Assay
Potassium stock solution
Dissolve 190.7 mg of potassium chloride, previously dried at 105
for 2 hours, in water. Transfer to a 1000-mL volumetric flask, dilute with water to volume, and mix. Transfer 100.0 mL of this solution to a 1000-mL volumetric flask, dilute with water to volume, and mix. This solution contains 10 µg of potassium (equivalent to 19.07 µg of potassium chloride) per mL.
Standard preparations
To separate 100-mL volumetric flasks transfer 10.0, 15.0, and 20.0 mL, respectively, of Potassium stock solution. To each flask add 2.0 mL of sodium chloride solution (1 in 5) and 1.0 mL of hydrochloric acid, dilute with water to volume, and mix. The Standard preparations contain, respectively, 1.0, 1.5, and 2.0 µg of potassium per mL.
Assay preparation
Transfer an accurately measured volume of Injection, equivalent to about 2 g of potassium acetate, to a 500-mL volumetric flask, dilute with water to volume, and mix. Transfer 5.0 mL of the solution to a 250-mL volumetric flask, dilute with water to volume, and mix. Transfer 5.0 mL of the resulting solution to a 100-mL volumetric flask, add 2.0 mL of sodium chloride solution (1 in 5) and 1.0 mL of hydrochloric acid, dilute with water to volume, and mix.
Procedure
Concomitantly determine the absorbances of the
Standard preparations and the
Assay preparation at the potassium emission line of 766.5 nm, with a suitable atomic absorption spectrophotometer (see
Spectrophotometry and Light-scattering 851) equipped with a potassium hollow-cathode lamp and an airacetylene flame, using water as the blank. Plot the absorbance of the
Standard preparation versus concentration, in µg per mL, of potassium, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, in µg per mL, of potassium in the
Assay preparation. Calculate the quantity, in mg, of C
2H
3KO
2 in the portion of Injection taken by the formula:
500C(2.510),
in which
C is the concentration, in µg per mL, of potassium in the
Assay preparation, and 2.510 is the ratio of the molecular weight of potassium acetate to the atomic weight of potassium.