Standard solution
Dissolve accurately weighed quantities of
USP Alprostadil RS, USP Prostaglandin A
1 RS, and USP Prostaglandin B
1 RS in a mixture of methanol and water (9:1), and dilute quantitatively, and stepwise if necessary, with a mixture of methanol and water (9:1) to obtain a solution having known concentrations of about 6 µg per mL, 15 µg per mL, and 6 µg per mL, respectively.
Procedure
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the peak responses at 200 nm, 224 nm, and 280 nm. Calculate the percentage of prostaglandin A
1 and prostaglandin B
1 in the portion of Alprostadil taken by the formula:
500(CS / W)(rI / rS),
in which
CS is the concentration, in mg per mL, of USP Prostaglandin A
1 RS or USP Prostaglandin B
1 RS in the
Standard solution; W is the weight, in mg, of Alprostadil taken for the
Test solution; ri is the peak response for prostaglandin A
1 or prostaglandin B
1 obtained from the
Test solution; and
rS is the peak response of prostaglandin A
1 or prostaglandin B
1 obtained from the
Standard solution: not more than 1.5% of prostaglandin A
1 is found; and not more than 0.1% of prostaglandin B
1 is found. Calculate the percentage of each impurity occurring at 200 nm and eluting before prostaglandin A
1 in the portion of Alprostadil taken by the formula:
500(CS / W)(rI / rS),
in which
CS is the concentration, in mg per mL, of
USP Alprostadil RS in the
Standard solution; ri is the peak response for each impurity obtained from the
Test solution; rS is the peak response for alprostadil obtained from the
Standard solution; and the other terms are as defined herein: not more than 0.9% of any foreign prostaglandin impurity is found. Calculate the percentage of any impurity having a relative retention time of 0.6, relative to the prostaglandin A
1 peak detected at 224 nm, in the portion of Alprostadil taken by the formula:
500(CS / W)(rI / rS),
in which
CS is the concentration, in mg per mL, of USP Prostaglandin A
1 RS in the
Standard solution; rI is the peak response for any impurity having a relative retention time of 0.6, relative to the prostaglandin A
1 peak, obtained from the
Test solution; rS is the peak response of prostaglandin A
1 obtained from the
Standard solution; and the other terms are as defined herein: not more than 0.9% of any impurity having a relative retention time of 0.6, relative to the prostaglandin A
1 peak, is found.