Chemistry Reference
In-Depth Information
Problems
The assay for Diazepam Tablets BP is as follows.
Q7.1
Weigh and powder 20 tablets. To a quantity of the powder
containing 10 mg of diazepam, add 5 mL of water, mix and
allow to stand for 15 minutes. Add 70 mL of a 0.5% w/v
solution of sulfuric acid in methanol, shake for 15 minutes,
add sufficient of the methanolic sulfuric acid to produce
100 mL and filter. Dilute 10 mL of the filtrate to 50 mL with
the same solvent and measure the absorbance of the
resulting solution at the maximum at 248 nm. Calculate the
content of C
16
H
13
ClN
2
O taking 450 as the value of
A
1
at this
wavelength.
(a)
Draw the part of the molecule responsible for the absorption
of light in this assay (see Figure 7.28). What is this part of
the molecule called?
(b)
What assumptions are made in this assay?
(c)
When this assay was carried out on 5 mg diazepam tablets,
the following results were obtained:
Weight of 20 tablets
7.4878 g
Weight of sample taken
0.7450 g
Absorbance of a 1 cm layer at 284 nm
0.848
Calculate the content of diazepam in a tablet of average
weight and hence calculate the percentage of the stated
amount of diazepam in the tablets.
(d)
Suggest another assay method for the determination of
diazepam in Diazepam Tablets.
CH
3
O
N
N
Cl
Figure 7.28
The structure of diazepam.
