Dear Chukwuebuka Egbuna,
The equation:
Amount of drug released / amount of drug used in the dissolution x 100%
For example, If you are testing a dissolution of a tablet containing 500 mg paracetamol and you are checking the release of paracetamol from the tablet every 1 hr for 8 hours and you determine the amount of the released drug by HPLC, first you should make a calibration curve for paracetamol standard using HPLC. The standard curve should be a plot of the concentration of paracetamol versus area under the peak. This curve is done in order to calculate the concentration (amount) of the samples taken according to their area under the curve.
If after 1 hour 100 mg were released, the % dissolution will be
100/500 x 100 % = 20 %
if after 2 hours 180 mg were released, the % Dissolution will be
180/500 x 100 % = 36 % and so until reaching a release of 75% or 80% (depending on the value depicted in the monograph) of paracetamol tablet.
The advantage of using HPLC is that you do not lose volume since you take a negligible volume when injecting to the HPLC, thus you do not have to compensate for a loss of a volume.
The same calculations are applicable when determining the amount (concentration) of the samples using other instrumental methods such as UV-vis.
Hoping this will be helpful,
Rafik
Thank you very very much Dear Rafik Karaman. It really gave me an insight of what I wanted but I am using a Uv-vis spectrophotometer not HPLC. Please I need more guide on it.
Best regards.
Dear Chukwuebuka Egbuna,
In case you use UV-vis, you should do the following:
1-Make a UV spectrum (scanning from 220 nm -350 nm) for your standard to determine its lamda max.
2-Make a standard curve using the absorbance at lamda max and different concentrations by plotting the absorbance versus concentration.
3-Use the same equation depicted in my first answer to calculate the % of the released drug.
Please note, since for UV measurement you take about 2 mL from the dissolution apparatus, you should compensate by adding 2 mL of the medium after each time you take samples. This is done for getting precise results.
Hoping this will be helpful,
Rafik
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