Theophylline (180.17 g/mol) is a pharmaceutical used for chronic asthma treatmen
ID: 500495 • Letter: T
Question
Theophylline (180.17 g/mol) is a pharmaceutical used for chronic asthma treatment. Its stable form is that of the monohydrate (198.18 g/mol). The amount of water in the samples can be used to determine purity and ensure accurate dosage. TGA is commonly used to determine purity.
a. Calculate the expected percent mass loss for complete dehydration, which occurs at 110 °C.
b. Below are the TGA curves obtained for two samples (A & B) of theophylline tablets. Determine the purity of theophylline in each sample.
c. Sketch the differential thermogram (DTG) curve you would expect to obtain upon heating these sample over the same temperature range.
d. Describe how you could modify the TGA experiment such that greater resolution and/or a shorter analysis time could be achieved.
Stoichiometric Content 100 99 4,13% 98 Sample A de 97 96 2 95 869% 93 Sample B 92 91 30 40 50 60 70 80 90 100 1100 120 130 Temperature CExplanation / Answer
Part.a
Part.b
% purity of sample A= (95.82/ 100)* 100 = 95.82%
5. For 100gm of Sample B, 8.69gm of mass is reduced after complete dehydration at 110oC. It means mass of pure product will be 91.31 gm. Therefore %purity of sample B is 91.31%.
Part.c
DTG of Differential Thermogram is drawn for differential thermal analysis. In this, compound and inert refernce compound undergo same thermal change and temperature differences are recorded. DTG also represent any other physical or chemical change in sample other than weight loss as depicted in TGA.
DTG curve will have a sharp bend downwards in place where %mass becomes constant (straight line) in TGA curve for above study.
Part.d
For TGA-DTG successful experiments, sample should be finely powdered so that to have high contact area. Sample should be pure. It will give higher resolutions and shorter analysis time.
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