á206ñALUMINUM
This procedure is provided to demonstrate that the content of aluminum (Al)does not exceed the limit given in the individual monograph of a substance labeled as intended for use in hemodialysis.[NOTE—The Standard Preparationsand the Test Preparationmay be modified,if necessary,to obtain solutions of suitable concentrations adaptable to the linear or working range of the instrument.]
Nitric Acid Diluent— Transfer 40mLof nitric acid to a 1000-mLvolumetric flask,and dilute with water to volume.
Standard Preparations— Treat some aluminum wire with 6Nhydrochloric acid at 80
for a few minutes.Dissolve about 100mg of the treated wire,accurately weighed,in a mixture of 10mLof hydrochloric acid and 2mLof nitric acid by heating at about 80for approximately 30minutes.Continue heating until the volume is reduced to about 4mL.Cool to room temperature,and add 4mLof water.Evaporate to about 2mLby heating.Cool,and transfer this solution,with the aid of water,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a second 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 1.0mLof this solution to a third 100-mLvolumetric flask,dilute with water to volume,and mix.The concentration of aluminum in this Standard Preparationis about 1.0µg per mL.If a more diluted Standard Preparationis required,transfer 1.0-,2.0-,and 4.0-mLportions of this solution to separate 100-mLvolumetric flasks,dilute with Nitric Acid Diluentto volume,and mix.These solutions contain 0.01,0.02,and 0.04µg of Al per mL,respectively.
Test Preparation— Unless otherwise directed in the monograph,transfer an accurately weighed amount (in g)of the test substance,as specified in the monograph,to a 100-mLplastic volumetric flask,add 50mLof water,and sonicate for 30minutes.Add 4mLof nitric acid,dilute with water to volume,and mix.
Procedure— Determine the absorbances of the Standard Preparationsand the Test Preparationat the aluminum emission line at 309.3nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering á851ñ)equipped with an aluminum hollow-cathode lamp and a flameless electrically heated furnace,using the Nitric Acid Diluentas the blank.Plot the absorbances of the Standard Preparationsversus the content of Al,in µg per mL,drawing a straight line best fitting the three points.From the graph so obtained,determine the quantity,in µg,of Al in each mLof the Test Preparation.Calculate the amount of Al in the specimen taken,in µg per g,by multiplying this value by 100/W,where Wis the weight,in g,of the substance taken to prepare the Test Preparation.