Identification—
Place a volume of Injection,equivalent to about 40mg of metoprolol tartrate,in a separator,add 4mLof dilute ammonium hydroxide (1in 3),and extract with 20mLof chloroform,filtering the chloroform extract through chloroform-pre-rinsed anhydrous sodium sulfate.Evaporate the chloroform to dryness,and place in a freezer to congeal the residue:the IRabsorption spectrum of a potassium bromide dispersion of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of
USP Metoprolol Tartrate RS.
Assay—
Mobile phase—
Prepare a degassed solution by dissolving 961mg of 1-pentanesulfonic acid sodium salt (monohydrate)and 82mg of anhydrous sodium acetate in a mixture of 550mLof methanol and 470mLof water and adding 0.57mLof glacial acetic acid.
Sodium chloride solution—
Dissolve 9.0g of sodium chloride in water to make 1000mL.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Metoprolol Tartrate RSin
Sodium chloride solutionto obtain a stock solution having a known concentration of about 1000µg per mL.Mix equal volumes,accurately measured,of this stock solution and of
Internal standard solution.
Assay preparation—
Dilute an accurately measured volume of Injection,if necessary,quantitatively with Sodium chloride solutionto obtain a stock solution having a concentration of about 1000µg per mL.Mix equal volumes,accurately measured,of this stock solution and of Internal standard solution.
Chromatographic system
(see
Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph three replicate injections of the
Standard preparation,and record the peak responses as directed under
Procedure:the relative standard deviation is not more than 2.0%,and the resolution factor between metoprolol tartrate and oxprenolol hydrochloride is not less than 2.0.
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.The relative retention times are about 0.8for metoprolol tartrate and 1.0for oxprenolol hydrochloride.Calculate the quantity,in mg,of metoprolol tartrate [(C
15H
25NO
3)
2·C
4H
6O
6]in each mLof the Injection taken by the formula:
(L/D)(C)(RU/RS),
in which
Lis the labeled quantity,in mg,of metoprolol tartrate in the Injection;
Dis the concentration,in µg per mL,of metoprolol tartrate in the
Assay preparation,on the basis of the labeled quantity in each mLof Injection taken and the extent of dilution;
Cis the concentration,in µg per mL,of
USP Metoprolol Tartrate RSin the
Standard preparation;and
RUand
RSare the peak response ratios of metoprolol tartrate to oxprenolol hydrochloride obtained from the
Assay preparationand the
Standard preparation,respectively.