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HNMR Analysis of Diphenhydramine in the Antihistamine Capsule by Using Internal Standard
Zahid Shaikh, Summer Veheim and Tia Shuler
The goal of this experiment was to investigate the % purity of the diphenhydramine in new antihistamine
capsule by
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HNMR spectroscopy. Diphenhydramine is an active ingredient in antihistamine capsule to treat allergies
and insomnia. DME (1,4-dimethoxybenzene) was used as the internal standard to integrate distinctive peak at δ
6.3873 that would be used to target the analyte peaks at δ 7.2420-7.3790 (see Table 1 & Figure 1). The % purity was
calculated from the following equation 1:
%
Purity
=
Integral
analyte
Integral
Std
x
¿
Protons
Std peak
¿
Protons
Std peak
x
Mass
Std
Mass
Analyte
x
MW
Analyte
MW
Std
x Purity
Std
(Equation 1)
Results
The mathematical relationship was
used to determine the % purity of
diphenhydramine by measuring the molar
ratio of the compounds and the number of
protons in a signal (see equation 1). Due to
the overlapped signals, the aromatic peaks
from DME and diphenhydramine were
chosen to be integrated as the peaks were
better resolved and consistent compared to
peaks at b, c, d and f (see Table 1 and Figure

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