pH 6.0 acetate buffer— Dissolve 50 g of ammonium acetate in 150 mL of water, adjust with glacial acetic acid to a pH of 6.0, dilute with water to 250 mL, and mix.

Procedure— Dissolve 1.0 g of it in 50 mL of water, and add 5 mL of pH 6.0 acetate buffer. Extract this solution with successive portions of 10, 10, and 5 mL of a 0.5% solution of 8-hydroxyquinoline in chloroform, combining the chloroform extracts in a 50-mL volumetric flask. Dilute the combined extracts with chloroform to volume, and mix (test solution). Prepare a Standard solution from a mixture of 2.0 mL of a solution containing 1.0 µg of Al per mL, prepared as directed for Standard Preparations under Aluminum 206, 5 mL of pH 6.0 acetate buffer, and 48 mL of water, and extract as described above. Prepare a blank solution from a mixture of 50 mL of water and 5 mL of pH 6.0 acetate buffer, and extract as described above. Determine the fluorescence intensities of the test solution and the Standard solution in a fluorometer set at an excitation wavelength of 392 nm and an emission wavelength of 518 nm, using the blank solution to set the instrument to zero. The fluorescence of the test solution does not exceed that of the Standard solution (2 µg per g).

Stock test solution— Dissolve 50 g of it and 5 g of ammonium acetate in 200 mL of 1 N hydrochloric acid, and filter. The pH of this solution is between 4.5 and 5.5. [NOTE—Cover the solution.]

Barium chloride solution— Dissolve an accurately weighed quantity of anhydrous barium chloride in water to obtain a solution having a concentration of 0.758 mg per mL. This solution contains 500 µg of barium per mL.

Test solutions— To four separate tubes add 1.0, 1.5, 2.0, and 2.5 mL of Barium chloride solution. To each tube add a sufficient volume of the Stock test solution to bring the volume to 40 mL.

Standard solution— To a fifth tube add 1 g of ammonium acetate, 2 mL of 1 N hydrochloric acid, 3.0 mL of Barium chloride solution, and sufficient water to bring the volume to 40 mL.

Ammonium sulfate solution— Use a solution of ammonium sulfate (1 in 10).

Procedure— To the Test solutions and the Standard solution add, with brisk stirring, 3.0 mL of Ammonium sulfate solution, and allow to stand for 20 minutes. The Test solutions containing 1.0 and 1.5 mL of Barium chloride solution remain clear or are only faintly turbid. The Test solution containing 2.0 mL of Barium chloride solution is not more turbid than the Standard solution.

Standard preparation— Dissolve an accurately weighed quantity of magnesium oxide in 1 N nitric acid to obtain a solution having a concentration of 1.516 mg per mL. This solution contains 1000 µg of magnesium per mL. Dilute an accurately measured volume of this solution quantitatively, and stepwise if necessary, with water to obtain a solution containing 5.0 µg of magnesium per mL.

Test preparation— Transfer 200 mg of Calcium Acetate to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Procedure— To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard preparation. To each flask add 20.0 mL of the Test preparation, dilute with water to volume, and mix. These test solutions contain, respectively, 0, 0.4, and 0.8 µg per mL of magnesium from the Standard preparation. Concomitantly determine the absorbances of the test solutions at the magnesium emission line at 285.2 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with an air–acetylene flame, using water as the blank. Plot the absorbances of the test solutions versus their contents of magnesium, in µg per mL, as furnished by the Standard preparation, draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the amount, in µg, of magnesium in each mL of the test solution containing 0 mL of the Standard preparation. Calculate the percentage of magnesium in the specimen by multiplying this value by 0.0625: the limit is 0.05%.

Standard preparation— Transfer 5.959 g of potassium chloride, previously dried at 105 for 2 hours and accurately weighed, to a 250-mL volumetric flask, dilute with water to volume, and mix. This solution contains 12.5 mg of potassium per mL. Dilute an accurately measured volume of this solution quantitatively, and stepwise if necessary, with water to obtain a solution containing 31.25 µg of potassium per mL.

Test preparation— Transfer 1.25 g of Calcium Acetate to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Procedure— To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard preparation. To each flask add 20.0 mL of the Test preparation, dilute with water to volume, and mix. These test solutions contain, respectively, 0, 2.5, and 5.0 µg per mL of potassium from the Standard preparation. Concomitantly determine the absorbances of the test solutions at the potassium emission line at 766.7 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with an air–acetylene flame, using water as the blank. Plot the absorbances of the test solutions versus their contents of potassium, in µg per mL, as furnished by the Standard preparation, draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the amount, in µg, of potassium in each mL of the test solution containing 0 mL of the Standard preparation. Calculate the percentage of potassium in the specimen by multiplying this value by 0.01: the limit is 0.05%.

Standard preparation— Transfer 6.355 g of sodium chloride, previously dried at 105 for 2 hours and accurately weighed, to a 250-mL volumetric flask, dilute with water to volume, and mix. This solution contains 10.0 mg of sodium per mL. Dilute an accurately measured volume of this solution quantitatively, and stepwise if necessary, with water to obtain a solution containing 250 µg of sodium per mL.

Test preparation— Transfer 1.0 g of Calcium Acetate to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Procedure— To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard preparation. To each flask add 20.0 mL of the Test preparation, dilute with water to volume, and mix. These test solutions contain, respectively, 0, 20.0, and 40.0 µg per mL of sodium from the Standard preparation. Concomitantly determine the absorbances of the test solutions at the sodium emission line at 589.0 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with an air–acetylene flame, using water as the blank. Plot the absorbances of the test solutions versus their contents of sodium, in µg per mL, as furnished by the Standard preparation, draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the amount, in µg, of sodium in each mL of the test solution containing 0 mL of the Standard preparation. Calculate the percentage of sodium in the specimen by multiplying this value by 0.0125: the limit is 0.5%.

Standard preparation— Dissolve an accurately weighed quantity of strontium acetate in water to obtain a solution having a concentration of 2.45 mg per mL. This solution contains 1000 µg of strontium per mL. Dilute an accurately measured volume of this solution quantitatively, and stepwise if necessary, with water to obtain a solution containing 50.0 µg of strontium per mL.

Test preparation— Transfer 2.0 g of Calcium Acetate to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix.

Procedure— To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard preparation. To each flask add 20.0 mL of the Test preparation, dilute with water to volume, and mix. These test solutions contain, respectively, 0, 4.0, and 8.0 µg per mL of strontium from the Standard preparation. Concomitantly determine the absorbances of the test solutions at the strontium emission line at 460.7 nm with a suitable atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a nitrous oxide–acetylene flame, using water as the blank. Plot the absorbances of the test solutions versus their contents of strontium, in µg per mL, as furnished by the Standard preparation, draw the straight line best fitting the three points, and extrapolate the line until it intercepts the concentration axis. From the intercept determine the amount, in µg, of strontium in each mL of the test solution containing 0 mL of the Standard preparation. Calculate the percentage of strontium in the specimen by multiplying this value by 0.00625: the limit is 0.05%.

(Official January 1, 2007)