Potassium chloride solution— Dissolve 100 g of potassium chloride in water to make 1000 mL.

Standard solutions— Transfer 127.1 mg of sodium chloride, previously dried at 105 for 2 hours and accurately weighed, to a 500-mL volumetric flask, add water to volume, and mix. Transfer 10.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix. Transfer 2.0, 5.0, and 10.0 mL of this solution to separate 100-mL volumetric flasks, add 10.0 mL of Potassium chloride solution to each flask, dilute with water to volume, and mix. These Standard solutions contain 0.2, 0.5, and 1.0 µg of sodium per mL, respectively. [note—Concentrations of sodium in the Standard solutions may be modified to fit the linear or working range of the atomic absorption spectrophotometer.]

Test solution— Transfer about 0.2 g of Potassium Acetate, accurately weighed, to a 100-mL volumetric flask containing about 50 mL of water, and swirl to dissolve. Add 10.0 mL of Potassium chloride solution, dilute with water to volume, and mix. [note—The concentration of Potassium Acetate in the Test solution may be modified by using a different quantity or by further dilution to bring the absorption response within the range of responses obtained from the Standard solutions.]

Blank solution— Transfer 10.0 mL of Potassium chloride solution to a 100-mL volumetric flask, dilute with water to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard solutions and the Test solution at the sodium emission line of 589 nm, with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a sodium hollow-cathode lamp and an oxidizing air–acetylene flame, using the Blank solution to zero the instrument. Plot the absorbances of the Standard solutions versus concentration, in µg per mL, of sodium, and draw the straight line best fitting the plotted points. From the graph so obtained, determine the concentration C, in µg per mL, of sodium in the Test solution. Calculate the percentage of sodium in the portion of Potassium Acetate taken by the formula: in which W is the quantity, in g, of Potassium Acetate taken to prepare the Test solution; and D is the extent of dilution of the Test solution: not more than 0.03% of sodium is found.