Chemistry Reference
In-Depth Information
Mepyramine (Figure 7.29) is an antihistamine used in the
treatment of insect bites and stings. The BP assay for 50 mg
Mepyramine Tablets is as follows.
Q7.2
Weigh and powder 20 tablets. To a quantity of the powder
containing 0.1 g of mepyramine, add 75 mL of water and
5 mL of 2
M
hydrochloric acid, shake vigorously for 15
minutes, and dilute to 100 mL with water. Centrifuge and
dilute 10 mL of the clear supernatant liquid to 100 mL with
water. To 10.0 mL of this solution add 10 mL of 0.1
M
hydrochloric acid and dilute to 100 mL with water. Measure
the absorbance of the resulting solution at the maximum at
316 nm taking 206 as the value of
A
1
.
This assay was carried out and the following data were obtained:
Weight of 20 tablets
2.1361 g
Weight of sample used in assay
0.2214 g
Absorbance at 316 nm (measured in 1 cm cell)
0.225
(a)
Calculate the content of mepyramine in a tablet of average
weight and the % stated amount.
(b)
Why was the sample centrifuged prior to assay?
(c)
Using the structure shown in Figure 7.29 as a guide, classify
mepyramine as acidic, basic or neutral and hence explain
the role of the hydrochloric acid in this assay.
(d)
Explain fully how the blank solution for this assay would be
prepared.
N
CH
3
N
N
CH
3
H
3
CO
Figure 7.29
The structure of mepyramine.
Determine the structure of the unknown compound from the
spectral data shown in Figure 7.30.
Q7.3
