Assay
Sodium chloride solution
Dissolve 54g of sodium chloride in water,dilute with water to 2000mL,and mix.
Chromium stock solution
Transfer 2.829g of potassium dichromate,accurately weighed,to a 1000-mLvolumetric flask,dissolve in water,dilute with water to volume,and mix.This solution contains 1000µg of chromium per mL.Store in a polyethylene bottle.
Standard preparations
Pipet 10mLof the Chromium stock solutioninto a 1000-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLand 20.0mL,respectively,of this stock solution to separate 100-mLvolumetric flasks,and transfer 15.0mLand 20.0mL,respectively,of the stock solution to separate 50-mLvolumetric flasks.Add 20mLof Sodium chloride solutionto each 100-mLvolumetric flask,and 10mLof Sodium chloride solutionto each 50-mLvolumetric flask,dilute the contents of each flask with water to volume,and mix.These Standard preparationscontain,respectively,1.0,2.0,3.0,and 4.0µg of chromium per mL.
Assay preparation
Transfer an accurately measured volume of Injection,equivalent to about 60µg of chromium,to a 25-mLvolumetric flask.From the labeled amount of sodium chloride,if any,in the Injection,calculate the amount,in mg,of sodium chloride in the volume of Injection taken,and add sufficient Sodium chloride solutionto bring the total sodium chloride content of the flask to 135mg.Dilute with water to volume,and mix.
Procedure
Concomitantly determine the absorbances of the
Standard preparationsand the
Assay preparationat the chromium emission line of 357.9nm,with a suitable atomic absorption spectrophotometer (see
Spectrophotometry and Light-Scattering á851ñ)equipped with a chromium hollow-cathode lamp and an airacetylene flame,using a 1:5dilution of the
Sodium chloride solutionas the blank.Plot the absorbances of the
Standard preparationsversus concentration,in µg per mL,of chromium,and draw the straight line best fitting the four plotted points.From the graph so obtained,determine the concentration,in µg per mL,of chromium in the
Assay preparation.Calculate the quantity,in µg,of chromium in each mLof the Injection taken by the formula:
25C/V,
in which
Cis the concentration,in µg per mL,of chromium in the
Assay preparation,and
Vis the volume,in mL,of Injection taken.