Analysis of methyltestosterone in tablets

A calibration solution containing ca 0.04% w/v of methyltestosterone and ca 0.04% w/v testosterone in ethanol is prepared (Solution 1). A weight of tablet powder containing ca 20 mg of methyltestosterone is extracted with 50 ml of ethanol to prepare Solution 2. Solution 3 is prepared by dissolving tablet powder containing ca 20 mg of methyltestosterone in exactly 50 ml of ethanol containing exactly the same concentration of testosterone as Solution 1. In this example 0.5 ¡j\ amounts of the solutions were injected into the GC in the splitless mode.

Solution 1 gives a response factor for the calibration solution as follows:

area of methyltestosterone peak in calibration solution area of testosterone peak in calibration solution

Solution 3 gives a response factor for the sample as follows:

area of methyltestosterone peak in sample solution area of testosterone peak in sample solution

The amount of methyltestosterone in the tablet powder can be calculated as follows:

amount of methyltestosterone =

response factor for sample response factor for calibration solution x %w/v of methyltestosterone in calibration solution x sampk^solution

Data from analysis of methyltestosterone tablets

• Stated content of methyltestosterone per tablet = 25 mg

' Weight of tablet powder taken for assay = 0.1713 g

> Solution 1 contains: 0.04% w/v methyltestosterone and 0.043% w/v testosterone

> Solution 3 contains: the methyltestosterone extracted from the powder taken for assay and 0.043% w/v testosterone

> Solution 1: Peak area testosterone = 216 268; Peak area methyltestosterone = 212 992

1 Solution 3: Peak area testosterone = 191 146; Peak area methyltestosterone = 269 243.

Calculation example 11.1

212 992

Response factor for Solution 1 = "., „ ., = 0.9849 v 216 268

269 043

191 146

Amount of methyltestosterone in the tablet powder determined by analysis = ¿H x 0.04 xi|= 0.02861 g = 28.6. mg

Amount of methyltestosterone expected in tablet powder =

weight of powder analysed x ^ comeni q{. 5 ^^ = OI713 x 5 x 25 = 28 5? weight of 5 tablets 0.7496

Percentage of stated content = x 100 = I00.1 %

2o.57

A dilution factor may be incorporated into this calculation if the sample is first extracted and then diluted in order to bring it into the working range of the instrument. This approach to quantitation does not address the linearity of the method but since the variation in the composition of formulations should be within ± 10% of the stated amount there is some justification for using it. The precision of the method is readily addressed by carrying out repeat preparations of sample and calibration solutions.

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