Identification—
Transfer a volume of Injection,equivalent to about 6mg of leucovorin calcium,to a glass-stoppered,50-mLcentrifuge tube,add about 40mLof acetone,mix,centrifuge for a few minutes,and decant and discard the liquid phase.Repeat the washing process with an additional 40mLof acetone.Dry the precipitate so obtained with a stream of dry nitrogen:the residue responds to the
Identificationtest 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
,
2N Monobasic sodium phosphate solution,
Mobile phase,
Diluting solution,
Standard preparation,System suitability preparation,and
Chromatographic system—Prepare as directed in the
Assayunder
Leucovorin Calcium.
Assay preparation—
Transfer an accurately measured volume of Injection,equivalent to about 9mg of leucovorin,to a 50-mLvolumetric flask,dilute with Diluting solutionto volume,and mix.Pipet 25mLof this solution into a 60-mLseparator,add 25mLof methylene chloride,shake the mixture,allow the layers to separate,and discard the methylene chloride extract.Repeat the extraction with two more 25-mLportions of methylene chloride,discarding the methylene chloride extracts.Filter the aqueous layer,discarding the first 5mLof the filtrate,and collect the remaining filtrate in a glass-stoppered conical flask.
Procedure—
Proceed as directed for
Procedurein the
Assayunder
Leucovorin Calcium.Calculate the quantity,in mg,of leucovorin (C
20H
23N
7O
7)in each mLof the Injection taken by the formula:
(473.45/511.50)(50C/V)(rU/rS),
in which 473.45and 511.50are the molecular weights of leucovorin and anhydrous leucovorin calcium,respectively;
Cis the concentration,in mg per mL,of anhydrous
USP Leucovorin Calcium RSin the
Standard preparation;Vis the volume,in mL,of Injection taken,and
rUand
rSare the peak responses obtained from the
Assay preparationand the
Standard preparation,respectively.