted standard iron solution— Immediately before use,dilute 1volume of the Standard Iron Solution,prepared as directed under Iron á241ñ,with 9volumes of water.[NOTE—This solution contains the equivalent of 1µg of iron per mL.]

Potassium thiocyanate solution— Dissolve 9.7g of potassium thiocyanate in 100mLof water.

Test solution— Dissolve about 1g of Maleic Acid,accurately weighed,in 10mLof water.Add 2mLof diluted hydrochloric acid and 0.05mLof bromine TS.After 5minutes,remove the excess of bromine with the aid of a current of air,add 3mLof Potassium thiocyanate solution,and shake well.

Standard solution— To 5mLof Diluted standard iron solutionadd 6mLof water.Add 1mLof diluted hydrochloric acid and 0.05mLof bromine TS.After 5minutes,remove the excess of bromine with the aid of a current of air,add 3mLof Potassium thiocyanate solution,and shake well.

Procedure— Allow the Standard solutionand the Test solutionto stand for 5minutes.Any red color in the Test solutionis not more intense than that in the Standard solution:not more than 5µg per g.