Identification—
A:
Thin-Layer Chromatographic Identification Test á201ñ—
Test solution—
Transfer a weighed quantity of the Gel,equivalent to 7.5mg of metronidazole,to a suitable flask,add 15mLof water,shake to disperse,and sonicate for about 10minutes.Elute a portion of this solution through a 10-mm ×15-cm chromatographic column containing a 10-cm length of ion-exchange resin with a pledget of glass wool at the bottom and top of the resin,and collect the eluate in a suitable vial.
Standard solution:
0.5mg per mL.
Application volume:
5µL.
Developing solvent system:
a mixture of chloroform,methanol,and ammonium hydroxide (6:3:1).
B:
The retention time of the major peak in the chromatogram of the
Assay preparationcorresponds to that in the chromatogram of the
Standard preparation,as obtained in the
Assay.
Assay—
Mobile phase—
Dissolve 1.5g of monobasic potassium phosphate and 1.3g of dibasic sodium phosphate in 350mLof water,add 650mLof methanol,mix,filter,and degas.Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Metronidazole RSin
Mobile phase,and dilute quantitatively,and stepwise if necessary,with
Mobile phaseto obtain a solution having a known concentration of about 0.075mg per mL.
Assay preparation—
Transfer an accurately weighed quantity of Gel,equivalent to 7.5mg of metronidazole,to a 100-mLvolumetric flask,add 50mLof Mobile phase,and shake by mechanical means for 20minutes.Dilute with Mobile phaseto volume,and mix.Centrifuge a portion of this solution until clear,and use the supernatant for injection into the chromatograph.
Chromatographic system
(see
Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L7.The flow rate is about 1mLper minute.Chromatograph the
Standard preparation,and record the peak heights as directed for
Procedure:the tailing factor for the metronidazole 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 20µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the heights of the major peaks.Calculate the quantity,in mg,of metronidazole (C
6H
9N
3O
3)in the portion of Gel taken by the formula:
100C(rU/rS),
in which
Cis the concentration,in mg per mL,of
USP Metronidazole RSin the
Standard preparation;and
rUand
rSare the peak heights of metronidazole obtained from the
Assay preparationand the
Standard preparation,respectively.