Identification—
Transfer a volume of Injection, equivalent to about 6 mg of leucovorin calcium, to a glass-stoppered, 50-mL centrifuge tube, add about 40 mL of acetone, mix, centrifuge for a few minutes, and decant and discard the liquid phase. Repeat the washing process with an additional 40 mL of acetone. Dry the precipitate so obtained with a stream of dry nitrogen: the residue responds to the
Identification test under
Leucovorin Calcium.
Assay—
[NOTE—Use only freshly deionized water wherever water is specified throughout this procedure. Use low-actinic glassware for solutions containing leucovorin calcium, and otherwise protect the solutions from unnecessary exposure to light. Complete the assay without prolonged interruption.
]
Tetrabutylammonium hydroxide solution
,
2 N Monobasic sodium phosphate solution,
Mobile phase,
Diluting solution,
Standard preparation, System suitability preparation, and
Chromatographic system—Prepare as directed in the
Assay under
Leucovorin Calcium.
Assay preparation—
Transfer an accurately measured volume of Injection, equivalent to about 9 mg of leucovorin, to a 50-mL volumetric flask, dilute with Diluting solution to volume, and mix. Pipet 25 mL of this solution into a 60-mL separator, add 25 mL of methylene chloride, shake the mixture, allow the layers to separate, and discard the methylene chloride extract. Repeat the extraction with two more 25-mL portions of methylene chloride, discarding the methylene chloride extracts. Filter the aqueous layer, discarding the first 5 mL of the filtrate, and collect the remaining filtrate in a glass-stoppered conical flask.
Procedure—
Proceed as directed for
Procedure in the
Assay under
Leucovorin Calcium. Calculate the quantity, in mg, of leucovorin (C
20H
23N
7O
7) in each mL of the Injection taken by the formula:
(473.45 / 511.50)(50C / V)(rU / rS),
in which 473.45 and 511.50 are the molecular weights of leucovorin and anhydrous leucovorin calcium, respectively;
C is the concentration, in mg per mL, of anhydrous
USP Leucovorin Calcium RS in the
Standard preparation; V is the volume, in mL, of Injection taken, and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
85
—
It contains not more than 1.95 USP Endotoxin Units per mg of leucovorin calcium.