A: It responds to the flame tests for Sodium 191 and Potassium 191, to the oxalate test for Calcium 191, and to the tests for Magnesium 191 and Chloride 191.

B: The retention time of the acetate peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay for acetate.

C: Where citrate is purported to be present, the retention time of the citrate peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay for citrate.

D: Where lactate is purported to be present, the retention time of the lactate peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay for lactate.

(Official January 1, 2007)

Internal standard solution, Potassium stock solution, Sodium stock solution, Stock standard preparation, and Standard preparation— Prepare as directed in the Assay for potassium and sodium under Potassium Chloride in Sodium Chloride Injection.

Assay preparation— Transfer 5.0 mL of Injection to a 500-mL volumetric flask, dilute with Internal standard solution to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay for potassium and sodium under Potassium Chloride in Sodium Chloride Injection. Calculate the quantity, in mg, of potassium (K) in each mL of the Injection taken by the formula: in which the terms are as defined therein. Each mg of potassium is equivalent to 0.02558 mEq of potassium. Calculate the quantity, in mg, of sodium (Na) in each mL of the Injection taken by the formula: in which the terms are as defined therein. Each mg of sodium is equivalent to 0.04350 mEq of sodium.

Lanthanum chloride solution, Dilute hydrochloric acid, Blank solution, Magnesium stock solution, and Standard preparations— Prepare as directed in the Assay for magnesium under Multiple Electrolytes Injection Type 1.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 20 mg (1.65 mEq) of magnesium, to a 1000-mL volumetric flask containing 50.0 mL of Lanthanum chloride solution. Dilute the contents of the flask with Dilute hydrochloric acid to volume, and mix.

Procedure— Proceed as directed for Procedure in the Assay for magnesium under Multiple Electrolytes Injection Type 1. Calculate the quantity, in µg, of magnesium (Mg) in each mL of the Injection taken by the formula: in which V is the volume, in mL, of Injection taken to prepare the Assay preparation, and the other terms are as defined therein.

Lanthanum chloride solution, Dilute hydrochloric acid, and Blank solution— Prepare as directed in the Assay for magnesium under Multiple Electrolytes Injection Type 1.

Calcium stock solution— Transfer 499.5 mg of primary standard calcium carbonate to a 200-mL volumetric flask, and add 10 mL of water. Carefully add 5 mL of Dilute hydrochloric acid, and swirl to dissolve the calcium carbonate. Dilute with water to volume, and mix. This solution contains 1000 µg of calcium (Ca) per mL.

Standard preparations— To three separate 100-mL volumetric flasks, each containing 5.0 mL of Lanthanum chloride solution, add 1.0, 1.5, and 2.0 mL, respectively, of Calcium stock solution. Dilute the contents of each flask with Dilute hydrochloric acid to volume, and mix. These three solutions contain 10.0, 15.0, and 20.0 µg, respectively, of calcium (Ca) per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 20 mg (1 mEq) of calcium, to a 1000-mL volumetric flask containing 50.0 mL of Lanthanum chloride solution. Dilute the contents of the flask with Dilute hydrochloric acid to volume, and mix.

Procedure— Concomitantly determine the absorbances of the Standard preparations and the Assay preparation at the calcium emission line at 422.7 nm, with an atomic absorption spectrophotometer (see Spectrophotometry and Light-scattering 851) equipped with a calcium hollow-cathode lamp and an air–acetylene flame, using the Blank solution as the blank. Plot the absorbances of the Standard preparations versus concentration, in µg per mL, of calcium, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, C, in µg per mL, of calcium in the Assay preparation. Calculate the quantity, in µg, of calcium in each mL of the Injection taken by the formula: in which V is the volume, in mL, of Injection taken to prepare the Assay preparation.

Mobile phase, Standard preparation, and Chromatographic system— Prepare as directed in the Assay for acetate under Multiple Electrolytes Injection Type 1.

Assay preparation— Quantitatively dilute an accurately measured volume of Injection with water to obtain a solution containing about 0.0088 mEq of acetate per mL.

Procedure— Proceed as directed for Procedure in the Assay for acetate under Multiple Electrolytes Injection Type 1. Calculate the quantity, in mEq per L, of acetate (C2H3O2) in the Injection taken by the formula: in which the terms are as defined therein.

Mobile phase— Prepare a filtered and degassed solution of 0.05 N sulfuric acid. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparations— Dissolve an accurately weighed quantity of anhydrous sodium citrate, previously dried at 180 for 18 hours, in water to obtain a stock solution having a known concentration of about 10 mg per mL. Quantitatively dilute accurately measured volumes of this stock solution with water to obtain three Standard preparations having known concentrations of about 0.5, 1.0, and 2.0 mg, respectively, of anhydrous sodium citrate per mL.

Assay preparation— Where the labeled quantity is greater than 10 mEq of citrate per L, quantitatively dilute an accurately measured volume of Injection with water to obtain a solution containing about 0.01 mEq of citrate per mL. Where the labeled quantity is 10 mEq of citrate or less per L, use the undiluted Injection as the Assay preparation.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector, a 7.8-mm × 4-cm guard column containing packing L17, and a 7.8-mm × 30-cm analytical column containing packing L17, and is maintained at about 60. The flow rate is about 0.8 mL per minute. Chromatograph the Standard preparation containing 1 mg of anhydrous sodium citrate per mL, and record the responses as directed for Procedure: the tailing factor for the analyte peak is not more than 1.5, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparations and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Plot the responses of the Standard preparations versus concentration, in mg of anhydrous sodium citrate per mL, and draw the straight line best fitting the three plotted points. From the graph so obtained, determine the concentration, C, in mg of anhydrous sodium citrate equivalent per mL, in the Assay preparation. Calculate the quantity, in mEq per L, of citrate (C6H5O7) in the Injection taken by the formula: in which 258.07 is the molecular weight of anhydrous sodium citrate, L is the labeled quantity, in mEq per L, of citrate in the Injection, and D is the quantity, in mEq per mL, of citrate in the Assay preparation, based on the labeled quantity and the extent of dilution.

Mobile phase— Prepare a solution in water containing about 1 mL of formic acid and 1 mL of dicyclohexylamine per L, filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Prepare a solution in water containing about 3 mg of anhydrous sodium acetate and 3 mg of USP RS per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Sodium Lactate RS in water to obtain a solution having a known concentration of about 2 mg per mL.

Assay preparation— Where the labeled quantity of lactate is greater than 20 mEq per L, quantitatively dilute an accurately measured volume of Injection with water to obtain a solution containing about 0.02 mEq of lactate per mL. Where the labeled quantity of lactate is 20 mEq or less per L, use the undiluted Injection as the Assay preparation.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between acetate and lactate is not less than 2. Chromatograph the Standard preparation, and record the responses as directed for Procedure: the tailing factor for the analyte peak is not more than 2.0, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mEq per L, of lactate (C3H5O3) in the Injection taken by the formula: in which C is the concentration, in mg per mL, of USP Sodium Lactate RS in the Standard preparation; 112.06 is the molecular weight of sodium lactate; L is the labeled quantity, in mEq per L, of lactate in Injection; D is the quantity, in mEq per mL, of lactate in the Assay preparation, based on the labeled quantity and the extent of dilution; and rU and rS are the lactate peak responses obtained from the Assay preparation and the Standard preparation, respectively.