Loss on drying (see Thermal Analysis á891ñ)
[NOTEIn this procedure,perform weighings rapidly with minimum exposure of the substances to air.
]Determine the percentage of volatile substances by thermogravimetric analysis on an appropriately calibrated instrument,using about 10mg of Vincristine Sulfate,accurately weighed.Heat the specimen at the rate of 5

per minute between ambient temperature and 200

in an atmosphere of nitrogen at a flow rate of 40mLper minute.From the thermogram,determine the accumulated loss in weight between ambient temperature and a point on the plateau before decomposition is indicated (at about 160

):it loses not more than 12.0%of its weight.
Related compounds
Solvent A
Prepare a filtered and degassed mixture of water and diethylamine (985:15),adjusted with phosphoric acid to a pHof 7.5.
Solvent B
Use methanol.
High load test preparation
Prepare as directed for
Assay preparationin the
Assay.
Low load test preparation
Pipet 1mLof High load test preparationinto a 25-mLvolumetric flask,dilute with water to volume,and mix.
Chromatographic system
(see
Chromatography á621ñ)Use the liquid chromatograph equipped as directed in the
Assay.The mobile phase is maintained at a flow rate of about 2mLper minute,with an initial gradient of 62%of
Solvent Band 38%of
Solvent Afor 12minutes,then changed to increase
Solvent Bat a rate of 2%per minute,so that after 15minutes it will comprise 92%of the mixture,then changed to decrease
Solvent Bat a rate of 15%per minute,so that after 2minutes it will again comprise 62%of the mixture,then maintained at this ratio for 5minutes.
Procedure
Separately inject equal volumes (about 200µL)of the
Low load test preparationand of the
High load test preparationinto the chromatograph,record the chromatograms,and measure the peak responses,
ri,of any related substances appearing after the solvent peak in the chromatogram of the
High load test preparation.Calculate the total percentage of responses due to related substances taken by the formula:
100rt/(rt+25rv),
in which
rtis the sum of the
riresponses,and
rvis the vincristine peak response in the chromatogram of the
Low load test preparation.Not more than 4.0%is found.Calculate the percentage response of each related substance taken by the formula:
100ri/(rt+25rv).
Not more than 1.0%of response due to any individual related substance is found.
Assay
Diethylamine solution
Mix 5mLof diethylamine with 295mLof water,and adjust with phosphoric acid to a pHof 7.5.
Mobile phase
Prepare a filtered and degassed mixture of methanol and
Diethylamine solution(70:30).Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Standard preparation
Dissolve an accurately weighed quantity of
USP Vincristine Sulfate RSin water to obtain a solution having a known concentration of about 1mg per mL.
Assay preparation
Equilibrate a portion of Vincristine Sulfate for 30minutes with the ambient humidity,transfer about 10mg,accurately weighed,to a 10-mLvolumetric flask,dissolve in and dilute with water to volume,and mix.Using another portion of the equilibrated specimen,determine the loss in weight as directed for
USP Vincristine Sulfate RS.
Chromatographic system
(see
Chromatography á621ñ)The liquid chromatograph is equipped with a 297-nm detector,a precolumn packed with porous silica gel,a 2-to 5-cm guard column containing packing L1,and a 4.6-mm ×25-cm analytical column that contains packing L7.The flow rate is about 1.5mLper minute.Chromatograph the
Standard preparation,and record the peak responses as directed for
Procedure:the relative standard deviation for replicate injections is not more than 2.0%.Similarly chromatograph 10µLof the
System suitability preparation,and record the peak responses:the resolution,between vincristine sulfate and vinblastine sulfate is not less than 4.0.
[NOTEFor a particular column,the resolution may be increased by increasing the proportion of water in the
Mobile phase.]
Procedure
Separately inject equal volumes (about 10µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C
46H
56N
4O
10·H
2SO
4in the portion of Vincristine Sulfate taken,corrected for loss in weight in the
Assay preparation,by the formula:
10C(rU/rS),
in which
Cis the concentration,in mg per mL,of
USP Vincristine Sulfate RS,corrected for loss in weight in the
Standard preparation;and
rUand
rSare the peak responses obtained from the
Assay preparationand the
Standard preparation,respectively.