Assay: Determined by liquid chromatography.
Internal standard solution: Weigh a suitable quantity of prednisone in a 3 per cent w/v solution of glacial acetic acid in chloroform to obtain a solution having a known concentration of about 0.2mg per ml of prednisone.
Test solution: Weigh and powder 20 tablets. Weigh a quantity of the powder containing about 10mg of methylprednisolone transfer to a suitable container and add 2.5ml of water. Swirl to form slurry. Add 50.0ml of the internal standard solution, and shake for 15 minutes. Filter and centrifuge a portion of the filtrate if necessary and use this as the test solution.
Reference solution: Weigh a suitable quantity of methylprednisolone reference standard in the internal standard solution to obtain a solution having a known concentration of about 0.2mg per ml of methylprednisolone.
Chromatographic system:
- A stainless steel column 25cmX4 mm, packed with porous silica particles (3 to 10µm)
- Mobile phase: a mixture of 475 volumes of butyl chloride, 475 volumes of water-saturate butyl chloride, 70 volumes of tetrahydrofuran, 35 volumes of methanol, and 30 volumes of glacial acetic acid,
- Flow rate: 1ml per minute,
- Spectrophotometer set at 254nm,
- Injection volume: 10µl
Inject reference solution. The resolution between methylprednisolone and prednisone is not less than 4.0 and the relative standard deviation for replicate injections is not more than 2.0 per cent.
Inject reference solution and test solution. The relative retention time with reference to methylprednisolone for prednisone is about 0.7.
Calculate the content of Methylprednisolone in the tablets.
Alternative Method: By UV Spectrophotometer
Test Solution: Weigh and powder 20 tablets. Weight sample equivalent to 0.1g of methylprednisolone and dissolve in sufficient ethanol (95 per cent) and mix well. Dissolve the sample by ultrasonication and by shaking the sample. Filter the sample and dilute 2.0ml of this solution to 100.0 ml with ethanol. And mix well. Determine the absorbance of the resulting solution at maximum at about 243nm. Calculate the content of Methylprednisolone taking 395 as the specific absorbance at 243nm.
Formula for calculation:
Absorbance of TEST 1000 100 100
—————————-X———-X——————-X————–X Avg. Wt.
395 100 Test wt (mg) 2
