Test solution: 100 mg per mL, in water.

Standard solution— 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 solutions— Transfer 62.5 mg of Levocarnitine to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix to obtain a stock solution. To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard solution. To each flask add 20.0 mL of the stock solution, dilute with water to volume, and mix. These solutions contain 0 (Test solution A), 2.5 (Test solution B), and 5.0 (Test solution C) µg per mL of potassium.

Procedure— 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, 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 Test solution A. Calculate the percentage of potassium in the portion of Levocarnitine taken by multiplying the concentration, in µg per mL, of potassium found in Test solution A by 0.2: not more than 0.2% is found.

Standard solution— 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 solutions— Transfer 4.0 g of Levocarnitine to a 100-mL volumetric flask, dissolve in and dilute with water to volume, and mix to obtain a stock solution. To three separate 25-mL volumetric flasks add 0, 2.0, and 4.0 mL of the Standard solution. To each flask add 20.0 mL of the stock solution, dilute with water to volume, and mix. These solutions contain 0 (Test solution A), 20.0 (Test solution B), and 40.0 (Test solution C) µg per mL of sodium.

Procedure— 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, 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 Test solution A. Calculate the percentage of sodium in the portion of Levocarnitine taken by multiplying the concentration, in µg per mL, of sodium found in Test solution A by 0.003125: not more than 0.1% is found.

(Official January 1, 2007)