5.7
5.7
© Springer-Verlag Berlin Heidelberg 2005
II.5.7 p-Dichlorobenzene
by Kanako Watanabe
Introduction
Nowadays, p-dichlorobenzene ( paradichlorobenzene, 1,4-dichlorobenzene) is becoming more
popular than naphthalene as a moth repellant (insecticide) worldwide.  e discrimination be-
tween p-dichlorobenzene and naphthalene is usually di cult only by their smells and their
appearances. However, speci c gravities of their crystals are di erent; they are 1.152 and 1.5
for naphthalene and p-dichlorobenzene, respectively.  erefore, when the crystals sink in
NaCl-saturated water, it is estimated to be p-dichlorobenzene; while when they  oat in the
same solution, it may be naphthalene [1]. Camphor also gives a similar aromatic smell and
appearance, but its discrimination is even easier, because its speci c gravity is only 0.99; it
 oats in tap water.  e weight of p-dichlorobenzene being sold as a moth repellant is about 4 g;
the crystal mass of the same compound being used for a toilet mothball ranges from 40 to
200 g.  erefore, when a large amount of this compound is ingested, it is dangerous for life.
Like naphthalene, p-dichlorobenzene easily vaporizes from its solid into gas; in this chapter,
a method for headspace GC/MS analysis of p-dichlorobenzene is presented utilizing the vola-
tile property.
Reagents and their preparation
i. Reagents
p-Dichlorobenzene and p-dichlorobenzene-d
4
(product No. 32,933-9)
a
can be purchased from
Aldrich (Milwaukee, WI, USA). Other common chemicals used were of the highest purity
commercially available.
ii. Preparation
p-Dichlorobenzene and p-dichlorobenzene-d

cap, capped and mixed gently.
ii.  e vial is heated at 80 °C for 30 min on a heat block or in a water bath. At the same
time, the 5-mL volume syringe
e
is also heated on the block.  e needle
f
size for the syringe
is 23 G. A er heating, a 1-mL volume of the headspace vapor is withdrawn into the heated
syringe, and carefully injected into GC/MS not to in uence the vacuum degree of the MS
instrument.
iii. Detection is made using ions at m/z 146 and at m/z 152 for IS in the SIM mode.
iv. Construction of a calibration curve: to 0.2 mL each of blank whole blood (not less than 3
vials) obtained from healthy subjects, 2 µg of IS and a di erent amount of p-dichloroben-
zene are added.  e calibration curve consists of peak area ratio of p-dichlorobenzene to IS
on the vertical axis and p-dichlorobenzene concentration on the horizontal axis.  e peak
area ratio obtained from a blood specimen is applied to the calibration curve to obtain its
concentration
g
. It is essential that the concentration to be analyzed is within the concentra-
tion range of the calibration curve.
Assessment of the method
> Figure 7.1 shows mass spectra of p-dichlorobenzene and IS. p-Dichlorobenzene contains
two chlorine atoms, which give characteristic isotopic peaks at m/z M + 2 and M + 4.  ere-
fore, the molecular base peak of p-dichlorobenzene found at m/z 146 is not interfered with by
any peak of other compounds, while that of p-dichlorobenzene-d
4
found at m/z 150 is inter-
fered with by a minor peak of non-labelled p-dichlorobenzene (
> Figure 7.1). However,
the relatively intense isotopic peak at m/z 152 appearing for p-dichlorobenzene-d

and fell into clouding of her consciousness and severe constipation. When an enema was given
to her, strongly aromatic-smelled feces were excreted. Neither gastrolavage, intestinal lavage
nor administration of an adsorbent was performed. On day 13, she died of dysfunctions of the
liver and kidney.
Case 2 [3]: a 85-year-old female ingested 40 pieces of Neoparasol
®
(p-dichlorobenzene
140 g) due to senile dementia. At a clinic nearby, gastrolavage was performed, but she fell into
respiratory suppression, bradycardia and a shock state, and was sent to a general hospital. She
was treated with gastrolavage, purgative administration, enforced diuresis, oxygen inhalation
and administration of Alotec
®
(metaproterenol sulfate) and Inovan
®
(dopamine hydrochlo-
ride). On day 4, hemoperfusion was performed and she was discharged on day 34.
Case 3 [4]: a 73-year-old male kept Neoparaace
®
(p-dichlorobenzene) in a warm kotatsu
(Japanese quilt-covered frame with a heat source inside) to dry it up for 3 days, because it had
gotten wet with water.  erefore, a strongly irritable smell took place inside the kotatsu and
around it. When he was resting with his legs inside the kotatsu, he fell into dyspnea suddenly
and was sent to a hospital. Upon his arrival, there was a mild clouding of his consciousness, but
no orientation disturbance. He showed tachypnea, cyanosis in every part of his body, and crep-
itations audible for both lungs by auscultation. PaO
2
was as low as 34.1 mmHg even under
oxygen inhalation; PaCO
2
was 58.7 mmHg. Severe lung edema was observed for both lungs by

4) Tamagawa R, Ito H, Kamihira A et al. (1995) A case of lung edema caused by inhalation of p-dichlorobenzene.
Jpn J Toxicol 8:450–451 (in Japanese)