Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
Title of the Invention
Basic-gas Detection Paper
Background of the Invention
This invention relates to basic gas detection paper
that detects ammonia, amines and other basin gases present
in the atmosphere and other gases by means of coloring
reaction.
Description of the Prior Art
The presence of ammonia, amines and other basic gases
in the atmosphere is usually detected by using a hydrogen
ion concentration sensor comprising glass electrodes im-
mersed in the electrolyte. However, this type of sensor
requires considerably demanding maintenance, such as the
frequent replacement of the electrolyte. This replacement
is necessary because the sensitivity to basic gases of low
concentrations drops sharply when 'the reference hydrogen
ion concentration of the electrolyte changes under the
influence of acid gases present in the atmosphere.
On the other hand, fluorescein test paper, which is
prepared by dyeing paper with a neutral solution of fluo-
resdein, is used as a handy means for identifying some
specific gas contained in a gas mixture with high sensitiv-
ity. However, fluorescein test paper does not have high
enough sensitivity to detect basic gases i.n the atmosphere
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or other gases, is highly susceptible to discoloration in
the atmosphere, and, therefore, is unsuited for such appli-
rations as 'the collection of environmental data in which
the test paper must be left in the atmosphere for a long
period of time.
Summary of the Invention
The basic-gas detection paper according to -this inven-
Lion carries a fluorescein-based dye and a strong organic
acid thereon, together with a humectant. A fluorescein-
based dye, which has a valor when it exists singly, is
calorless in the presence of a strong organic acid. When
the basic gas to be examined is exposed to the moisture
held by the humectant and thus makes the paper alkaline,
the fluorescein-based dye colors according to the concen-
tration of hydrogen ion.
A first object of this invention is to pravide high-
sensitivity basic-gas detection paper that can detect basic
gases of the order of ppb (parts per billion) present in
various kinds of gases.
A second object of this invention is to provide basic-
gas detection paper that does not discolor in 'the atma-
sphere and maintains stable sensitivity over a long period
of time.
Carrying a fluorescein-based dye and a strong organic
acid together with a humectant, the basic-gas detection
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paper according to this invention can detect ammonia,
amines and other basic gases of as low concentrations as of
the order of 100 ppb. The organic acid of high molecular
weight used as the hydrogen ion concentration adjuster pre-
vents the deterioration of the carrier during long storage,
keeps the hydrogen ion concentration at a constant level,
prevents discoloration that can otherwise result from
exposure to the atmasphere, and maintains stable
sensitivity over a long period of time. Accordingly, -the
basic-gas detection paper according to this invention is
very suitable for such applications as the collection of
environmental data that may last long.
Brief Description of the Drawings
Fig. 1 shows an example of an apparatus suited for
using a tape of the gas detection paper according to -this
invention.
Fig. 2 graphically shows the concentration of ammonia,
which is a kind of basic gases, measured by the gas detec-
~tion paper according to this invention.
Description of the Preferred Embodiments
[Example 1]
A reaction solution is prepared by dissolving 0.05
weight percent of rose benzal (CZOHzCI4Naz05; solar index:
acid red 94), which is a fluorescein-based dye, 1.5 weight
percent of para-toluenesulfonic acid, and 15 volume percent
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of polyhydric alcohol, such as glycerin, in water or an
organic solvent such as methanol.
Some suitable organic solvent should preferably be
used to shorten 'the drying time.
A sheet of paper is immersed in a bath of the prepared
reaction solution. The paper impregnated with the reaction
solution is pulled out of the bath to air-dry the solvent.
The sheet of paper thus carrying rose benzal, para-
toluenesulfonic acid and glycerin 'thereon is slit into a
tape or other form suited for use on a measuring apparatus.
On absorbing the moisture in the atmosphere, the
glycerin contained in the paper forms an aqueous solution
of pare--toluenesulfonic acid, thus keeping -the hydrogen ion
concentration at approximately pH 1 to pH 2. Therefore,
the rose benzal becomes substantially colorless and trans-
parent. As a consequence, 'the color of the detection paper
is the same as that of the base paper :itself before it is
exposed to the gas to be examined.
Fig. 1 shows an example of a measuring apparatus
suited :Eor the use of the gas detection paper described
above. Reference numeral 1 designates a gas suction unit
facing a path in which a gas detection tape 2 travels, with
a through hole having a diameter of approximately 1 cm
opening in the surface thereof opposite the tape 2. A
negative pressure created by a suction pump not shown works
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thereat through a pipe 4.
Reference numeral 5 denotes a measuring head located
opposite 'the through hole 3 in the gas suction unit 1 on
the other side of the gas detection tape 2. The measuring
head 5 constitutes a light-shielded container having a
through hale 6 opposite the through hole 3 in the suction
unit 1. The measuring head 5 contains a light-emitting
diode 7 having a peak wavelength of 555 nm and a pin-type
photodiode 8 that exhibits the highest sensitivity to a
light having a wavelength of 560 nm that are disposed in
such a configuration that they can determine the optical
concentration of the trace of reaction formed on the tape
2.
With a tape slit from the detection paper passed over
reels 10 and 11, a suction pressure from a pump not shown
is introduced to tho pipe 4 connected to the suction unit 1
to draw in a specimen gas through, a specimen gas inlet 9.
The gas passes from 'the -through hole 6, through -the detec-
tion tape 2, and then outside ~thraugh the through hole 3.
With the tape passed over the reels 10 and 11, to be
more specific, the suction pressure from the pump not shown
is introduced to the pipe 4 over a sampling period of 30
seconds at a sampling rate of 400 milliliters per minute.
Then, the specimen gas is drawn into the measuring head 5
-through the inlet 9.
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The gas passes from the through hole 6, through the
detection tape 2, and then outside through the through hole
3. When the gas passes through the detection tape 2, the
moisture held by the glycerin thereon captures the ammonia
contained in the gas, whereupon the hydrogen ion concentra-
tion 'turns to the alkaline side. With this change, the
rose benzal that has been colorless and transparent takes
on color in accordance with the hydrogen ion concentration.
When the sampling period of 30 seconds is over, the
suction of the specimen gas is stopped to start the meas-
urement of the optical concentration of the trace of reac-
tion formed on the surface of the tape. The light from the
light-emitting diode 7 is absorbed in proportion to the
optical concentration of the trace of reaction formed.
Therefore, the cancentration of ammonia gas can be deter-
mined by obtaining the difference between the optical
concentration bofore the start of measurement or 'the opti-
cal concentration of the background of the tape and the
optical concentration of 'the 'trace of .reaction. When 'the
measurement of one sampled unit of gas is complete, the
take-up reel 11 is moved to feed an unused part of the tape
into the measuring zone.
Changes in the optical concentration of the trace of
reaotion was measured by using the detection tape set on
the measuring apparatus described above while changing the
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concentration of ammonia gas. Curve I in Fig. 2 shows the
measurements obtained with a sampling period of approxi-
mately 30 seconds. The detection paper proved to be capa-
ble of detecting ammonia gas in the atmosphere with a high
linearity and a high sensitivity of the order of 100 ppm.
Curve II in Fig. 2 shows the measurements obtained with a
sampling period of 60 seconds. The outputs plotted by
curve II are approximately twice greater than those of
curve I.
When the sampling period is extended, as is obvious
from these two curves, the detention paper according to
this invention detects gases of extremely low concentra-
tions because of the cumulative effect of the lengthened
time.
The reaction solution used in the example just de-
scribed is prepared by dissolving all ingredients in the
organic solvent. However, soma of them, such as pares-tol-
uenesulfonic acid alorxe, may be dissolved in water before-
hand. Then, the prepared aqueous solution of pares-~toluene-
sulfonic acid is added to a solution prepared by dissolving
rose benzal and glycerin in alcohol. This method facili-
testes the adjustment of the hydrogen ion concentration of
the reaction solution.
[Example 2]
A reaction solution is prepared by dissolving 0.1
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weight percent of phloxine (CZOH205Br4C1nNa?; color index:
acid red 92), which is a fluorescein-based dye, 0.3 weight
percent of para-toluenesulfonic acid, and 15 volume percent
of polyhydric alcohol, such as glycerin, in water or an
organic solvent such as methanol.
A sheet of paper is immersed in a bath of the prepared
reaction solution. The paper impregnated with the reaction
solution is pulled out of the bath to air-dry the solvent.
The sheet of paper thus carrying phloxine, para-tol-
uenesulfonic acid and glycerin thereon is slit iwto a tape
or other form suited for use on a measuring apparatus.
On absorbing the moisture in the atmosphere, the
glycerin contained in the paper forms an aqueous solution
of para-toluenesulfonic acid, thus keeping the hydrogen ion
concentration at approximately pH 1 to pH 2. Therefore,
the phloxine becomes substantially colorless and transpar-
ent. As a consequence, the co7.or of the detectian paper is
the same as that of 'the base paper itself before it is
exposed to the gas to be examined.
[Example 3a
A reaction solution is prepared by dissolving 0.1
weight percent of eosine yellowish ( CZOH60~Br4Na2; color
index: acid red 87), which is a fluorescein-based dye, 0.3
weight percent of para-toluenesulfonic acid, and 15 volume
percent of polyhydri.c alcohol, such as glycerin, in water
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or an organic solvent such as methanol.
A sheet of paper of such substance as cellulose having
a high affinity for water and a high acid resistance is im-
mersed in a bath of the prepared reaction solution to
impregnate it with the ingredients of the solution.
The paper impregnated with the reaction solution is
then pulled out of the bath to air-dry the solvent metha-
nol. Thus, a sheet of paper carrying eosine yellowish,
para-toluenesulfonic said and glycerin thereon is obtained.
On absorbing the moisture in the atmosphere, the
glycerin contained in the paper forms an agueous solution
of para-toluenesulfonic acid, thus keeping the hydrogen ion
concentration at approximately pH 1 to pH 2. Therefore,
the eosine yellowish becomes substantially transparent and
very pale pink in color.
The gas detection paper is usually stored in gas-tight
containers as their proper~tios change when the ingredients
carried thereon react with 'the constituents of the atmos-
phere. During use, however, degeneration is likely to
occur because the gas detection paper is taken out of such
containers and put an measuring devices exposed to the
atmosphere.
When placed in the atmosphere not exposed to light far
several days,however, the gas detection paper according to
this invention neither discolored nor underwent any changes
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in detection sensitivity.
Another gas detection paper was prepared by a similar
method, except that pares-toluenesulfonic acid was replaced
with hydrochloric acid -that seldom deteriorates cellulose.
When subjected to the same test, however, the hydrochloric
acid volatilized, -the paper discolored in less than one
hour, and its detection sensitivity dropped with time.
Thus, the use of pares-toluenesulfonic acid proved to be
very beneficial to the lengthening of the shelf life of the
gas detection paper.
As has been mentioned, the fluorescein-based dye
carried by the gas detection paper of this invention nor-
molly remains substantially colorless, but takes on color
when it comes in contact with the specimen gas to be exam-
ined. There-fore, the detection sensitivity of the paper
increases as the concentration of the dye carried thereon
increases. However, -the concentration of the fluorescein-
based dye should be such that the coloration -thereof can be
controlled by means of a strong organic acid and no
precipitation thereof occurs on the paper.
Instead of the rose benzal, phloxine and eosine yel-
lowish used in -the examples described before, other fluo-
rescein-based dyes, such as eosine bluish (CZOH6Hr2C1NaZO9;
color index: acid red 91) and erythrasine (CZ~HZ9Nz0~Sz%
color index: acid red 52) may also be used. The detection
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paper prepared with such other fluorescein-based dyes
proved to be capable of detecting basic gases with practi-
cal accuracy, though the detection sensitivity is somewhat
more susceptible to variations.
In the examples described before, pare-toluenesulfonic
acid is used as the hydrogen ion concentration adjuster.
Other strong organic acids, such as naphthalenesulfonic
acid and benzensulfonic acid, also proved to be much more
beneficial than hydrochloric acid in the lengthening of the
shelf life of the detention paper.
Furthermore, glycerin, which is used as the humectant,
may also be replaced with other substances that do not
change the hydrogen ion concentration, such as ethylene
glycol and polyalcohol. The paper prepared with such
humectants also produce similar effects.
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