Int.Areh.Arbeitsmed.34, 25-37 (1975) 9 by Springer-Verlag 1975
Sampling and Analysis of Some Aromatic, Aliphatic and Chlorinated Hydrocarbon Vapours in Air, a Gas-Liquid Chromatographic and Colorimetric Method* Masana Ogata1,Hiroko Asahara1and Takao Saeki 2 Department of Public Health I, and Department of Dispensary 2, 0kayama University Medical School, Okayama Received June 17, 1974 / Accepted September 26, 1974 Summary. This paper describes the sampling of air and its analysis for mixtures of organic solvent vapours by personal and room air samplers. The application of a potassium carbonate to remove water vapour, and silica gel adsorption tube cooled by dry ice for collection of organic solvents were investigated. The development of a method for the extraction of organic solvents from silica gel by cumene, ethyl ether, pyridine and dimethyl sulfoxide and subsequent estimation of their amounts by gas chromatography or colorimetry is reported. This method was useful for the personal air sampler in the workshop using thinner. Ethyl cellosolve acetate, and N,N-dimethyl formamide being cooled by dry ice and mixture of dimethyl sulfoxide and N,N-dimethyl formamide being cooled by ice were useful as absorbing agents of organic solvents particularly in the room air sampler. Key words: Aromatic Hydrocarbons - Aliphatic Hydrocarbons - Chlorinated Hydrocarbons - Silica Gel - Personal Air Sampler.
Introduction
Aromatic and some aliphatic hydrocarbons are widely used both together and separately, as organic industrial solvents: toluene, xylenes, ethyl acetate, butyl alcohol, and cellsolve acetate are common ingredients of paint thinner, and chlorinated hydrocarbons are used extensively in the metal degreasing process.
In the factory using these organic solvents, however, it is quite difficult to estimate the average concentrations of these substances in the air as these concentrations vary considerably within one working day. Furthermore,
~Read before the 46th Annual Meeting of Japan Industrial Health Association, Osaka, April 8, 1973, and 47th Annual Meeting of Japan Industrial Health Association, Nagoya, March 29, 1974.
25
it is also difficult to determine the average concentration of organic solvent that each worker is exposed to in various locations in the factory. For determining the average concentration of organic solvent in the air, a room air sampler is needed, along with a personal air sampler to analyze each worker's actual exposure. Numerous methods of sampling and analysis of trace quantities of organic solvents in the air have been investigated to date. The sampling was to adsorb gases and vapours on silica gel. Water vapour's interference with the collection of many substances on silica gel has been described by Eggertsen et al. (1958), Farrinoton et al. (]959), Whitman et al. (1964), Feldstein et al. (]967), Weat et al. (1958), Bennett et al. (1958), and Mckee et al. (1959). They had recommended the use of anhydrous sodium carbonate, sodium hydrate and a molecular sieve to minimize this interference. Removal from silica gel has been accomplished by using organic solvent. However, the recovery rate from silica gel at room temperature is not complete. Seki et al. (1972) reported the use of silica gel cooled by dry ice for the analysis of the trichloroethane concentration in the factory.
Our experiment centered around three problems; the efficient collection of organic vapours on silica gels cooled by dry ice, the quantitative removal of the materials adsorbed for subsequent analysis, and their analysis by simple gas chromatography and colorimetry.
This report describes the results of silica gel cooled by dry ice as an adsorbant for various organic solvents, and of application of this method for the personal air sampler. In addition to this, the liquid absorption method is also described.
Materials and Methods I. Adsorption and Absorption of Organic Solvents I. Evaporation of Organic Solvents and Their AdsorEtion with Silica Gel .-.--~176176176
a) Discontinuous Vapour Flow Method . . . . . , . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
Evaporation apparatus described by Feldstein et al. (]967) and Seki et al. (1972) was used for the adsorption tests of silica gel (Fig.]). Organic solvents were injected at IO min intervals 6 times, and 10 min after the last injection, the sampling process was stopped. For adsorption of known
26
6 8-Fig. l. Apparatus used for adsorption of known concentrations of solvent vapours on silica gel (discontinuous method). ] = injector, 2 = flask, 3 = electric water bath, 4 = tube containing anhydrous potassium carbonate, 5 = U-tube containing silica gel (4~8 mesh), 6 = dry ice, 7 = synthetic rubber, 8 = vinyl chloride
concentrations
of solvent vapours on silica gel cooled by dry ice, the method
of Seki et al.
(1972) for sampling methyl chloride was used.
b) Continuous Vapour Flow Method 9
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Adsorption with Silica Gel. A modification of the method of McKelvey et al. (1957) was used. The system was arranged so that the sample was put into the lower part of the flask in the diffusion cell, and the gas released by warming was supplied to the silica gel sample from the upper part of the flask (Fig.2). As some of the aromatic,
aliphatic and chlorinated hydrocarbons
in this experiment have relatively high boiling points, controlled at 40~
used
a mantle heater
covered the top of the beaker to protect against condensa-
tion of vapours as shown in Fig.2. Air was drawn for 7 hrs at a rate of l~/min by suction pump for the personal air sampler
(Unico Model-t10),
and
method of adsorption of organic solvents on silica gel is the same as in the injection method as shown in Figs.1 and 2~ The schema of personal and room air samplers for practical use on the workshop are shown in Figs.3 and 4. Liquid Absorption.
Absorption
tube: The tube (Fig.5) used was 3.0 cm in dia-
meter and 15.0 cm in length. The tip of the glass inlet tube was fixed with a teflon tube, and another teflon tube was fixed to the orifice of the outlet inside the absorption bottle to prevent the leakage of fluid. The absorption (plastic),
tube was put in the plastic bottle,
coated with foam polystylene
then dry ice filled around the tube. A lead plate was placed on the
bottom of the tube. This can be useful for room air sampler. For personal air sampler,
the tube was suspended with a hinge and axis to balance it and was
attached to a belt fitted to the worker. 27
5
D
6
-
IO
Fig.2. Apparatus used for adsorption of known concentrations of solvent vapours on silica gel (continuous method). | = lower flask containing solvent, 2 = upper flask, 3 = needle, 4 = electric water bath, 5 = mantle heater, 6 = anhydrous p o t a s s i u m carbonate, 7 = side arm for determing density of solvent, 8 = U-tube containing silica gel, 9 = dry ice, ]0 = synthetic rubber, ! ] = vinyl chloride
Fig.3. Schema of personal air sampler attached adsorbing materials. 1 = rotameter A 2 = suction containing silica gel dried at l love for 2 hrs 5 = plastic case (inside: 9 . 0 cm i n w i d t h , 5 . 0 height), 6 = teflon 7 = collection tube containing anhydrous potassium carbonate
tubd,
to workers using silica gel as pump, 3 = U-tube (0.5emx26.0cm) prior to use, 4 = dry ice, cm i n d e p t h a n d l l . O cm i n (l.5cmx7.0cm) of water vapour
Fig.4. Schema of room air sampler (left figure: front view; right figure: side view). I = rotameter, 2 = suction pump, 3 = U-tube (].Ocmx45.Ocm) containing silica gel, 4 = dry ice, 5 = plastic box (inside;21.0 cm in width,]6.O cm in depth and 25.0 cm in height), 6 = to tube containing anhydrous p o t a s s i u m carbonate, 7 = cooling case (9.0 cm in w i d t h , 9 . 0 c m in depth and 22.0 cm in height), 8 = dry battery
IThe use of glass tube covered with teflon tube is more efficient concentration of organic solvents in the air. 28
in the low
Fig.5~ Schema
of liquid absorption bottle for organic solvent for personal air sampler (left figure: front view; right figure: side view). ] = teflon tube, 2 = glass outlet tube, 3 = absorption bottle (3.0cmxl5.0cm), 4 = plastic bottle (6.0cmxl5.0cm), 5 = dry ice, 6 = glass inlet tube, 7 = glass beads (3.0 ~m), 8 = teflon tube, 9 = lead plate, IO = hinge, 11 = rotameter, 12 = tube to suction pump
The stopper was placed in the tube and N,N-dimethyl
formamide
I0 ml of ethyl cellosolve acetate
(DMFA), and mixture of dimethylsulfoxide
(7:3) as absorbing solution was introduced pipette respectively. and DMFA,
and at O~
through the top by means of a I0 ml
Then the tubes were kept at -20~
by dry ice with ECA
by ice with the mixture of DMSO and DMFA. This filled tube
to a level above the beads. recovery experiment,
(ECA),
(DMSO) and DMFA
Three absorbers were connected
discontinuous
method
was
in series.
In the
used and air was drawn for 1 hr
at a rate of 0.3s
The apparatus ls
shown in Fig.3 was used and the air was drawn at a rate of
by air suction pump
sampler was attached
(Shibata,
to two workers
mini type MP 2 pump).
in a furniture factory and the working
time was 7.5 hrs as described
in the item on results.
II. The Procedure
from Silica Gel
for Removal
The personal air
6g of the silica gel layer from a U-tube were transferred 40 ml of cumene where it stood for I hr with occasional the solvent were then taken for gas chromatographic
to a flask with
shaking. Aliquots
of
analysis.
29
Where cumene and water was used as the releasing agent, follows:
the procedure was as
8 ml of cumene was added to the flask containing the silica gel, and
the mixture was shaken. Then 4 ml of water was added and the mixture, well shaken9 The cumene layer separated and rose to the surface, layer was transferred
again
and this
to a tube. This procedure was repeated again, and the
two cumene extracts were mixed. Aliquots of the cumene solution were then taken for colorimetric
analysis 9
When pyridine was used as the releasing agent, the procedure was as follows: 6g of the silica gel layer from a U-tube were transferred
to a flask with
40 ml of pyridine where it stood for 1 hr with occasional shaking, and aliquots of the solvent was then taken for colorimetric analysis.
III. Analysis of Organic Solvents 1. Gas Chromatography._Conditions 9
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9
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9
9
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~
of_GasChromatography
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9
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9
9
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a) The Gas Chromatography with FID Detector 9
1
7
6
1
4
9
1
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9
1
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1
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1
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1
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1
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1
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1
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1
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1
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1
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1
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1
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The gas chromatograph used was a Hitachi 063 type. The operating conditions were as follows:
Column:
Injection-chamber's gas: Nitrogen,
2mx3mm. Dionyl phthalate,
temperature:
|50~
chromosorb WAW 60/80 mesh.
Column temperature:
lO0~
Carrier
40m~/min.
b) Conditions of Gas Chromatography with ECD Detector o
.
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9
1
4
9
1
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1
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1
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1
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1
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1
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1
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6 .1 . 7 . 6. 1
7 . 6 ~ 1 1 44 99 11 77 6 6
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1
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1
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The gas chromatograph used was a Hitachi K-23. The operating conditions were as follows:
Column:
Imx3mm. Reoplex 400+H3PO 4 (15+2 Wt%). Support:
WAW, mesh: 60/809 Injection-chamber's II0~
Carrier gas: Nitrogen,
temperature:
150~
chromosorb
Column temperature:
4Omg/min.
2: Colorimetr ~ a) Experiment with Cumene as Adsorbing Agent . . . . . . .
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To the cumene solution in the test tube, 3.5 ml of pyridine,
0.5 ml of H20
and 1 ml of 8Og/d~ potassium hydroxide solution were added. The mixture was well shaken9 The test tube was held at IOO~ development,
3O
for 30 minutes for color
cooled in an ice bath for 5 min, 3 ml of aliquot of pyridine
6
1
7
6
layer transferred to the test tube, and 0.5 ml of the benzidine formic acid reagent (Leibman et al., 1964) added, after which the solution was well mixed. In the case of tetrachloroethylene,
the ethyl ether layer was used as the
desorbing agent. After standing 30 min at room temperature, the absorhance of the colored solution was read in a spectrophotometer (Hitachi 139) at 535 m~.
b) Experiment Using Pyridine as Releasing Agent . . . .
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To the pyridine solution (5ml), 2 ml of I O N potassium hydroxide solution was added and the mixture shaken. The test tube was held at IO0~
for 3 min for
color development, repeating the colorimetric determination as described with the cumene extract.
Results Sampling and Analysis of Organic Solvents in Air by Silica Gel and Liquid in the Personal and Air Samplers Respectively I. Silica Gel Adsorption Known amounts of mixed solutions of benzene, toluene, m-xylene, o-xylene, ethyl acetate and butyl alcohol were injected into a micro gas cell, using the technique described below. Recoveries of these solvent vapours were 95%, 99%, 87%, 86%, 94% and 93% respectively and very consistent reproducibility was obtained. In the case of organic chloride, recoveries ranging from 81 to 95% by colorimetric method and from 75 to 100% by gas chromatographic method were obtained (Table I). The recovery rate of aromatic hydrocarbon vapours evaporated by the discontinuous method ranged between 84 and 97%, that of butyl alcohol was 89%, and that of chlorinated hydrocarbons between 87 and 103%, results being obtained by gas chromatography as shown in Table 2. Analysis for each of the materials was performed separately on each silica gel probe. There were no solvents found on the second probe in the discontinuous or continuous system.
II._ Liqu_id_Absorp t ion The recovery rate of benzene, toluene, m-xylene and o-xylene, in the three tubes combined using ECA, DMFA, and mixture of DMSO and DMFA, as absorbing solution respectively is shown in Table l, indicating that almost all the material is absorbed on the three tubes.
31
Table 1. Absorption and recovery of organic solvents from liquid phase and adsorption and recovery of those from solid phase (flow-O.3~/min vapour was taken from micro gas chamber for 1 hr) Sampler Absorb.or Organic solvents
Desorbing Added Recovery(%)
% to Ist bot.
phase
Adsorb. a
solvent
2nd
Liquid
ECA in dry ice
Solid
Benzene
(mg) 8.8
G.C. 91
Col. /
3rd
5
Toluene
8.7
85
/
3
m-Xylene
8.7
IO0
/
O
o-Xylene
9.0
IOO
/
O
DMFA in
Benzene
9.0
98
/
14
0
dry ice
Toluene
8.7
85
/
19
0
m-Xylene
8.7
72
/
16
0.015
o-Xylene
8.7
70
/
7
0.015
DMSO and
Benzene
8.8
96
/
26
30% DMFA
Toluene
8.7
88
/
3
in ice
m-Xylene
8.7
71
/
4
o-Xylene
9.0
70
4
Silica
Benzene
DMSO
4.7
O
0
gel in
Toluene
DMSO
5.6
99
O
O
dry ice
m-Xylene
DMSO
6.4
87
0
O
95
o-Xylene
DMSO
6.4
86
0
O
Ethyl acetate
DMSO
5.4
94
O
0
Butyl alcohol
DMSO
4.7
93
0
0
1.1.1 -Trichloroethane
Cumene Pyridine
8.1
I00 c /
89 86
0 O
O O
1. I. 2.2 -Tetrachloroethane
Cumene Pyridine
9.5
75 c /
90 81
O 0
O 0
Trichloroethylene
Cumene Pyridine
8.8
93 c /
87 89
0 0
O 0
9.8
82 c /
95 90
O 0
0 O
Cumene Tetrachloroethylempyridine .
.
DMSO=dimethyl sulfoxide; DMFA=dimethyl formamide; ECA=ethyl cellosolve acetate; G.C.=gas chromatography; Col.=colorimetry; bot.=bottle. a 9 9 " n materlal. ~ bAbSorblng solutlons or adsorptlo Percent of the concentration of organic solvents in 2nd or 3rd bottle to Ist bottle (average of two experiments). CGas chromatograph attached with ECD detector.
32
b
Table 2. Adsorption and recovery of organic solvents from silica gel (flowl~/min vapour was taken from McKelvey's diffusion cell with constant air flow for 7 hrs) Organic hydrocarbons
ppm
Solvent
Recovery %
Toluene
48
DMSO
97
Benzene
82
DMSO
90
m-Xylene
58
DMSO
84
o-Xylene
30
DMSO
88
Butanol
23
DMSO
89
l.].l-Trichloroethane
46
Cumene
93
l.l.2.2-Tetrachloroethane
48
Cumene
87
Trichloroethylene
44
Cumene
96
Tetrachloroethylene
32
Cumene
I03
The ratio of the concentration
of benzene,
toluene, m-xylene and o-xylene in
the second or the third tube to the first tube using ECA, DMFA and mixture of DMSO and DMFA was shown in Table necessary
I. From this, it is considered
to use 2 tubes.
The recovery rate of aromatic hydrocarbons signed for practical use (Fig.3)
using personal air sampler de-
shows similar results.
DMFA is used as the absorbing solution for the determination tion of the organic solvents.
of the concentra-
Since DMFA is dangerous at room temperature,
complete adsorption by silica gel of possible necessary.
to be
leaking evaporated gases is
To accomplish this a silica gel probe is recommended
to be placed
before the suction pump for the adsorption of DMFA. Therefore,
less toxic ECA should be used for the personal air sampler and the
use of DMFA or the mixture of DMSO and DMFA for the room air sampler is recommended.
III. Application
of Personal Air Sampler
The location was a furniture-making
factory, where varnish dissolved in
thinner, was used. The thinner's main ingredients were ethyl acetate,
butyl
acetate and toluene.
The organic solvent vapours were controlled by suction,
where two men worked,
one (A) engaged in spraying and the other (B), doing
hand painting work.
33
Fig.6 Variation in concentration of toluene (T), ethyl acetate (EA) and butyl acetate (BA) at the center of the working room (lower figure), and amount of urinary hippuric acid (upper figure) in worker A (white column) and worker B (black column)
mg/min 0.5 0.4 0.3 0.2 0.1
ppm
5,58
1.0 0.8 0.6 0.4
\!: ,X 7 \',,
..'1,.
!\It
/..,\
0.2
, 5.30 8
i 9
10 II
~ EA
12 13 14 15 20
B
(hours)
Air from the worker's breathing zone sucked through the teflon tube by personal sampling pump, operated by dry battery kept at constant current. Sampler and pump held on by harness fitted to the worker. Air was drawn 1~/min,
through the cooled silica gel probe and calculated
atmospheric
concentration
exposed to the two workers.
to the average
The air at the center
of the room was trapped by gas sampling bottle at ! hr intervals and the average concentration was calculated.
The place, about 2 m from worker A, had
an average air density of 0.62 ppm of toluene, 0.76 ppm of ethyl acetate and 0.23 ppm of butyl acetate. Kitagawa detector, other hand,
Toluene concentration was also estimated by
showing that its maximum value was below I ppm. On the
it was found by personal air sampler that the average concentra-
tion of solvent that worker A was exposed to was 2.0 ppm, which was higher than that of worker B (1.3 ppm), and the average exposure to worker A and B was found to be higher than detected at the center of the room due to their proximity to the thinner.
There was an increased amount of hippuric acid in
worker A's urine which paralleled changes in toluene concentration, worker A's acid level was higher than that of B, corresponding exposure to a higher concentration
34
of toluene
and
to his
(Fig.6 and Table 3).
Table 3 Concentration of organic solvents in the air of the room and concentration detected by the personal air sampler attached to two workers using thinner Concentration
In the room
a
Toluene (ppm)
Ethyl acetate (ppm)
Butyl acetate (ppm)
TLV b
0.62
0.76
0.23
0.010
Personal air
worker A
2.08
5.75
4.09
0.062
sampler
worker B
1.40
2.06
1.78
0.031
100
400
150
TLV by ACGIH a
bConcentrat~on measured at the center of the room. Threshold l i m i t v a l u e f o r t h e m i x t u r e s d o c u m e n t e d by ACGIH.
Discussion
The approximate concentrations hydrocarbons
of benzene,
were found by discontinuous
toluene,
xylenes and chlorinated
and continuous
gas-evaporation
tests.
Samples were collected with silica gel cooled to a solid state, with ECA and DMFA cooled by dry ice and mixture of DMSO and DMFA by ice in a liquid state. However,
at least 2 bottles were necessary for the liquid absorption method.
The sampling technique utilizing both silica gel cooled by dry ice and anhydrous
sodium carbonate,
and subsequent
gas chromatography
of the sample
was found useful for the personal and room air samplers.
The colorimetric hydrocarbons benzene,
method also offered a simple and useful assay of chlorinated
adsorbed on silica gel. No apparent difficulty resulted when
toluene,
ethyl acetate,
butyl alcohol and chlorinated hydrocarbon
vapours were collected from silica gel by gas chromatography.
In the air samplers used in this experiment, applicable with a steady concentration
the continuous
in the workshop,
system was most
and the discontinuous
system with conditions of changing concentration.
In the workshop using organic solvents,
absorption with DMSO or cooled DMFA
is simpler than with silica gel in the room air sampler,
the absorption bottles
can be devised for protecting against fluid leaking from the bottles.
35
In the factory using thinner, we can calculate the TLV of the mixture of organic solvent concentration in the room, or the average concentration, the workmen are exposed to, by using the equation for the threshold limit value (TLV) for the mixtures documented by ACGIH is E Ci/Ti, where Ci indicates the observed atmospheric concentration and Ti corresponding threshold concentration. Using the above equation with the observed concentration and with the TLV of toluene (IOO ppm), ethyl acetate (400 ppm), and butyl acetate (150 ppm), documented by ACGIH, calculation was made. The results are shown in Table 3. The value in the center of the room and the personal air sampler of the two workers were lower than I respectively.
For some organic solvents, which were excreted as metabolites in urine (Ogata et ai.,1970), the amount of organic solvents absorbed by the body can be determined by the measurement of the urinary metabolite concentration as described previously. Still the personal air sampler can measure the personal exposure to organic solvent, whether the solvent itself or its metabolites are excreted in the urine or not.
In a survey of the exposure of workers to organic solvents in the factory, where the concentration of the solvent is kept low by suction, the personal air sampler can be useful in determining their exposure, and with workers exposed to a low concentration of toluene, hippuric acid determination should be done with the urine, before, during and after the exposure, since the increase of hippuric acid is thought to indicate toluene exposure, as diurnal variations of the level of urinary hippuric acid are relatively small (Ogata et ai.,1963).
References
Bennett,C.E., Dal Nooare,S., Safranski,L.W., Lewis,C.D.: Trace analysis by gas chromatography. Anal. Chem. 30, 898 (1958) Eggertsen,F.T., Nelson,F.M.: Gas chromatographic analysis of engine exhaust and atmospheric samples. Anal. Chem. 30, 1040 (1958) Farrinoton,P.S., Pecsok,R.L., Merker,R.L., Olson,T.J.: Detection of trace constituents by gas chromatography. Anal.Chem. 31, 1512 (1959) Feldstein,M., Balestrieri,S., Levaggi,D.A.: The use of silica gel in source testing. Amer.lnd.Hyg.Assoc. J. 28, 381-385 (1967) Leibmann,K.C., Hindman,J.D.: Modification of the Fujiwara reaction for determination of polyhalogenated organic compounds. Anal.Chem. 36, 348 (1964)
36
Mckee,H.G., Rhoades,J.W., McMahon,W.A.: Use of drying agents in atmospheric sampling. A.C.S. Pro 136. Z4U no.52 (]959) McKelvey,J.M., Hoelsher,H.E.: Apparatus for preparation of very dilute gas mixtures. Anal.Chem. 29, 123 (1957) 0gata,M., Nagao,I.: Urinary m-methyl hippuric acid excretion and physiological changes in persons exposed to 200 ppm. m-xylene in exposure chamber (in Japanese). Jap.J.industr.Health 10, 75-79 (1963) Ogata,M., Takastuka,Y., Tomokuni,K.: Excretion of organic chlorine compounds in the urine of persons exposed to vapours of trichloroethylene and tetrachloroethylene. Brit.J.industr.Med. 28, 386-391 (1971) Ogata,M., Tomokuni,K., Takatuka,Y.: Urinary excretion of hippuric acid and m- or p-methyl hippuric acid in the urine of persons exposed to vapours of toluene and m- or p-xylene as a test of exposure. Brit.J.industr.Med. 27, 43-50 (1970) Seki,Y., Ichikawa,M., Minaguchi,H.: Methods of sampling industrial solvents in the air: A vapour sampler for an individual (in Japanese). Jap.J. industr.Health 14, 138-139 (1972) West,P.W., Buddhadev,S., Giason,N.A.: Gas liquid chromatographic analysis. Anal.Chem. 30, 1390 (1958) Whitman,N.E., Johuston,A.E.: Sampling and analysis of aromatic hydrocarbon vapors in air: A gas-liquid chromatographic method. Amer.lnd.Hyg.Assoc.J~ 25, 464 (1964)
Dr.Masana Ogata Department of Public Health Okayama University Medical School Okayama, Japan
37
Sampling and Analysis of Some Aromatic, Aliphatic and Chlorinated Hydrocarbon Vapours in Air, a Gas-Liquid Chromatographic and Colorimetric Method* Masana Ogata1,Hiroko Asahara1and Takao Saeki 2 Department of Public Health I, and Department of Dispensary 2, 0kayama University Medical School, Okayama Received June 17, 1974 / Accepted September 26, 1974 Summary. This paper describes the sampling of air and its analysis for mixtures of organic solvent vapours by personal and room air samplers. The application of a potassium carbonate to remove water vapour, and silica gel adsorption tube cooled by dry ice for collection of organic solvents were investigated. The development of a method for the extraction of organic solvents from silica gel by cumene, ethyl ether, pyridine and dimethyl sulfoxide and subsequent estimation of their amounts by gas chromatography or colorimetry is reported. This method was useful for the personal air sampler in the workshop using thinner. Ethyl cellosolve acetate, and N,N-dimethyl formamide being cooled by dry ice and mixture of dimethyl sulfoxide and N,N-dimethyl formamide being cooled by ice were useful as absorbing agents of organic solvents particularly in the room air sampler. Key words: Aromatic Hydrocarbons - Aliphatic Hydrocarbons - Chlorinated Hydrocarbons - Silica Gel - Personal Air Sampler.
Introduction
Aromatic and some aliphatic hydrocarbons are widely used both together and separately, as organic industrial solvents: toluene, xylenes, ethyl acetate, butyl alcohol, and cellsolve acetate are common ingredients of paint thinner, and chlorinated hydrocarbons are used extensively in the metal degreasing process.
In the factory using these organic solvents, however, it is quite difficult to estimate the average concentrations of these substances in the air as these concentrations vary considerably within one working day. Furthermore,
~Read before the 46th Annual Meeting of Japan Industrial Health Association, Osaka, April 8, 1973, and 47th Annual Meeting of Japan Industrial Health Association, Nagoya, March 29, 1974.
25
it is also difficult to determine the average concentration of organic solvent that each worker is exposed to in various locations in the factory. For determining the average concentration of organic solvent in the air, a room air sampler is needed, along with a personal air sampler to analyze each worker's actual exposure. Numerous methods of sampling and analysis of trace quantities of organic solvents in the air have been investigated to date. The sampling was to adsorb gases and vapours on silica gel. Water vapour's interference with the collection of many substances on silica gel has been described by Eggertsen et al. (1958), Farrinoton et al. (]959), Whitman et al. (1964), Feldstein et al. (]967), Weat et al. (1958), Bennett et al. (1958), and Mckee et al. (1959). They had recommended the use of anhydrous sodium carbonate, sodium hydrate and a molecular sieve to minimize this interference. Removal from silica gel has been accomplished by using organic solvent. However, the recovery rate from silica gel at room temperature is not complete. Seki et al. (1972) reported the use of silica gel cooled by dry ice for the analysis of the trichloroethane concentration in the factory.
Our experiment centered around three problems; the efficient collection of organic vapours on silica gels cooled by dry ice, the quantitative removal of the materials adsorbed for subsequent analysis, and their analysis by simple gas chromatography and colorimetry.
This report describes the results of silica gel cooled by dry ice as an adsorbant for various organic solvents, and of application of this method for the personal air sampler. In addition to this, the liquid absorption method is also described.
Materials and Methods I. Adsorption and Absorption of Organic Solvents I. Evaporation of Organic Solvents and Their AdsorEtion with Silica Gel .-.--~176176176
a) Discontinuous Vapour Flow Method . . . . . , . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .
Evaporation apparatus described by Feldstein et al. (]967) and Seki et al. (1972) was used for the adsorption tests of silica gel (Fig.]). Organic solvents were injected at IO min intervals 6 times, and 10 min after the last injection, the sampling process was stopped. For adsorption of known
26
6 8-Fig. l. Apparatus used for adsorption of known concentrations of solvent vapours on silica gel (discontinuous method). ] = injector, 2 = flask, 3 = electric water bath, 4 = tube containing anhydrous potassium carbonate, 5 = U-tube containing silica gel (4~8 mesh), 6 = dry ice, 7 = synthetic rubber, 8 = vinyl chloride
concentrations
of solvent vapours on silica gel cooled by dry ice, the method
of Seki et al.
(1972) for sampling methyl chloride was used.
b) Continuous Vapour Flow Method 9
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Adsorption with Silica Gel. A modification of the method of McKelvey et al. (1957) was used. The system was arranged so that the sample was put into the lower part of the flask in the diffusion cell, and the gas released by warming was supplied to the silica gel sample from the upper part of the flask (Fig.2). As some of the aromatic,
aliphatic and chlorinated hydrocarbons
in this experiment have relatively high boiling points, controlled at 40~
used
a mantle heater
covered the top of the beaker to protect against condensa-
tion of vapours as shown in Fig.2. Air was drawn for 7 hrs at a rate of l~/min by suction pump for the personal air sampler
(Unico Model-t10),
and
method of adsorption of organic solvents on silica gel is the same as in the injection method as shown in Figs.1 and 2~ The schema of personal and room air samplers for practical use on the workshop are shown in Figs.3 and 4. Liquid Absorption.
Absorption
tube: The tube (Fig.5) used was 3.0 cm in dia-
meter and 15.0 cm in length. The tip of the glass inlet tube was fixed with a teflon tube, and another teflon tube was fixed to the orifice of the outlet inside the absorption bottle to prevent the leakage of fluid. The absorption (plastic),
tube was put in the plastic bottle,
coated with foam polystylene
then dry ice filled around the tube. A lead plate was placed on the
bottom of the tube. This can be useful for room air sampler. For personal air sampler,
the tube was suspended with a hinge and axis to balance it and was
attached to a belt fitted to the worker. 27
5
D
6
-
IO
Fig.2. Apparatus used for adsorption of known concentrations of solvent vapours on silica gel (continuous method). | = lower flask containing solvent, 2 = upper flask, 3 = needle, 4 = electric water bath, 5 = mantle heater, 6 = anhydrous p o t a s s i u m carbonate, 7 = side arm for determing density of solvent, 8 = U-tube containing silica gel, 9 = dry ice, ]0 = synthetic rubber, ! ] = vinyl chloride
Fig.3. Schema of personal air sampler attached adsorbing materials. 1 = rotameter A 2 = suction containing silica gel dried at l love for 2 hrs 5 = plastic case (inside: 9 . 0 cm i n w i d t h , 5 . 0 height), 6 = teflon 7 = collection tube containing anhydrous potassium carbonate
tubd,
to workers using silica gel as pump, 3 = U-tube (0.5emx26.0cm) prior to use, 4 = dry ice, cm i n d e p t h a n d l l . O cm i n (l.5cmx7.0cm) of water vapour
Fig.4. Schema of room air sampler (left figure: front view; right figure: side view). I = rotameter, 2 = suction pump, 3 = U-tube (].Ocmx45.Ocm) containing silica gel, 4 = dry ice, 5 = plastic box (inside;21.0 cm in width,]6.O cm in depth and 25.0 cm in height), 6 = to tube containing anhydrous p o t a s s i u m carbonate, 7 = cooling case (9.0 cm in w i d t h , 9 . 0 c m in depth and 22.0 cm in height), 8 = dry battery
IThe use of glass tube covered with teflon tube is more efficient concentration of organic solvents in the air. 28
in the low
Fig.5~ Schema
of liquid absorption bottle for organic solvent for personal air sampler (left figure: front view; right figure: side view). ] = teflon tube, 2 = glass outlet tube, 3 = absorption bottle (3.0cmxl5.0cm), 4 = plastic bottle (6.0cmxl5.0cm), 5 = dry ice, 6 = glass inlet tube, 7 = glass beads (3.0 ~m), 8 = teflon tube, 9 = lead plate, IO = hinge, 11 = rotameter, 12 = tube to suction pump
The stopper was placed in the tube and N,N-dimethyl
formamide
I0 ml of ethyl cellosolve acetate
(DMFA), and mixture of dimethylsulfoxide
(7:3) as absorbing solution was introduced pipette respectively. and DMFA,
and at O~
through the top by means of a I0 ml
Then the tubes were kept at -20~
by dry ice with ECA
by ice with the mixture of DMSO and DMFA. This filled tube
to a level above the beads. recovery experiment,
(ECA),
(DMSO) and DMFA
Three absorbers were connected
discontinuous
method
was
in series.
In the
used and air was drawn for 1 hr
at a rate of 0.3s
The apparatus ls
shown in Fig.3 was used and the air was drawn at a rate of
by air suction pump
sampler was attached
(Shibata,
to two workers
mini type MP 2 pump).
in a furniture factory and the working
time was 7.5 hrs as described
in the item on results.
II. The Procedure
from Silica Gel
for Removal
The personal air
6g of the silica gel layer from a U-tube were transferred 40 ml of cumene where it stood for I hr with occasional the solvent were then taken for gas chromatographic
to a flask with
shaking. Aliquots
of
analysis.
29
Where cumene and water was used as the releasing agent, follows:
the procedure was as
8 ml of cumene was added to the flask containing the silica gel, and
the mixture was shaken. Then 4 ml of water was added and the mixture, well shaken9 The cumene layer separated and rose to the surface, layer was transferred
again
and this
to a tube. This procedure was repeated again, and the
two cumene extracts were mixed. Aliquots of the cumene solution were then taken for colorimetric
analysis 9
When pyridine was used as the releasing agent, the procedure was as follows: 6g of the silica gel layer from a U-tube were transferred
to a flask with
40 ml of pyridine where it stood for 1 hr with occasional shaking, and aliquots of the solvent was then taken for colorimetric analysis.
III. Analysis of Organic Solvents 1. Gas Chromatography._Conditions 9
9
9
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9
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9
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9
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9
9
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~
of_GasChromatography
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9
9
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,
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9
9
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a) The Gas Chromatography with FID Detector 9
1
7
6
1
4
9
1
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9
1
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1
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1
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1
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1
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1
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1
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1
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1
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The gas chromatograph used was a Hitachi 063 type. The operating conditions were as follows:
Column:
Injection-chamber's gas: Nitrogen,
2mx3mm. Dionyl phthalate,
temperature:
|50~
chromosorb WAW 60/80 mesh.
Column temperature:
lO0~
Carrier
40m~/min.
b) Conditions of Gas Chromatography with ECD Detector o
.
.
9
1
4
9
1
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1
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6 .1 . 7 . 6. 1
7 . 6 ~ 1 1 44 99 11 77 6 6
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1
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The gas chromatograph used was a Hitachi K-23. The operating conditions were as follows:
Column:
Imx3mm. Reoplex 400+H3PO 4 (15+2 Wt%). Support:
WAW, mesh: 60/809 Injection-chamber's II0~
Carrier gas: Nitrogen,
temperature:
150~
chromosorb
Column temperature:
4Omg/min.
2: Colorimetr ~ a) Experiment with Cumene as Adsorbing Agent . . . . . . .
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To the cumene solution in the test tube, 3.5 ml of pyridine,
0.5 ml of H20
and 1 ml of 8Og/d~ potassium hydroxide solution were added. The mixture was well shaken9 The test tube was held at IOO~ development,
3O
for 30 minutes for color
cooled in an ice bath for 5 min, 3 ml of aliquot of pyridine
6
1
7
6
layer transferred to the test tube, and 0.5 ml of the benzidine formic acid reagent (Leibman et al., 1964) added, after which the solution was well mixed. In the case of tetrachloroethylene,
the ethyl ether layer was used as the
desorbing agent. After standing 30 min at room temperature, the absorhance of the colored solution was read in a spectrophotometer (Hitachi 139) at 535 m~.
b) Experiment Using Pyridine as Releasing Agent . . . .
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To the pyridine solution (5ml), 2 ml of I O N potassium hydroxide solution was added and the mixture shaken. The test tube was held at IO0~
for 3 min for
color development, repeating the colorimetric determination as described with the cumene extract.
Results Sampling and Analysis of Organic Solvents in Air by Silica Gel and Liquid in the Personal and Air Samplers Respectively I. Silica Gel Adsorption Known amounts of mixed solutions of benzene, toluene, m-xylene, o-xylene, ethyl acetate and butyl alcohol were injected into a micro gas cell, using the technique described below. Recoveries of these solvent vapours were 95%, 99%, 87%, 86%, 94% and 93% respectively and very consistent reproducibility was obtained. In the case of organic chloride, recoveries ranging from 81 to 95% by colorimetric method and from 75 to 100% by gas chromatographic method were obtained (Table I). The recovery rate of aromatic hydrocarbon vapours evaporated by the discontinuous method ranged between 84 and 97%, that of butyl alcohol was 89%, and that of chlorinated hydrocarbons between 87 and 103%, results being obtained by gas chromatography as shown in Table 2. Analysis for each of the materials was performed separately on each silica gel probe. There were no solvents found on the second probe in the discontinuous or continuous system.
II._ Liqu_id_Absorp t ion The recovery rate of benzene, toluene, m-xylene and o-xylene, in the three tubes combined using ECA, DMFA, and mixture of DMSO and DMFA, as absorbing solution respectively is shown in Table l, indicating that almost all the material is absorbed on the three tubes.
31
Table 1. Absorption and recovery of organic solvents from liquid phase and adsorption and recovery of those from solid phase (flow-O.3~/min vapour was taken from micro gas chamber for 1 hr) Sampler Absorb.or Organic solvents
Desorbing Added Recovery(%)
% to Ist bot.
phase
Adsorb. a
solvent
2nd
Liquid
ECA in dry ice
Solid
Benzene
(mg) 8.8
G.C. 91
Col. /
3rd
5
Toluene
8.7
85
/
3
m-Xylene
8.7
IO0
/
O
o-Xylene
9.0
IOO
/
O
DMFA in
Benzene
9.0
98
/
14
0
dry ice
Toluene
8.7
85
/
19
0
m-Xylene
8.7
72
/
16
0.015
o-Xylene
8.7
70
/
7
0.015
DMSO and
Benzene
8.8
96
/
26
30% DMFA
Toluene
8.7
88
/
3
in ice
m-Xylene
8.7
71
/
4
o-Xylene
9.0
70
4
Silica
Benzene
DMSO
4.7
O
0
gel in
Toluene
DMSO
5.6
99
O
O
dry ice
m-Xylene
DMSO
6.4
87
0
O
95
o-Xylene
DMSO
6.4
86
0
O
Ethyl acetate
DMSO
5.4
94
O
0
Butyl alcohol
DMSO
4.7
93
0
0
1.1.1 -Trichloroethane
Cumene Pyridine
8.1
I00 c /
89 86
0 O
O O
1. I. 2.2 -Tetrachloroethane
Cumene Pyridine
9.5
75 c /
90 81
O 0
O 0
Trichloroethylene
Cumene Pyridine
8.8
93 c /
87 89
0 0
O 0
9.8
82 c /
95 90
O 0
0 O
Cumene Tetrachloroethylempyridine .
.
DMSO=dimethyl sulfoxide; DMFA=dimethyl formamide; ECA=ethyl cellosolve acetate; G.C.=gas chromatography; Col.=colorimetry; bot.=bottle. a 9 9 " n materlal. ~ bAbSorblng solutlons or adsorptlo Percent of the concentration of organic solvents in 2nd or 3rd bottle to Ist bottle (average of two experiments). CGas chromatograph attached with ECD detector.
32
b
Table 2. Adsorption and recovery of organic solvents from silica gel (flowl~/min vapour was taken from McKelvey's diffusion cell with constant air flow for 7 hrs) Organic hydrocarbons
ppm
Solvent
Recovery %
Toluene
48
DMSO
97
Benzene
82
DMSO
90
m-Xylene
58
DMSO
84
o-Xylene
30
DMSO
88
Butanol
23
DMSO
89
l.].l-Trichloroethane
46
Cumene
93
l.l.2.2-Tetrachloroethane
48
Cumene
87
Trichloroethylene
44
Cumene
96
Tetrachloroethylene
32
Cumene
I03
The ratio of the concentration
of benzene,
toluene, m-xylene and o-xylene in
the second or the third tube to the first tube using ECA, DMFA and mixture of DMSO and DMFA was shown in Table necessary
I. From this, it is considered
to use 2 tubes.
The recovery rate of aromatic hydrocarbons signed for practical use (Fig.3)
using personal air sampler de-
shows similar results.
DMFA is used as the absorbing solution for the determination tion of the organic solvents.
of the concentra-
Since DMFA is dangerous at room temperature,
complete adsorption by silica gel of possible necessary.
to be
leaking evaporated gases is
To accomplish this a silica gel probe is recommended
to be placed
before the suction pump for the adsorption of DMFA. Therefore,
less toxic ECA should be used for the personal air sampler and the
use of DMFA or the mixture of DMSO and DMFA for the room air sampler is recommended.
III. Application
of Personal Air Sampler
The location was a furniture-making
factory, where varnish dissolved in
thinner, was used. The thinner's main ingredients were ethyl acetate,
butyl
acetate and toluene.
The organic solvent vapours were controlled by suction,
where two men worked,
one (A) engaged in spraying and the other (B), doing
hand painting work.
33
Fig.6 Variation in concentration of toluene (T), ethyl acetate (EA) and butyl acetate (BA) at the center of the working room (lower figure), and amount of urinary hippuric acid (upper figure) in worker A (white column) and worker B (black column)
mg/min 0.5 0.4 0.3 0.2 0.1
ppm
5,58
1.0 0.8 0.6 0.4
\!: ,X 7 \',,
..'1,.
!\It
/..,\
0.2
, 5.30 8
i 9
10 II
~ EA
12 13 14 15 20
B
(hours)
Air from the worker's breathing zone sucked through the teflon tube by personal sampling pump, operated by dry battery kept at constant current. Sampler and pump held on by harness fitted to the worker. Air was drawn 1~/min,
through the cooled silica gel probe and calculated
atmospheric
concentration
exposed to the two workers.
to the average
The air at the center
of the room was trapped by gas sampling bottle at ! hr intervals and the average concentration was calculated.
The place, about 2 m from worker A, had
an average air density of 0.62 ppm of toluene, 0.76 ppm of ethyl acetate and 0.23 ppm of butyl acetate. Kitagawa detector, other hand,
Toluene concentration was also estimated by
showing that its maximum value was below I ppm. On the
it was found by personal air sampler that the average concentra-
tion of solvent that worker A was exposed to was 2.0 ppm, which was higher than that of worker B (1.3 ppm), and the average exposure to worker A and B was found to be higher than detected at the center of the room due to their proximity to the thinner.
There was an increased amount of hippuric acid in
worker A's urine which paralleled changes in toluene concentration, worker A's acid level was higher than that of B, corresponding exposure to a higher concentration
34
of toluene
and
to his
(Fig.6 and Table 3).
Table 3 Concentration of organic solvents in the air of the room and concentration detected by the personal air sampler attached to two workers using thinner Concentration
In the room
a
Toluene (ppm)
Ethyl acetate (ppm)
Butyl acetate (ppm)
TLV b
0.62
0.76
0.23
0.010
Personal air
worker A
2.08
5.75
4.09
0.062
sampler
worker B
1.40
2.06
1.78
0.031
100
400
150
TLV by ACGIH a
bConcentrat~on measured at the center of the room. Threshold l i m i t v a l u e f o r t h e m i x t u r e s d o c u m e n t e d by ACGIH.
Discussion
The approximate concentrations hydrocarbons
of benzene,
were found by discontinuous
toluene,
xylenes and chlorinated
and continuous
gas-evaporation
tests.
Samples were collected with silica gel cooled to a solid state, with ECA and DMFA cooled by dry ice and mixture of DMSO and DMFA by ice in a liquid state. However,
at least 2 bottles were necessary for the liquid absorption method.
The sampling technique utilizing both silica gel cooled by dry ice and anhydrous
sodium carbonate,
and subsequent
gas chromatography
of the sample
was found useful for the personal and room air samplers.
The colorimetric hydrocarbons benzene,
method also offered a simple and useful assay of chlorinated
adsorbed on silica gel. No apparent difficulty resulted when
toluene,
ethyl acetate,
butyl alcohol and chlorinated hydrocarbon
vapours were collected from silica gel by gas chromatography.
In the air samplers used in this experiment, applicable with a steady concentration
the continuous
in the workshop,
system was most
and the discontinuous
system with conditions of changing concentration.
In the workshop using organic solvents,
absorption with DMSO or cooled DMFA
is simpler than with silica gel in the room air sampler,
the absorption bottles
can be devised for protecting against fluid leaking from the bottles.
35
In the factory using thinner, we can calculate the TLV of the mixture of organic solvent concentration in the room, or the average concentration, the workmen are exposed to, by using the equation for the threshold limit value (TLV) for the mixtures documented by ACGIH is E Ci/Ti, where Ci indicates the observed atmospheric concentration and Ti corresponding threshold concentration. Using the above equation with the observed concentration and with the TLV of toluene (IOO ppm), ethyl acetate (400 ppm), and butyl acetate (150 ppm), documented by ACGIH, calculation was made. The results are shown in Table 3. The value in the center of the room and the personal air sampler of the two workers were lower than I respectively.
For some organic solvents, which were excreted as metabolites in urine (Ogata et ai.,1970), the amount of organic solvents absorbed by the body can be determined by the measurement of the urinary metabolite concentration as described previously. Still the personal air sampler can measure the personal exposure to organic solvent, whether the solvent itself or its metabolites are excreted in the urine or not.
In a survey of the exposure of workers to organic solvents in the factory, where the concentration of the solvent is kept low by suction, the personal air sampler can be useful in determining their exposure, and with workers exposed to a low concentration of toluene, hippuric acid determination should be done with the urine, before, during and after the exposure, since the increase of hippuric acid is thought to indicate toluene exposure, as diurnal variations of the level of urinary hippuric acid are relatively small (Ogata et ai.,1963).
References
Bennett,C.E., Dal Nooare,S., Safranski,L.W., Lewis,C.D.: Trace analysis by gas chromatography. Anal. Chem. 30, 898 (1958) Eggertsen,F.T., Nelson,F.M.: Gas chromatographic analysis of engine exhaust and atmospheric samples. Anal. Chem. 30, 1040 (1958) Farrinoton,P.S., Pecsok,R.L., Merker,R.L., Olson,T.J.: Detection of trace constituents by gas chromatography. Anal.Chem. 31, 1512 (1959) Feldstein,M., Balestrieri,S., Levaggi,D.A.: The use of silica gel in source testing. Amer.lnd.Hyg.Assoc. J. 28, 381-385 (1967) Leibmann,K.C., Hindman,J.D.: Modification of the Fujiwara reaction for determination of polyhalogenated organic compounds. Anal.Chem. 36, 348 (1964)
36
Mckee,H.G., Rhoades,J.W., McMahon,W.A.: Use of drying agents in atmospheric sampling. A.C.S. Pro 136. Z4U no.52 (]959) McKelvey,J.M., Hoelsher,H.E.: Apparatus for preparation of very dilute gas mixtures. Anal.Chem. 29, 123 (1957) 0gata,M., Nagao,I.: Urinary m-methyl hippuric acid excretion and physiological changes in persons exposed to 200 ppm. m-xylene in exposure chamber (in Japanese). Jap.J.industr.Health 10, 75-79 (1963) Ogata,M., Takastuka,Y., Tomokuni,K.: Excretion of organic chlorine compounds in the urine of persons exposed to vapours of trichloroethylene and tetrachloroethylene. Brit.J.industr.Med. 28, 386-391 (1971) Ogata,M., Tomokuni,K., Takatuka,Y.: Urinary excretion of hippuric acid and m- or p-methyl hippuric acid in the urine of persons exposed to vapours of toluene and m- or p-xylene as a test of exposure. Brit.J.industr.Med. 27, 43-50 (1970) Seki,Y., Ichikawa,M., Minaguchi,H.: Methods of sampling industrial solvents in the air: A vapour sampler for an individual (in Japanese). Jap.J. industr.Health 14, 138-139 (1972) West,P.W., Buddhadev,S., Giason,N.A.: Gas liquid chromatographic analysis. Anal.Chem. 30, 1390 (1958) Whitman,N.E., Johuston,A.E.: Sampling and analysis of aromatic hydrocarbon vapors in air: A gas-liquid chromatographic method. Amer.lnd.Hyg.Assoc.J~ 25, 464 (1964)
Dr.Masana Ogata Department of Public Health Okayama University Medical School Okayama, Japan
37
