Assay
[NOTEThe
Standard preparations and the
Assay preparation may be diluted quantitatively with water,if necessary,to obtain solutions of suitable concentrations adaptable to the linear or working range of the instrument.
]
Sodium chloride solution
Dissolve 450mg of sodium chloride in water,dilute with water to 500mL,and mix.
Standard preparations
Transfer 3.11g of zinc oxide,accurately weighed,to a 250-mLvolumetric flask,add 80mLof 1Nsulfuric acid,warm to dissolve,cool,dilute with water to volume,and mix.This stock solution contains 10.0mg of zinc per mL.Dilute an accurately measured volume of this solution quantitatively with water to obtain a solution containing 125µg of zinc per mL.Transfer 2.0,3.0,and 4.0mL,respectively,of this solution to three separate 500-mLvolumetric flasks,each containing 5mLof Sodium chloride solution,dilute the contents of each flask with water to volume,and mix.These Standard preparationscontain,respectively,0.50,0.75,and 1.0µg of zinc per mL.
Assay preparation
Transfer an accurately measured volume of Injection,equivalent to about 5mg of zinc,to a 500-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 100-mLvolumetric flask.From the labeled amount of sodium chloride,if any,in the Injection,calculate the amount,in mg,of sodium chloride in the 10.0-mLportion and add sufficient Sodium chloride solutionto bring the total sodium chloride content of the 100-mLvolumetric flask to 9mg.Dilute with water to volume,and mix.
Procedure
Concomitantly determine the absorbances of the
Standard preparationsand the
Assay preparationat the zinc emission line at 213.8nm,with a suitable atomic absorption spectrophotometer (see
Spectrophotometry and Light-scattering á851ñ)equipped with a zinc hollow-cathode lamp and an airacetylene flame,using water as the blank.Plot the absorbances of the
Standard preparationsversus concentration,in µg per mL,of zinc,and draw the straight line best fitting the three plotted points.From the graph so obtained,determine the concentration,in µg per mL,of zinc in the
Assay preparation.Calculate the quantity,in mg,of zinc in each mLof the Injection taken by the formula:
5C/V,
in which
Cis the concentration,in µg per mL,of zinc in the
Assay preparation;and
Vis the volume,in mL,of Injection taken.